revive GlobalPhaseGate.is_identity()

Author: daxfohl

cirq-core/cirq/ops/common_gates.py

@@ -1532,6 +1532,6 @@ def _extract_phase(
         return NotImplemented
     result = [gate_class(exponent=gate.exponent).on(*qubits)]
     phase_gate = global_phase_op.from_phase_and_exponent(gate.global_shift, gate.exponent)
-    if phase_gate.coefficient != 1:
+    if not phase_gate.is_identity():
         result.append(phase_gate())
     return result

cirq-core/cirq/ops/global_phase_op.py

@@ -92,6 +92,9 @@ def _resolve_parameters_(
         coefficient = protocols.resolve_parameters(self.coefficient, resolver, recursive)
         return GlobalPhaseGate(coefficient=coefficient)
 
+    def is_identity(self) -> bool:
+        return not protocols.is_parameterized(self._coefficient) and np.isclose(self.coefficient, 1)
+
     def controlled(
         self,
         num_controls: int | None = None,

cirq-core/cirq/ops/global_phase_op_test.py

@@ -307,6 +307,15 @@ def test_global_phase_gate_controlled(coeff, exp) -> None:
     )
 
 
+def test_is_identity() -> None:
+    g = cirq.GlobalPhaseGate(1)
+    assert g.is_identity()
+    g = cirq.GlobalPhaseGate(1j)
+    assert not g.is_identity()
+    g = cirq.GlobalPhaseGate(-1)
+    assert not g.is_identity()
+
+
 def test_from_phase_and_exponent() -> None:
     g = global_phase_op.from_phase_and_exponent(2.5, 0.5)
     assert g.coefficient == np.exp(1.25j * np.pi)

cirq-core/cirq/ops/three_qubit_gates.py

@@ -110,9 +110,7 @@ def _decompose_(self, qubits):
         p = common_gates.T**exp
         sweep_abc = [common_gates.CNOT(a, b), common_gates.CNOT(b, c)]
         global_phase_gate = global_phase_op.from_phase_and_exponent(self.global_shift, exp)
-        global_phase_operation = (
-            [] if np.isclose(global_phase_gate.coefficient, 1) else [global_phase_gate()]
-        )
+        global_phase_operation = [] if global_phase_gate.is_identity() else [global_phase_gate()]
         return global_phase_operation + [
             p(a),
             p(b),