Fix MultiStateDiscrimination output

qiskit_experiments/library/characterization/analysis/multi_state_discrimination_analysis.py

@@ -117,7 +117,7 @@ def _run_analysis(
         for i in range(n_states):
             counts = [0] * n_states
             for point in predicted_data[i]:
-                counts[point] += 1
+                counts[int(point)] += 1
             for j in range(n_states):
                 if j != i:
                     prob_wrong += counts[j] / num_shots

qiskit_experiments/library/characterization/multi_state_discrimination.py

@@ -143,7 +143,7 @@ def circuits(self) -> List[QuantumCircuit]:
                         )
 
             # label the circuit
-            circuit.metadata = {"label": level}
+            circuit.metadata = {"label": str(level)}
 
             circuit.measure_all()
             circuits.append(circuit)

releasenotes/notes/fix-discriminator-exp-ff698816cea63099.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixed a bug where :class:`.MultiStateDiscrimination` outputted integer state labels rather than the
+    string labels expected by the :class:`.DiscriminatorNode`.

test/library/characterization/test_multi_state_discrimination.py

@@ -12,8 +12,9 @@
 
 """Test the multi state discrimination experiments."""
 from functools import wraps
-from test.base import QiskitExperimentsTestCase
+from test.data_processing import BaseDataProcessorTest
 from unittest import SkipTest
+import numpy as np
 
 from ddt import ddt, data
 
@@ -22,6 +23,8 @@
 
 from qiskit_experiments.library import MultiStateDiscrimination
 from qiskit_experiments.test.pulse_backend import SingleTransmonTestBackend
+from qiskit_experiments.data_processing import SkQDA
+from qiskit_experiments.data_processing.nodes import DiscriminatorNode
 
 from qiskit_experiments.warnings import HAS_SKLEARN
 
@@ -42,14 +45,14 @@ def wrapper(*args, **kwargs):
 
 
 @ddt
-class TestMultiStateDiscrimination(QiskitExperimentsTestCase):
+class TestMultiStateDiscrimination(BaseDataProcessorTest):
     """Tests of the multi state discrimination experiment."""
 
     def setUp(self):
         """Setup test variables."""
         super().setUp()
 
-        self.backend = SingleTransmonTestBackend(noise=False)
+        self.backend = SingleTransmonTestBackend(noise=False, seed=0)
 
         # Build x12 schedule
         self.qubit = 0
@@ -83,7 +86,7 @@ def test_circuit_generation(self, n_states):
         self.assertEqual(len(exp.circuits()), n_states)
 
         # check the metadata
-        self.assertEqual(exp.circuits()[-1].metadata["label"], n_states - 1)
+        self.assertEqual(exp.circuits()[-1].metadata["label"], str(n_states - 1))
 
     @data(2, 3)
     @requires_sklearn
@@ -104,3 +107,29 @@ def test_discrimination_analysis(self, n_states):
             "classes_"
         ]
         self.assertEqual(len(discrim_lbls), n_states)
+
+    @requires_sklearn
+    def test_discriminator_data_processing(self):
+        """Test that the discriminator experiment works with the discriminator node."""
+        discriminator = MultiStateDiscrimination([self.qubit], n_states=2, backend=self.backend)
+        discriminator_data = discriminator.run().block_for_results()
+        qda = SkQDA.from_config(discriminator_data.analysis_results("discriminator_config").value)
+        discriminatornode = DiscriminatorNode(discriminators=qda)
+
+        iq_data = [
+            [
+                [[0.8, -1.0], [0.1, 0.5], [-0.3, 0.4]],
+                [[-0.2, 0.4], [0.2, -1.0], [-0.5, 0.3]],
+            ],
+            [
+                [[0, -1.0], [0.1, -0.5], [0.9, 0]],
+                [[-0.8, -0.5], [-0.1, 0.5], [0.2, 1.5]],
+            ],
+        ]
+
+        self.create_experiment_data(np.array(iq_data) * 1e16, single_shot=True)
+        fake_data = np.asarray([datum["memory"] for datum in self.iq_experiment.data()])
+        classified = discriminatornode(fake_data)
+        expected = [["110", "101"], ["000", "111"]]
+
+        self.assertListEqual(classified.tolist(), expected)