Allow barriers in overlap circuit inputs

qiskit/circuit/library/overlap.py

@@ -15,6 +15,7 @@
 from qiskit.circuit import QuantumCircuit, Gate
 from qiskit.circuit.parametervector import ParameterVector
 from qiskit.circuit.exceptions import CircuitError
+from qiskit.circuit import Barrier
 
 
 class UnitaryOverlap(QuantumCircuit):
@@ -101,7 +102,7 @@ def _check_unitary(circuit):
     """Check a circuit is unitary by checking if all operations are of type ``Gate``."""
 
     for instruction in circuit.data:
-        if not isinstance(instruction.operation, Gate):
+        if not isinstance(instruction.operation, (Gate, Barrier)):
             raise CircuitError(
                 (
                     "One or more instructions cannot be converted to"

releasenotes/notes/overlap-circuit-barriers-63b9b1be9c1da100.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fixed a bug which caused :class:`~qiskit.circuit.library.UnitaryOverlap` to error upon initialization if given an input circuit containing a barrier.

test/python/circuit/library/test_overlap.py

@@ -82,6 +82,15 @@ def test_partial_parameterized_inputs2(self):
         overlap = UnitaryOverlap(unitary1, unitary2)
         self.assertEqual(overlap.num_parameters, unitary1.num_parameters)
 
+    def test_barrier(self):
+        """Test that barriers on input circuits are well handled"""
+        unitary1 = EfficientSU2(1, reps=0)
+        unitary1.barrier()
+        unitary2 = EfficientSU2(1, reps=1)
+        unitary2.barrier()
+        overlap = UnitaryOverlap(unitary1, unitary2)
+        self.assertEqual(overlap.num_parameters, unitary1.num_parameters + unitary2.num_parameters)
+
     def test_measurements(self):
         """Test that exception is thrown for measurements"""
         unitary1 = EfficientSU2(2)