Implement PhasedXZGate._unitary_ (quantumlib#4617)

Review: @MichaelBroughton
PhaseCraft · Nov 2, 2021 · f245eb2 · f245eb2
1 parent 5711353
commit f245eb2
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diff --git a/cirq/ops/phased_x_z_gate.py b/cirq/ops/phased_x_z_gate.py
@@ -141,6 +141,15 @@ def _qasm_(self, args: 'cirq.QasmArgs', qubits: Tuple['cirq.Qid', ...]) -> Optio
     def _has_unitary_(self) -> bool:
         return not self._is_parameterized_()
 
+    def _unitary_(self) -> Optional[np.ndarray]:
+        """See `cirq.SupportsUnitary`."""
+        if self._is_parameterized_():
+            return None
+        z_pre = protocols.unitary(ops.Z ** -self._axis_phase_exponent)
+        x = protocols.unitary(ops.X ** self._x_exponent)
+        z_post = protocols.unitary(ops.Z ** (self._axis_phase_exponent + self._z_exponent))
+        return z_post @ x @ z_pre
+
     def _decompose_(self, qubits: Sequence['cirq.Qid']) -> 'cirq.OP_TREE':
         q = qubits[0]
         yield ops.Z(q) ** -self._axis_phase_exponent

diff --git a/cirq/ops/phased_x_z_gate_test.py b/cirq/ops/phased_x_z_gate_test.py
@@ -199,6 +199,22 @@ def test_from_matrix_close_unitary(unitary: np.ndarray):
     )
 
 
+@pytest.mark.parametrize(
+    'unitary',
+    [
+        cirq.testing.random_unitary(2),
+        cirq.testing.random_unitary(2),
+        cirq.testing.random_unitary(2),
+        np.array([[0, 1], [1j, 0]]),
+    ],
+)
+def test_from_matrix_close_kraus(unitary: np.ndarray):
+    gate = cirq.PhasedXZGate.from_matrix(unitary)
+    kraus = cirq.kraus(gate)
+    assert len(kraus) == 1
+    cirq.testing.assert_allclose_up_to_global_phase(kraus[0], unitary, atol=1e-8)
+
+
 def test_protocols():
     a = random.random()
     b = random.random()