Add some more gates to CollectCliffords pass (Qiskit#13214)

* add matrix_based option to CollectClifford pass
Co-authored-by: Samantha Barron <[email protected]>

* add a test to collect matrix_based gates

* add release notes

* minor update following review

qiskit/transpiler/passes/optimization/collect_cliffords.py

@@ -15,6 +15,7 @@
 
 from functools import partial
 
+from qiskit.exceptions import QiskitError
 from qiskit.transpiler.passes.optimization.collect_and_collapse import (
     CollectAndCollapse,
     collect_using_filter_function,
@@ -37,6 +38,7 @@ def __init__(
         min_block_size=2,
         split_layers=False,
         collect_from_back=False,
+        matrix_based=False,
     ):
         """CollectCliffords initializer.
 
@@ -51,11 +53,13 @@ def __init__(
                 over disjoint qubit subsets.
             collect_from_back (bool): specifies if blocks should be collected started
                 from the end of the circuit.
+            matrix_based (bool): specifies whether to collect unitary gates
+               which are Clifford gates only for certain parameters (based on their unitary matrix).
         """
 
         collect_function = partial(
             collect_using_filter_function,
-            filter_function=_is_clifford_gate,
+            filter_function=partial(_is_clifford_gate, matrix_based=matrix_based),
             split_blocks=split_blocks,
             min_block_size=min_block_size,
             split_layers=split_layers,
@@ -77,9 +81,21 @@ def __init__(
 )
 
 
-def _is_clifford_gate(node):
+def _is_clifford_gate(node, matrix_based=False):
     """Specifies whether a node holds a clifford gate."""
-    return node.op.name in clifford_gate_names and getattr(node.op, "condition", None) is None
+    if getattr(node.op, "condition", None) is not None:
+        return False
+    if node.op.name in clifford_gate_names:
+        return True
+
+    if not matrix_based:
+        return False
+
+    try:
+        Clifford(node.op)
+        return True
+    except QiskitError:
+        return False
 
 
 def _collapse_to_clifford(circuit):

releasenotes/notes/add-gates-to-collect-clifford-af88dd8f7a2a4bf9.yaml

@@ -0,0 +1,8 @@
+---
+features_transpiler:
+  - |
+    Add an argument ``matrix_based`` to the :class:`.CollectCliffords()` transpiler pass.
+    If the new parameter ``matrix_based=True``, the :class:`.CollectCliffords()` transpiler pass
+    can collect :class:`.RZGate(np.pi/2)` gates and other unitary gates that are :class:`.Clifford()`
+    gates for certain parameters.
+

test/python/transpiler/test_clifford_passes.py

@@ -27,6 +27,39 @@
 from qiskit.compiler.transpiler import transpile
 from test import QiskitTestCase  # pylint: disable=wrong-import-order
 
+from qiskit.circuit.library import (
+    CPhaseGate,
+    CRXGate,
+    CRYGate,
+    CRZGate,
+    CXGate,
+    CYGate,
+    CZGate,
+    DCXGate,
+    ECRGate,
+    HGate,
+    IGate,
+    iSwapGate,
+    RXGate,
+    RYGate,
+    RZGate,
+    RXXGate,
+    RYYGate,
+    RZZGate,
+    RZXGate,
+    SGate,
+    SdgGate,
+    SXGate,
+    SXdgGate,
+    SwapGate,
+    UGate,
+    XGate,
+    XXMinusYYGate,
+    XXPlusYYGate,
+    YGate,
+    ZGate,
+)
+
 
 class TestCliffordPasses(QiskitTestCase):
     """Tests to verify correctness of transpiler passes and
@@ -381,15 +414,15 @@ def test_collect_cliffords_multiple_blocks(self):
         qc.cx(0, 1)
         qc.sdg(2)
         qc.swap(2, 1)
-        qc.rx(np.pi / 2, 1)
+        qc.t(1)
         qc.cz(0, 1)
         qc.z(0)
         qc.y(1)
 
         # We should end up with two Cliffords and one "rx" gate
         qct = PassManager(CollectCliffords()).run(qc)
         self.assertEqual(qct.size(), 3)
-        self.assertIn("rx", qct.count_ops().keys())
+        self.assertIn("t", qct.count_ops().keys())
         self.assertEqual(qct.count_ops()["clifford"], 2)
 
         self.assertIsInstance(qct.data[0].operation, Clifford)
@@ -479,9 +512,9 @@ def test_collect_cliffords_options_multiple_blocks(self):
         qc.x(2)
         qc.cx(2, 0)
 
-        qc.rx(np.pi / 2, 0)
-        qc.rx(np.pi / 2, 1)
-        qc.rx(np.pi / 2, 2)
+        qc.rx(np.pi / 4, 0)
+        qc.rx(np.pi / 4, 1)
+        qc.rx(np.pi / 4, 2)
 
         qc.cz(0, 1)
         qc.z(0)
@@ -524,7 +557,7 @@ def test_collect_from_back_corectness(self):
         qc.h(0)
         qc.x(1)
         qc.h(1)
-        qc.rx(np.pi / 2, 0)
+        qc.t(0)
         qc.y(0)
         qc.h(1)
 
@@ -541,7 +574,7 @@ def test_collect_from_back_as_expected(self):
         qc.h(0)
         qc.x(1)
         qc.h(1)
-        qc.rx(np.pi / 2, 0)
+        qc.t(0)
         qc.y(0)
         qc.h(1)
 
@@ -728,7 +761,7 @@ def test_collect_with_all_types(self):
         qc.cy(0, 1)
 
         # not a clifford gate (separating the circuit)
-        qc.rx(np.pi / 2, 0)
+        qc.t(0)
 
         qc.append(pauli_gate2, [0, 2, 1])
         qc.append(lf2, [2, 1, 0])
@@ -749,6 +782,53 @@ def test_collect_with_all_types(self):
         op2 = Operator(qct)
         self.assertTrue(op1.equiv(op2))
 
+    def test_collect_all_clifford_gates(self):
+        """Assert that CollectClifford collects all basis gates
+        (including certain rotation gates with pi/2 angles)"""
+        gates_1q = [
+            XGate(),
+            YGate(),
+            ZGate(),
+            IGate(),
+            HGate(),
+            SGate(),
+            SdgGate(),
+            SXGate(),
+            SXdgGate(),
+            RXGate(theta=np.pi / 2),
+            RYGate(theta=np.pi / 2),
+            RZGate(phi=np.pi / 2),
+            UGate(np.pi / 2, np.pi / 2, np.pi / 2),
+        ]
+        gates_2q = [
+            CXGate(),
+            CYGate(),
+            CZGate(),
+            DCXGate(),
+            ECRGate(),
+            SwapGate(),
+            iSwapGate(),
+            CPhaseGate(theta=np.pi),
+            CRXGate(theta=np.pi),
+            CRYGate(theta=np.pi),
+            CRZGate(theta=np.pi),
+            RXXGate(theta=np.pi / 2),
+            RYYGate(theta=np.pi / 2),
+            RZZGate(theta=np.pi / 2),
+            RZXGate(theta=np.pi / 2),
+            XXMinusYYGate(theta=np.pi),
+            XXPlusYYGate(theta=-np.pi),
+        ]
+
+        qc = QuantumCircuit(2)
+        for gate in gates_1q:
+            qc.append(gate, [0])
+        for gate in gates_2q:
+            qc.append(gate, [0, 1])
+
+        qct = PassManager(CollectCliffords(matrix_based=True)).run(qc)
+        self.assertEqual(qct.count_ops()["clifford"], 1)
+
 
 if __name__ == "__main__":
     unittest.main()