Fixed issue unitaryfund#2354 where a fallback was addded to conversio…

…ns.py to decompose a qiskit circuit to native gates if an error occured. A test with zne was added to test for this with the QFT gate.

mitiq/interface/mitiq_qiskit/conversions.py

@@ -14,7 +14,7 @@
 import numpy as np
 import qiskit
 from cirq.contrib.qasm_import import circuit_from_qasm
-from qiskit import qasm2
+from qiskit import compiler, qasm2
 from qiskit.transpiler import PassManager
 from qiskit.transpiler.layout import Layout
 from qiskit.transpiler.passes import SetLayout
@@ -248,7 +248,17 @@ def from_qiskit(circuit: qiskit.QuantumCircuit) -> cirq.Circuit:
     Returns:
         Mitiq circuit representation equivalent to the input Qiskit circuit.
     """
-    return from_qasm(qasm2.dumps(circuit))
+    try:
+        mitiq_circuit = from_qasm(qasm2.dumps(circuit))
+    except Exception:
+        # If the conversion fails, try to decompose and transpile the
+        # circuit to native gates
+        circuit = compiler.transpile(
+            circuit, basis_gates=["u1", "u2", "u3", "cx"]
+        )
+        circuit = circuit.decompose()
+        mitiq_circuit = from_qasm(qasm2.dumps(circuit))
+    return mitiq_circuit
 
 
 def from_qasm(qasm: QASMType) -> cirq.Circuit:

mitiq/zne/tests/test_zne.py

@@ -12,6 +12,7 @@
 import numpy as np
 import pytest
 import qiskit
+import qiskit.circuit
 from qiskit_aer import AerSimulator
 
 from mitiq import QPROGRAM, SUPPORTED_PROGRAM_TYPES
@@ -540,3 +541,22 @@ def execute(circuit: qiskit.QuantumCircuit, shots: int = 8192) -> float:
     # Note: Unmitigated value is also (usually) within 10% of the true value.
     # This is more to test usage than effectiveness.
     assert abs(zne_value - true_value) < 0.1
+
+
+def test_execute_zne_transpiled_qiskit_circuit_with_noise_and_QFT():
+    """Tests ZNE when transpiling to a Qiskit device with a QFT gate."""
+
+    def qs_noisy_simulation(
+        circuit: qiskit.QuantumCircuit, shots: int = 1
+    ) -> float:
+        noise_model = initialized_depolarizing_noise(noise_level=0.02)
+        backend = AerSimulator(noise_model=noise_model)
+        job = backend.run(circuit.decompose(), shots=shots)
+        return job.result().get_counts().get("0", 0.0) / shots
+
+    circuit = qiskit.QuantumCircuit(1)
+    circuit &= qiskit.circuit.library.QFT(1)
+    circuit.measure_all()
+
+    mitigated = execute_with_zne(circuit, qs_noisy_simulation)
+    assert abs(mitigated) < 1000