Fix Sampler with multiple classical registers

qiskit_aer/primitives/sampler.py

@@ -136,7 +136,7 @@ def _call(
                 shots = sum(counts.values())
                 quasis.append(
                     QuasiDistribution(
-                        {k: v / shots for k, v in counts.items()},
+                        {k.replace(" ", ""): v / shots for k, v in counts.items()},
                         shots=shots,
                     )
                 )

releasenotes/notes/fix-split-cregs-5b5494a92c4903e7.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Fix the bug where the :class:`.Sampler` fails if the input circuit has multiple classical
+    registers.

test/terra/primitives/test_sampler.py

@@ -20,7 +20,7 @@
 
 import numpy as np
 from ddt import data, ddt
-from qiskit import QuantumCircuit
+from qiskit import ClassicalRegister, QuantumCircuit
 from qiskit.circuit import Parameter
 from qiskit.circuit.library import RealAmplitudes
 from qiskit.exceptions import QiskitError
@@ -537,6 +537,19 @@ def test_num_clbits(self, shots):
         bin_probs = quasis.binary_probabilities()
         self.assertDictAlmostEqual(bin_probs, {"0000": 0.5, "0001": 0.5}, delta=1e-2)
 
+    def test_multiple_cregs(self):
+        """Test for the circuit with multipe cregs"""
+        qc = QuantumCircuit(2)
+        cr1 = ClassicalRegister(1, "cr1")
+        cr2 = ClassicalRegister(1, "cr2")
+        qc.add_register(cr1)
+        qc.add_register(cr2)
+        qc.measure(0, 0)
+        qc.measure(1, 1)
+
+        result = Sampler().run(qc, shots=100).result()
+        self.assertDictAlmostEqual(result.quasi_dists[0], {0: 1})
+
 
 if __name__ == "__main__":
     unittest.main()