Add missing delay instruction to fake backends

qiskit/test/mock/utils/backend_converter.py

@@ -21,6 +21,7 @@
 from qiskit.circuit.library.standard_gates import IGate, SXGate, XGate, CXGate, RZGate
 from qiskit.circuit.parameter import Parameter
 from qiskit.circuit.gate import Gate
+from qiskit.circuit.delay import Delay
 from qiskit.circuit.measure import Measure
 from qiskit.circuit.reset import Reset
 from qiskit.providers.models.pulsedefaults import PulseDefaults
@@ -123,6 +124,9 @@ def convert_to_target(conf_dict: dict, props_dict: dict = None, defs_dict: dict
                             target[inst][(qubit,)].calibration = sched
                     else:
                         target[inst][qarg].calibration = sched
+    target.add_instruction(
+        Delay(Parameter("t")), {(bit,): None for bit in range(target.num_qubits)}
+    )
     return target
 
 

qiskit/visualization/gate_map.py

@@ -958,6 +958,8 @@ def plot_error_map(backend, figsize=(12, 9), show_title=True, qubit_coordinates=
             if prop_dict is None or None in prop_dict:
                 continue
             for qargs, inst_props in prop_dict.items():
+                if inst_props is None:
+                    continue
                 if gate == "measure":
                     if inst_props.error is not None:
                         read_err[qargs[0]] = inst_props.error

releasenotes/notes/delay-fake-backends-3f68c074e85d531f.yaml

@@ -0,0 +1,12 @@
+---
+fixes:
+  - |
+    The :class:`~.BackendV2` based fake backends in
+    the :mod:`qiskit.providers.fake_provider` module, such as
+    ``FakeMontrealV2``, previously were missing the :class:`~qiskit.circuit.Delay` operation
+    support from their :attr:`~.BackendV2.target` attribute. This prevented
+    compiling some :class:`~.QuantumCircuit` objects that contained
+    :class:`~qiskit.circuit.Delay` instructions to these backends. This has been corrected
+    by adding the :class:`~qiskit.circuit.Delay` to the :class:`~.Target` object for each
+    fake backend to ensure that the compiler knows that :class:`~qiskit.circuit.Delay` is
+    a valid operation on the fake backends.

test/python/providers/test_fake_backends.py

@@ -25,6 +25,7 @@
 from qiskit.execute_function import execute
 from qiskit.test.base import QiskitTestCase
 from qiskit.test.mock import FakeProviderForBackendV2, FakeProvider
+from qiskit.test.mock import FakeMumbaiV2
 from qiskit.utils import optionals
 
 FAKE_PROVIDER_FOR_BACKEND_V2 = FakeProviderForBackendV2()
@@ -146,3 +147,13 @@ def test_defaults_to_dict(self, backend):
                 self.assertGreater(i, 1e6)
         else:
             self.skipTest("Backend %s does not have defaults" % backend)
+
+    def test_delay_circuit(self):
+        backend = FakeMumbaiV2()
+        qc = QuantumCircuit(2)
+        qc.delay(502, 0, unit="ns")
+        qc.x(1)
+        qc.delay(250, 1, unit="ns")
+        qc.measure_all()
+        res = transpile(qc, backend)
+        self.assertIn("delay", res.count_ops())