Fix Qiskit interop with v1.3 (#2050)

Qiskit v1.3 changed the behavior of `num_qubits` on the `Target` class
in way that broke our `QirTarget` usage, since we expect to default to
`None` but the new logic ignores the `num_qubits` parameter to
`__init__` and always defaults to zero qubits, failing later calls to
transpilation. By shadowing the parent class property in `QirTarget` we
can continue returning `None` and trigger the right behavior in
transpilation while preserving a setter for use with v1.2.

Note: I tested locally with both v1.2.4 and v1.3.0 integration tests to
confirm the behavior is as expected.

Fixes #2047

build.py

@@ -514,7 +514,7 @@ def run_ci_historic_benchmark():
         "ipykernel",
         "nbconvert",
         "pandas",
-        "qiskit>=1.2.2,<1.3.0",
+        "qiskit>=1.3.0,<2.0.0",
     ]
     subprocess.run(pip_install_args, check=True, text=True, cwd=root_dir, env=pip_env)
 

pip/qsharp/interop/qiskit/backends/backend_base.py

@@ -12,6 +12,7 @@
 from qiskit.circuit import (
     QuantumCircuit,
 )
+from qiskit.version import get_version_info
 
 from qiskit.qasm3.exporter import Exporter
 from qiskit.providers import BackendV2, Options
@@ -319,19 +320,26 @@ def _transpile(self, circuit: QuantumCircuit, **options) -> QuantumCircuit:
 
         circuit = self.run_qiskit_passes(circuit, options)
 
-        orig = self.target.num_qubits
-        try:
-            self.target.num_qubits = circuit.num_qubits
-            transpile_options = self._build_transpile_options(**options)
-            backend = transpile_options.pop("backend", self)
-            target = transpile_options.pop("target", self.target)
-            # in 1.3 add qubits_initially_zero=True to the transpile call
+        transpile_options = self._build_transpile_options(**options)
+        backend = transpile_options.pop("backend", self)
+        target = transpile_options.pop("target", self.target)
+        if get_version_info().startswith("1.2"):
+            # The older Qiskit version does not support the `qubits_initially_zero` option
             transpiled_circuit = transpile(
-                circuit, backend=backend, target=target, **transpile_options
+                circuit,
+                backend=backend,
+                target=target,
+                **transpile_options,
             )
-            return transpiled_circuit
-        finally:
-            self.target.num_qubits = orig
+        else:
+            transpiled_circuit = transpile(
+                circuit,
+                backend=backend,
+                target=target,
+                qubits_initially_zero=True,
+                **transpile_options,
+            )
+        return transpiled_circuit
 
     def run_qiskit_passes(self, circuit, options):
         pass_options = self._build_qiskit_pass_options(**options)

pip/qsharp/interop/qiskit/backends/qirtarget.py

@@ -61,6 +61,8 @@ def __init__(
     ):
         super().__init__(num_qubits=num_qubits)
 
+        self._num_qubits = num_qubits
+
         if target_profile != TargetProfile.Base:
             self.add_instruction(ControlFlowOp, name="control_flow")
             self.add_instruction(IfElseOp, name="if_else")
@@ -121,3 +123,16 @@ def __init__(
         self.add_instruction(IGate, name="id")
 
         self.add_instruction(CHGate, name="ch")
+
+    # NOTE: The follow property intentionally shadows the property on the parent class to allow it to return `None`
+    # when the value is not set, which allows bypassing transpilation checks for number of qubits. Without this,
+    # versions of Qiskit 1.3.0 and higher default to `0` which will fail later checks.
+    @property
+    def num_qubits(self):
+        return self._num_qubits
+
+    # NOTE: The follow property setter intentionally shadows the property on the parent class to allow it to be set, which
+    # maintains compatiblity with Qiskit versions before 1.3.0 where the property was settable.
+    @num_qubits.setter
+    def num_qubits(self, value):
+        self._num_qubits = value

pip/tests-integration/interop_qiskit/test_gate_correctness.py

@@ -242,7 +242,13 @@ def _test_circuit(
 ):
     target_profile = TargetProfile.Base
     seed = 42
-    backend = QSharpBackend(target_profile=target_profile, seed=seed)
+    backend = QSharpBackend(
+        target_profile=target_profile,
+        seed=seed,
+        transpile_options={
+            "optimization_level": 0  # Use no optimization to get consistent results in simulations
+        },
+    )
     try:
         job = backend.run(circuit, shots=num_shots)
         result = job.result()

pip/tests-integration/interop_qiskit/test_gateset_qasm.py

@@ -16,6 +16,9 @@ def run_transpile_test(
 ) -> None:
     circuit = QuantumCircuit(3, 3)
     operation(circuit)
+    if "optimization_level" not in options:
+        # Use no optimization so gate transpilation is consistent
+        options["optimization_level"] = 0
     info = QSharpBackend()._qasm3(circuit, **options)
     lines = info.splitlines()
     # remove the first four lines, which are the header

pip/tests-integration/interop_qiskit/test_re.py

@@ -38,7 +38,7 @@ def test_qsharp_estimation_with_single_params() -> None:
     for index in range(10):
         circuit.t(index)
         circuit.measure(index, index)
-    sim = ResourceEstimatorBackend()
+    sim = ResourceEstimatorBackend(transpile_options={"optimization_level": 0})
     res = sim.run(circuit, params=params).result()
 
     assert res["status"] == "success"
@@ -69,8 +69,8 @@ def test_estimate_qiskit_rgqft_multiplier() -> None:
         {
             "numQubits": 16,
             "tCount": 90,
-            "rotationCount": 958,
-            "rotationDepth": 658,
+            "rotationCount": 1002,
+            "rotationDepth": 680,
             "cczCount": 0,
             "ccixCount": 0,
             "measurementCount": 0,
@@ -94,8 +94,8 @@ def test_estimate_qiskit_rgqft_multiplier_in_threadpool() -> None:
         {
             "numQubits": 16,
             "tCount": 90,
-            "rotationCount": 958,
-            "rotationDepth": 658,
+            "rotationCount": 1002,
+            "rotationDepth": 680,
             "cczCount": 0,
             "ccixCount": 0,
             "measurementCount": 0,

pip/tests-integration/test_requirements.txt

@@ -1,5 +1,5 @@
 pytest==8.2.2
-qiskit>=1.2.2,<1.3.0
+qiskit>=1.3.0,<2.0.0
 qirrunner==0.7.1
 pyqir==0.10.2
 qiskit-aer==0.14.2