fix #727

qiskit_experiments/library/randomized_benchmarking/rb_experiment.py

@@ -188,7 +188,7 @@ def _generate_circuit(
                 group_elt_gate = group_elt_circ
                 group_elt_op = Clifford(group_elt_circ)
 
-            if not isinstance(group_elt_gate, Gate):
+            if hasattr(group_elt_gate, "to_gate"):
                 group_elt_gate = group_elt_gate.to_gate()
             circ_op = circ_op.compose(group_elt_op)
             for circ in circs:

test/randomized_benchmarking/test_randomized_benchmarking.py

@@ -17,6 +17,7 @@
 import numpy as np
 from ddt import ddt, data, unpack
 from qiskit.circuit.library import SXGate, CXGate, TGate, XGate
+from qiskit.circuit import Delay
 from qiskit.exceptions import QiskitError
 from qiskit.providers.aer import AerSimulator
 from qiskit.providers.aer.noise import NoiseModel, depolarizing_error
@@ -345,6 +346,22 @@ def test_non_clifford_interleaved_element(self):
             lengths=lengths,
         )
 
+    def test_interleaving_delay(self):
+        """Test delay instruction can be interleaved."""
+        # See qiskit-experiments/#727 for details
+        interleaved_element = Delay(10, unit="us")
+        exp = InterleavedRB(
+            interleaved_element,
+            qubits=[0],
+            lengths=[1],
+            num_samples=1,
+        )
+        # Not raises an error
+        _, int_circ = exp.circuits()
+
+        # barrier, clifford, barrier, "delay", barrier, ...
+        self.assertEqual(int_circ.data[3][0], interleaved_element)
+
     def test_experiment_config(self):
         """Test converting to and from config works"""
         exp = rb.InterleavedRB(