Ancilla-Free Quantum Adder with Sublinear Depth #13975
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Summary
This PR introduces an implementation of Ancilla-Free Quantum Adder with Sublinear Depth. The implementation follows the paper’s methodology, leveraging optimized CNOT and Toffoli ladder constructions to achieve an efficient ripple-carry addition without ancillary qubits. It achieves an overall depth of O(log² n) and gate count of O(n log(n)) without using any ancillae.
Details and comments
The implementation relies on the Log-depth MCX using conditionally clean ancillae introduced in #13922. The current version is not functional because log-depth MCX is not yet merged into main. I welcome any suggestions in the meantime. Since #13922 is part of the Qiskit 2.0 feature, I thought this might make a good addition. Tagging @ShellyGarion as you are already familiar with some of the changes.