Bug fix: ISA check to correctly map qubit indices inside blocks of control flow operations

qiskit_ibm_runtime/utils/utils.py

@@ -48,7 +48,7 @@ def is_simulator(backend: BackendV1 | BackendV2) -> bool:
     return getattr(backend, "simulator", False)
 
 
-def _is_isa_circuit_helper(circuit: QuantumCircuit, target: Target) -> str:
+def _is_isa_circuit_helper(circuit: QuantumCircuit, target: Target, qubit_map: Dict) -> str:
     """
     A section of is_isa_circuit, separated to allow recursive calls
     within blocks of conditional operations.
@@ -57,7 +57,7 @@ def _is_isa_circuit_helper(circuit: QuantumCircuit, target: Target) -> str:
         operation = instruction.operation
 
         name = operation.name
-        qargs = tuple(circuit.find_bit(x).index for x in instruction.qubits)
+        qargs = tuple(qubit_map[bit] for bit in instruction.qubits)
         if (
             not target.instruction_supported(name, qargs)
             and name != "barrier"
@@ -69,7 +69,7 @@ def _is_isa_circuit_helper(circuit: QuantumCircuit, target: Target) -> str:
 
         if isinstance(operation, ControlFlowOp):
             for sub_circ in operation.blocks:
-                sub_string = _is_isa_circuit_helper(sub_circ, target)
+                sub_string = _is_isa_circuit_helper(sub_circ, target, qubit_map)
                 if sub_string:
                     return sub_string
 
@@ -93,7 +93,8 @@ def is_isa_circuit(circuit: QuantumCircuit, target: Target) -> str:
             f"but the target system requires {target.num_qubits} qubits."
         )
 
-    return _is_isa_circuit_helper(circuit, target)
+    qubit_map = {qubit: index for index, qubit in enumerate(circuit.qubits)}
+    return _is_isa_circuit_helper(circuit, target, qubit_map)
 
 
 def are_circuits_dynamic(circuits: List[QuantumCircuit], qasm_default: bool = True) -> bool:

test/unit/test_sampler.py

@@ -21,7 +21,7 @@
 from qiskit.primitives.containers.sampler_pub import SamplerPub
 from qiskit.circuit.library import RealAmplitudes
 from qiskit_ibm_runtime import Session, SamplerV2, SamplerOptions, IBMInputValueError
-from qiskit_ibm_runtime.fake_provider import FakeFractionalBackend, FakeSherbrooke
+from qiskit_ibm_runtime.fake_provider import FakeFractionalBackend, FakeSherbrooke, FakeCusco
 
 from ..ibm_test_case import IBMTestCase
 from ..utils import MockSession, dict_paritally_equal, get_mocked_backend, transpile_pubs
@@ -241,3 +241,22 @@ def test_gate_not_in_target(self):
 
         with self.assertRaisesRegex(IBMInputValueError, " h "):
             sampler.run(pubs=[(circ)])
+
+    @data(FakeSherbrooke(), FakeCusco())
+    def test_isa_inside_condition_block(self, backend):
+        """Test no exception for 2q gates involving qubits that are not connected in
+        the coupling map, inside control operation blocks; and yes exception for
+        qubit pairs that are not connected"""
+        # pylint: disable=invalid-name,not-context-manager
+
+        circ = QuantumCircuit(5, 1)
+        circ.x(0)
+        circ.measure(0, 0)
+        with circ.if_test((0, 1)):
+            circ.ecr(1, 2)
+
+        if backend.name == "fake_sherbrooke":
+            SamplerV2(backend).run(pubs=[(circ)])
+        else:
+            with self.assertRaises(IBMInputValueError):
+                SamplerV2(backend).run(pubs=[(circ)])