Fixes Clifford, Pauli, CNOTDihedral to handle Delay

qiskit/quantum_info/operators/dihedral/dihedral_circuits.py

@@ -17,6 +17,8 @@
 
 from qiskit.exceptions import QiskitError
 from qiskit.circuit import QuantumCircuit
+from qiskit.circuit.barrier import Barrier
+from qiskit.circuit.delay import Delay
 
 
 def _append_circuit(elem, circuit, qargs=None):
@@ -35,6 +37,9 @@ def _append_circuit(elem, circuit, qargs=None):
     if qargs is None:
         qargs = list(range(elem.num_qubits))
 
+    if isinstance(circuit, (Barrier, Delay)):
+        return elem
+
     if isinstance(circuit, QuantumCircuit):
         gate = circuit.to_instruction()
     else:
@@ -81,6 +86,8 @@ def _append_circuit(elem, circuit, qargs=None):
     }
 
     for instr, qregs, _ in gate.definition:
+        if isinstance(instr, (Barrier, Delay)):
+            continue
         # Get the integer position of the flat register
         new_qubits = [qargs[bit_indices[tup]] for tup in qregs]
 

qiskit/quantum_info/operators/symplectic/base_pauli.py

@@ -20,6 +20,7 @@
 
 from qiskit.circuit import QuantumCircuit
 from qiskit.circuit.barrier import Barrier
+from qiskit.circuit.delay import Delay
 from qiskit.exceptions import QiskitError
 from qiskit.quantum_info.operators.base_operator import BaseOperator
 from qiskit.quantum_info.operators.mixins import AdjointMixin, MultiplyMixin
@@ -507,7 +508,7 @@ def _append_circuit(self, circuit, qargs=None):
         Raises:
             QiskitError: if input gate cannot be decomposed into Clifford gates.
         """
-        if isinstance(circuit, Barrier):
+        if isinstance(circuit, (Barrier, Delay)):
             return self
 
         if qargs is None:

qiskit/quantum_info/operators/symplectic/clifford_circuits.py

@@ -16,6 +16,7 @@
 from qiskit.exceptions import QiskitError
 from qiskit.circuit import QuantumCircuit
 from qiskit.circuit.barrier import Barrier
+from qiskit.circuit.delay import Delay
 
 
 def _append_circuit(clifford, circuit, qargs=None):
@@ -32,7 +33,7 @@ def _append_circuit(clifford, circuit, qargs=None):
     Raises:
         QiskitError: if input gate cannot be decomposed into Clifford gates.
     """
-    if isinstance(circuit, Barrier):
+    if isinstance(circuit, (Barrier, Delay)):
         return clifford
 
     if qargs is None:

qiskit/quantum_info/operators/symplectic/pauli.py

@@ -22,6 +22,7 @@
 
 from qiskit.circuit import Instruction, QuantumCircuit
 from qiskit.circuit.barrier import Barrier
+from qiskit.circuit.delay import Delay
 from qiskit.circuit.library.generalized_gates import PauliGate
 from qiskit.circuit.library.standard_gates import IGate, XGate, YGate, ZGate
 from qiskit.exceptions import QiskitError
@@ -681,7 +682,7 @@ def _from_circuit(cls, instr):
                 raise QiskitError(
                     f"Cannot apply instruction with classical registers: {dinstr.name}"
                 )
-            if not isinstance(dinstr, Barrier):
+            if not isinstance(dinstr, (Barrier, Delay)):
                 next_instr = BasePauli(*cls._from_circuit(dinstr))
                 if next_instr is not None:
                     qargs = [tup.index for tup in qregs]

releasenotes/notes/clifford_delay-be1a835413e2531e.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixes the :class:`.Clifford`, :class:`.Pauli` and :class:`.CNOTDihedral`
+    operators support initializing from compatible circuits that contain
+    :class:`~qiskit.circuit.Delay` instructions. These instructions are
+    treated as identity when converting to operators.

test/python/quantum_info/operators/symplectic/test_clifford.py

@@ -392,6 +392,21 @@ def test_2_qubit_relations(self):
             cliff = _append_circuit(cliff, "sdg", [0])
             self.assertEqual(cliff, cliff1)
 
+    def test_barrier_delay_sim(self):
+        """Test barrier and delay instructions can be simulated"""
+        target_circ = QuantumCircuit(2)
+        target_circ.h(0)
+        target_circ.cx(0, 1)
+        target = Clifford(target_circ)
+
+        circ = QuantumCircuit(2)
+        circ.h(0)
+        circ.delay(100, 0)
+        circ.barrier([0, 1])
+        circ.cx(0, 1)
+        value = Clifford(circ)
+        self.assertEqual(value, target)
+
 
 @ddt
 class TestCliffordSynthesis(QiskitTestCase):

test/python/quantum_info/operators/symplectic/test_pauli.py

@@ -21,6 +21,7 @@
 import numpy as np
 from ddt import ddt, data, unpack
 
+from qiskit import QuantumCircuit
 from qiskit.exceptions import QiskitError
 from qiskit.circuit.library import (
     IGate,
@@ -413,6 +414,21 @@ def test_evolve_clifford_qargs(self):
         self.assertEqual(value, value_h)
         self.assertEqual(value_inv, value_s)
 
+    def test_barrier_delay_sim(self):
+        """Test barrier and delay instructions can be simulated"""
+        target_circ = QuantumCircuit(2)
+        target_circ.x(0)
+        target_circ.y(1)
+        target = Pauli(target_circ)
+
+        circ = QuantumCircuit(2)
+        circ.x(0)
+        circ.delay(100, 0)
+        circ.barrier([0, 1])
+        circ.y(1)
+        value = Pauli(circ)
+        self.assertEqual(value, target)
+
 
 if __name__ == "__main__":
     unittest.main()

test/python/quantum_info/operators/test_dihedral.py

@@ -716,6 +716,21 @@ def test_init_from_pauli(self):
                 target = Operator(elem)
                 self.assertTrue(value.equiv(target), "Error: Pauli operator is not the same.")
 
+    def test_barrier_delay_sim(self):
+        """Test barrier and delay instructions can be simulated"""
+        target_circ = QuantumCircuit(2)
+        target_circ.x(0)
+        target_circ.cx(0, 1)
+        target = CNOTDihedral(target_circ)
+
+        circ = QuantumCircuit(2)
+        circ.x(0)
+        circ.delay(100, 0)
+        circ.barrier([0, 1])
+        circ.cx(0, 1)
+        value = CNOTDihedral(circ)
+        self.assertEqual(value, target)
+
 
 if __name__ == "__main__":
     unittest.main()