Fixed calibration experiments failing on backends with no coupling map (#1117)

On backends with no coupling map (such as one could configure with
`DynamicsBackend` from qiskit-dynamics), calibration experiments failed
because the `BaseCalibrationExperiment` tried to pass the backend's
`coupling_map` (run through `BackendData`) to terra's `CouplingMap`
which acceprts `None`. The transpiler pass `FullAncillaAllocation`
behaves differently when passed `None` than when passed
`CouplingMap(None)`.

Author: wshanks

qiskit_experiments/calibration_management/base_calibration_experiment.py

@@ -316,10 +316,14 @@ def _map_to_physical_qubits(self, circuit: QuantumCircuit) -> QuantumCircuit:
         """
         initial_layout = Layout.from_intlist(list(self.physical_qubits), *circuit.qregs)
 
+        coupling_map = self._backend_data.coupling_map
+        if coupling_map is not None:
+            coupling_map = CouplingMap(self._backend_data.coupling_map)
+
         layout = PassManager(
             [
                 SetLayout(initial_layout),
-                FullAncillaAllocation(CouplingMap(self._backend_data.coupling_map)),
+                FullAncillaAllocation(coupling_map),
                 EnlargeWithAncilla(),
                 ApplyLayout(),
             ]

releasenotes/notes/cals-no-coupling-map-5114ae9faa2f9e69.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixed error generating circuits for :class:`.BaseCalibrationExperiment`
+    subclasses when the backend instance had no coupling map. Fixed `#1116
+    <https://github.com/Qiskit/qiskit-experiments/issues/1116>`_.

test/calibration/test_base_calibration_experiment.py

@@ -14,16 +14,18 @@
 
 from test.base import QiskitExperimentsTestCase
 
+from qiskit import QuantumCircuit
 from qiskit.circuit import Parameter
 from qiskit.pulse import Play, Constant, DriveChannel, ScheduleBlock
 
-from qiskit_experiments.library import QubitSpectroscopy
 from qiskit_experiments.calibration_management.base_calibration_experiment import (
     BaseCalibrationExperiment,
     Calibrations,
 )
 from qiskit_experiments.framework.composite import ParallelExperiment, BatchExperiment
+from qiskit_experiments.library import QubitSpectroscopy
 from qiskit_experiments.test.fake_backend import FakeBackend
+
 from .utils import MockCalExperiment, DoNothingAnalysis
 
 
@@ -324,3 +326,36 @@ def test_update_calibration_parallel(self):
         new_schedule2 = cals.get_schedule("test2", (1,))
         ref_schedule2 = schedule2.assign_parameters({param2: ref_new_value2}, inplace=False)
         self.assertEqual(new_schedule2, ref_schedule2)
+
+    def test_transpiled_circuits_no_coupling_map(self):
+        """Test transpilation of calibration experiment with no coupling map"""
+        # This test was added to catch errors found when running calibration
+        # experiments against DynamicsBackend from qiskit-dynamics for which
+        # the coupling map could be None. Previously, this led to
+        # BaseCalibrationExperiment's custom pass manager failing.
+        backend = FakeBackend(num_qubits=2)
+        # If the following fails, it should be reassessed if this test is still
+        # useful
+        self.assertTrue(backend.coupling_map is None)
+
+        cals = Calibrations()
+
+        # Build a circuit to be passed through transpilation pipeline
+        qc = QuantumCircuit(1, 1)
+        qc.x(0)
+        qc.measure(0, 0)
+
+        exp = MockCalExperiment(
+            physical_qubits=(1,),
+            calibrations=cals,
+            new_value=0.2,
+            param_name="amp",
+            sched_name="x",
+            backend=backend,
+            circuits=[qc],
+        )
+        transpiled = exp._transpiled_circuits()[0]
+        # Make sure circuit was expanded with the ancilla on qubit 0
+        self.assertEqual(len(transpiled.qubits), 2)
+        # Make sure instructions were unchanged
+        self.assertDictEqual(transpiled.count_ops(), qc.count_ops())

test/calibration/utils.py

@@ -13,7 +13,10 @@
 """Utility to test calibration module."""
 
 import datetime
-from typing import Sequence
+from typing import Optional, Sequence
+
+from qiskit import QuantumCircuit
+from qiskit.providers import Backend
 
 from qiskit_experiments.calibration_management import (
     BaseCalibrationExperiment,
@@ -46,12 +49,25 @@ def _run_analysis(
 class DoNothingExperiment(BaseExperiment):
     """Experiment doesn't provide any circuit to run."""
 
-    def __init__(self, physical_qubits: Sequence[int], return_value: float):
-        super().__init__(physical_qubits=physical_qubits, analysis=DoNothingAnalysis())
+    def __init__(
+        self,
+        physical_qubits: Sequence[int],
+        return_value: float,
+        circuits: Optional[Sequence[QuantumCircuit]] = None,
+        backend: Optional[Backend] = None,
+    ):
+        super().__init__(
+            physical_qubits=physical_qubits, analysis=DoNothingAnalysis(), backend=backend
+        )
         self.analysis.set_options(return_value=return_value)
 
+        if circuits is not None:
+            self._circuits = circuits
+        else:
+            self._circuits = []
+
     def circuits(self):
-        return []
+        return self._circuits
 
 
 class MockCalExperiment(BaseCalibrationExperiment, DoNothingExperiment):
@@ -69,6 +85,8 @@ def __init__(
         new_value: float,
         param_name: str,
         sched_name: str,
+        circuits: Optional[Sequence[QuantumCircuit]] = None,
+        backend: Optional[Backend] = None,
     ):
         """Create mock calibration experiment.
 
@@ -78,11 +96,15 @@ def __init__(
             new_value: New parameter value obtained by the calibration experiment.
             param_name: Name of parameter to update.
             sched_name: Name of schedule to update.
+            circuits: List of QuantumCircuits for the circuits() method
+            backend: Backend to set on experiment
         """
         super().__init__(
             physical_qubits=physical_qubits,
             calibrations=calibrations,
             return_value=new_value,
+            circuits=circuits,
+            backend=backend,
         )
         self.to_update = {
             "param": param_name,