quantumcircuit.py

# This code is part of Qiskit.
#
# (C) Copyright IBM 2017.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.

# pylint: disable=bad-docstring-quotes,invalid-name

"""Quantum circuit object."""

from __future__ import annotations
import copy
import itertools
import multiprocessing as mp
import typing
from collections import OrderedDict, defaultdict, namedtuple
from typing import (
    Union,
    Optional,
    Tuple,
    Type,
    TypeVar,
    Sequence,
    Callable,
    Mapping,
    Iterable,
    Any,
    DefaultDict,
    Literal,
    overload,
)
import numpy as np
from qiskit._accelerate.quantum_circuit import CircuitData
from qiskit.exceptions import QiskitError
from qiskit.utils.multiprocessing import is_main_process
from qiskit.circuit.instruction import Instruction
from qiskit.circuit.gate import Gate
from qiskit.circuit.parameter import Parameter
from qiskit.circuit.exceptions import CircuitError
from . import _classical_resource_map
from ._utils import sort_parameters
from .controlflow import ControlFlowOp
from .controlflow.builder import CircuitScopeInterface, ControlFlowBuilderBlock
from .controlflow.break_loop import BreakLoopOp, BreakLoopPlaceholder
from .controlflow.continue_loop import ContinueLoopOp, ContinueLoopPlaceholder
from .controlflow.for_loop import ForLoopOp, ForLoopContext
from .controlflow.if_else import IfElseOp, IfContext
from .controlflow.switch_case import SwitchCaseOp, SwitchContext
from .controlflow.while_loop import WhileLoopOp, WhileLoopContext
from .classical import expr, types
from .parameterexpression import ParameterExpression, ParameterValueType
from .quantumregister import QuantumRegister, Qubit, AncillaRegister, AncillaQubit
from .classicalregister import ClassicalRegister, Clbit
from .parametertable import ParameterReferences, ParameterTable, ParameterView
from .parametervector import ParameterVector
from .instructionset import InstructionSet
from .operation import Operation
from .register import Register
from .bit import Bit
from .quantumcircuitdata import QuantumCircuitData, CircuitInstruction
from .delay import Delay
from .store import Store

if typing.TYPE_CHECKING:
    import qiskit  # pylint: disable=cyclic-import
    from qiskit.transpiler.layout import TranspileLayout  # pylint: disable=cyclic-import
    from qiskit.quantum_info.operators.base_operator import BaseOperator
    from qiskit.quantum_info.states.statevector import Statevector  # pylint: disable=cyclic-import

BitLocations = namedtuple("BitLocations", ("index", "registers"))


# The following types are not marked private to avoid leaking this "private/public" abstraction out
# into the documentation.  They are not imported by circuit.__init__, nor are they meant to be.

# Arbitrary type variables for marking up generics.
S = TypeVar("S")
T = TypeVar("T")

# Types that can be coerced to a valid Qubit specifier in a circuit.
QubitSpecifier = Union[
    Qubit,
    QuantumRegister,
    int,
    slice,
    Sequence[Union[Qubit, int]],
]

# Types that can be coerced to a valid Clbit specifier in a circuit.
ClbitSpecifier = Union[
    Clbit,
    ClassicalRegister,
    int,
    slice,
    Sequence[Union[Clbit, int]],
]

# Generic type which is either :obj:`~Qubit` or :obj:`~Clbit`, used to specify types of functions
# which operate on either type of bit, but not both at the same time.
BitType = TypeVar("BitType", Qubit, Clbit)


class QuantumCircuit:
    """Create a new circuit.

    A circuit is a list of instructions bound to some registers.

    Args:
        regs (list(:class:`~.Register`) or list(``int``) or list(list(:class:`~.Bit`))): The
            registers to be included in the circuit.

            * If a list of :class:`~.Register` objects, represents the :class:`.QuantumRegister`
              and/or :class:`.ClassicalRegister` objects to include in the circuit.

              For example:

                * ``QuantumCircuit(QuantumRegister(4))``
                * ``QuantumCircuit(QuantumRegister(4), ClassicalRegister(3))``
                * ``QuantumCircuit(QuantumRegister(4, 'qr0'), QuantumRegister(2, 'qr1'))``

            * If a list of ``int``, the amount of qubits and/or classical bits to include in
              the circuit. It can either be a single int for just the number of quantum bits,
              or 2 ints for the number of quantum bits and classical bits, respectively.

              For example:

                * ``QuantumCircuit(4) # A QuantumCircuit with 4 qubits``
                * ``QuantumCircuit(4, 3) # A QuantumCircuit with 4 qubits and 3 classical bits``

            * If a list of python lists containing :class:`.Bit` objects, a collection of
              :class:`.Bit` s to be added to the circuit.


        name (str): the name of the quantum circuit. If not set, an
            automatically generated string will be assigned.
        global_phase (float or ParameterExpression): The global phase of the circuit in radians.
        metadata (dict): Arbitrary key value metadata to associate with the
            circuit. This gets stored as free-form data in a dict in the
            :attr:`~qiskit.circuit.QuantumCircuit.metadata` attribute. It will
            not be directly used in the circuit.
        inputs: any variables to declare as ``input`` runtime variables for this circuit.  These
            should already be existing :class:`.expr.Var` nodes that you build from somewhere else;
            if you need to create the inputs as well, use :meth:`QuantumCircuit.add_input`.  The
            variables given in this argument will be passed directly to :meth:`add_input`.  A
            circuit cannot have both ``inputs`` and ``captures``.
        captures: any variables that that this circuit scope should capture from a containing scope.
            The variables given here will be passed directly to :meth:`add_capture`.  A circuit
            cannot have both ``inputs`` and ``captures``.
        declarations: any variables that this circuit should declare and initialize immediately.
            You can order this input so that later declarations depend on earlier ones (including
            inputs or captures). If you need to depend on values that will be computed later at
            runtime, use :meth:`add_var` at an appropriate point in the circuit execution.

            This argument is intended for convenient circuit initialization when you already have a
            set of created variables.  The variables used here will be directly passed to
            :meth:`add_var`, which you can use directly if this is the first time you are creating
            the variable.

    Raises:
        CircuitError: if the circuit name, if given, is not valid.
        CircuitError: if both ``inputs`` and ``captures`` are given.

    Examples:

        Construct a simple Bell state circuit.

        .. plot::
           :include-source:

           from qiskit import QuantumCircuit

           qc = QuantumCircuit(2, 2)
           qc.h(0)
           qc.cx(0, 1)
           qc.measure([0, 1], [0, 1])
           qc.draw('mpl')

        Construct a 5-qubit GHZ circuit.

        .. code-block::

           from qiskit import QuantumCircuit

           qc = QuantumCircuit(5)
           qc.h(0)
           qc.cx(0, range(1, 5))
           qc.measure_all()

        Construct a 4-qubit Bernstein-Vazirani circuit using registers.

        .. plot::
           :include-source:

           from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit

           qr = QuantumRegister(3, 'q')
           anc = QuantumRegister(1, 'ancilla')
           cr = ClassicalRegister(3, 'c')
           qc = QuantumCircuit(qr, anc, cr)

           qc.x(anc[0])
           qc.h(anc[0])
           qc.h(qr[0:3])
           qc.cx(qr[0:3], anc[0])
           qc.h(qr[0:3])
           qc.barrier(qr)
           qc.measure(qr, cr)

           qc.draw('mpl')
    """

    instances = 0
    prefix = "circuit"

    def __init__(
        self,
        *regs: Register | int | Sequence[Bit],
        name: str | None = None,
        global_phase: ParameterValueType = 0,
        metadata: dict | None = None,
        inputs: Iterable[expr.Var] = (),
        captures: Iterable[expr.Var] = (),
        declarations: Mapping[expr.Var, expr.Expr] | Iterable[Tuple[expr.Var, expr.Expr]] = (),
    ):
        if any(not isinstance(reg, (list, QuantumRegister, ClassicalRegister)) for reg in regs):
            # check if inputs are integers, but also allow e.g. 2.0

            try:
                valid_reg_size = all(reg == int(reg) for reg in regs)
            except (ValueError, TypeError):
                valid_reg_size = False

            if not valid_reg_size:
                raise CircuitError(
                    "Circuit args must be Registers or integers. (%s '%s' was "
                    "provided)" % ([type(reg).__name__ for reg in regs], regs)
                )

            regs = tuple(int(reg) for reg in regs)  # cast to int
        self._base_name = None
        if name is None:
            self._base_name = self.cls_prefix()
            self._name_update()
        elif not isinstance(name, str):
            raise CircuitError(
                "The circuit name should be a string (or None to auto-generate a name)."
            )
        else:
            self._base_name = name
            self.name = name
        self._increment_instances()

        # An explicit implementation of the circuit scope builder interface used to dispatch appends
        # and the like to the relevant control-flow scope.
        self._builder_api = _OuterCircuitScopeInterface(self)

        self._op_start_times = None

        # A stack to hold the instruction sets that are being built up during for-, if- and
        # while-block construction.  These are stored as a stripped down sequence of instructions,
        # and sets of qubits and clbits, rather than a full QuantumCircuit instance because the
        # builder interfaces need to wait until they are completed before they can fill in things
        # like `break` and `continue`.  This is because these instructions need to "operate" on the
        # full width of bits, but the builder interface won't know what bits are used until the end.
        self._control_flow_scopes: list[
            "qiskit.circuit.controlflow.builder.ControlFlowBuilderBlock"
        ] = []

        self.qregs: list[QuantumRegister] = []
        self.cregs: list[ClassicalRegister] = []

        # Dict mapping Qubit or Clbit instances to tuple comprised of 0) the
        # corresponding index in circuit.{qubits,clbits} and 1) a list of
        # Register-int pairs for each Register containing the Bit and its index
        # within that register.
        self._qubit_indices: dict[Qubit, BitLocations] = {}
        self._clbit_indices: dict[Clbit, BitLocations] = {}

        # Data contains a list of instructions and their contexts,
        # in the order they were applied.
        self._data: CircuitData = CircuitData()

        self._ancillas: list[AncillaQubit] = []
        self._calibrations: DefaultDict[str, dict[tuple, Any]] = defaultdict(dict)
        self.add_register(*regs)

        # Parameter table tracks instructions with variable parameters.
        self._parameter_table = ParameterTable()

        # Cache to avoid re-sorting parameters
        self._parameters = None

        self._layout = None
        self._global_phase: ParameterValueType = 0
        self.global_phase = global_phase

        # Add classical variables.  Resolve inputs and captures first because they can't depend on
        # anything, but declarations might depend on them.
        self._vars_input: dict[str, expr.Var] = {}
        self._vars_capture: dict[str, expr.Var] = {}
        self._vars_local: dict[str, expr.Var] = {}
        for input_ in inputs:
            self.add_input(input_)
        for capture in captures:
            self.add_capture(capture)
        if isinstance(declarations, Mapping):
            declarations = declarations.items()
        for var, initial in declarations:
            self.add_var(var, initial)

        self.duration = None
        self.unit = "dt"
        self.metadata = {} if metadata is None else metadata

    @staticmethod
    def from_instructions(
        instructions: Iterable[
            CircuitInstruction
            | tuple[qiskit.circuit.Instruction]
            | tuple[qiskit.circuit.Instruction, Iterable[Qubit]]
            | tuple[qiskit.circuit.Instruction, Iterable[Qubit], Iterable[Clbit]]
        ],
        *,
        qubits: Iterable[Qubit] = (),
        clbits: Iterable[Clbit] = (),
        name: str | None = None,
        global_phase: ParameterValueType = 0,
        metadata: dict | None = None,
    ) -> "QuantumCircuit":
        """Construct a circuit from an iterable of CircuitInstructions.

        Args:
            instructions: The instructions to add to the circuit.
            qubits: Any qubits to add to the circuit. This argument can be used,
                for example, to enforce a particular ordering of qubits.
            clbits: Any classical bits to add to the circuit. This argument can be used,
                for example, to enforce a particular ordering of classical bits.
            name: The name of the circuit.
            global_phase: The global phase of the circuit in radians.
            metadata: Arbitrary key value metadata to associate with the circuit.

        Returns:
            The quantum circuit.
        """
        circuit = QuantumCircuit(name=name, global_phase=global_phase, metadata=metadata)
        added_qubits = set()
        added_clbits = set()
        if qubits:
            qubits = list(qubits)
            circuit.add_bits(qubits)
            added_qubits.update(qubits)
        if clbits:
            clbits = list(clbits)
            circuit.add_bits(clbits)
            added_clbits.update(clbits)
        for instruction in instructions:
            if not isinstance(instruction, CircuitInstruction):
                instruction = CircuitInstruction(*instruction)
            qubits = [qubit for qubit in instruction.qubits if qubit not in added_qubits]
            clbits = [clbit for clbit in instruction.clbits if clbit not in added_clbits]
            circuit.add_bits(qubits)
            circuit.add_bits(clbits)
            added_qubits.update(qubits)
            added_clbits.update(clbits)
            circuit._append(instruction)
        return circuit

    @property
    def layout(self) -> Optional[TranspileLayout]:
        r"""Return any associated layout information about the circuit

        This attribute contains an optional :class:`~.TranspileLayout`
        object. This is typically set on the output from :func:`~.transpile`
        or :meth:`.PassManager.run` to retain information about the
        permutations caused on the input circuit by transpilation.

        There are two types of permutations caused by the :func:`~.transpile`
        function, an initial layout which permutes the qubits based on the
        selected physical qubits on the :class:`~.Target`, and a final layout
        which is an output permutation caused by :class:`~.SwapGate`\s
        inserted during routing.
        """
        return self._layout

    @property
    def data(self) -> QuantumCircuitData:
        """Return the circuit data (instructions and context).

        Returns:
            QuantumCircuitData: a list-like object containing the :class:`.CircuitInstruction`\\ s
            for each instruction.
        """
        return QuantumCircuitData(self)

    @data.setter
    def data(self, data_input: Iterable):
        """Sets the circuit data from a list of instructions and context.

        Args:
            data_input (Iterable): A sequence of instructions with their execution contexts.  The
                elements must either be instances of :class:`.CircuitInstruction` (preferred), or a
                3-tuple of ``(instruction, qargs, cargs)`` (legacy).  In the legacy format,
                ``instruction`` must be an :class:`~.circuit.Instruction`, while ``qargs`` and
                ``cargs`` must be iterables of :class:`~.circuit.Qubit` or :class:`.Clbit`
                specifiers (similar to the allowed forms in calls to :meth:`append`).
        """
        # If data_input is QuantumCircuitData(self), clearing self._data
        # below will also empty data_input, so make a shallow copy first.
        if isinstance(data_input, CircuitData):
            data_input = data_input.copy()
        else:
            data_input = list(data_input)
        self._data.clear()
        self._parameters = None
        self._parameter_table = ParameterTable()
        # Repopulate the parameter table with any global-phase entries.
        self.global_phase = self.global_phase
        if not data_input:
            return
        if isinstance(data_input[0], CircuitInstruction):
            for instruction in data_input:
                self.append(instruction)
        else:
            for instruction, qargs, cargs in data_input:
                self.append(instruction, qargs, cargs)

    @property
    def op_start_times(self) -> list[int]:
        """Return a list of operation start times.

        This attribute is enabled once one of scheduling analysis passes
        runs on the quantum circuit.

        Returns:
            List of integers representing instruction start times.
            The index corresponds to the index of instruction in :attr:`QuantumCircuit.data`.

        Raises:
            AttributeError: When circuit is not scheduled.
        """
        if self._op_start_times is None:
            raise AttributeError(
                "This circuit is not scheduled. "
                "To schedule it run the circuit through one of the transpiler scheduling passes."
            )
        return self._op_start_times

    @property
    def calibrations(self) -> dict:
        """Return calibration dictionary.

        The custom pulse definition of a given gate is of the form
        ``{'gate_name': {(qubits, params): schedule}}``
        """
        return dict(self._calibrations)

    @calibrations.setter
    def calibrations(self, calibrations: dict):
        """Set the circuit calibration data from a dictionary of calibration definition.

        Args:
            calibrations (dict): A dictionary of input in the format
               ``{'gate_name': {(qubits, gate_params): schedule}}``
        """
        self._calibrations = defaultdict(dict, calibrations)

    def has_calibration_for(self, instruction: CircuitInstruction | tuple):
        """Return True if the circuit has a calibration defined for the instruction context. In this
        case, the operation does not need to be translated to the device basis.
        """
        if isinstance(instruction, CircuitInstruction):
            operation = instruction.operation
            qubits = instruction.qubits
        else:
            operation, qubits, _ = instruction
        if not self.calibrations or operation.name not in self.calibrations:
            return False
        qubits = tuple(self.qubits.index(qubit) for qubit in qubits)
        params = []
        for p in operation.params:
            if isinstance(p, ParameterExpression) and not p.parameters:
                params.append(float(p))
            else:
                params.append(p)
        params = tuple(params)
        return (qubits, params) in self.calibrations[operation.name]

    @property
    def metadata(self) -> dict:
        """The user provided metadata associated with the circuit.

        The metadata for the circuit is a user provided ``dict`` of metadata
        for the circuit. It will not be used to influence the execution or
        operation of the circuit, but it is expected to be passed between
        all transforms of the circuit (ie transpilation) and that providers will
        associate any circuit metadata with the results it returns from
        execution of that circuit.
        """
        return self._metadata

    @metadata.setter
    def metadata(self, metadata: dict):
        """Update the circuit metadata"""
        if not isinstance(metadata, dict):
            raise TypeError("Only a dictionary is accepted for circuit metadata")
        self._metadata = metadata

    def __str__(self) -> str:
        return str(self.draw(output="text"))

    def __eq__(self, other) -> bool:
        if not isinstance(other, QuantumCircuit):
            return False

        # TODO: remove the DAG from this function
        from qiskit.converters import circuit_to_dag

        return circuit_to_dag(self, copy_operations=False) == circuit_to_dag(
            other, copy_operations=False
        )

    def __deepcopy__(self, memo=None):
        # This is overridden to minimize memory pressure when we don't
        # actually need to pickle (i.e. the typical deepcopy case).
        # Note:
        #   This is done here instead of in CircuitData since PyO3
        #   doesn't include a native way to recursively call
        #   copy.deepcopy(memo).
        cls = self.__class__
        result = cls.__new__(cls)
        for k in self.__dict__.keys() - {"_data", "_builder_api"}:
            setattr(result, k, copy.deepcopy(self.__dict__[k], memo))

        result._builder_api = _OuterCircuitScopeInterface(result)

        # Avoids pulling self._data into a Python list
        # like we would when pickling.
        result._data = self._data.copy()
        result._data.replace_bits(
            qubits=copy.deepcopy(self._data.qubits, memo),
            clbits=copy.deepcopy(self._data.clbits, memo),
        )
        result._data.map_ops(lambda op: copy.deepcopy(op, memo))
        return result

    @classmethod
    def _increment_instances(cls):
        cls.instances += 1

    @classmethod
    def cls_instances(cls) -> int:
        """Return the current number of instances of this class,
        useful for auto naming."""
        return cls.instances

    @classmethod
    def cls_prefix(cls) -> str:
        """Return the prefix to use for auto naming."""
        return cls.prefix

    def _name_update(self) -> None:
        """update name of instance using instance number"""
        if not is_main_process():
            pid_name = f"-{mp.current_process().pid}"
        else:
            pid_name = ""

        self.name = f"{self._base_name}-{self.cls_instances()}{pid_name}"

    def has_register(self, register: Register) -> bool:
        """
        Test if this circuit has the register r.

        Args:
            register (Register): a quantum or classical register.

        Returns:
            bool: True if the register is contained in this circuit.
        """
        has_reg = False
        if isinstance(register, QuantumRegister) and register in self.qregs:
            has_reg = True
        elif isinstance(register, ClassicalRegister) and register in self.cregs:
            has_reg = True
        return has_reg

    def reverse_ops(self) -> "QuantumCircuit":
        """Reverse the circuit by reversing the order of instructions.

        This is done by recursively reversing all instructions.
        It does not invert (adjoint) any gate.

        Returns:
            QuantumCircuit: the reversed circuit.

        Examples:

            input:

            .. parsed-literal::

                     ┌───┐
                q_0: ┤ H ├─────■──────
                     └───┘┌────┴─────┐
                q_1: ─────┤ RX(1.57) ├
                          └──────────┘

            output:

            .. parsed-literal::

                                 ┌───┐
                q_0: ─────■──────┤ H ├
                     ┌────┴─────┐└───┘
                q_1: ┤ RX(1.57) ├─────
                     └──────────┘
        """
        reverse_circ = QuantumCircuit(
            self.qubits, self.clbits, *self.qregs, *self.cregs, name=self.name + "_reverse"
        )

        for instruction in reversed(self.data):
            reverse_circ._append(instruction.replace(operation=instruction.operation.reverse_ops()))

        reverse_circ.duration = self.duration
        reverse_circ.unit = self.unit
        return reverse_circ

    def reverse_bits(self) -> "QuantumCircuit":
        """Return a circuit with the opposite order of wires.

        The circuit is "vertically" flipped. If a circuit is
        defined over multiple registers, the resulting circuit will have
        the same registers but with their order flipped.

        This method is useful for converting a circuit written in little-endian
        convention to the big-endian equivalent, and vice versa.

        Returns:
            QuantumCircuit: the circuit with reversed bit order.

        Examples:

            input:

            .. parsed-literal::

                     ┌───┐
                a_0: ┤ H ├──■─────────────────
                     └───┘┌─┴─┐
                a_1: ─────┤ X ├──■────────────
                          └───┘┌─┴─┐
                a_2: ──────────┤ X ├──■───────
                               └───┘┌─┴─┐
                b_0: ───────────────┤ X ├──■──
                                    └───┘┌─┴─┐
                b_1: ────────────────────┤ X ├
                                         └───┘

            output:

            .. parsed-literal::

                                         ┌───┐
                b_0: ────────────────────┤ X ├
                                    ┌───┐└─┬─┘
                b_1: ───────────────┤ X ├──■──
                               ┌───┐└─┬─┘
                a_0: ──────────┤ X ├──■───────
                          ┌───┐└─┬─┘
                a_1: ─────┤ X ├──■────────────
                     ┌───┐└─┬─┘
                a_2: ┤ H ├──■─────────────────
                     └───┘
        """
        circ = QuantumCircuit(
            list(reversed(self.qubits)),
            list(reversed(self.clbits)),
            name=self.name,
            global_phase=self.global_phase,
        )
        new_qubit_map = circ.qubits[::-1]
        new_clbit_map = circ.clbits[::-1]
        for reg in reversed(self.qregs):
            bits = [new_qubit_map[self.find_bit(qubit).index] for qubit in reversed(reg)]
            circ.add_register(QuantumRegister(bits=bits, name=reg.name))
        for reg in reversed(self.cregs):
            bits = [new_clbit_map[self.find_bit(clbit).index] for clbit in reversed(reg)]
            circ.add_register(ClassicalRegister(bits=bits, name=reg.name))

        for instruction in self.data:
            qubits = [new_qubit_map[self.find_bit(qubit).index] for qubit in instruction.qubits]
            clbits = [new_clbit_map[self.find_bit(clbit).index] for clbit in instruction.clbits]
            circ._append(instruction.replace(qubits=qubits, clbits=clbits))
        return circ

    def inverse(self, annotated: bool = False) -> "QuantumCircuit":
        """Invert (take adjoint of) this circuit.

        This is done by recursively inverting all gates.

        Args:
            annotated: indicates whether the inverse gate can be implemented
                as an annotated gate.

        Returns:
            QuantumCircuit: the inverted circuit

        Raises:
            CircuitError: if the circuit cannot be inverted.

        Examples:

            input:

            .. parsed-literal::

                     ┌───┐
                q_0: ┤ H ├─────■──────
                     └───┘┌────┴─────┐
                q_1: ─────┤ RX(1.57) ├
                          └──────────┘

            output:

            .. parsed-literal::

                                  ┌───┐
                q_0: ──────■──────┤ H ├
                     ┌─────┴─────┐└───┘
                q_1: ┤ RX(-1.57) ├─────
                     └───────────┘
        """
        inverse_circ = QuantumCircuit(
            self.qubits,
            self.clbits,
            *self.qregs,
            *self.cregs,
            name=self.name + "_dg",
            global_phase=-self.global_phase,
        )

        for instruction in reversed(self._data):
            inverse_circ._append(
                instruction.replace(operation=instruction.operation.inverse(annotated=annotated))
            )
        return inverse_circ

    def repeat(self, reps: int) -> "QuantumCircuit":
        """Repeat this circuit ``reps`` times.

        Args:
            reps (int): How often this circuit should be repeated.

        Returns:
            QuantumCircuit: A circuit containing ``reps`` repetitions of this circuit.
        """
        repeated_circ = QuantumCircuit(
            self.qubits, self.clbits, *self.qregs, *self.cregs, name=self.name + f"**{reps}"
        )

        # benefit of appending instructions: decomposing shows the subparts, i.e. the power
        # is actually `reps` times this circuit, and it is currently much faster than `compose`.
        if reps > 0:
            try:  # try to append as gate if possible to not disallow to_gate
                inst: Instruction = self.to_gate()
            except QiskitError:
                inst = self.to_instruction()
            for _ in range(reps):
                repeated_circ._append(inst, self.qubits, self.clbits)

        return repeated_circ

    def power(
        self, power: float, matrix_power: bool = False, annotated: bool = False
    ) -> "QuantumCircuit":
        """Raise this circuit to the power of ``power``.

        If ``power`` is a positive integer and both ``matrix_power`` and ``annotated``
        are ``False``, this implementation defaults to calling ``repeat``. Otherwise,
        the circuit is converted into a gate, and a new circuit, containing this gate
        raised to the given power, is returned. The gate raised to the given power is
        implemented either as a unitary gate if ``annotated`` is ``False`` or as an
        annotated operation if ``annotated`` is ``True``.

        Args:
            power (float): The power to raise this circuit to.
            matrix_power (bool): indicates whether the inner power gate can be implemented
                as a unitary gate.
            annotated (bool): indicates whether the inner power gate can be implemented
                as an annotated operation.

        Raises:
            CircuitError: If the circuit needs to be converted to a unitary gate, but is
                not unitary.

        Returns:
            QuantumCircuit: A circuit implementing this circuit raised to the power of ``power``.
        """
        if (
            power >= 0
            and isinstance(power, (int, np.integer))
            and not matrix_power
            and not annotated
        ):
            return self.repeat(power)

        # attempt conversion to gate
        if self.num_parameters > 0:
            raise CircuitError(
                "Cannot raise a parameterized circuit to a non-positive power "
                "or matrix-power, please bind the free parameters: "
                "{}".format(self.parameters)
            )

        try:
            gate = self.to_gate()
        except QiskitError as ex:
            raise CircuitError(
                "The circuit contains non-unitary operations and cannot be "
                "raised to a power. Note that no qiskit.circuit.Instruction "
                "objects may be in the circuit for this operation."
            ) from ex

        power_circuit = QuantumCircuit(self.qubits, self.clbits, *self.qregs, *self.cregs)
        power_circuit.append(gate.power(power, annotated=annotated), list(range(gate.num_qubits)))
        return power_circuit

    def control(
        self,
        num_ctrl_qubits: int = 1,
        label: str | None = None,
        ctrl_state: str | int | None = None,
        annotated: bool = False,
    ) -> "QuantumCircuit":
        """Control this circuit on ``num_ctrl_qubits`` qubits.

        Args:
            num_ctrl_qubits (int): The number of control qubits.
            label (str): An optional label to give the controlled operation for visualization.
            ctrl_state (str or int): The control state in decimal or as a bitstring
                (e.g. '111'). If None, use ``2**num_ctrl_qubits - 1``.
            annotated: indicates whether the controlled gate can be implemented
                as an annotated gate.

        Returns:
            QuantumCircuit: The controlled version of this circuit.

        Raises:
            CircuitError: If the circuit contains a non-unitary operation and cannot be controlled.
        """
        try:
            gate = self.to_gate()
        except QiskitError as ex:
            raise CircuitError(
                "The circuit contains non-unitary operations and cannot be "
                "controlled. Note that no qiskit.circuit.Instruction objects may "
                "be in the circuit for this operation."
            ) from ex

        controlled_gate = gate.control(num_ctrl_qubits, label, ctrl_state, annotated)
        control_qreg = QuantumRegister(num_ctrl_qubits)
        controlled_circ = QuantumCircuit(
            control_qreg, self.qubits, *self.qregs, name=f"c_{self.name}"
        )
        controlled_circ.append(controlled_gate, controlled_circ.qubits)

        return controlled_circ

    def compose(
        self,
        other: Union["QuantumCircuit", Instruction],
        qubits: QubitSpecifier | Sequence[QubitSpecifier] | None = None,
        clbits: ClbitSpecifier | Sequence[ClbitSpecifier] | None = None,
        front: bool = False,
        inplace: bool = False,
        wrap: bool = False,
    ) -> Optional["QuantumCircuit"]:
        """Compose circuit with ``other`` circuit or instruction, optionally permuting wires.

        ``other`` can be narrower or of equal width to ``self``.

        Args:
            other (qiskit.circuit.Instruction or QuantumCircuit):
                (sub)circuit or instruction to compose onto self.  If not a :obj:`.QuantumCircuit`,
                this can be anything that :obj:`.append` will accept.
            qubits (list[Qubit|int]): qubits of self to compose onto.
            clbits (list[Clbit|int]): clbits of self to compose onto.
            front (bool): If True, front composition will be performed.  This is not possible within
                control-flow builder context managers.
            inplace (bool): If True, modify the object. Otherwise return composed circuit.
            wrap (bool): If True, wraps the other circuit into a gate (or instruction, depending on
                whether it contains only unitary instructions) before composing it onto self.

        Returns:
            QuantumCircuit: the composed circuit (returns None if inplace==True).

        Raises:
            CircuitError: if no correct wire mapping can be made between the two circuits, such as
                if ``other`` is wider than ``self``.
            CircuitError: if trying to emit a new circuit while ``self`` has a partially built
                control-flow context active, such as the context-manager forms of :meth:`if_test`,
                :meth:`for_loop` and :meth:`while_loop`.
            CircuitError: if trying to compose to the front of a circuit when a control-flow builder
                block is active; there is no clear meaning to this action.

        Examples:
            .. code-block:: python

                >>> lhs.compose(rhs, qubits=[3, 2], inplace=True)

            .. parsed-literal::

                            ┌───┐                   ┌─────┐                ┌───┐
                lqr_1_0: ───┤ H ├───    rqr_0: ──■──┤ Tdg ├    lqr_1_0: ───┤ H ├───────────────
                            ├───┤              ┌─┴─┐└─────┘                ├───┤
                lqr_1_1: ───┤ X ├───    rqr_1: ┤ X ├───────    lqr_1_1: ───┤ X ├───────────────
                         ┌──┴───┴──┐           └───┘                    ┌──┴───┴──┐┌───┐
                lqr_1_2: ┤ U1(0.1) ├  +                     =  lqr_1_2: ┤ U1(0.1) ├┤ X ├───────
                         └─────────┘                                    └─────────┘└─┬─┘┌─────┐
                lqr_2_0: ─────■─────                           lqr_2_0: ─────■───────■──┤ Tdg ├
                            ┌─┴─┐                                          ┌─┴─┐        └─────┘
                lqr_2_1: ───┤ X ├───                           lqr_2_1: ───┤ X ├───────────────
                            └───┘                                          └───┘
                lcr_0: 0 ═══════════                           lcr_0: 0 ═══════════════════════

                lcr_1: 0 ═══════════                           lcr_1: 0 ═══════════════════════

        """

        if inplace and front and self._control_flow_scopes:
            # If we're composing onto ourselves while in a stateful control-flow builder context,
            # there's no clear meaning to composition to the "front" of the circuit.
            raise CircuitError(
                "Cannot compose to the front of a circuit while a control-flow context is active."
            )
        if not inplace and self._control_flow_scopes:
            # If we're inside a stateful control-flow builder scope, even if we successfully cloned
            # the partial builder scope (not simple), the scope wouldn't be controlled by an active
            # `with` statement, so the output circuit would be permanently broken.
            raise CircuitError(
                "Cannot emit a new composed circuit while a control-flow context is active."
            )

        # Avoid mutating `dest` until as much of the error checking as possible is complete, to
        # avoid an in-place composition getting `self` in a partially mutated state for a simple
        # error that the user might want to correct in an interactive session.
        dest = self if inplace else self.copy()

        # As a special case, allow composing some clbits onto no clbits - normally the destination
        # has to be strictly larger. This allows composing final measurements onto unitary circuits.
        if isinstance(other, QuantumCircuit):
            if not self.clbits and other.clbits:
                if dest._control_flow_scopes:
                    raise CircuitError(
                        "cannot implicitly add clbits while within a control-flow scope"
                    )
                dest.add_bits(other.clbits)
                for reg in other.cregs:
                    dest.add_register(reg)

        if wrap and isinstance(other, QuantumCircuit):
            other = (
                other.to_gate()
                if all(isinstance(ins.operation, Gate) for ins in other.data)
                else other.to_instruction()
            )

        if not isinstance(other, QuantumCircuit):
            if qubits is None:
                qubits = self.qubits[: other.num_qubits]
            if clbits is None:
                clbits = self.clbits[: other.num_clbits]
            if front:
                # Need to keep a reference to the data for use after we've emptied it.
                old_data = dest._data.copy()
                dest.clear()
                dest.append(other, qubits, clbits)
                for instruction in old_data:
                    dest._append(instruction)
            else:
                dest.append(other, qargs=qubits, cargs=clbits)
            return None if inplace else dest

        if other.num_qubits > dest.num_qubits or other.num_clbits > dest.num_clbits:
            raise CircuitError(
                "Trying to compose with another QuantumCircuit which has more 'in' edges."
            )

        # Maps bits in 'other' to bits in 'dest'.
        mapped_qubits: list[Qubit]
        mapped_clbits: list[Clbit]
        edge_map: dict[Qubit | Clbit, Qubit | Clbit] = {}
        if qubits is None:
            mapped_qubits = dest.qubits
            edge_map.update(zip(other.qubits, dest.qubits))
        else:
            mapped_qubits = dest.qbit_argument_conversion(qubits)
            if len(mapped_qubits) != len(other.qubits):
                raise CircuitError(
                    f"Number of items in qubits parameter ({len(mapped_qubits)}) does not"
                    f" match number of qubits in the circuit ({len(other.qubits)})."
                )
            if len(set(mapped_qubits)) != len(mapped_qubits):
                raise CircuitError(
                    f"Duplicate qubits referenced in 'qubits' parameter: '{mapped_qubits}'"
                )
            edge_map.update(zip(other.qubits, mapped_qubits))

        if clbits is None:
            mapped_clbits = dest.clbits
            edge_map.update(zip(other.clbits, dest.clbits))
        else:
            mapped_clbits = dest.cbit_argument_conversion(clbits)
            if len(mapped_clbits) != len(other.clbits):
                raise CircuitError(
                    f"Number of items in clbits parameter ({len(mapped_clbits)}) does not"
                    f" match number of clbits in the circuit ({len(other.clbits)})."
                )
            if len(set(mapped_clbits)) != len(mapped_clbits):
                raise CircuitError(
                    f"Duplicate clbits referenced in 'clbits' parameter: '{mapped_clbits}'"
                )
            edge_map.update(zip(other.clbits, dest.cbit_argument_conversion(clbits)))

        for gate, cals in other.calibrations.items():
            dest._calibrations[gate].update(cals)

        dest.duration = None
        dest.unit = "dt"
        dest.global_phase += other.global_phase

        if not other.data:
            # Nothing left to do. Plus, accessing 'data' here is necessary
            # to trigger any lazy building since we now access '_data'
            # directly.
            return None if inplace else dest

        variable_mapper = _classical_resource_map.VariableMapper(
            dest.cregs, edge_map, dest.add_register
        )

        def map_vars(op):
            n_op = op.copy()
            if (condition := getattr(n_op, "condition", None)) is not None:
                n_op.condition = variable_mapper.map_condition(condition)
            if isinstance(n_op, SwitchCaseOp):
                n_op.target = variable_mapper.map_target(n_op.target)
            return n_op

        mapped_instrs: CircuitData = other._data.copy()
        mapped_instrs.replace_bits(qubits=mapped_qubits, clbits=mapped_clbits)
        mapped_instrs.map_ops(map_vars)

        append_existing = None
        if front:
            append_existing = dest._data.copy()
            dest.clear()

        circuit_scope = dest._current_scope()
        circuit_scope.extend(mapped_instrs)
        if append_existing:
            circuit_scope.extend(append_existing)

        return None if inplace else dest

    def tensor(self, other: "QuantumCircuit", inplace: bool = False) -> Optional["QuantumCircuit"]:
        """Tensor ``self`` with ``other``.

        Remember that in the little-endian convention the leftmost operation will be at the bottom
        of the circuit. See also
        `the docs <https://docs.quantum.ibm.com/build/circuit-construction>`__
        for more information.

        .. parsed-literal::

                 ┌────────┐        ┌─────┐          ┌─────┐
            q_0: ┤ bottom ├ ⊗ q_0: ┤ top ├  = q_0: ─┤ top ├──
                 └────────┘        └─────┘         ┌┴─────┴─┐
                                              q_1: ┤ bottom ├
                                                   └────────┘

        Args:
            other (QuantumCircuit): The other circuit to tensor this circuit with.
            inplace (bool): If True, modify the object. Otherwise return composed circuit.

        Examples:

            .. plot::
               :include-source:

               from qiskit import QuantumCircuit
               top = QuantumCircuit(1)
               top.x(0);
               bottom = QuantumCircuit(2)
               bottom.cry(0.2, 0, 1);
               tensored = bottom.tensor(top)
               tensored.draw('mpl')

        Returns:
            QuantumCircuit: The tensored circuit (returns None if inplace==True).
        """
        num_qubits = self.num_qubits + other.num_qubits
        num_clbits = self.num_clbits + other.num_clbits

        # If a user defined both circuits with via register sizes and not with named registers
        # (e.g. QuantumCircuit(2, 2)) then we have a naming collision, as the registers are by
        # default called "q" resp. "c". To still allow tensoring we define new registers of the
        # correct sizes.
        if (
            len(self.qregs) == len(other.qregs) == 1
            and self.qregs[0].name == other.qregs[0].name == "q"
        ):
            # check if classical registers are in the circuit
            if num_clbits > 0:
                dest = QuantumCircuit(num_qubits, num_clbits)
            else:
                dest = QuantumCircuit(num_qubits)

        # handle case if ``measure_all`` was called on both circuits, in which case the
        # registers are both named "meas"
        elif (
            len(self.cregs) == len(other.cregs) == 1
            and self.cregs[0].name == other.cregs[0].name == "meas"
        ):
            cr = ClassicalRegister(self.num_clbits + other.num_clbits, "meas")
            dest = QuantumCircuit(*other.qregs, *self.qregs, cr)

        # Now we don't have to handle any more cases arising from special implicit naming
        else:
            dest = QuantumCircuit(
                other.qubits,
                self.qubits,
                other.clbits,
                self.clbits,
                *other.qregs,
                *self.qregs,
                *other.cregs,
                *self.cregs,
            )

        # compose self onto the output, and then other
        dest.compose(other, range(other.num_qubits), range(other.num_clbits), inplace=True)
        dest.compose(
            self,
            range(other.num_qubits, num_qubits),
            range(other.num_clbits, num_clbits),
            inplace=True,
        )

        # Replace information from tensored circuit into self when inplace = True
        if inplace:
            self.__dict__.update(dest.__dict__)
            return None
        return dest

    @property
    def qubits(self) -> list[Qubit]:
        """
        Returns a list of quantum bits in the order that the registers were added.
        """
        return self._data.qubits

    @property
    def clbits(self) -> list[Clbit]:
        """
        Returns a list of classical bits in the order that the registers were added.
        """
        return self._data.clbits

    @property
    def ancillas(self) -> list[AncillaQubit]:
        """
        Returns a list of ancilla bits in the order that the registers were added.
        """
        return self._ancillas

    @property
    def num_vars(self) -> int:
        """The number of runtime classical variables in the circuit.

        This is the length of the :meth:`iter_vars` iterable."""
        return self.num_input_vars + self.num_captured_vars + self.num_declared_vars

    @property
    def num_input_vars(self) -> int:
        """The number of runtime classical variables in the circuit marked as circuit inputs.

        This is the length of the :meth:`iter_input_vars` iterable.  If this is non-zero,
        :attr:`num_captured_vars` must be zero."""
        return len(self._vars_input)

    @property
    def num_captured_vars(self) -> int:
        """The number of runtime classical variables in the circuit marked as captured from an
        enclosing scope.

        This is the length of the :meth:`iter_captured_vars` iterable.  If this is non-zero,
        :attr:`num_input_vars` must be zero."""
        return len(self._vars_capture)

    @property
    def num_declared_vars(self) -> int:
        """The number of runtime classical variables in the circuit that are declared by this
        circuit scope, excluding inputs or captures.

        This is the length of the :meth:`iter_declared_vars` iterable."""
        return len(self._vars_local)

    def iter_vars(self) -> typing.Iterable[expr.Var]:
        """Get an iterable over all runtime classical variables in scope within this circuit.

        This method will iterate over all variables in scope.  For more fine-grained iterators, see
        :meth:`iter_declared_vars`, :meth:`iter_input_vars` and :meth:`iter_captured_vars`."""
        if self._control_flow_scopes:
            builder = self._control_flow_scopes[-1]
            return itertools.chain(builder.iter_captured_vars(), builder.iter_local_vars())
        return itertools.chain(
            self._vars_input.values(), self._vars_capture.values(), self._vars_local.values()
        )

    def iter_declared_vars(self) -> typing.Iterable[expr.Var]:
        """Get an iterable over all runtime classical variables that are declared with automatic
        storage duration in this scope.  This excludes input variables (see :meth:`iter_input_vars`)
        and captured variables (see :meth:`iter_captured_vars`)."""
        if self._control_flow_scopes:
            return self._control_flow_scopes[-1].iter_local_vars()
        return self._vars_local.values()

    def iter_input_vars(self) -> typing.Iterable[expr.Var]:
        """Get an iterable over all runtime classical variables that are declared as inputs to this
        circuit scope.  This excludes locally declared variables (see :meth:`iter_declared_vars`)
        and captured variables (see :meth:`iter_captured_vars`)."""
        if self._control_flow_scopes:
            return ()
        return self._vars_input.values()

    def iter_captured_vars(self) -> typing.Iterable[expr.Var]:
        """Get an iterable over all runtime classical variables that are captured by this circuit
        scope from a containing scope.  This excludes input variables (see :meth:`iter_input_vars`)
        and locally declared variables (see :meth:`iter_declared_vars`)."""
        if self._control_flow_scopes:
            return self._control_flow_scopes[-1].iter_captured_vars()
        return self._vars_capture.values()

    def __and__(self, rhs: "QuantumCircuit") -> "QuantumCircuit":
        """Overload & to implement self.compose."""
        return self.compose(rhs)

    def __iand__(self, rhs: "QuantumCircuit") -> "QuantumCircuit":
        """Overload &= to implement self.compose in place."""
        self.compose(rhs, inplace=True)
        return self

    def __xor__(self, top: "QuantumCircuit") -> "QuantumCircuit":
        """Overload ^ to implement self.tensor."""
        return self.tensor(top)

    def __ixor__(self, top: "QuantumCircuit") -> "QuantumCircuit":
        """Overload ^= to implement self.tensor in place."""
        self.tensor(top, inplace=True)
        return self

    def __len__(self) -> int:
        """Return number of operations in circuit."""
        return len(self._data)

    @typing.overload
    def __getitem__(self, item: int) -> CircuitInstruction: ...

    @typing.overload
    def __getitem__(self, item: slice) -> list[CircuitInstruction]: ...

    def __getitem__(self, item):
        """Return indexed operation."""
        return self._data[item]

    @staticmethod
    def cast(value: S, type_: Callable[..., T]) -> Union[S, T]:
        """Best effort to cast value to type. Otherwise, returns the value."""
        try:
            return type_(value)
        except (ValueError, TypeError):
            return value

    def qbit_argument_conversion(self, qubit_representation: QubitSpecifier) -> list[Qubit]:
        """
        Converts several qubit representations (such as indexes, range, etc.)
        into a list of qubits.

        Args:
            qubit_representation (Object): representation to expand

        Returns:
            List(Qubit): the resolved instances of the qubits.
        """
        return _bit_argument_conversion(
            qubit_representation, self.qubits, self._qubit_indices, Qubit
        )

    def cbit_argument_conversion(self, clbit_representation: ClbitSpecifier) -> list[Clbit]:
        """
        Converts several classical bit representations (such as indexes, range, etc.)
        into a list of classical bits.

        Args:
            clbit_representation (Object): representation to expand

        Returns:
            List(tuple): Where each tuple is a classical bit.
        """
        return _bit_argument_conversion(
            clbit_representation, self.clbits, self._clbit_indices, Clbit
        )

    def append(
        self,
        instruction: Operation | CircuitInstruction,
        qargs: Sequence[QubitSpecifier] | None = None,
        cargs: Sequence[ClbitSpecifier] | None = None,
    ) -> InstructionSet:
        """Append one or more instructions to the end of the circuit, modifying the circuit in
        place.

        The ``qargs`` and ``cargs`` will be expanded and broadcast according to the rules of the
        given :class:`~.circuit.Instruction`, and any non-:class:`.Bit` specifiers (such as
        integer indices) will be resolved into the relevant instances.

        If a :class:`.CircuitInstruction` is given, it will be unwrapped, verified in the context of
        this circuit, and a new object will be appended to the circuit.  In this case, you may not
        pass ``qargs`` or ``cargs`` separately.

        Args:
            instruction: :class:`~.circuit.Instruction` instance to append, or a
                :class:`.CircuitInstruction` with all its context.
            qargs: specifiers of the :class:`~.circuit.Qubit`\\ s to attach instruction to.
            cargs: specifiers of the :class:`.Clbit`\\ s to attach instruction to.

        Returns:
            qiskit.circuit.InstructionSet: a handle to the :class:`.CircuitInstruction`\\ s that
            were actually added to the circuit.

        Raises:
            CircuitError: if the operation passed is not an instance of :class:`~.circuit.Instruction` .
        """
        if isinstance(instruction, CircuitInstruction):
            operation = instruction.operation
            qargs = instruction.qubits
            cargs = instruction.clbits
        else:
            operation = instruction

        # Convert input to instruction
        if not isinstance(operation, Operation):
            if hasattr(operation, "to_instruction"):
                operation = operation.to_instruction()
                if not isinstance(operation, Operation):
                    raise CircuitError("operation.to_instruction() is not an Operation.")
            else:
                if issubclass(operation, Operation):
                    raise CircuitError(
                        "Object is a subclass of Operation, please add () to "
                        "pass an instance of this object."
                    )

                raise CircuitError(
                    "Object to append must be an Operation or have a to_instruction() method."
                )

        circuit_scope = self._current_scope()

        # Make copy of parameterized gate instances
        if params := getattr(operation, "params", ()):
            is_parameter = False
            for param in params:
                is_parameter = is_parameter or isinstance(param, Parameter)
                if isinstance(param, expr.Expr):
                    param = _validate_expr(circuit_scope, param)
            if is_parameter:
                operation = copy.deepcopy(operation)
        if isinstance(operation, ControlFlowOp):
            # Verify that any variable bindings are valid.  Control-flow ops are already enforced
            # by the class not to contain 'input' variables.
            if bad_captures := {
                var
                for var in itertools.chain.from_iterable(
                    block.iter_captured_vars() for block in operation.blocks
                )
                if not self.has_var(var)
            }:
                raise CircuitError(
                    f"Control-flow op attempts to capture '{bad_captures}'"
                    " which are not in this circuit"
                )

        expanded_qargs = [self.qbit_argument_conversion(qarg) for qarg in qargs or []]
        expanded_cargs = [self.cbit_argument_conversion(carg) for carg in cargs or []]

        instructions = InstructionSet(resource_requester=circuit_scope.resolve_classical_resource)
        # For Operations that are non-Instructions, we use the Instruction's default method
        broadcast_iter = (
            operation.broadcast_arguments(expanded_qargs, expanded_cargs)
            if isinstance(operation, Instruction)
            else Instruction.broadcast_arguments(operation, expanded_qargs, expanded_cargs)
        )
        for qarg, carg in broadcast_iter:
            self._check_dups(qarg)
            instruction = CircuitInstruction(operation, qarg, carg)
            circuit_scope.append(instruction)
            instructions._add_ref(circuit_scope.instructions, len(circuit_scope.instructions) - 1)
        return instructions

    # Preferred new style.
    @typing.overload
    def _append(
        self, instruction: CircuitInstruction, _qargs: None = None, _cargs: None = None
    ) -> CircuitInstruction: ...

    # To-be-deprecated old style.
    @typing.overload
    def _append(
        self,
        operation: Operation,
        qargs: Sequence[Qubit],
        cargs: Sequence[Clbit],
    ) -> Operation: ...

    def _append(
        self,
        instruction: CircuitInstruction | Instruction,
        qargs: Sequence[Qubit] | None = None,
        cargs: Sequence[Clbit] | None = None,
    ):
        """Append an instruction to the end of the circuit, modifying the circuit in place.

        .. warning::

            This is an internal fast-path function, and it is the responsibility of the caller to
            ensure that all the arguments are valid; there is no error checking here.  In
            particular, all the qubits and clbits must already exist in the circuit and there can be
            no duplicates in the list.

        .. note::

            This function may be used by callers other than :obj:`.QuantumCircuit` when the caller
            is sure that all error-checking, broadcasting and scoping has already been performed,
            and the only reference to the circuit the instructions are being appended to is within
            that same function.  In particular, it is not safe to call
            :meth:`QuantumCircuit._append` on a circuit that is received by a function argument.
            This is because :meth:`.QuantumCircuit._append` will not recognise the scoping
            constructs of the control-flow builder interface.

        Args:
            instruction: Operation instance to append
            qargs: Qubits to attach the instruction to.
            cargs: Clbits to attach the instruction to.

        Returns:
            Operation: a handle to the instruction that was just added

        :meta public:
        """
        old_style = not isinstance(instruction, CircuitInstruction)
        if old_style:
            instruction = CircuitInstruction(instruction, qargs, cargs)
        self._data.append(instruction)
        self._track_operation(instruction.operation)
        return instruction.operation if old_style else instruction

    def _track_operation(self, operation: Operation):
        """Sync all non-data-list internal data structures for a newly tracked operation."""
        if isinstance(operation, Instruction):
            self._update_parameter_table(operation)
        self.duration = None
        self.unit = "dt"

    def _update_parameter_table(self, instruction: Instruction):
        for param_index, param in enumerate(instruction.params):
            if isinstance(param, (ParameterExpression, QuantumCircuit)):
                # Scoped constructs like the control-flow ops use QuantumCircuit as a parameter.
                atomic_parameters = set(param.parameters)
            else:
                atomic_parameters = set()

            for parameter in atomic_parameters:
                if parameter in self._parameter_table:
                    self._parameter_table[parameter].add((instruction, param_index))
                else:
                    if parameter.name in self._parameter_table.get_names():
                        raise CircuitError(f"Name conflict on adding parameter: {parameter.name}")
                    self._parameter_table[parameter] = ParameterReferences(
                        ((instruction, param_index),)
                    )

                    # clear cache if new parameter is added
                    self._parameters = None

    @typing.overload
    def get_parameter(self, name: str, default: T) -> Union[Parameter, T]: ...

    # The builtin `types` module has `EllipsisType`, but only from 3.10+!
    @typing.overload
    def get_parameter(self, name: str, default: type(...) = ...) -> Parameter: ...

    # We use a _literal_ `Ellipsis` as the marker value to leave `None` available as a default.
    def get_parameter(self, name: str, default: typing.Any = ...) -> Parameter:
        """Retrieve a compile-time parameter that is accessible in this circuit scope by name.

        Args:
            name: the name of the parameter to retrieve.
            default: if given, this value will be returned if the parameter is not present.  If it
                is not given, a :exc:`KeyError` is raised instead.

        Returns:
            The corresponding parameter.

        Raises:
            KeyError: if no default is given, but the parameter does not exist in the circuit.

        Examples:
            Retrieve a parameter by name from a circuit::

                from qiskit.circuit import QuantumCircuit, Parameter

                my_param = Parameter("my_param")

                # Create a parametrised circuit.
                qc = QuantumCircuit(1)
                qc.rx(my_param, 0)

                # We can use 'my_param' as a parameter, but let's say we've lost the Python object
                # and need to retrieve it.
                my_param_again = qc.get_parameter("my_param")

                assert my_param is my_param_again

            Get a variable from a circuit by name, returning some default if it is not present::

                assert qc.get_parameter("my_param", None) is my_param
                assert qc.get_parameter("unknown_param", None) is None

        See also:
            :meth:`get_var`
                A similar method, but for :class:`.expr.Var` run-time variables instead of
                :class:`.Parameter` compile-time parameters.
        """
        if (parameter := self._parameter_table.parameter_from_name(name, None)) is None:
            if default is Ellipsis:
                raise KeyError(f"no parameter named '{name}' is present")
            return default
        return parameter

    def has_parameter(self, name_or_param: str | Parameter, /) -> bool:
        """Check whether a parameter object exists in this circuit.

        Args:
            name_or_param: the parameter, or name of a parameter to check.  If this is a
                :class:`.Parameter` node, the parameter must be exactly the given one for this
                function to return ``True``.

        Returns:
            whether a matching parameter is assignable in this circuit.

        See also:
            :meth:`QuantumCircuit.get_parameter`
                Retrieve the :class:`.Parameter` instance from this circuit by name.
            :meth:`QuantumCircuit.has_var`
                A similar method to this, but for run-time :class:`.expr.Var` variables instead of
                compile-time :class:`.Parameter`\\ s.
        """
        if isinstance(name_or_param, str):
            return self.get_parameter(name_or_param, None) is not None
        return self.get_parameter(name_or_param.name) == name_or_param

    @typing.overload
    def get_var(self, name: str, default: T) -> Union[expr.Var, T]: ...

    # The builtin `types` module has `EllipsisType`, but only from 3.10+!
    @typing.overload
    def get_var(self, name: str, default: type(...) = ...) -> expr.Var: ...

    # We use a _literal_ `Ellipsis` as the marker value to leave `None` available as a default.
    def get_var(self, name: str, default: typing.Any = ...):
        """Retrieve a variable that is accessible in this circuit scope by name.

        Args:
            name: the name of the variable to retrieve.
            default: if given, this value will be returned if the variable is not present.  If it
                is not given, a :exc:`KeyError` is raised instead.

        Returns:
            The corresponding variable.

        Raises:
            KeyError: if no default is given, but the variable does not exist.

        Examples:
            Retrieve a variable by name from a circuit::

                from qiskit.circuit import QuantumCircuit

                # Create a circuit and create a variable in it.
                qc = QuantumCircuit()
                my_var = qc.add_var("my_var", False)

                # We can use 'my_var' as a variable, but let's say we've lost the Python object and
                # need to retrieve it.
                my_var_again = qc.get_var("my_var")

                assert my_var is my_var_again

            Get a variable from a circuit by name, returning some default if it is not present::

                assert qc.get_var("my_var", None) is my_var
                assert qc.get_var("unknown_variable", None) is None

        See also:
            :meth:`get_parameter`
                A similar method, but for :class:`.Parameter` compile-time parameters instead of
                :class:`.expr.Var` run-time variables.
        """
        if (out := self._current_scope().get_var(name)) is not None:
            return out
        if default is Ellipsis:
            raise KeyError(f"no variable named '{name}' is present")
        return default

    def has_var(self, name_or_var: str | expr.Var, /) -> bool:
        """Check whether a variable is accessible in this scope.

        Args:
            name_or_var: the variable, or name of a variable to check.  If this is a
                :class:`.expr.Var` node, the variable must be exactly the given one for this
                function to return ``True``.

        Returns:
            whether a matching variable is accessible.

        See also:
            :meth:`QuantumCircuit.get_var`
                Retrieve the :class:`.expr.Var` instance from this circuit by name.
            :meth:`QuantumCircuit.has_parameter`
                A similar method to this, but for compile-time :class:`.Parameter`\\ s instead of
                run-time :class:`.expr.Var` variables.
        """
        if isinstance(name_or_var, str):
            return self.get_var(name_or_var, None) is not None
        return self.get_var(name_or_var.name, None) == name_or_var

    def _prepare_new_var(
        self, name_or_var: str | expr.Var, type_: types.Type | None, /
    ) -> expr.Var:
        """The common logic for preparing and validating a new :class:`~.expr.Var` for the circuit.

        The given ``type_`` can be ``None`` if the variable specifier is already a :class:`.Var`,
        and must be a :class:`~.types.Type` if it is a string.  The argument is ignored if the given
        first argument is a :class:`.Var` already.

        Returns the validated variable, which is guaranteed to be safe to add to the circuit."""
        if isinstance(name_or_var, str):
            if type_ is None:
                raise CircuitError("the type must be known when creating a 'Var' from a string")
            var = expr.Var.new(name_or_var, type_)
        else:
            var = name_or_var
            if not var.standalone:
                raise CircuitError(
                    "cannot add variables that wrap `Clbit` or `ClassicalRegister` instances."
                    " Use `add_bits` or `add_register` as appropriate."
                )

        # The `var` is guaranteed to have a name because we already excluded the cases where it's
        # wrapping a bit/register.
        if (previous := self.get_var(var.name, default=None)) is not None:
            if previous == var:
                raise CircuitError(f"'{var}' is already present in the circuit")
            raise CircuitError(f"cannot add '{var}' as its name shadows the existing '{previous}'")
        return var

    def add_var(self, name_or_var: str | expr.Var, /, initial: typing.Any) -> expr.Var:
        """Add a classical variable with automatic storage and scope to this circuit.

        The variable is considered to have been "declared" at the beginning of the circuit, but it
        only becomes initialized at the point of the circuit that you call this method, so it can
        depend on variables defined before it.

        Args:
            name_or_var: either a string of the variable name, or an existing instance of
                :class:`~.expr.Var` to re-use.  Variables cannot shadow names that are already in
                use within the circuit.
            initial: the value to initialize this variable with.  If the first argument was given
                as a string name, the type of the resulting variable is inferred from the initial
                expression; to control this more manually, either use :meth:`.Var.new` to manually
                construct a new variable with the desired type, or use :func:`.expr.cast` to cast
                the initializer to the desired type.

                This must be either a :class:`~.expr.Expr` node, or a value that can be lifted to
                one using :class:`.expr.lift`.

        Returns:
            The created variable.  If a :class:`~.expr.Var` instance was given, the exact same
            object will be returned.

        Raises:
            CircuitError: if the variable cannot be created due to shadowing an existing variable.

        Examples:
            Define a new variable given just a name and an initializer expression::

                from qiskit.circuit import QuantumCircuit

                qc = QuantumCircuit(2)
                my_var = qc.add_var("my_var", False)

            Reuse a variable that may have been taken from a related circuit, or otherwise
            constructed manually, and initialize it to some more complicated expression::

                from qiskit.circuit import QuantumCircuit, QuantumRegister, ClassicalRegister
                from qiskit.circuit.classical import expr, types

                my_var = expr.Var.new("my_var", types.Uint(8))

                cr1 = ClassicalRegister(8, "cr1")
                cr2 = ClassicalRegister(8, "cr2")
                qc = QuantumCircuit(QuantumRegister(8), cr1, cr2)

                # Get some measurement results into each register.
                qc.h(0)
                for i in range(1, 8):
                    qc.cx(0, i)
                qc.measure(range(8), cr1)

                qc.reset(range(8))
                qc.h(0)
                for i in range(1, 8):
                    qc.cx(0, i)
                qc.measure(range(8), cr2)

                # Now when we add the variable, it is initialized using the runtime state of the two
                # classical registers we measured into above.
                qc.add_var(my_var, expr.bit_and(cr1, cr2))
        """
        # Validate the initialiser first to catch cases where the variable to be declared is being
        # used in the initialiser.
        circuit_scope = self._current_scope()
        initial = _validate_expr(circuit_scope, expr.lift(initial))
        if isinstance(name_or_var, str):
            var = expr.Var.new(name_or_var, initial.type)
        elif not name_or_var.standalone:
            raise CircuitError(
                "cannot add variables that wrap `Clbit` or `ClassicalRegister` instances."
            )
        else:
            var = name_or_var
        circuit_scope.add_uninitialized_var(var)
        try:
            # Store is responsible for ensuring the type safety of the initialisation.
            store = Store(var, initial)
        except CircuitError:
            circuit_scope.remove_var(var)
            raise
        circuit_scope.append(CircuitInstruction(store, (), ()))
        return var

    def add_uninitialized_var(self, var: expr.Var, /):
        """Add a variable with no initializer.

        In most cases, you should use :meth:`add_var` to initialize the variable.  To use this
        function, you must already hold a :class:`~.expr.Var` instance, as the use of the function
        typically only makes sense in copying contexts.

        .. warning::

            Qiskit makes no assertions about what an uninitialized variable will evaluate to at
            runtime, and some hardware may reject this as an error.

            You should treat this function with caution, and as a low-level primitive that is useful
            only in special cases of programmatically rebuilding two like circuits.

        Args:
            var: the variable to add.
        """
        # This function is deliberately meant to be a bit harder to find, to have a long descriptive
        # name, and to be a bit less ergonomic than `add_var` (i.e. not allowing the (name, type)
        # overload) to discourage people from using it when they should use `add_var`.
        #
        # This function exists so that there is a method to emulate `copy_empty_like`'s behaviour of
        # adding uninitialised variables, which there's no obvious way around.  We need to be sure
        # that _some_ sort of handling of uninitialised variables is taken into account in our
        # structures, so that doesn't become a huge edge case, even though we make no assertions
        # about the _meaning_ if such an expression was run on hardware.
        if self._control_flow_scopes:
            raise CircuitError("cannot add an uninitialized variable in a control-flow scope")
        if not var.standalone:
            raise CircuitError("cannot add a variable wrapping a bit or register to a circuit")
        self._builder_api.add_uninitialized_var(var)

    def add_capture(self, var: expr.Var):
        """Add a variable to the circuit that it should capture from a scope it will be contained
        within.

        This method requires a :class:`~.expr.Var` node to enforce that you've got a handle to one,
        because you will need to declare the same variable using the same object into the outer
        circuit.

        This is a low-level method, which is only really useful if you are manually constructing
        control-flow operations. You typically will not need to call this method, assuming you
        are using the builder interface for control-flow scopes (``with`` context-manager statements
        for :meth:`if_test` and the other scoping constructs).  The builder interface will
        automatically make the inner scopes closures on your behalf by capturing any variables that
        are used within them.

        Args:
            var: the variable to capture from an enclosing scope.

        Raises:
            CircuitError: if the variable cannot be created due to shadowing an existing variable.
        """
        if self._control_flow_scopes:
            # Allow manual capturing.  Not sure why it'd be useful, but there's a clear expected
            # behaviour here.
            self._control_flow_scopes[-1].use_var(var)
            return
        if self._vars_input:
            raise CircuitError(
                "circuits with input variables cannot be enclosed, so cannot be closures"
            )
        self._vars_capture[var.name] = self._prepare_new_var(var, None)

    @typing.overload
    def add_input(self, name_or_var: str, type_: types.Type, /) -> expr.Var: ...

    @typing.overload
    def add_input(self, name_or_var: expr.Var, type_: None = None, /) -> expr.Var: ...

    def add_input(  # pylint: disable=missing-raises-doc
        self, name_or_var: str | expr.Var, type_: types.Type | None = None, /
    ) -> expr.Var:
        """Register a variable as an input to the circuit.

        Args:
            name_or_var: either a string name, or an existing :class:`~.expr.Var` node to use as the
                input variable.
            type_: if the name is given as a string, then this must be a :class:`~.types.Type` to
                use for the variable.  If the variable is given as an existing :class:`~.expr.Var`,
                then this must not be given, and will instead be read from the object itself.

        Returns:
            the variable created, or the same variable as was passed in.

        Raises:
            CircuitError: if the variable cannot be created due to shadowing an existing variable.
        """
        if self._control_flow_scopes:
            raise CircuitError("cannot add an input variable in a control-flow scope")
        if self._vars_capture:
            raise CircuitError("circuits to be enclosed with captures cannot have input variables")
        if isinstance(name_or_var, expr.Var) and type_ is not None:
            raise ValueError("cannot give an explicit type with an existing Var")
        var = self._prepare_new_var(name_or_var, type_)
        self._vars_input[var.name] = var
        return var

    def add_register(self, *regs: Register | int | Sequence[Bit]) -> None:
        """Add registers."""
        if not regs:
            return

        if any(isinstance(reg, int) for reg in regs):
            # QuantumCircuit defined without registers
            if len(regs) == 1 and isinstance(regs[0], int):
                # QuantumCircuit with anonymous quantum wires e.g. QuantumCircuit(2)
                if regs[0] == 0:
                    regs = ()
                else:
                    regs = (QuantumRegister(regs[0], "q"),)
            elif len(regs) == 2 and all(isinstance(reg, int) for reg in regs):
                # QuantumCircuit with anonymous wires e.g. QuantumCircuit(2, 3)
                if regs[0] == 0:
                    qregs: tuple[QuantumRegister, ...] = ()
                else:
                    qregs = (QuantumRegister(regs[0], "q"),)
                if regs[1] == 0:
                    cregs: tuple[ClassicalRegister, ...] = ()
                else:
                    cregs = (ClassicalRegister(regs[1], "c"),)
                regs = qregs + cregs
            else:
                raise CircuitError(
                    "QuantumCircuit parameters can be Registers or Integers."
                    " If Integers, up to 2 arguments. QuantumCircuit was called"
                    " with %s." % (regs,)
                )

        for register in regs:
            if isinstance(register, Register) and any(
                register.name == reg.name for reg in self.qregs + self.cregs
            ):
                raise CircuitError('register name "%s" already exists' % register.name)

            if isinstance(register, AncillaRegister):
                for bit in register:
                    if bit not in self._qubit_indices:
                        self._ancillas.append(bit)

            if isinstance(register, QuantumRegister):
                self.qregs.append(register)

                for idx, bit in enumerate(register):
                    if bit in self._qubit_indices:
                        self._qubit_indices[bit].registers.append((register, idx))
                    else:
                        self._data.add_qubit(bit)
                        self._qubit_indices[bit] = BitLocations(
                            len(self._data.qubits) - 1, [(register, idx)]
                        )

            elif isinstance(register, ClassicalRegister):
                self.cregs.append(register)

                for idx, bit in enumerate(register):
                    if bit in self._clbit_indices:
                        self._clbit_indices[bit].registers.append((register, idx))
                    else:
                        self._data.add_clbit(bit)
                        self._clbit_indices[bit] = BitLocations(
                            len(self._data.clbits) - 1, [(register, idx)]
                        )

            elif isinstance(register, list):
                self.add_bits(register)
            else:
                raise CircuitError("expected a register")

    def add_bits(self, bits: Iterable[Bit]) -> None:
        """Add Bits to the circuit."""
        duplicate_bits = {
            bit for bit in bits if bit in self._qubit_indices or bit in self._clbit_indices
        }
        if duplicate_bits:
            raise CircuitError(f"Attempted to add bits found already in circuit: {duplicate_bits}")

        for bit in bits:
            if isinstance(bit, AncillaQubit):
                self._ancillas.append(bit)
            if isinstance(bit, Qubit):
                self._data.add_qubit(bit)
                self._qubit_indices[bit] = BitLocations(len(self._data.qubits) - 1, [])
            elif isinstance(bit, Clbit):
                self._data.add_clbit(bit)
                self._clbit_indices[bit] = BitLocations(len(self._data.clbits) - 1, [])
            else:
                raise CircuitError(
                    "Expected an instance of Qubit, Clbit, or "
                    "AncillaQubit, but was passed {}".format(bit)
                )

    def find_bit(self, bit: Bit) -> BitLocations:
        """Find locations in the circuit which can be used to reference a given :obj:`~Bit`.

        Args:
            bit (Bit): The bit to locate.

        Returns:
            namedtuple(int, List[Tuple(Register, int)]): A 2-tuple. The first element (``index``)
                contains the index at which the ``Bit`` can be found (in either
                :obj:`~QuantumCircuit.qubits`, :obj:`~QuantumCircuit.clbits`, depending on its
                type). The second element (``registers``) is a list of ``(register, index)``
                pairs with an entry for each :obj:`~Register` in the circuit which contains the
                :obj:`~Bit` (and the index in the :obj:`~Register` at which it can be found).

        Notes:
            The circuit index of an :obj:`~AncillaQubit` will be its index in
            :obj:`~QuantumCircuit.qubits`, not :obj:`~QuantumCircuit.ancillas`.

        Raises:
            CircuitError: If the supplied :obj:`~Bit` was of an unknown type.
            CircuitError: If the supplied :obj:`~Bit` could not be found on the circuit.
        """

        try:
            if isinstance(bit, Qubit):
                return self._qubit_indices[bit]
            elif isinstance(bit, Clbit):
                return self._clbit_indices[bit]
            else:
                raise CircuitError(f"Could not locate bit of unknown type: {type(bit)}")
        except KeyError as err:
            raise CircuitError(
                f"Could not locate provided bit: {bit}. Has it been added to the QuantumCircuit?"
            ) from err

    def _check_dups(self, qubits: Sequence[Qubit]) -> None:
        """Raise exception if list of qubits contains duplicates."""
        squbits = set(qubits)
        if len(squbits) != len(qubits):
            raise CircuitError("duplicate qubit arguments")

    def to_instruction(
        self,
        parameter_map: dict[Parameter, ParameterValueType] | None = None,
        label: str | None = None,
    ) -> Instruction:
        """Create an Instruction out of this circuit.

        Args:
            parameter_map(dict): For parameterized circuits, a mapping from
               parameters in the circuit to parameters to be used in the
               instruction. If None, existing circuit parameters will also
               parameterize the instruction.
            label (str): Optional gate label.

        Returns:
            qiskit.circuit.Instruction: a composite instruction encapsulating this circuit
            (can be decomposed back)
        """
        from qiskit.converters.circuit_to_instruction import circuit_to_instruction

        return circuit_to_instruction(self, parameter_map, label=label)

    def to_gate(
        self,
        parameter_map: dict[Parameter, ParameterValueType] | None = None,
        label: str | None = None,
    ) -> Gate:
        """Create a Gate out of this circuit.

        Args:
            parameter_map(dict): For parameterized circuits, a mapping from
               parameters in the circuit to parameters to be used in the
               gate. If None, existing circuit parameters will also
               parameterize the gate.
            label (str): Optional gate label.

        Returns:
            Gate: a composite gate encapsulating this circuit
            (can be decomposed back)
        """
        from qiskit.converters.circuit_to_gate import circuit_to_gate

        return circuit_to_gate(self, parameter_map, label=label)

    def decompose(
        self,
        gates_to_decompose: Type[Gate] | Sequence[Type[Gate]] | Sequence[str] | str | None = None,
        reps: int = 1,
    ) -> "QuantumCircuit":
        """Call a decomposition pass on this circuit,
        to decompose one level (shallow decompose).

        Args:
            gates_to_decompose (type or str or list(type, str)): Optional subset of gates
                to decompose. Can be a gate type, such as ``HGate``, or a gate name, such
                as 'h', or a gate label, such as 'My H Gate', or a list of any combination
                of these. If a gate name is entered, it will decompose all gates with that
                name, whether the gates have labels or not. Defaults to all gates in circuit.
            reps (int): Optional number of times the circuit should be decomposed.
                For instance, ``reps=2`` equals calling ``circuit.decompose().decompose()``.
                can decompose specific gates specific time

        Returns:
            QuantumCircuit: a circuit one level decomposed
        """
        # pylint: disable=cyclic-import
        from qiskit.transpiler.passes.basis.decompose import Decompose
        from qiskit.transpiler.passes.synthesis import HighLevelSynthesis
        from qiskit.converters.circuit_to_dag import circuit_to_dag
        from qiskit.converters.dag_to_circuit import dag_to_circuit

        dag = circuit_to_dag(self, copy_operations=True)
        dag = HighLevelSynthesis().run(dag)
        pass_ = Decompose(gates_to_decompose)
        for _ in range(reps):
            dag = pass_.run(dag)
        # do not copy operations, this is done in the conversion with circuit_to_dag
        return dag_to_circuit(dag, copy_operations=False)

    def draw(
        self,
        output: str | None = None,
        scale: float | None = None,
        filename: str | None = None,
        style: dict | str | None = None,
        interactive: bool = False,
        plot_barriers: bool = True,
        reverse_bits: bool | None = None,
        justify: str | None = None,
        vertical_compression: str | None = "medium",
        idle_wires: bool = True,
        with_layout: bool = True,
        fold: int | None = None,
        # The type of ax is matplotlib.axes.Axes, but this is not a fixed dependency, so cannot be
        # safely forward-referenced.
        ax: Any | None = None,
        initial_state: bool = False,
        cregbundle: bool | None = None,
        wire_order: list[int] | None = None,
        expr_len: int = 30,
    ):
        r"""Draw the quantum circuit. Use the output parameter to choose the drawing format:

        **text**: ASCII art TextDrawing that can be printed in the console.

        **mpl**: images with color rendered purely in Python using matplotlib.

        **latex**: high-quality images compiled via latex.

        **latex_source**: raw uncompiled latex output.

        .. warning::

            Support for :class:`~.expr.Expr` nodes in conditions and :attr:`.SwitchCaseOp.target`
            fields is preliminary and incomplete.  The ``text`` and ``mpl`` drawers will make a
            best-effort attempt to show data dependencies, but the LaTeX-based drawers will skip
            these completely.

        Args:
            output: Select the output method to use for drawing the circuit.
                Valid choices are ``text``, ``mpl``, ``latex``, ``latex_source``.
                By default the `text` drawer is used unless the user config file
                (usually ``~/.qiskit/settings.conf``) has an alternative backend set
                as the default. For example, ``circuit_drawer = latex``. If the output
                kwarg is set, that backend will always be used over the default in
                the user config file.
            scale: Scale of image to draw (shrink if ``< 1.0``). Only used by
                the ``mpl``, ``latex`` and ``latex_source`` outputs. Defaults to ``1.0``.
            filename: File path to save image to. Defaults to ``None`` (result not saved in a file).
            style: Style name, file name of style JSON file, or a dictionary specifying the style.

                * The supported style names are ``"iqp"`` (default), ``"iqp-dark"``, ``"clifford"``,
                  ``"textbook"`` and ``"bw"``.
                * If given a JSON file, e.g. ``my_style.json`` or ``my_style`` (the ``.json``
                  extension may be omitted), this function attempts to load the style dictionary
                  from that location. Note, that the JSON file must completely specify the
                  visualization specifications. The file is searched for in
                  ``qiskit/visualization/circuit/styles``, the current working directory, and
                  the location specified in ``~/.qiskit/settings.conf``.
                * If a dictionary, every entry overrides the default configuration. If the
                  ``"name"`` key is given, the default configuration is given by that style.
                  For example, ``{"name": "textbook", "subfontsize": 5}`` loads the ``"texbook"``
                  style and sets the subfontsize (e.g. the gate angles) to ``5``.
                * If ``None`` the default style ``"iqp"`` is used or, if given, the default style
                  specified in ``~/.qiskit/settings.conf``.

            interactive: When set to ``True``, show the circuit in a new window
                (for ``mpl`` this depends on the matplotlib backend being used
                supporting this). Note when used with either the `text` or the
                ``latex_source`` output type this has no effect and will be silently
                ignored. Defaults to ``False``.
            reverse_bits: When set to ``True``, reverse the bit order inside
                registers for the output visualization. Defaults to ``False`` unless the
                user config file (usually ``~/.qiskit/settings.conf``) has an
                alternative value set. For example, ``circuit_reverse_bits = True``.
            plot_barriers: Enable/disable drawing barriers in the output
                circuit. Defaults to ``True``.
            justify: Options are ``left``, ``right`` or ``none``. If
                anything else is supplied, it defaults to left justified. It refers
                to where gates should be placed in the output circuit if there is
                an option. ``none`` results in each gate being placed in its own
                column.
            vertical_compression: ``high``, ``medium`` or ``low``. It
                merges the lines generated by the `text` output so the drawing
                will take less vertical room.  Default is ``medium``. Only used by
                the ``text`` output, will be silently ignored otherwise.
            idle_wires: Include idle wires (wires with no circuit elements)
                in output visualization. Default is ``True``.
            with_layout: Include layout information, with labels on the
                physical layout. Default is ``True``.
            fold: Sets pagination. It can be disabled using -1. In ``text``,
                sets the length of the lines. This is useful when the drawing does
                not fit in the console. If None (default), it will try to guess the
                console width using ``shutil.get_terminal_size()``. However, if
                running in jupyter, the default line length is set to 80 characters.
                In ``mpl``, it is the number of (visual) layers before folding.
                Default is 25.
            ax: Only used by the `mpl` backend. An optional ``matplotlib.axes.Axes``
                object to be used for the visualization output. If none is
                specified, a new matplotlib Figure will be created and used.
                Additionally, if specified there will be no returned Figure since
                it is redundant.
            initial_state: Adds :math:`|0\rangle` in the beginning of the qubit wires and
                :math:`0` to classical wires. Default is ``False``.
            cregbundle: If set to ``True``, bundle classical registers.
                Default is ``True``, except for when ``output`` is set to  ``"text"``.
            wire_order: A list of integers used to reorder the display
                of the bits. The list must have an entry for every bit with the bits
                in the range 0 to (``num_qubits`` + ``num_clbits``).
            expr_len: The number of characters to display if an :class:`~.expr.Expr`
                is used for the condition in a :class:`.ControlFlowOp`. If this number is exceeded,
                the string will be truncated at that number and '...' added to the end.

        Returns:
            :class:`.TextDrawing` or :class:`matplotlib.figure` or :class:`PIL.Image` or
            :class:`str`:

            * ``TextDrawing`` (if ``output='text'``)
                A drawing that can be printed as ascii art.
            * ``matplotlib.figure.Figure`` (if ``output='mpl'``)
                A matplotlib figure object for the circuit diagram.
            * ``PIL.Image`` (if ``output='latex``')
                An in-memory representation of the image of the circuit diagram.
            * ``str`` (if ``output='latex_source'``)
                The LaTeX source code for visualizing the circuit diagram.

        Raises:
            VisualizationError: when an invalid output method is selected
            ImportError: when the output methods requires non-installed libraries.

        Example:
            .. plot::
               :include-source:

               from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit
               qc = QuantumCircuit(1, 1)
               qc.h(0)
               qc.measure(0, 0)
               qc.draw(output='mpl', style={'backgroundcolor': '#EEEEEE'})
        """

        # pylint: disable=cyclic-import
        from qiskit.visualization import circuit_drawer

        return circuit_drawer(
            self,
            scale=scale,
            filename=filename,
            style=style,
            output=output,
            interactive=interactive,
            plot_barriers=plot_barriers,
            reverse_bits=reverse_bits,
            justify=justify,
            vertical_compression=vertical_compression,
            idle_wires=idle_wires,
            with_layout=with_layout,
            fold=fold,
            ax=ax,
            initial_state=initial_state,
            cregbundle=cregbundle,
            wire_order=wire_order,
            expr_len=expr_len,
        )

    def size(
        self,
        filter_function: Callable[..., int] = lambda x: not getattr(
            x.operation, "_directive", False
        ),
    ) -> int:
        """Returns total number of instructions in circuit.

        Args:
            filter_function (callable): a function to filter out some instructions.
                Should take as input a tuple of (Instruction, list(Qubit), list(Clbit)).
                By default filters out "directives", such as barrier or snapshot.

        Returns:
            int: Total number of gate operations.
        """
        return sum(map(filter_function, self._data))

    def depth(
        self,
        filter_function: Callable[..., int] = lambda x: not getattr(
            x.operation, "_directive", False
        ),
    ) -> int:
        """Return circuit depth (i.e., length of critical path).

        Args:
            filter_function (callable): A function to filter instructions.
                Should take as input a tuple of (Instruction, list(Qubit), list(Clbit)).
                Instructions for which the function returns False are ignored in the
                computation of the circuit depth.
                By default filters out "directives", such as barrier or snapshot.

        Returns:
            int: Depth of circuit.

        Notes:
            The circuit depth and the DAG depth need not be the
            same.
        """
        # Assign each bit in the circuit a unique integer
        # to index into op_stack.
        bit_indices: dict[Qubit | Clbit, int] = {
            bit: idx for idx, bit in enumerate(self.qubits + self.clbits)
        }

        # If no bits, return 0
        if not bit_indices:
            return 0

        # A list that holds the height of each qubit
        # and classical bit.
        op_stack = [0] * len(bit_indices)

        # Here we are playing a modified version of
        # Tetris where we stack gates, but multi-qubit
        # gates, or measurements have a block for each
        # qubit or cbit that are connected by a virtual
        # line so that they all stacked at the same depth.
        # Conditional gates act on all cbits in the register
        # they are conditioned on.
        # The max stack height is the circuit depth.
        for instruction in self._data:
            levels = []
            reg_ints = []
            for ind, reg in enumerate(instruction.qubits + instruction.clbits):
                # Add to the stacks of the qubits and
                # cbits used in the gate.
                reg_ints.append(bit_indices[reg])
                if filter_function(instruction):
                    levels.append(op_stack[reg_ints[ind]] + 1)
                else:
                    levels.append(op_stack[reg_ints[ind]])
            # Assuming here that there is no conditional
            # snapshots or barriers ever.
            if getattr(instruction.operation, "condition", None):
                # Controls operate over all bits of a classical register
                # or over a single bit
                if isinstance(instruction.operation.condition[0], Clbit):
                    condition_bits = [instruction.operation.condition[0]]
                else:
                    condition_bits = instruction.operation.condition[0]
                for cbit in condition_bits:
                    idx = bit_indices[cbit]
                    if idx not in reg_ints:
                        reg_ints.append(idx)
                        levels.append(op_stack[idx] + 1)

            max_level = max(levels)
            for ind in reg_ints:
                op_stack[ind] = max_level

        return max(op_stack)

    def width(self) -> int:
        """Return number of qubits plus clbits in circuit.

        Returns:
            int: Width of circuit.

        """
        return len(self.qubits) + len(self.clbits)

    @property
    def num_qubits(self) -> int:
        """Return number of qubits."""
        return len(self.qubits)

    @property
    def num_ancillas(self) -> int:
        """Return the number of ancilla qubits."""
        return len(self.ancillas)

    @property
    def num_clbits(self) -> int:
        """Return number of classical bits."""
        return len(self.clbits)

    # The stringified return type is because OrderedDict can't be subscripted before Python 3.9, and
    # typing.OrderedDict wasn't added until 3.7.2.  It can be turned into a proper type once 3.6
    # support is dropped.
    def count_ops(self) -> "OrderedDict[Instruction, int]":
        """Count each operation kind in the circuit.

        Returns:
            OrderedDict: a breakdown of how many operations of each kind, sorted by amount.
        """
        count_ops: dict[Instruction, int] = {}
        for instruction in self._data:
            count_ops[instruction.operation.name] = count_ops.get(instruction.operation.name, 0) + 1
        return OrderedDict(sorted(count_ops.items(), key=lambda kv: kv[1], reverse=True))

    def num_nonlocal_gates(self) -> int:
        """Return number of non-local gates (i.e. involving 2+ qubits).

        Conditional nonlocal gates are also included.
        """
        multi_qubit_gates = 0
        for instruction in self._data:
            if instruction.operation.num_qubits > 1 and not getattr(
                instruction.operation, "_directive", False
            ):
                multi_qubit_gates += 1
        return multi_qubit_gates

    def get_instructions(self, name: str) -> list[CircuitInstruction]:
        """Get instructions matching name.

        Args:
            name (str): The name of instruction to.

        Returns:
            list(tuple): list of (instruction, qargs, cargs).
        """
        return [match for match in self._data if match.operation.name == name]

    def num_connected_components(self, unitary_only: bool = False) -> int:
        """How many non-entangled subcircuits can the circuit be factored to.

        Args:
            unitary_only (bool): Compute only unitary part of graph.

        Returns:
            int: Number of connected components in circuit.
        """
        # Convert registers to ints (as done in depth).
        bits = self.qubits if unitary_only else (self.qubits + self.clbits)
        bit_indices: dict[Qubit | Clbit, int] = {bit: idx for idx, bit in enumerate(bits)}

        # Start with each qubit or cbit being its own subgraph.
        sub_graphs = [[bit] for bit in range(len(bit_indices))]

        num_sub_graphs = len(sub_graphs)

        # Here we are traversing the gates and looking to see
        # which of the sub_graphs the gate joins together.
        for instruction in self._data:
            if unitary_only:
                args = instruction.qubits
                num_qargs = len(args)
            else:
                args = instruction.qubits + instruction.clbits
                num_qargs = len(args) + (
                    1 if getattr(instruction.operation, "condition", None) else 0
                )

            if num_qargs >= 2 and not getattr(instruction.operation, "_directive", False):
                graphs_touched = []
                num_touched = 0
                # Controls necessarily join all the cbits in the
                # register that they use.
                if not unitary_only:
                    for bit in instruction.operation.condition_bits:
                        idx = bit_indices[bit]
                        for k in range(num_sub_graphs):
                            if idx in sub_graphs[k]:
                                graphs_touched.append(k)
                                break

                for item in args:
                    reg_int = bit_indices[item]
                    for k in range(num_sub_graphs):
                        if reg_int in sub_graphs[k]:
                            if k not in graphs_touched:
                                graphs_touched.append(k)
                                break

                graphs_touched = list(set(graphs_touched))
                num_touched = len(graphs_touched)

                # If the gate touches more than one subgraph
                # join those graphs together and return
                # reduced number of subgraphs
                if num_touched > 1:
                    connections = []
                    for idx in graphs_touched:
                        connections.extend(sub_graphs[idx])
                    _sub_graphs = []
                    for idx in range(num_sub_graphs):
                        if idx not in graphs_touched:
                            _sub_graphs.append(sub_graphs[idx])
                    _sub_graphs.append(connections)
                    sub_graphs = _sub_graphs
                    num_sub_graphs -= num_touched - 1
            # Cannot go lower than one so break
            if num_sub_graphs == 1:
                break
        return num_sub_graphs

    def num_unitary_factors(self) -> int:
        """Computes the number of tensor factors in the unitary
        (quantum) part of the circuit only.
        """
        return self.num_connected_components(unitary_only=True)

    def num_tensor_factors(self) -> int:
        """Computes the number of tensor factors in the unitary
        (quantum) part of the circuit only.

        Notes:
            This is here for backwards compatibility, and will be
            removed in a future release of Qiskit. You should call
            `num_unitary_factors` instead.
        """
        return self.num_unitary_factors()

    def copy(self, name: str | None = None) -> "QuantumCircuit":
        """Copy the circuit.

        Args:
          name (str): name to be given to the copied circuit. If None, then the name stays the same.

        Returns:
          QuantumCircuit: a deepcopy of the current circuit, with the specified name
        """
        cpy = self.copy_empty_like(name)
        cpy._data = self._data.copy()

        # The special global-phase sentinel doesn't need copying, but it's
        # added here to ensure it's recognised. The global phase itself was
        # already copied over in `copy_empty_like`.
        operation_copies = {id(ParameterTable.GLOBAL_PHASE): ParameterTable.GLOBAL_PHASE}

        def memo_copy(op):
            if (out := operation_copies.get(id(op))) is not None:
                return out
            copied = op.copy()
            operation_copies[id(op)] = copied
            return copied

        cpy._data.map_ops(memo_copy)
        cpy._parameter_table = ParameterTable(
            {
                param: ParameterReferences(
                    (operation_copies[id(operation)], param_index)
                    for operation, param_index in self._parameter_table[param]
                )
                for param in self._parameter_table
            }
        )
        return cpy

    def copy_empty_like(self, name: str | None = None) -> "QuantumCircuit":
        """Return a copy of self with the same structure but empty.

        That structure includes:
            * name, calibrations and other metadata
            * global phase
            * all the qubits and clbits, including the registers

        .. warning::

            If the circuit contains any local variable declarations (those added by the
            ``declarations`` argument to the circuit constructor, or using :meth:`add_var`), they
            will be **uninitialized** in the output circuit.  You will need to manually add store
            instructions for them (see :class:`.Store` and :meth:`.QuantumCircuit.store`) to
            initialize them.

        Args:
            name (str): Name for the copied circuit. If None, then the name stays the same.

        Returns:
            QuantumCircuit: An empty copy of self.
        """
        if not (name is None or isinstance(name, str)):
            raise TypeError(
                f"invalid name for a circuit: '{name}'. The name must be a string or 'None'."
            )
        cpy = copy.copy(self)
        # copy registers correctly, in copy.copy they are only copied via reference
        cpy.qregs = self.qregs.copy()
        cpy.cregs = self.cregs.copy()
        cpy._builder_api = _OuterCircuitScopeInterface(cpy)
        cpy._ancillas = self._ancillas.copy()
        cpy._qubit_indices = self._qubit_indices.copy()
        cpy._clbit_indices = self._clbit_indices.copy()

        # Note that this causes the local variables to be uninitialised, because the stores are not
        # copied.  This can leave the circuit in a potentially dangerous state for users if they
        # don't re-add initialiser stores.
        cpy._vars_local = self._vars_local.copy()
        cpy._vars_input = self._vars_input.copy()
        cpy._vars_capture = self._vars_capture.copy()

        cpy._parameter_table = ParameterTable()
        for parameter in getattr(cpy.global_phase, "parameters", ()):
            cpy._parameter_table[parameter] = ParameterReferences(
                [(ParameterTable.GLOBAL_PHASE, None)]
            )
        cpy._data = CircuitData(self._data.qubits, self._data.clbits)

        cpy._calibrations = copy.deepcopy(self._calibrations)
        cpy._metadata = copy.deepcopy(self._metadata)

        if name:
            cpy.name = name
        return cpy

    def clear(self) -> None:
        """Clear all instructions in self.

        Clearing the circuits will keep the metadata and calibrations.
        """
        self._data.clear()
        self._parameter_table.clear()
        # Repopulate the parameter table with any phase symbols.
        self.global_phase = self.global_phase

    def _create_creg(self, length: int, name: str) -> ClassicalRegister:
        """Creates a creg, checking if ClassicalRegister with same name exists"""
        if name in [creg.name for creg in self.cregs]:
            save_prefix = ClassicalRegister.prefix
            ClassicalRegister.prefix = name
            new_creg = ClassicalRegister(length)
            ClassicalRegister.prefix = save_prefix
        else:
            new_creg = ClassicalRegister(length, name)
        return new_creg

    def _create_qreg(self, length: int, name: str) -> QuantumRegister:
        """Creates a qreg, checking if QuantumRegister with same name exists"""
        if name in [qreg.name for qreg in self.qregs]:
            save_prefix = QuantumRegister.prefix
            QuantumRegister.prefix = name
            new_qreg = QuantumRegister(length)
            QuantumRegister.prefix = save_prefix
        else:
            new_qreg = QuantumRegister(length, name)
        return new_qreg

    def reset(self, qubit: QubitSpecifier) -> InstructionSet:
        """Reset the quantum bit(s) to their default state.

        Args:
            qubit: qubit(s) to reset.

        Returns:
            qiskit.circuit.InstructionSet: handle to the added instruction.
        """
        from .reset import Reset

        return self.append(Reset(), [qubit], [])

    def store(self, lvalue: typing.Any, rvalue: typing.Any, /) -> InstructionSet:
        """Store the result of the given runtime classical expression ``rvalue`` in the memory
        location defined by ``lvalue``.

        Typically ``lvalue`` will be a :class:`~.expr.Var` node and ``rvalue`` will be some
        :class:`~.expr.Expr` to write into it, but anything that :func:`.expr.lift` can raise to an
        :class:`~.expr.Expr` is permissible in both places, and it will be called on them.

        Args:
            lvalue: a valid specifier for a memory location in the circuit.  This will typically be
                a :class:`~.expr.Var` node, but you can also write to :class:`.Clbit` or
                :class:`.ClassicalRegister` memory locations if your hardware supports it.  The
                memory location must already be present in the circuit.
            rvalue: a runtime classical expression whose result should be written into the given
                memory location.

        .. seealso::
            :class:`~.circuit.Store`
                The backing :class:`~.circuit.Instruction` class that represents this operation.

            :meth:`add_var`
                Create a new variable in the circuit that can be written to with this method.
        """
        return self.append(Store(expr.lift(lvalue), expr.lift(rvalue)), (), ())

    def measure(self, qubit: QubitSpecifier, cbit: ClbitSpecifier) -> InstructionSet:
        r"""Measure a quantum bit (``qubit``) in the Z basis into a classical bit (``cbit``).

        When a quantum state is measured, a qubit is projected in the computational (Pauli Z) basis
        to either :math:`\lvert 0 \rangle` or :math:`\lvert 1 \rangle`. The classical bit ``cbit``
        indicates the result
        of that projection as a ``0`` or a ``1`` respectively. This operation is non-reversible.

        Args:
            qubit: qubit(s) to measure.
            cbit: classical bit(s) to place the measurement result(s) in.

        Returns:
            qiskit.circuit.InstructionSet: handle to the added instructions.

        Raises:
            CircuitError: if arguments have bad format.

        Examples:
            In this example, a qubit is measured and the result of that measurement is stored in the
            classical bit (usually expressed in diagrams as a double line):

            .. code-block::

               from qiskit import QuantumCircuit
               circuit = QuantumCircuit(1, 1)
               circuit.h(0)
               circuit.measure(0, 0)
               circuit.draw()


            .. parsed-literal::

                      ┌───┐┌─┐
                   q: ┤ H ├┤M├
                      └───┘└╥┘
                 c: 1/══════╩═
                            0

            It is possible to call ``measure`` with lists of ``qubits`` and ``cbits`` as a shortcut
            for one-to-one measurement. These two forms produce identical results:

            .. code-block::

               circuit = QuantumCircuit(2, 2)
               circuit.measure([0,1], [0,1])

            .. code-block::

               circuit = QuantumCircuit(2, 2)
               circuit.measure(0, 0)
               circuit.measure(1, 1)

            Instead of lists, you can use :class:`~qiskit.circuit.QuantumRegister` and
            :class:`~qiskit.circuit.ClassicalRegister` under the same logic.

            .. code-block::

                from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister
                qreg = QuantumRegister(2, "qreg")
                creg = ClassicalRegister(2, "creg")
                circuit = QuantumCircuit(qreg, creg)
                circuit.measure(qreg, creg)

            This is equivalent to:

            .. code-block::

                circuit = QuantumCircuit(qreg, creg)
                circuit.measure(qreg[0], creg[0])
                circuit.measure(qreg[1], creg[1])

        """
        from .measure import Measure

        return self.append(Measure(), [qubit], [cbit])

    def measure_active(self, inplace: bool = True) -> Optional["QuantumCircuit"]:
        """Adds measurement to all non-idle qubits. Creates a new ClassicalRegister with
        a size equal to the number of non-idle qubits being measured.

        Returns a new circuit with measurements if `inplace=False`.

        Args:
            inplace (bool): All measurements inplace or return new circuit.

        Returns:
            QuantumCircuit: Returns circuit with measurements when `inplace = False`.
        """
        from qiskit.converters.circuit_to_dag import circuit_to_dag

        if inplace:
            circ = self
        else:
            circ = self.copy()
        dag = circuit_to_dag(circ)
        qubits_to_measure = [qubit for qubit in circ.qubits if qubit not in dag.idle_wires()]
        new_creg = circ._create_creg(len(qubits_to_measure), "measure")
        circ.add_register(new_creg)
        circ.barrier()
        circ.measure(qubits_to_measure, new_creg)

        if not inplace:
            return circ
        else:
            return None

    def measure_all(
        self, inplace: bool = True, add_bits: bool = True
    ) -> Optional["QuantumCircuit"]:
        """Adds measurement to all qubits.

        By default, adds new classical bits in a :obj:`.ClassicalRegister` to store these
        measurements.  If ``add_bits=False``, the results of the measurements will instead be stored
        in the already existing classical bits, with qubit ``n`` being measured into classical bit
        ``n``.

        Returns a new circuit with measurements if ``inplace=False``.

        Args:
            inplace (bool): All measurements inplace or return new circuit.
            add_bits (bool): Whether to add new bits to store the results.

        Returns:
            QuantumCircuit: Returns circuit with measurements when ``inplace=False``.

        Raises:
            CircuitError: if ``add_bits=False`` but there are not enough classical bits.
        """
        if inplace:
            circ = self
        else:
            circ = self.copy()
        if add_bits:
            new_creg = circ._create_creg(len(circ.qubits), "meas")
            circ.add_register(new_creg)
            circ.barrier()
            circ.measure(circ.qubits, new_creg)
        else:
            if len(circ.clbits) < len(circ.qubits):
                raise CircuitError(
                    "The number of classical bits must be equal or greater than "
                    "the number of qubits."
                )
            circ.barrier()
            circ.measure(circ.qubits, circ.clbits[0 : len(circ.qubits)])

        if not inplace:
            return circ
        else:
            return None

    def remove_final_measurements(self, inplace: bool = True) -> Optional["QuantumCircuit"]:
        """Removes final measurements and barriers on all qubits if they are present.
        Deletes the classical registers that were used to store the values from these measurements
        that become idle as a result of this operation, and deletes classical bits that are
        referenced only by removed registers, or that aren't referenced at all but have
        become idle as a result of this operation.

        Measurements and barriers are considered final if they are
        followed by no other operations (aside from other measurements or barriers.)

        Args:
            inplace (bool): All measurements removed inplace or return new circuit.

        Returns:
            QuantumCircuit: Returns the resulting circuit when ``inplace=False``, else None.
        """
        # pylint: disable=cyclic-import
        from qiskit.transpiler.passes import RemoveFinalMeasurements
        from qiskit.converters import circuit_to_dag

        if inplace:
            circ = self
        else:
            circ = self.copy()

        dag = circuit_to_dag(circ)
        remove_final_meas = RemoveFinalMeasurements()
        new_dag = remove_final_meas.run(dag)
        kept_cregs = set(new_dag.cregs.values())
        kept_clbits = set(new_dag.clbits)

        # Filter only cregs/clbits still in new DAG, preserving original circuit order
        cregs_to_add = [creg for creg in circ.cregs if creg in kept_cregs]
        clbits_to_add = [clbit for clbit in circ._data.clbits if clbit in kept_clbits]

        # Clear cregs and clbits
        circ.cregs = []
        circ._clbit_indices = {}

        # Clear instruction info
        circ._data = CircuitData(qubits=circ._data.qubits, reserve=len(circ._data))
        circ._parameter_table.clear()
        # Repopulate the parameter table with any global-phase entries.
        circ.global_phase = circ.global_phase

        # We must add the clbits first to preserve the original circuit
        # order. This way, add_register never adds clbits and just
        # creates registers that point to them.
        circ.add_bits(clbits_to_add)
        for creg in cregs_to_add:
            circ.add_register(creg)

        # Set circ instructions to match the new DAG
        for node in new_dag.topological_op_nodes():
            # Get arguments for classical condition (if any)
            inst = node.op.copy()
            circ.append(inst, node.qargs, node.cargs)

        if not inplace:
            return circ
        else:
            return None

    @staticmethod
    def from_qasm_file(path: str) -> "QuantumCircuit":
        """Read an OpenQASM 2.0 program from a file and convert to an instance of
        :class:`.QuantumCircuit`.

        Args:
          path (str): Path to the file for an OpenQASM 2 program

        Return:
          QuantumCircuit: The QuantumCircuit object for the input OpenQASM 2.

        See also:
            :func:`.qasm2.load`: the complete interface to the OpenQASM 2 importer.
        """
        # pylint: disable=cyclic-import
        from qiskit import qasm2

        return qasm2.load(
            path,
            include_path=qasm2.LEGACY_INCLUDE_PATH,
            custom_instructions=qasm2.LEGACY_CUSTOM_INSTRUCTIONS,
            custom_classical=qasm2.LEGACY_CUSTOM_CLASSICAL,
            strict=False,
        )

    @staticmethod
    def from_qasm_str(qasm_str: str) -> "QuantumCircuit":
        """Convert a string containing an OpenQASM 2.0 program to a :class:`.QuantumCircuit`.

        Args:
          qasm_str (str): A string containing an OpenQASM 2.0 program.
        Return:
          QuantumCircuit: The QuantumCircuit object for the input OpenQASM 2

        See also:
            :func:`.qasm2.loads`: the complete interface to the OpenQASM 2 importer.
        """
        # pylint: disable=cyclic-import
        from qiskit import qasm2

        return qasm2.loads(
            qasm_str,
            include_path=qasm2.LEGACY_INCLUDE_PATH,
            custom_instructions=qasm2.LEGACY_CUSTOM_INSTRUCTIONS,
            custom_classical=qasm2.LEGACY_CUSTOM_CLASSICAL,
            strict=False,
        )

    @property
    def global_phase(self) -> ParameterValueType:
        """Return the global phase of the current circuit scope in radians."""
        if self._control_flow_scopes:
            return self._control_flow_scopes[-1].global_phase
        return self._global_phase

    @global_phase.setter
    def global_phase(self, angle: ParameterValueType):
        """Set the phase of the current circuit scope.

        Args:
            angle (float, ParameterExpression): radians
        """
        # If we're currently parametric, we need to throw away the references.  This setter is
        # called by some subclasses before the inner `_global_phase` is initialised.
        global_phase_reference = (ParameterTable.GLOBAL_PHASE, None)
        if isinstance(previous := getattr(self, "_global_phase", None), ParameterExpression):
            self._parameters = None
            self._parameter_table.discard_references(previous, global_phase_reference)

        if isinstance(angle, ParameterExpression) and angle.parameters:
            for parameter in angle.parameters:
                if parameter not in self._parameter_table:
                    self._parameters = None
                    self._parameter_table[parameter] = ParameterReferences(())
                self._parameter_table[parameter].add(global_phase_reference)
        else:
            angle = _normalize_global_phase(angle)
        if self._control_flow_scopes:
            self._control_flow_scopes[-1].global_phase = angle
        else:
            self._global_phase = angle

    @property
    def parameters(self) -> ParameterView:
        """The parameters defined in the circuit.

        This attribute returns the :class:`.Parameter` objects in the circuit sorted
        alphabetically. Note that parameters instantiated with a :class:`.ParameterVector`
        are still sorted numerically.

        Examples:

            The snippet below shows that insertion order of parameters does not matter.

            .. code-block:: python

                >>> from qiskit.circuit import QuantumCircuit, Parameter
                >>> a, b, elephant = Parameter("a"), Parameter("b"), Parameter("elephant")
                >>> circuit = QuantumCircuit(1)
                >>> circuit.rx(b, 0)
                >>> circuit.rz(elephant, 0)
                >>> circuit.ry(a, 0)
                >>> circuit.parameters  # sorted alphabetically!
                ParameterView([Parameter(a), Parameter(b), Parameter(elephant)])

            Bear in mind that alphabetical sorting might be unintuitive when it comes to numbers.
            The literal "10" comes before "2" in strict alphabetical sorting.

            .. code-block:: python

                >>> from qiskit.circuit import QuantumCircuit, Parameter
                >>> angles = [Parameter("angle_1"), Parameter("angle_2"), Parameter("angle_10")]
                >>> circuit = QuantumCircuit(1)
                >>> circuit.u(*angles, 0)
                >>> circuit.draw()
                   ┌─────────────────────────────┐
                q: ┤ U(angle_1,angle_2,angle_10) ├
                   └─────────────────────────────┘
                >>> circuit.parameters
                ParameterView([Parameter(angle_1), Parameter(angle_10), Parameter(angle_2)])

            To respect numerical sorting, a :class:`.ParameterVector` can be used.

            .. code-block:: python

                >>> from qiskit.circuit import QuantumCircuit, Parameter, ParameterVector
                >>> x = ParameterVector("x", 12)
                >>> circuit = QuantumCircuit(1)
                >>> for x_i in x:
                ...     circuit.rx(x_i, 0)
                >>> circuit.parameters
                ParameterView([
                    ParameterVectorElement(x[0]), ParameterVectorElement(x[1]),
                    ParameterVectorElement(x[2]), ParameterVectorElement(x[3]),
                    ..., ParameterVectorElement(x[11])
                ])


        Returns:
            The sorted :class:`.Parameter` objects in the circuit.
        """
        # parameters from gates
        if self._parameters is None:
            self._parameters = sort_parameters(self._unsorted_parameters())
        # return as parameter view, which implements the set and list interface
        return ParameterView(self._parameters)

    @property
    def num_parameters(self) -> int:
        """The number of parameter objects in the circuit."""
        return len(self._parameter_table)

    def _unsorted_parameters(self) -> set[Parameter]:
        """Efficiently get all parameters in the circuit, without any sorting overhead.

        .. warning::

            The returned object may directly view onto the ``ParameterTable`` internals, and so
            should not be mutated.  This is an internal performance detail.  Code outside of this
            package should not use this method.
        """
        # This should be free, by accessing the actual backing data structure of the table, but that
        # means that we need to copy it if adding keys from the global phase.
        return self._parameter_table.get_keys()

    @overload
    def assign_parameters(
        self,
        parameters: Union[Mapping[Parameter, ParameterValueType], Sequence[ParameterValueType]],
        inplace: Literal[False] = ...,
        *,
        flat_input: bool = ...,
        strict: bool = ...,
    ) -> "QuantumCircuit": ...

    @overload
    def assign_parameters(
        self,
        parameters: Union[Mapping[Parameter, ParameterValueType], Sequence[ParameterValueType]],
        inplace: Literal[True] = ...,
        *,
        flat_input: bool = ...,
        strict: bool = ...,
    ) -> None: ...

    def assign_parameters(  # pylint: disable=missing-raises-doc
        self,
        parameters: Union[Mapping[Parameter, ParameterValueType], Sequence[ParameterValueType]],
        inplace: bool = False,
        *,
        flat_input: bool = False,
        strict: bool = True,
    ) -> Optional["QuantumCircuit"]:
        """Assign parameters to new parameters or values.

        If ``parameters`` is passed as a dictionary, the keys should be :class:`.Parameter`
        instances in the current circuit. The values of the dictionary can either be numeric values
        or new parameter objects.

        If ``parameters`` is passed as a list or array, the elements are assigned to the
        current parameters in the order of :attr:`parameters` which is sorted
        alphabetically (while respecting the ordering in :class:`.ParameterVector` objects).

        The values can be assigned to the current circuit object or to a copy of it.

        .. note::
            When ``parameters`` is given as a mapping, it is permissible to have keys that are
            strings of the parameter names; these will be looked up using :meth:`get_parameter`.
            You can also have keys that are :class:`.ParameterVector` instances, and in this case,
            the dictionary value should be a sequence of values of the same length as the vector.

            If you use either of these cases, you must leave the setting ``flat_input=False``;
            changing this to ``True`` enables the fast path, where all keys must be
            :class:`.Parameter` instances.

        Args:
            parameters: Either a dictionary or iterable specifying the new parameter values.
            inplace: If False, a copy of the circuit with the bound parameters is returned.
                If True the circuit instance itself is modified.
            flat_input: If ``True`` and ``parameters`` is a mapping type, it is assumed to be
                exactly a mapping of ``{parameter: value}``.  By default (``False``), the mapping
                may also contain :class:`.ParameterVector` keys that point to a corresponding
                sequence of values, and these will be unrolled during the mapping, or string keys,
                which will be converted to :class:`.Parameter` instances using
                :meth:`get_parameter`.
            strict: If ``False``, any parameters given in the mapping that are not used in the
                circuit will be ignored.  If ``True`` (the default), an error will be raised
                indicating a logic error.

        Raises:
            CircuitError: If parameters is a dict and contains parameters not present in the
                circuit.
            ValueError: If parameters is a list/array and the length mismatches the number of free
                parameters in the circuit.

        Returns:
            A copy of the circuit with bound parameters if ``inplace`` is False, otherwise None.

        Examples:

            Create a parameterized circuit and assign the parameters in-place.

            .. plot::
               :include-source:

               from qiskit.circuit import QuantumCircuit, Parameter

               circuit = QuantumCircuit(2)
               params = [Parameter('A'), Parameter('B'), Parameter('C')]
               circuit.ry(params[0], 0)
               circuit.crx(params[1], 0, 1)
               circuit.draw('mpl')
               circuit.assign_parameters({params[0]: params[2]}, inplace=True)
               circuit.draw('mpl')

            Bind the values out-of-place by list and get a copy of the original circuit.

            .. plot::
               :include-source:

               from qiskit.circuit import QuantumCircuit, ParameterVector

               circuit = QuantumCircuit(2)
               params = ParameterVector('P', 2)
               circuit.ry(params[0], 0)
               circuit.crx(params[1], 0, 1)

               bound_circuit = circuit.assign_parameters([1, 2])
               bound_circuit.draw('mpl')

               circuit.draw('mpl')

        """
        if inplace:
            target = self
        else:
            target = self.copy()
            target._increment_instances()
            target._name_update()

        # Normalise the inputs into simple abstract interfaces, so we've dispatched the "iteration"
        # logic in one place at the start of the function.  This lets us do things like calculate
        # and cache expensive properties for (e.g.) the sequence format only if they're used; for
        # many large, close-to-hardware circuits, we won't need the extra handling for
        # `global_phase` or recursive definition binding.
        #
        # During normalisation, be sure to reference 'parameters' and related things from 'self' not
        # 'target' so we can take advantage of any caching we might be doing.
        if isinstance(parameters, dict):
            raw_mapping = parameters if flat_input else self._unroll_param_dict(parameters)
            # Remember that we _must not_ mutate the output of `_unsorted_parameters`.
            our_parameters = self._unsorted_parameters()
            if strict and (extras := raw_mapping.keys() - our_parameters):
                raise CircuitError(
                    f"Cannot bind parameters ({', '.join(str(x) for x in extras)}) not present in"
                    " the circuit."
                )
            parameter_binds = _ParameterBindsDict(raw_mapping, our_parameters)
        else:
            our_parameters = self.parameters
            if len(parameters) != len(our_parameters):
                raise ValueError(
                    "Mismatching number of values and parameters. For partial binding "
                    "please pass a dictionary of {parameter: value} pairs."
                )
            parameter_binds = _ParameterBindsSequence(our_parameters, parameters)

        # Clear out the parameter table for the relevant entries, since we'll be binding those.
        # Any new references to parameters are reinserted as part of the bind.
        target._parameters = None
        # This is deliberately eager, because we want the side effect of clearing the table.
        all_references = [
            (parameter, value, target._parameter_table.pop(parameter, ()))
            for parameter, value in parameter_binds.items()
        ]
        seen_operations = {}
        # The meat of the actual binding for regular operations.
        for to_bind, bound_value, references in all_references:
            update_parameters = (
                tuple(bound_value.parameters)
                if isinstance(bound_value, ParameterExpression)
                else ()
            )
            for operation, index in references:
                seen_operations[id(operation)] = operation
                if operation is ParameterTable.GLOBAL_PHASE:
                    assignee = target.global_phase
                    validate = _normalize_global_phase
                else:
                    assignee = operation.params[index]
                    validate = operation.validate_parameter
                if isinstance(assignee, ParameterExpression):
                    new_parameter = assignee.assign(to_bind, bound_value)
                    for parameter in update_parameters:
                        if parameter not in target._parameter_table:
                            target._parameter_table[parameter] = ParameterReferences(())
                        target._parameter_table[parameter].add((operation, index))
                    if not new_parameter.parameters:
                        new_parameter = validate(new_parameter.numeric())
                elif isinstance(assignee, QuantumCircuit):
                    new_parameter = assignee.assign_parameters(
                        {to_bind: bound_value}, inplace=False, flat_input=True
                    )
                else:
                    raise RuntimeError(  # pragma: no cover
                        f"Saw an unknown type during symbolic binding: {assignee}."
                        " This may indicate an internal logic error in symbol tracking."
                    )
                if operation is ParameterTable.GLOBAL_PHASE:
                    # We've already handled parameter table updates in bulk, so we need to skip the
                    # public setter trying to do it again.
                    target._global_phase = new_parameter
                else:
                    operation.params[index] = new_parameter

        # After we've been through everything at the top level, make a single visit to each
        # operation we've seen, rebinding its definition if necessary.
        for operation in seen_operations.values():
            if (
                definition := getattr(operation, "_definition", None)
            ) is not None and definition.num_parameters:
                definition.assign_parameters(
                    parameter_binds.mapping, inplace=True, flat_input=True, strict=False
                )

        # Finally, assign the parameters inside any of the calibrations.  We don't track these in
        # the `ParameterTable`, so we manually reconstruct things.
        def map_calibration(qubits, parameters, schedule):
            modified = False
            new_parameters = list(parameters)
            for i, parameter in enumerate(new_parameters):
                if not isinstance(parameter, ParameterExpression):
                    continue
                if not (contained := parameter.parameters & parameter_binds.mapping.keys()):
                    continue
                for to_bind in contained:
                    parameter = parameter.assign(to_bind, parameter_binds.mapping[to_bind])
                if not parameter.parameters:
                    parameter = parameter.numeric()
                    if isinstance(parameter, complex):
                        raise TypeError(f"Calibration cannot use complex number: '{parameter}'")
                new_parameters[i] = parameter
                modified = True
            if modified:
                schedule.assign_parameters(parameter_binds.mapping)
            return (qubits, tuple(new_parameters)), schedule

        target._calibrations = defaultdict(
            dict,
            (
                (
                    gate,
                    dict(
                        map_calibration(qubits, parameters, schedule)
                        for (qubits, parameters), schedule in calibrations.items()
                    ),
                )
                for gate, calibrations in target._calibrations.items()
            ),
        )
        return None if inplace else target

    def _unroll_param_dict(
        self, parameter_binds: Mapping[Parameter, ParameterValueType]
    ) -> Mapping[Parameter, ParameterValueType]:
        out = {}
        for parameter, value in parameter_binds.items():
            if isinstance(parameter, ParameterVector):
                if len(parameter) != len(value):
                    raise CircuitError(
                        f"Parameter vector '{parameter.name}' has length {len(parameter)},"
                        f" but was assigned to {len(value)} values."
                    )
                out.update(zip(parameter, value))
            elif isinstance(parameter, str):
                out[self.get_parameter(parameter)] = value
            else:
                out[parameter] = value
        return out

    def barrier(self, *qargs: QubitSpecifier, label=None) -> InstructionSet:
        """Apply :class:`~.library.Barrier`. If ``qargs`` is empty, applies to all qubits
        in the circuit.

        Args:
            qargs (QubitSpecifier): Specification for one or more qubit arguments.
            label (str): The string label of the barrier.

        Returns:
            qiskit.circuit.InstructionSet: handle to the added instructions.
        """
        from .barrier import Barrier

        if qargs:
            # This uses a `dict` not a `set` to guarantee a deterministic order to the arguments.
            qubits = tuple({q: None for qarg in qargs for q in self.qbit_argument_conversion(qarg)})
            return self.append(CircuitInstruction(Barrier(len(qubits), label=label), qubits, ()))
        else:
            qubits = self.qubits.copy()
            return self._current_scope().append(
                CircuitInstruction(Barrier(len(qubits), label=label), qubits, ())
            )

    def delay(
        self,
        duration: ParameterValueType,
        qarg: QubitSpecifier | None = None,
        unit: str = "dt",
    ) -> InstructionSet:
        """Apply :class:`~.circuit.Delay`. If qarg is ``None``, applies to all qubits.
        When applying to multiple qubits, delays with the same duration will be created.

        Args:
            duration (int or float or ParameterExpression): duration of the delay.
            qarg (Object): qubit argument to apply this delay.
            unit (str): unit of the duration. Supported units: ``'s'``, ``'ms'``, ``'us'``,
                ``'ns'``, ``'ps'``, and ``'dt'``. Default is ``'dt'``, i.e. integer time unit
                depending on the target backend.

        Returns:
            qiskit.circuit.InstructionSet: handle to the added instructions.

        Raises:
            CircuitError: if arguments have bad format.
        """
        if qarg is None:
            qarg = self.qubits
        return self.append(Delay(duration, unit=unit), [qarg], [])

    def h(self, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.HGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.h import HGate

        return self.append(HGate(), [qubit], [])

    def ch(
        self,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CHGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.h import CHGate

        return self.append(
            CHGate(label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def id(self, qubit: QubitSpecifier) -> InstructionSet:  # pylint: disable=invalid-name
        """Apply :class:`~qiskit.circuit.library.IGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.i import IGate

        return self.append(IGate(), [qubit], [])

    def ms(self, theta: ParameterValueType, qubits: Sequence[QubitSpecifier]) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.MSGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The angle of the rotation.
            qubits: The qubits to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        # pylint: disable=cyclic-import
        from .library.generalized_gates.gms import MSGate

        return self.append(MSGate(len(qubits), theta), qubits)

    def p(self, theta: ParameterValueType, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.PhaseGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: THe angle of the rotation.
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.p import PhaseGate

        return self.append(PhaseGate(theta), [qubit], [])

    def cp(
        self,
        theta: ParameterValueType,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CPhaseGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The angle of the rotation.
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.p import CPhaseGate

        return self.append(
            CPhaseGate(theta, label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def mcp(
        self,
        lam: ParameterValueType,
        control_qubits: Sequence[QubitSpecifier],
        target_qubit: QubitSpecifier,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.MCPhaseGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            lam: The angle of the rotation.
            control_qubits: The qubits used as the controls.
            target_qubit: The qubit(s) targeted by the gate.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.p import MCPhaseGate

        num_ctrl_qubits = len(control_qubits)
        return self.append(
            MCPhaseGate(lam, num_ctrl_qubits, ctrl_state=ctrl_state),
            control_qubits[:] + [target_qubit],
            [],
        )

    def r(
        self, theta: ParameterValueType, phi: ParameterValueType, qubit: QubitSpecifier
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The angle of the rotation.
            phi: The angle of the axis of rotation in the x-y plane.
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.r import RGate

        return self.append(RGate(theta, phi), [qubit], [])

    def rv(
        self,
        vx: ParameterValueType,
        vy: ParameterValueType,
        vz: ParameterValueType,
        qubit: QubitSpecifier,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RVGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Rotation around an arbitrary rotation axis :math:`v`, where :math:`|v|` is the angle of
        rotation in radians.

        Args:
            vx: x-component of the rotation axis.
            vy: y-component of the rotation axis.
            vz: z-component of the rotation axis.
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.generalized_gates.rv import RVGate

        return self.append(RVGate(vx, vy, vz), [qubit], [])

    def rccx(
        self,
        control_qubit1: QubitSpecifier,
        control_qubit2: QubitSpecifier,
        target_qubit: QubitSpecifier,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RCCXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit1: The qubit(s) used as the first control.
            control_qubit2: The qubit(s) used as the second control.
            target_qubit: The qubit(s) targeted by the gate.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.x import RCCXGate

        return self.append(RCCXGate(), [control_qubit1, control_qubit2, target_qubit], [])

    def rcccx(
        self,
        control_qubit1: QubitSpecifier,
        control_qubit2: QubitSpecifier,
        control_qubit3: QubitSpecifier,
        target_qubit: QubitSpecifier,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RC3XGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit1: The qubit(s) used as the first control.
            control_qubit2: The qubit(s) used as the second control.
            control_qubit3: The qubit(s) used as the third control.
            target_qubit: The qubit(s) targeted by the gate.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.x import RC3XGate

        return self.append(
            RC3XGate(), [control_qubit1, control_qubit2, control_qubit3, target_qubit], []
        )

    def rx(
        self, theta: ParameterValueType, qubit: QubitSpecifier, label: str | None = None
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The rotation angle of the gate.
            qubit: The qubit(s) to apply the gate to.
            label: The string label of the gate in the circuit.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.rx import RXGate

        return self.append(RXGate(theta, label=label), [qubit], [])

    def crx(
        self,
        theta: ParameterValueType,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CRXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The angle of the rotation.
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.rx import CRXGate

        return self.append(
            CRXGate(theta, label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def rxx(
        self, theta: ParameterValueType, qubit1: QubitSpecifier, qubit2: QubitSpecifier
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RXXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The angle of the rotation.
            qubit1: The qubit(s) to apply the gate to.
            qubit2: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.rxx import RXXGate

        return self.append(RXXGate(theta), [qubit1, qubit2], [])

    def ry(
        self, theta: ParameterValueType, qubit: QubitSpecifier, label: str | None = None
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RYGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The rotation angle of the gate.
            qubit: The qubit(s) to apply the gate to.
            label: The string label of the gate in the circuit.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.ry import RYGate

        return self.append(RYGate(theta, label=label), [qubit], [])

    def cry(
        self,
        theta: ParameterValueType,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CRYGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The angle of the rotation.
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.ry import CRYGate

        return self.append(
            CRYGate(theta, label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def ryy(
        self, theta: ParameterValueType, qubit1: QubitSpecifier, qubit2: QubitSpecifier
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RYYGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The rotation angle of the gate.
            qubit1: The qubit(s) to apply the gate to.
            qubit2: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.ryy import RYYGate

        return self.append(RYYGate(theta), [qubit1, qubit2], [])

    def rz(self, phi: ParameterValueType, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RZGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            phi: The rotation angle of the gate.
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.rz import RZGate

        return self.append(RZGate(phi), [qubit], [])

    def crz(
        self,
        theta: ParameterValueType,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CRZGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The angle of the rotation.
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.rz import CRZGate

        return self.append(
            CRZGate(theta, label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def rzx(
        self, theta: ParameterValueType, qubit1: QubitSpecifier, qubit2: QubitSpecifier
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RZXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The rotation angle of the gate.
            qubit1: The qubit(s) to apply the gate to.
            qubit2: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.rzx import RZXGate

        return self.append(RZXGate(theta), [qubit1, qubit2], [])

    def rzz(
        self, theta: ParameterValueType, qubit1: QubitSpecifier, qubit2: QubitSpecifier
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.RZZGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The rotation angle of the gate.
            qubit1: The qubit(s) to apply the gate to.
            qubit2: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.rzz import RZZGate

        return self.append(RZZGate(theta), [qubit1, qubit2], [])

    def ecr(self, qubit1: QubitSpecifier, qubit2: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.ECRGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit1, qubit2: The qubits to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.ecr import ECRGate

        return self.append(ECRGate(), [qubit1, qubit2], [])

    def s(self, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.SGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.s import SGate

        return self.append(SGate(), [qubit], [])

    def sdg(self, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.SdgGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.s import SdgGate

        return self.append(SdgGate(), [qubit], [])

    def cs(
        self,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CSGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.s import CSGate

        return self.append(
            CSGate(label=label, ctrl_state=ctrl_state),
            [control_qubit, target_qubit],
            [],
        )

    def csdg(
        self,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CSdgGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.s import CSdgGate

        return self.append(
            CSdgGate(label=label, ctrl_state=ctrl_state),
            [control_qubit, target_qubit],
            [],
        )

    def swap(self, qubit1: QubitSpecifier, qubit2: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.SwapGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit1, qubit2: The qubits to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.swap import SwapGate

        return self.append(SwapGate(), [qubit1, qubit2], [])

    def iswap(self, qubit1: QubitSpecifier, qubit2: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.iSwapGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit1, qubit2: The qubits to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.iswap import iSwapGate

        return self.append(iSwapGate(), [qubit1, qubit2], [])

    def cswap(
        self,
        control_qubit: QubitSpecifier,
        target_qubit1: QubitSpecifier,
        target_qubit2: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CSwapGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the control.
            target_qubit1: The qubit(s) targeted by the gate.
            target_qubit2: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. ``'1'``).  Defaults to controlling
                on the ``'1'`` state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.swap import CSwapGate

        return self.append(
            CSwapGate(label=label, ctrl_state=ctrl_state),
            [control_qubit, target_qubit1, target_qubit2],
            [],
        )

    def sx(self, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.SXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.sx import SXGate

        return self.append(SXGate(), [qubit], [])

    def sxdg(self, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.SXdgGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.sx import SXdgGate

        return self.append(SXdgGate(), [qubit], [])

    def csx(
        self,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.CSXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.sx import CSXGate

        return self.append(
            CSXGate(label=label, ctrl_state=ctrl_state),
            [control_qubit, target_qubit],
            [],
        )

    def t(self, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.TGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.t import TGate

        return self.append(TGate(), [qubit], [])

    def tdg(self, qubit: QubitSpecifier) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.TdgGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.t import TdgGate

        return self.append(TdgGate(), [qubit], [])

    def u(
        self,
        theta: ParameterValueType,
        phi: ParameterValueType,
        lam: ParameterValueType,
        qubit: QubitSpecifier,
    ) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.UGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The :math:`\theta` rotation angle of the gate.
            phi: The :math:`\phi` rotation angle of the gate.
            lam: The :math:`\lambda` rotation angle of the gate.
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.u import UGate

        return self.append(UGate(theta, phi, lam), [qubit], [])

    def cu(
        self,
        theta: ParameterValueType,
        phi: ParameterValueType,
        lam: ParameterValueType,
        gamma: ParameterValueType,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.CUGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            theta: The :math:`\theta` rotation angle of the gate.
            phi: The :math:`\phi` rotation angle of the gate.
            lam: The :math:`\lambda` rotation angle of the gate.
            gamma: The global phase applied of the U gate, if applied.
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.u import CUGate

        return self.append(
            CUGate(theta, phi, lam, gamma, label=label, ctrl_state=ctrl_state),
            [control_qubit, target_qubit],
            [],
        )

    def x(self, qubit: QubitSpecifier, label: str | None = None) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.XGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.
            label: The string label of the gate in the circuit.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.x import XGate

        return self.append(XGate(label=label), [qubit], [])

    def cx(
        self,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.CXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """

        from .library.standard_gates.x import CXGate

        return self.append(
            CXGate(label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def dcx(self, qubit1: QubitSpecifier, qubit2: QubitSpecifier) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.DCXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit1: The qubit(s) to apply the gate to.
            qubit2: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.dcx import DCXGate

        return self.append(DCXGate(), [qubit1, qubit2], [])

    def ccx(
        self,
        control_qubit1: QubitSpecifier,
        control_qubit2: QubitSpecifier,
        target_qubit: QubitSpecifier,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.CCXGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit1: The qubit(s) used as the first control.
            control_qubit2: The qubit(s) used as the second control.
            target_qubit: The qubit(s) targeted by the gate.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.x import CCXGate

        return self.append(
            CCXGate(ctrl_state=ctrl_state),
            [control_qubit1, control_qubit2, target_qubit],
            [],
        )

    def mcx(
        self,
        control_qubits: Sequence[QubitSpecifier],
        target_qubit: QubitSpecifier,
        ancilla_qubits: QubitSpecifier | Sequence[QubitSpecifier] | None = None,
        mode: str = "noancilla",
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.MCXGate`.

        The multi-cX gate can be implemented using different techniques, which use different numbers
        of ancilla qubits and have varying circuit depth. These modes are:

        - ``'noancilla'``: Requires 0 ancilla qubits.
        - ``'recursion'``: Requires 1 ancilla qubit if more than 4 controls are used, otherwise 0.
        - ``'v-chain'``: Requires 2 less ancillas than the number of control qubits.
        - ``'v-chain-dirty'``: Same as for the clean ancillas (but the circuit will be longer).

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubits: The qubits used as the controls.
            target_qubit: The qubit(s) targeted by the gate.
            ancilla_qubits: The qubits used as the ancillae, if the mode requires them.
            mode: The choice of mode, explained further above.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.

        Raises:
            ValueError: if the given mode is not known, or if too few ancilla qubits are passed.
            AttributeError: if no ancilla qubits are passed, but some are needed.
        """
        from .library.standard_gates.x import MCXGrayCode, MCXRecursive, MCXVChain

        num_ctrl_qubits = len(control_qubits)

        available_implementations = {
            "noancilla": MCXGrayCode(num_ctrl_qubits, ctrl_state=ctrl_state),
            "recursion": MCXRecursive(num_ctrl_qubits, ctrl_state=ctrl_state),
            "v-chain": MCXVChain(num_ctrl_qubits, False, ctrl_state=ctrl_state),
            "v-chain-dirty": MCXVChain(num_ctrl_qubits, dirty_ancillas=True, ctrl_state=ctrl_state),
            # outdated, previous names
            "advanced": MCXRecursive(num_ctrl_qubits, ctrl_state=ctrl_state),
            "basic": MCXVChain(num_ctrl_qubits, dirty_ancillas=False, ctrl_state=ctrl_state),
            "basic-dirty-ancilla": MCXVChain(
                num_ctrl_qubits, dirty_ancillas=True, ctrl_state=ctrl_state
            ),
        }

        # check ancilla input
        if ancilla_qubits:
            _ = self.qbit_argument_conversion(ancilla_qubits)

        try:
            gate = available_implementations[mode]
        except KeyError as ex:
            all_modes = list(available_implementations.keys())
            raise ValueError(
                f"Unsupported mode ({mode}) selected, choose one of {all_modes}"
            ) from ex

        if hasattr(gate, "num_ancilla_qubits") and gate.num_ancilla_qubits > 0:
            required = gate.num_ancilla_qubits
            if ancilla_qubits is None:
                raise AttributeError(f"No ancillas provided, but {required} are needed!")

            # convert ancilla qubits to a list if they were passed as int or qubit
            if not hasattr(ancilla_qubits, "__len__"):
                ancilla_qubits = [ancilla_qubits]

            if len(ancilla_qubits) < required:
                actually = len(ancilla_qubits)
                raise ValueError(f"At least {required} ancillas required, but {actually} given.")
            # size down if too many ancillas were provided
            ancilla_qubits = ancilla_qubits[:required]
        else:
            ancilla_qubits = []

        return self.append(gate, control_qubits[:] + [target_qubit] + ancilla_qubits[:], [])

    def y(self, qubit: QubitSpecifier) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.YGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.y import YGate

        return self.append(YGate(), [qubit], [])

    def cy(
        self,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.CYGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the controls.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.y import CYGate

        return self.append(
            CYGate(label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def z(self, qubit: QubitSpecifier) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.ZGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            qubit: The qubit(s) to apply the gate to.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.z import ZGate

        return self.append(ZGate(), [qubit], [])

    def cz(
        self,
        control_qubit: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.CZGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit: The qubit(s) used as the controls.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
                on the '1' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.z import CZGate

        return self.append(
            CZGate(label=label, ctrl_state=ctrl_state), [control_qubit, target_qubit], []
        )

    def ccz(
        self,
        control_qubit1: QubitSpecifier,
        control_qubit2: QubitSpecifier,
        target_qubit: QubitSpecifier,
        label: str | None = None,
        ctrl_state: str | int | None = None,
    ) -> InstructionSet:
        r"""Apply :class:`~qiskit.circuit.library.CCZGate`.

        For the full matrix form of this gate, see the underlying gate documentation.

        Args:
            control_qubit1: The qubit(s) used as the first control.
            control_qubit2: The qubit(s) used as the second control.
            target_qubit: The qubit(s) targeted by the gate.
            label: The string label of the gate in the circuit.
            ctrl_state:
                The control state in decimal, or as a bitstring (e.g. '10').  Defaults to controlling
                on the '11' state.

        Returns:
            A handle to the instructions created.
        """
        from .library.standard_gates.z import CCZGate

        return self.append(
            CCZGate(label=label, ctrl_state=ctrl_state),
            [control_qubit1, control_qubit2, target_qubit],
            [],
        )

    def pauli(
        self,
        pauli_string: str,
        qubits: Sequence[QubitSpecifier],
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.library.PauliGate`.

        Args:
            pauli_string: A string representing the Pauli operator to apply, e.g. 'XX'.
            qubits: The qubits to apply this gate to.

        Returns:
            A handle to the instructions created.
        """
        from qiskit.circuit.library.generalized_gates.pauli import PauliGate

        return self.append(PauliGate(pauli_string), qubits, [])

    def prepare_state(
        self,
        state: Statevector | Sequence[complex] | str | int,
        qubits: Sequence[QubitSpecifier] | None = None,
        label: str | None = None,
        normalize: bool = False,
    ) -> InstructionSet:
        r"""Prepare qubits in a specific state.

        This class implements a state preparing unitary. Unlike
        :meth:`.initialize` it does not reset the qubits first.

        Args:
            state: The state to initialize to, can be either of the following.

                * Statevector or vector of complex amplitudes to initialize to.
                * Labels of basis states of the Pauli eigenstates Z, X, Y. See
                  :meth:`.Statevector.from_label`. Notice the order of the labels is reversed with
                  respect to the qubit index to be applied to. Example label '01' initializes the
                  qubit zero to :math:`|1\rangle` and the qubit one to :math:`|0\rangle`.
                * An integer that is used as a bitmap indicating which qubits to initialize to
                  :math:`|1\rangle`. Example: setting params to 5 would initialize qubit 0 and qubit
                  2 to :math:`|1\rangle` and qubit 1 to :math:`|0\rangle`.

            qubits: Qubits to initialize. If ``None`` the initialization is applied to all qubits in
                the circuit.
            label: An optional label for the gate
            normalize: Whether to normalize an input array to a unit vector.

        Returns:
            A handle to the instruction that was just initialized

        Examples:
            Prepare a qubit in the state :math:`(|0\rangle - |1\rangle) / \sqrt{2}`.

            .. code-block::

                import numpy as np
                from qiskit import QuantumCircuit

                circuit = QuantumCircuit(1)
                circuit.prepare_state([1/np.sqrt(2), -1/np.sqrt(2)], 0)
                circuit.draw()

            output:

            .. parsed-literal::

                     ┌─────────────────────────────────────┐
                q_0: ┤ State Preparation(0.70711,-0.70711) ├
                     └─────────────────────────────────────┘


            Prepare from a string two qubits in the state :math:`|10\rangle`.
            The order of the labels is reversed with respect to qubit index.
            More information about labels for basis states are in
            :meth:`.Statevector.from_label`.

            .. code-block::

                import numpy as np
                from qiskit import QuantumCircuit

                circuit = QuantumCircuit(2)
                circuit.prepare_state('01', circuit.qubits)
                circuit.draw()

            output:

            .. parsed-literal::

                     ┌─────────────────────────┐
                q_0: ┤0                        ├
                     │  State Preparation(0,1) │
                q_1: ┤1                        ├
                     └─────────────────────────┘


            Initialize two qubits from an array of complex amplitudes
            .. code-block::

                import numpy as np
                from qiskit import QuantumCircuit

                circuit = QuantumCircuit(2)
                circuit.prepare_state([0, 1/np.sqrt(2), -1.j/np.sqrt(2), 0], circuit.qubits)
                circuit.draw()

            output:

            .. parsed-literal::

                     ┌───────────────────────────────────────────┐
                q_0: ┤0                                          ├
                     │  State Preparation(0,0.70711,-0.70711j,0) │
                q_1: ┤1                                          ├
                     └───────────────────────────────────────────┘
        """
        # pylint: disable=cyclic-import
        from qiskit.circuit.library.data_preparation import StatePreparation

        if qubits is None:
            qubits = self.qubits
        elif isinstance(qubits, (int, np.integer, slice, Qubit)):
            qubits = [qubits]

        num_qubits = len(qubits) if isinstance(state, int) else None

        return self.append(
            StatePreparation(state, num_qubits, label=label, normalize=normalize), qubits
        )

    def initialize(
        self,
        params: Statevector | Sequence[complex] | str | int,
        qubits: Sequence[QubitSpecifier] | None = None,
        normalize: bool = False,
    ):
        r"""Initialize qubits in a specific state.

        Qubit initialization is done by first resetting the qubits to :math:`|0\rangle`
        followed by calling :class:`~qiskit.circuit.library.StatePreparation`
        class to prepare the qubits in a specified state.
        Both these steps are included in the
        :class:`~qiskit.circuit.library.Initialize` instruction.

        Args:
            params: The state to initialize to, can be either of the following.

                * Statevector or vector of complex amplitudes to initialize to.
                * Labels of basis states of the Pauli eigenstates Z, X, Y. See
                  :meth:`.Statevector.from_label`. Notice the order of the labels is reversed with
                  respect to the qubit index to be applied to. Example label '01' initializes the
                  qubit zero to :math:`|1\rangle` and the qubit one to :math:`|0\rangle`.
                * An integer that is used as a bitmap indicating which qubits to initialize to
                  :math:`|1\rangle`. Example: setting params to 5 would initialize qubit 0 and qubit
                  2 to :math:`|1\rangle` and qubit 1 to :math:`|0\rangle`.

            qubits: Qubits to initialize. If ``None`` the initialization is applied to all qubits in
                the circuit.
            normalize: Whether to normalize an input array to a unit vector.

        Returns:
            A handle to the instructions created.

        Examples:
            Prepare a qubit in the state :math:`(|0\rangle - |1\rangle) / \sqrt{2}`.

            .. code-block::

                import numpy as np
                from qiskit import QuantumCircuit

                circuit = QuantumCircuit(1)
                circuit.initialize([1/np.sqrt(2), -1/np.sqrt(2)], 0)
                circuit.draw()

            output:

            .. parsed-literal::

                     ┌──────────────────────────────┐
                q_0: ┤ Initialize(0.70711,-0.70711) ├
                     └──────────────────────────────┘


            Initialize from a string two qubits in the state :math:`|10\rangle`.
            The order of the labels is reversed with respect to qubit index.
            More information about labels for basis states are in
            :meth:`.Statevector.from_label`.

            .. code-block::

                import numpy as np
                from qiskit import QuantumCircuit

                circuit = QuantumCircuit(2)
                circuit.initialize('01', circuit.qubits)
                circuit.draw()

            output:

            .. parsed-literal::

                     ┌──────────────────┐
                q_0: ┤0                 ├
                     │  Initialize(0,1) │
                q_1: ┤1                 ├
                     └──────────────────┘

            Initialize two qubits from an array of complex amplitudes.

            .. code-block::

                import numpy as np
                from qiskit import QuantumCircuit

                circuit = QuantumCircuit(2)
                circuit.initialize([0, 1/np.sqrt(2), -1.j/np.sqrt(2), 0], circuit.qubits)
                circuit.draw()

            output:

            .. parsed-literal::

                     ┌────────────────────────────────────┐
                q_0: ┤0                                   ├
                     │  Initialize(0,0.70711,-0.70711j,0) │
                q_1: ┤1                                   ├
                     └────────────────────────────────────┘
        """
        # pylint: disable=cyclic-import
        from .library.data_preparation.initializer import Initialize

        if qubits is None:
            qubits = self.qubits
        elif isinstance(qubits, (int, np.integer, slice, Qubit)):
            qubits = [qubits]

        num_qubits = len(qubits) if isinstance(params, int) else None

        return self.append(Initialize(params, num_qubits, normalize), qubits)

    def unitary(
        self,
        obj: np.ndarray | Gate | BaseOperator,
        qubits: Sequence[QubitSpecifier],
        label: str | None = None,
    ):
        """Apply unitary gate specified by ``obj`` to ``qubits``.

        Args:
            obj: Unitary operator.
            qubits: The circuit qubits to apply the transformation to.
            label: Unitary name for backend [Default: None].

        Returns:
            QuantumCircuit: The quantum circuit.

        Example:

            Apply a gate specified by a unitary matrix to a quantum circuit

            .. code-block:: python

                from qiskit import QuantumCircuit
                matrix = [[0, 0, 0, 1],
                        [0, 0, 1, 0],
                        [1, 0, 0, 0],
                        [0, 1, 0, 0]]
                circuit = QuantumCircuit(2)
                circuit.unitary(matrix, [0, 1])
        """
        # pylint: disable=cyclic-import
        from .library.generalized_gates.unitary import UnitaryGate

        gate = UnitaryGate(obj, label=label)

        # correctly treat as single-qubit gate if it only acts as 1 qubit, i.e.
        # allow a single qubit specifier and enable broadcasting
        if gate.num_qubits == 1:
            if isinstance(qubits, (int, Qubit)) or len(qubits) > 1:
                qubits = [qubits]

        return self.append(gate, qubits, [])

    def _current_scope(self) -> CircuitScopeInterface:
        if self._control_flow_scopes:
            return self._control_flow_scopes[-1]
        return self._builder_api

    def _push_scope(
        self,
        qubits: Iterable[Qubit] = (),
        clbits: Iterable[Clbit] = (),
        registers: Iterable[Register] = (),
        allow_jumps: bool = True,
        forbidden_message: Optional[str] = None,
    ):
        """Add a scope for collecting instructions into this circuit.

        This should only be done by the control-flow context managers, which will handle cleaning up
        after themselves at the end as well.

        Args:
            qubits: Any qubits that this scope should automatically use.
            clbits: Any clbits that this scope should automatically use.
            allow_jumps: Whether this scope allows jumps to be used within it.
            forbidden_message: If given, all attempts to add instructions to this scope will raise a
                :exc:`.CircuitError` with this message.
        """
        self._control_flow_scopes.append(
            ControlFlowBuilderBlock(
                qubits,
                clbits,
                parent=self._current_scope(),
                registers=registers,
                allow_jumps=allow_jumps,
                forbidden_message=forbidden_message,
            )
        )

    def _pop_scope(self) -> ControlFlowBuilderBlock:
        """Finish a scope used in the control-flow builder interface, and return it to the caller.

        This should only be done by the control-flow context managers, since they naturally
        synchronise the creation and deletion of stack elements."""
        return self._control_flow_scopes.pop()

    def _peek_previous_instruction_in_scope(self) -> CircuitInstruction:
        """Return the instruction 3-tuple of the most recent instruction in the current scope, even
        if that scope is currently under construction.

        This function is only intended for use by the control-flow ``if``-statement builders, which
        may need to modify a previous instruction."""
        if self._control_flow_scopes:
            return self._control_flow_scopes[-1].peek()
        if not self._data:
            raise CircuitError("This circuit contains no instructions.")
        return self._data[-1]

    def _pop_previous_instruction_in_scope(self) -> CircuitInstruction:
        """Return the instruction 3-tuple of the most recent instruction in the current scope, even
        if that scope is currently under construction, and remove it from that scope.

        This function is only intended for use by the control-flow ``if``-statement builders, which
        may need to replace a previous instruction with another.
        """
        if self._control_flow_scopes:
            return self._control_flow_scopes[-1].pop()
        if not self._data:
            raise CircuitError("This circuit contains no instructions.")
        instruction = self._data.pop()
        if isinstance(instruction.operation, Instruction):
            self._update_parameter_table_on_instruction_removal(instruction)
        return instruction

    def _update_parameter_table_on_instruction_removal(self, instruction: CircuitInstruction):
        """Update the :obj:`.ParameterTable` of this circuit given that an instance of the given
        ``instruction`` has just been removed from the circuit.

        .. note::

            This does not account for the possibility for the same instruction instance being added
            more than once to the circuit.  At the time of writing (2021-11-17, main commit 271a82f)
            there is a defensive ``deepcopy`` of parameterised instructions inside
            :meth:`.QuantumCircuit.append`, so this should be safe.  Trying to account for it would
            involve adding a potentially quadratic-scaling loop to check each entry in ``data``.
        """
        atomic_parameters: list[tuple[Parameter, int]] = []
        for index, parameter in enumerate(instruction.operation.params):
            if isinstance(parameter, (ParameterExpression, QuantumCircuit)):
                atomic_parameters.extend((p, index) for p in parameter.parameters)
        for atomic_parameter, index in atomic_parameters:
            new_entries = self._parameter_table[atomic_parameter].copy()
            new_entries.discard((instruction.operation, index))
            if not new_entries:
                del self._parameter_table[atomic_parameter]
                # Invalidate cache.
                self._parameters = None
            else:
                self._parameter_table[atomic_parameter] = new_entries

    @typing.overload
    def while_loop(
        self,
        condition: tuple[ClassicalRegister | Clbit, int] | expr.Expr,
        body: None,
        qubits: None,
        clbits: None,
        *,
        label: str | None,
    ) -> WhileLoopContext: ...

    @typing.overload
    def while_loop(
        self,
        condition: tuple[ClassicalRegister | Clbit, int] | expr.Expr,
        body: "QuantumCircuit",
        qubits: Sequence[QubitSpecifier],
        clbits: Sequence[ClbitSpecifier],
        *,
        label: str | None,
    ) -> InstructionSet: ...

    def while_loop(self, condition, body=None, qubits=None, clbits=None, *, label=None):
        """Create a ``while`` loop on this circuit.

        There are two forms for calling this function.  If called with all its arguments (with the
        possible exception of ``label``), it will create a
        :obj:`~qiskit.circuit.controlflow.WhileLoopOp` with the given ``body``.  If ``body`` (and
        ``qubits`` and ``clbits``) are *not* passed, then this acts as a context manager, which
        will automatically build a :obj:`~qiskit.circuit.controlflow.WhileLoopOp` when the scope
        finishes.  In this form, you do not need to keep track of the qubits or clbits you are
        using, because the scope will handle it for you.

        Example usage::

            from qiskit.circuit import QuantumCircuit, Clbit, Qubit
            bits = [Qubit(), Qubit(), Clbit()]
            qc = QuantumCircuit(bits)

            with qc.while_loop((bits[2], 0)):
                qc.h(0)
                qc.cx(0, 1)
                qc.measure(0, 0)

        Args:
            condition (Tuple[Union[ClassicalRegister, Clbit], int]): An equality condition to be
                checked prior to executing ``body``. The left-hand side of the condition must be a
                :obj:`~ClassicalRegister` or a :obj:`~Clbit`, and the right-hand side must be an
                integer or boolean.
            body (Optional[QuantumCircuit]): The loop body to be repeatedly executed.  Omit this to
                use the context-manager mode.
            qubits (Optional[Sequence[Qubit]]): The circuit qubits over which the loop body should
                be run.  Omit this to use the context-manager mode.
            clbits (Optional[Sequence[Clbit]]): The circuit clbits over which the loop body should
                be run.  Omit this to use the context-manager mode.
            label (Optional[str]): The string label of the instruction in the circuit.

        Returns:
            InstructionSet or WhileLoopContext: If used in context-manager mode, then this should be
            used as a ``with`` resource, which will infer the block content and operands on exit.
            If the full form is used, then this returns a handle to the instructions created.

        Raises:
            CircuitError: if an incorrect calling convention is used.
        """
        circuit_scope = self._current_scope()
        if isinstance(condition, expr.Expr):
            condition = _validate_expr(circuit_scope, condition)
        else:
            condition = (circuit_scope.resolve_classical_resource(condition[0]), condition[1])

        if body is None:
            if qubits is not None or clbits is not None:
                raise CircuitError(
                    "When using 'while_loop' as a context manager,"
                    " you cannot pass qubits or clbits."
                )
            return WhileLoopContext(self, condition, label=label)
        elif qubits is None or clbits is None:
            raise CircuitError(
                "When using 'while_loop' with a body, you must pass qubits and clbits."
            )

        return self.append(WhileLoopOp(condition, body, label), qubits, clbits)

    @typing.overload
    def for_loop(
        self,
        indexset: Iterable[int],
        loop_parameter: Parameter | None,
        body: None,
        qubits: None,
        clbits: None,
        *,
        label: str | None,
    ) -> ForLoopContext: ...

    @typing.overload
    def for_loop(
        self,
        indexset: Iterable[int],
        loop_parameter: Union[Parameter, None],
        body: "QuantumCircuit",
        qubits: Sequence[QubitSpecifier],
        clbits: Sequence[ClbitSpecifier],
        *,
        label: str | None,
    ) -> InstructionSet: ...

    def for_loop(
        self, indexset, loop_parameter=None, body=None, qubits=None, clbits=None, *, label=None
    ):
        """Create a ``for`` loop on this circuit.

        There are two forms for calling this function.  If called with all its arguments (with the
        possible exception of ``label``), it will create a
        :class:`~qiskit.circuit.ForLoopOp` with the given ``body``.  If ``body`` (and
        ``qubits`` and ``clbits``) are *not* passed, then this acts as a context manager, which,
        when entered, provides a loop variable (unless one is given, in which case it will be
        reused) and will automatically build a :class:`~qiskit.circuit.ForLoopOp` when the
        scope finishes.  In this form, you do not need to keep track of the qubits or clbits you are
        using, because the scope will handle it for you.

        For example::

            from qiskit import QuantumCircuit
            qc = QuantumCircuit(2, 1)

            with qc.for_loop(range(5)) as i:
                qc.h(0)
                qc.cx(0, 1)
                qc.measure(0, 0)
                qc.break_loop().c_if(0, True)

        Args:
            indexset (Iterable[int]): A collection of integers to loop over.  Always necessary.
            loop_parameter (Optional[Parameter]): The parameter used within ``body`` to which
                the values from ``indexset`` will be assigned.  In the context-manager form, if this
                argument is not supplied, then a loop parameter will be allocated for you and
                returned as the value of the ``with`` statement.  This will only be bound into the
                circuit if it is used within the body.

                If this argument is ``None`` in the manual form of this method, ``body`` will be
                repeated once for each of the items in ``indexset`` but their values will be
                ignored.
            body (Optional[QuantumCircuit]): The loop body to be repeatedly executed.  Omit this to
                use the context-manager mode.
            qubits (Optional[Sequence[QubitSpecifier]]): The circuit qubits over which the loop body
                should be run.  Omit this to use the context-manager mode.
            clbits (Optional[Sequence[ClbitSpecifier]]): The circuit clbits over which the loop body
                should be run.  Omit this to use the context-manager mode.
            label (Optional[str]): The string label of the instruction in the circuit.

        Returns:
            InstructionSet or ForLoopContext: depending on the call signature, either a context
            manager for creating the for loop (it will automatically be added to the circuit at the
            end of the block), or an :obj:`~InstructionSet` handle to the appended loop operation.

        Raises:
            CircuitError: if an incorrect calling convention is used.
        """
        if body is None:
            if qubits is not None or clbits is not None:
                raise CircuitError(
                    "When using 'for_loop' as a context manager, you cannot pass qubits or clbits."
                )
            return ForLoopContext(self, indexset, loop_parameter, label=label)
        elif qubits is None or clbits is None:
            raise CircuitError(
                "When using 'for_loop' with a body, you must pass qubits and clbits."
            )

        return self.append(ForLoopOp(indexset, loop_parameter, body, label), qubits, clbits)

    @typing.overload
    def if_test(
        self,
        condition: tuple[ClassicalRegister | Clbit, int],
        true_body: None,
        qubits: None,
        clbits: None,
        *,
        label: str | None,
    ) -> IfContext: ...

    @typing.overload
    def if_test(
        self,
        condition: tuple[ClassicalRegister | Clbit, int],
        true_body: "QuantumCircuit",
        qubits: Sequence[QubitSpecifier],
        clbits: Sequence[ClbitSpecifier],
        *,
        label: str | None = None,
    ) -> InstructionSet: ...

    def if_test(
        self,
        condition,
        true_body=None,
        qubits=None,
        clbits=None,
        *,
        label=None,
    ):
        """Create an ``if`` statement on this circuit.

        There are two forms for calling this function.  If called with all its arguments (with the
        possible exception of ``label``), it will create a
        :obj:`~qiskit.circuit.IfElseOp` with the given ``true_body``, and there will be
        no branch for the ``false`` condition (see also the :meth:`.if_else` method).  However, if
        ``true_body`` (and ``qubits`` and ``clbits``) are *not* passed, then this acts as a context
        manager, which can be used to build ``if`` statements.  The return value of the ``with``
        statement is a chainable context manager, which can be used to create subsequent ``else``
        blocks.  In this form, you do not need to keep track of the qubits or clbits you are using,
        because the scope will handle it for you.

        For example::

            from qiskit.circuit import QuantumCircuit, Qubit, Clbit
            bits = [Qubit(), Qubit(), Qubit(), Clbit(), Clbit()]
            qc = QuantumCircuit(bits)

            qc.h(0)
            qc.cx(0, 1)
            qc.measure(0, 0)
            qc.h(0)
            qc.cx(0, 1)
            qc.measure(0, 1)

            with qc.if_test((bits[3], 0)) as else_:
                qc.x(2)
            with else_:
                qc.h(2)
                qc.z(2)

        Args:
            condition (Tuple[Union[ClassicalRegister, Clbit], int]): A condition to be evaluated at
                circuit runtime which, if true, will trigger the evaluation of ``true_body``. Can be
                specified as either a tuple of a ``ClassicalRegister`` to be tested for equality
                with a given ``int``, or as a tuple of a ``Clbit`` to be compared to either a
                ``bool`` or an ``int``.
            true_body (Optional[QuantumCircuit]): The circuit body to be run if ``condition`` is
                true.
            qubits (Optional[Sequence[QubitSpecifier]]): The circuit qubits over which the if/else
                should be run.
            clbits (Optional[Sequence[ClbitSpecifier]]): The circuit clbits over which the if/else
                should be run.
            label (Optional[str]): The string label of the instruction in the circuit.

        Returns:
            InstructionSet or IfContext: depending on the call signature, either a context
            manager for creating the ``if`` block (it will automatically be added to the circuit at
            the end of the block), or an :obj:`~InstructionSet` handle to the appended conditional
            operation.

        Raises:
            CircuitError: If the provided condition references Clbits outside the
                enclosing circuit.
            CircuitError: if an incorrect calling convention is used.

        Returns:
            A handle to the instruction created.
        """
        circuit_scope = self._current_scope()
        if isinstance(condition, expr.Expr):
            condition = _validate_expr(circuit_scope, condition)
        else:
            condition = (circuit_scope.resolve_classical_resource(condition[0]), condition[1])

        if true_body is None:
            if qubits is not None or clbits is not None:
                raise CircuitError(
                    "When using 'if_test' as a context manager, you cannot pass qubits or clbits."
                )
            # We can only allow jumps if we're in a loop block, but the default path (no scopes)
            # also allows adding jumps to support the more verbose internal mode.
            in_loop = bool(self._control_flow_scopes and self._control_flow_scopes[-1].allow_jumps)
            return IfContext(self, condition, in_loop=in_loop, label=label)
        elif qubits is None or clbits is None:
            raise CircuitError("When using 'if_test' with a body, you must pass qubits and clbits.")

        return self.append(IfElseOp(condition, true_body, None, label), qubits, clbits)

    def if_else(
        self,
        condition: tuple[ClassicalRegister, int] | tuple[Clbit, int] | tuple[Clbit, bool],
        true_body: "QuantumCircuit",
        false_body: "QuantumCircuit",
        qubits: Sequence[QubitSpecifier],
        clbits: Sequence[ClbitSpecifier],
        label: str | None = None,
    ) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.IfElseOp`.

        .. note::

            This method does not have an associated context-manager form, because it is already
            handled by the :meth:`.if_test` method.  You can use the ``else`` part of that with
            something such as::

                from qiskit.circuit import QuantumCircuit, Qubit, Clbit
                bits = [Qubit(), Qubit(), Clbit()]
                qc = QuantumCircuit(bits)
                qc.h(0)
                qc.cx(0, 1)
                qc.measure(0, 0)
                with qc.if_test((bits[2], 0)) as else_:
                    qc.h(0)
                with else_:
                    qc.x(0)

        Args:
            condition: A condition to be evaluated at circuit runtime which,
                if true, will trigger the evaluation of ``true_body``. Can be
                specified as either a tuple of a ``ClassicalRegister`` to be
                tested for equality with a given ``int``, or as a tuple of a
                ``Clbit`` to be compared to either a ``bool`` or an ``int``.
            true_body: The circuit body to be run if ``condition`` is true.
            false_body: The circuit to be run if ``condition`` is false.
            qubits: The circuit qubits over which the if/else should be run.
            clbits: The circuit clbits over which the if/else should be run.
            label: The string label of the instruction in the circuit.

        Raises:
            CircuitError: If the provided condition references Clbits outside the
                enclosing circuit.

        Returns:
            A handle to the instruction created.
        """
        circuit_scope = self._current_scope()
        if isinstance(condition, expr.Expr):
            condition = _validate_expr(circuit_scope, condition)
        else:
            condition = (circuit_scope.resolve_classical_resource(condition[0]), condition[1])

        return self.append(IfElseOp(condition, true_body, false_body, label), qubits, clbits)

    @typing.overload
    def switch(
        self,
        target: Union[ClbitSpecifier, ClassicalRegister],
        cases: None,
        qubits: None,
        clbits: None,
        *,
        label: Optional[str],
    ) -> SwitchContext: ...

    @typing.overload
    def switch(
        self,
        target: Union[ClbitSpecifier, ClassicalRegister],
        cases: Iterable[Tuple[typing.Any, QuantumCircuit]],
        qubits: Sequence[QubitSpecifier],
        clbits: Sequence[ClbitSpecifier],
        *,
        label: Optional[str],
    ) -> InstructionSet: ...

    def switch(self, target, cases=None, qubits=None, clbits=None, *, label=None):
        """Create a ``switch``/``case`` structure on this circuit.

        There are two forms for calling this function.  If called with all its arguments (with the
        possible exception of ``label``), it will create a :class:`.SwitchCaseOp` with the given
        case structure.  If ``cases`` (and ``qubits`` and ``clbits``) are *not* passed, then this
        acts as a context manager, which will automatically build a :class:`.SwitchCaseOp` when the
        scope finishes.  In this form, you do not need to keep track of the qubits or clbits you are
        using, because the scope will handle it for you.

        Example usage::

            from qiskit.circuit import QuantumCircuit, ClassicalRegister, QuantumRegister
            qreg = QuantumRegister(3)
            creg = ClassicalRegister(3)
            qc = QuantumCircuit(qreg, creg)
            qc.h([0, 1, 2])
            qc.measure([0, 1, 2], [0, 1, 2])

            with qc.switch(creg) as case:
                with case(0):
                    qc.x(0)
                with case(1, 2):
                    qc.z(1)
                with case(case.DEFAULT):
                    qc.cx(0, 1)

        Args:
            target (Union[ClassicalRegister, Clbit]): The classical value to switch one.  This must
                be integer-like.
            cases (Iterable[Tuple[typing.Any, QuantumCircuit]]): A sequence of case specifiers.
                Each tuple defines one case body (the second item).  The first item of the tuple can
                be either a single integer value, the special value :data:`.CASE_DEFAULT`, or a
                tuple of several integer values.  Each of the integer values will be tried in turn;
                control will then pass to the body corresponding to the first match.
                :data:`.CASE_DEFAULT` matches all possible values.  Omit in context-manager form.
            qubits (Sequence[Qubit]): The circuit qubits over which all case bodies execute. Omit in
                context-manager form.
            clbits (Sequence[Clbit]): The circuit clbits over which all case bodies execute. Omit in
                context-manager form.
            label (Optional[str]): The string label of the instruction in the circuit.

        Returns:
            InstructionSet or SwitchCaseContext: If used in context-manager mode, then this should
            be used as a ``with`` resource, which will return an object that can be repeatedly
            entered to produce cases for the switch statement.  If the full form is used, then this
            returns a handle to the instructions created.

        Raises:
            CircuitError: if an incorrect calling convention is used.
        """

        circuit_scope = self._current_scope()
        if isinstance(target, expr.Expr):
            target = _validate_expr(circuit_scope, target)
        else:
            target = circuit_scope.resolve_classical_resource(target)
        if cases is None:
            if qubits is not None or clbits is not None:
                raise CircuitError(
                    "When using 'switch' as a context manager, you cannot pass qubits or clbits."
                )
            in_loop = bool(self._control_flow_scopes and self._control_flow_scopes[-1].allow_jumps)
            return SwitchContext(self, target, in_loop=in_loop, label=label)

        if qubits is None or clbits is None:
            raise CircuitError("When using 'switch' with cases, you must pass qubits and clbits.")
        return self.append(SwitchCaseOp(target, cases, label=label), qubits, clbits)

    def break_loop(self) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.BreakLoopOp`.

        .. warning::

            If you are using the context-manager "builder" forms of :meth:`.if_test`,
            :meth:`.for_loop` or :meth:`.while_loop`, you can only call this method if you are
            within a loop context, because otherwise the "resource width" of the operation cannot be
            determined.  This would quickly lead to invalid circuits, and so if you are trying to
            construct a reusable loop body (without the context managers), you must also use the
            non-context-manager form of :meth:`.if_test` and :meth:`.if_else`.  Take care that the
            :obj:`.BreakLoopOp` instruction must span all the resources of its containing loop, not
            just the immediate scope.

        Returns:
            A handle to the instruction created.

        Raises:
            CircuitError: if this method was called within a builder context, but not contained
                within a loop.
        """
        if self._control_flow_scopes:
            operation = BreakLoopPlaceholder()
            resources = operation.placeholder_resources()
            return self.append(operation, resources.qubits, resources.clbits)
        return self.append(BreakLoopOp(self.num_qubits, self.num_clbits), self.qubits, self.clbits)

    def continue_loop(self) -> InstructionSet:
        """Apply :class:`~qiskit.circuit.ContinueLoopOp`.

        .. warning::

            If you are using the context-manager "builder" forms of :meth:`.if_test`,
            :meth:`.for_loop` or :meth:`.while_loop`, you can only call this method if you are
            within a loop context, because otherwise the "resource width" of the operation cannot be
            determined.  This would quickly lead to invalid circuits, and so if you are trying to
            construct a reusable loop body (without the context managers), you must also use the
            non-context-manager form of :meth:`.if_test` and :meth:`.if_else`.  Take care that the
            :class:`~qiskit.circuit.ContinueLoopOp` instruction must span all the resources of its
            containing loop, not just the immediate scope.

        Returns:
            A handle to the instruction created.

        Raises:
            CircuitError: if this method was called within a builder context, but not contained
                within a loop.
        """
        if self._control_flow_scopes:
            operation = ContinueLoopPlaceholder()
            resources = operation.placeholder_resources()
            return self.append(operation, resources.qubits, resources.clbits)
        return self.append(
            ContinueLoopOp(self.num_qubits, self.num_clbits), self.qubits, self.clbits
        )

    def add_calibration(
        self,
        gate: Union[Gate, str],
        qubits: Sequence[int],
        # Schedule has the type `qiskit.pulse.Schedule`, but `qiskit.pulse` cannot be imported
        # while this module is, and so Sphinx will not accept a forward reference to it.  Sphinx
        # needs the types available at runtime, whereas mypy will accept it, because it handles the
        # type checking by static analysis.
        schedule,
        params: Sequence[ParameterValueType] | None = None,
    ) -> None:
        """Register a low-level, custom pulse definition for the given gate.

        Args:
            gate (Union[Gate, str]): Gate information.
            qubits (Union[int, Tuple[int]]): List of qubits to be measured.
            schedule (Schedule): Schedule information.
            params (Optional[List[Union[float, Parameter]]]): A list of parameters.

        Raises:
            Exception: if the gate is of type string and params is None.
        """

        def _format(operand):
            try:
                # Using float/complex value as a dict key is not good idea.
                # This makes the mapping quite sensitive to the rounding error.
                # However, the mechanism is already tied to the execution model (i.e. pulse gate)
                # and we cannot easily update this rule.
                # The same logic exists in DAGCircuit.add_calibration.
                evaluated = complex(operand)
                if np.isreal(evaluated):
                    evaluated = float(evaluated.real)
                    if evaluated.is_integer():
                        evaluated = int(evaluated)
                return evaluated
            except TypeError:
                # Unassigned parameter
                return operand

        if isinstance(gate, Gate):
            params = gate.params
            gate = gate.name
        if params is not None:
            params = tuple(map(_format, params))
        else:
            params = ()

        self._calibrations[gate][(tuple(qubits), params)] = schedule

    # Functions only for scheduled circuits
    def qubit_duration(self, *qubits: Union[Qubit, int]) -> float:
        """Return the duration between the start and stop time of the first and last instructions,
        excluding delays, over the supplied qubits. Its time unit is ``self.unit``.

        Args:
            *qubits: Qubits within ``self`` to include.

        Returns:
            Return the duration between the first start and last stop time of non-delay instructions
        """
        return self.qubit_stop_time(*qubits) - self.qubit_start_time(*qubits)

    def qubit_start_time(self, *qubits: Union[Qubit, int]) -> float:
        """Return the start time of the first instruction, excluding delays,
        over the supplied qubits. Its time unit is ``self.unit``.

        Return 0 if there are no instructions over qubits

        Args:
            *qubits: Qubits within ``self`` to include. Integers are allowed for qubits, indicating
            indices of ``self.qubits``.

        Returns:
            Return the start time of the first instruction, excluding delays, over the qubits

        Raises:
            CircuitError: if ``self`` is a not-yet scheduled circuit.
        """
        if self.duration is None:
            # circuit has only delays, this is kind of scheduled
            for instruction in self._data:
                if not isinstance(instruction.operation, Delay):
                    raise CircuitError(
                        "qubit_start_time undefined. Circuit must be scheduled first."
                    )
            return 0

        qubits = [self.qubits[q] if isinstance(q, int) else q for q in qubits]

        starts = {q: 0 for q in qubits}
        dones = {q: False for q in qubits}
        for instruction in self._data:
            for q in qubits:
                if q in instruction.qubits:
                    if isinstance(instruction.operation, Delay):
                        if not dones[q]:
                            starts[q] += instruction.operation.duration
                    else:
                        dones[q] = True
            if len(qubits) == len([done for done in dones.values() if done]):  # all done
                return min(start for start in starts.values())

        return 0  # If there are no instructions over bits

    def qubit_stop_time(self, *qubits: Union[Qubit, int]) -> float:
        """Return the stop time of the last instruction, excluding delays, over the supplied qubits.
        Its time unit is ``self.unit``.

        Return 0 if there are no instructions over qubits

        Args:
            *qubits: Qubits within ``self`` to include. Integers are allowed for qubits, indicating
            indices of ``self.qubits``.

        Returns:
            Return the stop time of the last instruction, excluding delays, over the qubits

        Raises:
            CircuitError: if ``self`` is a not-yet scheduled circuit.
        """
        if self.duration is None:
            # circuit has only delays, this is kind of scheduled
            for instruction in self._data:
                if not isinstance(instruction.operation, Delay):
                    raise CircuitError(
                        "qubit_stop_time undefined. Circuit must be scheduled first."
                    )
            return 0

        qubits = [self.qubits[q] if isinstance(q, int) else q for q in qubits]

        stops = {q: self.duration for q in qubits}
        dones = {q: False for q in qubits}
        for instruction in reversed(self._data):
            for q in qubits:
                if q in instruction.qubits:
                    if isinstance(instruction.operation, Delay):
                        if not dones[q]:
                            stops[q] -= instruction.operation.duration
                    else:
                        dones[q] = True
            if len(qubits) == len([done for done in dones.values() if done]):  # all done
                return max(stop for stop in stops.values())

        return 0  # If there are no instructions over bits


class _OuterCircuitScopeInterface(CircuitScopeInterface):
    # This is an explicit interface-fulfilling object friend of QuantumCircuit that acts as its
    # implementation of the control-flow builder scope methods.

    __slots__ = ("circuit",)

    def __init__(self, circuit: QuantumCircuit):
        self.circuit = circuit

    @property
    def instructions(self):
        return self.circuit._data

    def append(self, instruction):
        # QuantumCircuit._append is semi-public, so we just call back to it.
        return self.circuit._append(instruction)

    def extend(self, data: CircuitData):
        self.circuit._data.extend(data)
        data.foreach_op(self.circuit._track_operation)

    def resolve_classical_resource(self, specifier):
        # This is slightly different to cbit_argument_conversion, because it should not
        # unwrap :obj:`.ClassicalRegister` instances into lists, and in general it should not allow
        # iterables or broadcasting.  It is expected to be used as a callback for things like
        # :meth:`.InstructionSet.c_if` to check the validity of their arguments.
        if isinstance(specifier, Clbit):
            if specifier not in self.circuit._clbit_indices:
                raise CircuitError(f"Clbit {specifier} is not present in this circuit.")
            return specifier
        if isinstance(specifier, ClassicalRegister):
            # This is linear complexity for something that should be constant, but QuantumCircuit
            # does not currently keep a hashmap of registers, and requires non-trivial changes to
            # how it exposes its registers publically before such a map can be safely stored so it
            # doesn't miss updates. (Jake, 2021-11-10).
            if specifier not in self.circuit.cregs:
                raise CircuitError(f"Register {specifier} is not present in this circuit.")
            return specifier
        if isinstance(specifier, int):
            try:
                return self.circuit._data.clbits[specifier]
            except IndexError:
                raise CircuitError(f"Classical bit index {specifier} is out-of-range.") from None
        raise CircuitError(f"Unknown classical resource specifier: '{specifier}'.")

    def add_uninitialized_var(self, var):
        var = self.circuit._prepare_new_var(var, None)
        self.circuit._vars_local[var.name] = var

    def remove_var(self, var):
        self.circuit._vars_local.pop(var.name)

    def get_var(self, name):
        if (out := self.circuit._vars_local.get(name)) is not None:
            return out
        if (out := self.circuit._vars_capture.get(name)) is not None:
            return out
        return self.circuit._vars_input.get(name)

    def use_var(self, var):
        if self.get_var(var.name) != var:
            raise CircuitError(f"'{var}' is not present in this circuit")


def _validate_expr(circuit_scope: CircuitScopeInterface, node: expr.Expr) -> expr.Expr:
    # This takes the `circuit_scope` object as an argument rather than being a circuit method and
    # inferring it because we may want to call this several times, and we almost invariably already
    # need the interface implementation for something else anyway.
    for var in set(expr.iter_vars(node)):
        if var.standalone:
            circuit_scope.use_var(var)
        else:
            circuit_scope.resolve_classical_resource(var.var)
    return node


class _ParameterBindsDict:
    __slots__ = ("mapping", "allowed_keys")

    def __init__(self, mapping, allowed_keys):
        self.mapping = mapping
        self.allowed_keys = allowed_keys

    def items(self):
        """Iterator through all the keys in the mapping that we care about.  Wrapping the main
        mapping allows us to avoid reconstructing a new 'dict', but just use the given 'mapping'
        without any copy / reconstruction."""
        for parameter, value in self.mapping.items():
            if parameter in self.allowed_keys:
                yield parameter, value


class _ParameterBindsSequence:
    __slots__ = ("parameters", "values", "mapping_cache")

    def __init__(self, parameters, values):
        self.parameters = parameters
        self.values = values
        self.mapping_cache = None

    def items(self):
        """Iterator through all the keys in the mapping that we care about."""
        return zip(self.parameters, self.values)

    @property
    def mapping(self):
        """Cached version of a mapping.  This is only generated on demand."""
        if self.mapping_cache is None:
            self.mapping_cache = dict(zip(self.parameters, self.values))
        return self.mapping_cache


def _bit_argument_conversion(specifier, bit_sequence, bit_set, type_) -> list[Bit]:
    """Get the list of bits referred to by the specifier ``specifier``.

    Valid types for ``specifier`` are integers, bits of the correct type (as given in ``type_``), or
    iterables of one of those two scalar types.  Integers are interpreted as indices into the
    sequence ``bit_sequence``.  All allowed bits must be in ``bit_set`` (which should implement
    fast lookup), which is assumed to contain the same bits as ``bit_sequence``.

    Returns:
        List[Bit]: a list of the specified bits from ``bits``.

    Raises:
        CircuitError: if an incorrect type or index is encountered, if the same bit is specified
            more than once, or if the specifier is to a bit not in the ``bit_set``.
    """
    # The duplication between this function and `_bit_argument_conversion_scalar` is so that fast
    # paths return as quickly as possible, and all valid specifiers will resolve without needing to
    # try/catch exceptions (which is too slow for inner-loop code).
    if isinstance(specifier, type_):
        if specifier in bit_set:
            return [specifier]
        raise CircuitError(f"Bit '{specifier}' is not in the circuit.")
    if isinstance(specifier, (int, np.integer)):
        try:
            return [bit_sequence[specifier]]
        except IndexError as ex:
            raise CircuitError(
                f"Index {specifier} out of range for size {len(bit_sequence)}."
            ) from ex
    # Slices can't raise IndexError - they just return an empty list.
    if isinstance(specifier, slice):
        return bit_sequence[specifier]
    try:
        return [
            _bit_argument_conversion_scalar(index, bit_sequence, bit_set, type_)
            for index in specifier
        ]
    except TypeError as ex:
        message = (
            f"Incorrect bit type: expected '{type_.__name__}' but got '{type(specifier).__name__}'"
            if isinstance(specifier, Bit)
            else f"Invalid bit index: '{specifier}' of type '{type(specifier)}'"
        )
        raise CircuitError(message) from ex


def _bit_argument_conversion_scalar(specifier, bit_sequence, bit_set, type_):
    if isinstance(specifier, type_):
        if specifier in bit_set:
            return specifier
        raise CircuitError(f"Bit '{specifier}' is not in the circuit.")
    if isinstance(specifier, (int, np.integer)):
        try:
            return bit_sequence[specifier]
        except IndexError as ex:
            raise CircuitError(
                f"Index {specifier} out of range for size {len(bit_sequence)}."
            ) from ex
    message = (
        f"Incorrect bit type: expected '{type_.__name__}' but got '{type(specifier).__name__}'"
        if isinstance(specifier, Bit)
        else f"Invalid bit index: '{specifier}' of type '{type(specifier)}'"
    )
    raise CircuitError(message)


def _normalize_global_phase(angle):
    """Return the normalized form of an angle for use in the global phase.  This coerces to float if
    possible, and fixes to the interval :math:`[0, 2\\pi)`."""
    if isinstance(angle, ParameterExpression) and angle.parameters:
        return angle
    return float(angle) % (2.0 * np.pi)