Implement GlobalPhaseGate (quantumlib#4697)

Implements GlobalPhaseOperation in terms of a GateOperation on a new class GlobalPhaseGate.

Mostly involved moving existing functions from the operation to the gate, and then having the operation call those methods under the hood.

cirq-core/cirq/__init__.py

@@ -219,7 +219,9 @@
     generalized_amplitude_damp,
     GeneralizedAmplitudeDampingChannel,
     givens,
+    GlobalPhaseGate,
     GlobalPhaseOperation,
+    global_phase_operation,
     H,
     HPowGate,
     I,

cirq-core/cirq/circuits/circuit.py

@@ -1193,7 +1193,7 @@ def default_namer(label_entity):
             diagram.write(0, i, name)
         first_annotation_row = max(label_map.values(), default=0) + 1
 
-        if any(isinstance(op.untagged, cirq.GlobalPhaseOperation) for op in self.all_operations()):
+        if any(isinstance(op.gate, cirq.GlobalPhaseGate) for op in self.all_operations()):
             diagram.write(0, max(label_map.values(), default=0) + 1, 'global phase:')
             first_annotation_row += 1
 
@@ -2359,7 +2359,7 @@ def _get_moment_annotations(
         if op.qubits:
             continue
         op = op.untagged
-        if isinstance(op, ops.GlobalPhaseOperation):
+        if isinstance(op.gate, ops.GlobalPhaseGate):
             continue
         if isinstance(op, CircuitOperation):
             for m in op.circuit:
@@ -2493,8 +2493,8 @@ def _draw_moment_in_diagram(
 
 
 def _get_global_phase_and_tags_for_op(op: 'cirq.Operation') -> Tuple[Optional[complex], List[Any]]:
-    if isinstance(op.untagged, ops.GlobalPhaseOperation):
-        return complex(op.untagged.coefficient), list(op.tags)
+    if isinstance(op.gate, ops.GlobalPhaseGate):
+        return complex(op.gate.coefficient), list(op.tags)
     elif isinstance(op.untagged, CircuitOperation):
         op_phase, op_tags = _get_global_phase_and_tags_for_ops(op.untagged.circuit.all_operations())
         return op_phase, list(op.tags) + op_tags

cirq-core/cirq/circuits/circuit_operation_test.py

@@ -324,11 +324,11 @@ def test_string_format():
     assert str(op0) == f"[  ]"
 
     fc0_global_phase_inner = cirq.FrozenCircuit(
-        cirq.GlobalPhaseOperation(1j), cirq.GlobalPhaseOperation(1j)
+        cirq.global_phase_operation(1j), cirq.global_phase_operation(1j)
     )
     op0_global_phase_inner = cirq.CircuitOperation(fc0_global_phase_inner)
     fc0_global_phase_outer = cirq.FrozenCircuit(
-        op0_global_phase_inner, cirq.GlobalPhaseOperation(1j)
+        op0_global_phase_inner, cirq.global_phase_operation(1j)
     )
     op0_global_phase_outer = cirq.CircuitOperation(fc0_global_phase_outer)
     assert (

cirq-core/cirq/circuits/circuit_test.py

@@ -2568,7 +2568,7 @@ def test_diagram_wgate_none_precision(circuit_cls):
 @pytest.mark.parametrize('circuit_cls', [cirq.Circuit, cirq.FrozenCircuit])
 def test_diagram_global_phase(circuit_cls):
     qa = cirq.NamedQubit('a')
-    global_phase = cirq.GlobalPhaseOperation(coefficient=1j)
+    global_phase = cirq.global_phase_operation(coefficient=1j)
     c = circuit_cls([global_phase])
     cirq.testing.assert_has_diagram(
         c, "\n\nglobal phase:   0.5pi", use_unicode_characters=False, precision=2
@@ -2601,7 +2601,9 @@ def test_diagram_global_phase(circuit_cls):
 
     c = circuit_cls(
         cirq.X(cirq.LineQubit(2)),
-        cirq.CircuitOperation(circuit_cls(cirq.GlobalPhaseOperation(-1).with_tags("tag")).freeze()),
+        cirq.CircuitOperation(
+            circuit_cls(cirq.global_phase_operation(-1).with_tags("tag")).freeze()
+        ),
     )
     cirq.testing.assert_has_diagram(
         c,
@@ -5131,7 +5133,7 @@ def _circuit_diagram_info_(self, args) -> str:
             cirq.Moment(
                 cirq.H(cirq.LineQubit(0)),
                 CustomOperationAnnotation("a"),
-                cirq.GlobalPhaseOperation(1j),
+                cirq.global_phase_operation(1j),
             ),
         ),
         """

cirq-core/cirq/interop/quirk/cells/scalar_cells.py

@@ -21,11 +21,11 @@
 
 
 def generate_all_scalar_cell_makers() -> Iterator[CellMaker]:
-    yield _scalar("NeGate", ops.GlobalPhaseOperation(-1))
-    yield _scalar("i", ops.GlobalPhaseOperation(1j))
-    yield _scalar("-i", ops.GlobalPhaseOperation(-1j))
-    yield _scalar("√i", ops.GlobalPhaseOperation(1j ** 0.5))
-    yield _scalar("√-i", ops.GlobalPhaseOperation((-1j) ** 0.5))
+    yield _scalar("NeGate", ops.global_phase_operation(-1))
+    yield _scalar("i", ops.global_phase_operation(1j))
+    yield _scalar("-i", ops.global_phase_operation(-1j))
+    yield _scalar("√i", ops.global_phase_operation(1j ** 0.5))
+    yield _scalar("√-i", ops.global_phase_operation((-1j) ** 0.5))
 
 
 def _scalar(identifier: str, operation: 'cirq.Operation') -> CellMaker:

cirq-core/cirq/interop/quirk/cells/scalar_cells_test.py

@@ -20,17 +20,19 @@ def test_scalar_operations():
     assert_url_to_circuit_returns('{"cols":[["…"]]}', cirq.Circuit())
 
     assert_url_to_circuit_returns(
-        '{"cols":[["NeGate"]]}', cirq.Circuit(cirq.GlobalPhaseOperation(-1))
+        '{"cols":[["NeGate"]]}', cirq.Circuit(cirq.global_phase_operation(-1))
     )
 
-    assert_url_to_circuit_returns('{"cols":[["i"]]}', cirq.Circuit(cirq.GlobalPhaseOperation(1j)))
+    assert_url_to_circuit_returns('{"cols":[["i"]]}', cirq.Circuit(cirq.global_phase_operation(1j)))
 
-    assert_url_to_circuit_returns('{"cols":[["-i"]]}', cirq.Circuit(cirq.GlobalPhaseOperation(-1j)))
+    assert_url_to_circuit_returns(
+        '{"cols":[["-i"]]}', cirq.Circuit(cirq.global_phase_operation(-1j))
+    )
 
     assert_url_to_circuit_returns(
-        '{"cols":[["√i"]]}', cirq.Circuit(cirq.GlobalPhaseOperation(1j ** 0.5))
+        '{"cols":[["√i"]]}', cirq.Circuit(cirq.global_phase_operation(1j ** 0.5))
     )
 
     assert_url_to_circuit_returns(
-        '{"cols":[["√-i"]]}', cirq.Circuit(cirq.GlobalPhaseOperation(1j ** -0.5))
+        '{"cols":[["√-i"]]}', cirq.Circuit(cirq.global_phase_operation(1j ** -0.5))
     )

cirq-core/cirq/json_resolver_cache.py

@@ -87,6 +87,7 @@ def _parallel_gate_op(gate, qubits):
         'GateOperation': cirq.GateOperation,
         'Gateset': cirq.Gateset,
         'GeneralizedAmplitudeDampingChannel': cirq.GeneralizedAmplitudeDampingChannel,
+        'GlobalPhaseGate': cirq.GlobalPhaseGate,
         'GlobalPhaseOperation': cirq.GlobalPhaseOperation,
         'GridInteractionLayer': GridInteractionLayer,
         'GridParallelXEBMetadata': GridParallelXEBMetadata,

cirq-core/cirq/linalg/decompositions.py

@@ -535,7 +535,7 @@ def _decompose_(self, qubits):
 
         a, b = qubits
         return [
-            ops.GlobalPhaseOperation(self.global_phase),
+            ops.global_phase_operation(self.global_phase),
             ops.MatrixGate(self.single_qubit_operations_before[0]).on(a),
             ops.MatrixGate(self.single_qubit_operations_before[1]).on(b),
             np.exp(1j * ops.X(a) * ops.X(b) * self.interaction_coefficients[0]),

cirq-core/cirq/ops/__init__.py

@@ -123,7 +123,9 @@
 )
 
 from cirq.ops.global_phase_op import (
+    GlobalPhaseGate,
     GlobalPhaseOperation,
+    global_phase_operation,
 )
 
 from cirq.ops.kraus_channel import (

cirq-core/cirq/ops/dense_pauli_string.py

@@ -162,7 +162,7 @@ def _decompose_(self, qubits):
             return NotImplemented
         result = [PAULI_GATES[p].on(q) for p, q in zip(self.pauli_mask, qubits) if p]
         if self.coefficient != 1:
-            result.append(global_phase_op.GlobalPhaseOperation(self.coefficient))
+            result.append(global_phase_op.global_phase_operation(self.coefficient))
         return result
 
     def _is_parameterized_(self) -> bool:

cirq-core/cirq/ops/diagonal_gate.py

@@ -187,7 +187,7 @@ def _decompose_(self, qubits: Sequence['cirq.Qid']) -> 'cirq.OP_TREE':
         # diagonal gate for sub-system like controlled gate, it is no longer equivalent. Hence,
         # we add global phase.
         decomposed_circ: List[Any] = [
-            global_phase_op.GlobalPhaseOperation(np.exp(1j * hat_angles[0]))
+            global_phase_op.global_phase_operation(np.exp(1j * hat_angles[0]))
         ]
         for i, bit_flip in _gen_gray_code(n):
             decomposed_circ.extend(self._decompose_for_basis(i, bit_flip, -hat_angles[i], qubits))

cirq-core/cirq/ops/gate_operation.py

@@ -128,7 +128,7 @@ def __repr__(self):
 
     def __str__(self) -> str:
         qubits = ', '.join(str(e) for e in self.qubits)
-        return f'{self.gate}({qubits})'
+        return f'{self.gate}({qubits})' if qubits else str(self.gate)
 
     def _json_dict_(self) -> Dict[str, Any]:
         return protocols.obj_to_dict_helper(self, ['gate', 'qubits'])

cirq-core/cirq/ops/gateset.py

@@ -326,6 +326,9 @@ def __contains__(self, item: Union[raw_types.Gate, raw_types.Operation]) -> bool
         g = item if isinstance(item, raw_types.Gate) else item.gate
         assert g is not None, f'`item`: {item} must be a gate or have a valid `item.gate`'
 
+        if isinstance(g, global_phase_op.GlobalPhaseGate):
+            return self._accept_global_phase_op
+
         if g in self._instance_gate_families:
             assert item in self._instance_gate_families[g], (
                 f"{item} instance matches {self._instance_gate_families[g]} but "
@@ -396,8 +399,6 @@ def _validate_operation(self, op: raw_types.Operation) -> bool:
                 lambda q: cast(circuit_operation.CircuitOperation, op).qubit_map.get(q, q)
             )
             return self.validate(op_circuit)
-        elif isinstance(op, global_phase_op.GlobalPhaseOperation):
-            return self._accept_global_phase_op
         else:
             return False
 

cirq-core/cirq/ops/gateset_test.py

@@ -132,7 +132,7 @@ def test_gate_family_eq():
                 (cirq.SingleQubitGate(), False),
                 (cirq.X ** 0.5, False),
                 (None, False),
-                (cirq.GlobalPhaseOperation(1j), False),
+                (cirq.global_phase_operation(1j), False),
             ],
         ),
         (
@@ -144,7 +144,7 @@ def test_gate_family_eq():
                 (CustomX ** 3, True),
                 (CustomX ** sympy.Symbol('theta'), False),
                 (None, False),
-                (cirq.GlobalPhaseOperation(1j), False),
+                (cirq.global_phase_operation(1j), False),
             ],
         ),
         (
@@ -255,7 +255,7 @@ def get_ops(use_circuit_op, use_global_phase):
             )
             yield [circuit_op, recursive_circuit_op]
         if use_global_phase:
-            yield cirq.GlobalPhaseOperation(1j)
+            yield cirq.global_phase_operation(1j)
 
     def assert_validate_and_contains_consistent(gateset, op_tree, result):
         assert all(op in gateset for op in cirq.flatten_to_ops(op_tree)) is result

cirq-core/cirq/ops/global_phase_op.py

@@ -12,42 +12,69 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 """A no-qubit global phase operation."""
-from typing import Any, Dict, Tuple, TYPE_CHECKING
+from typing import Any, Dict, Sequence, Tuple, TYPE_CHECKING
 
 import numpy as np
 
 from cirq import value, protocols
-from cirq.ops import raw_types
+from cirq._compat import deprecated_class
+from cirq.ops import gate_operation, raw_types
 
 if TYPE_CHECKING:
     import cirq
 
 
 @value.value_equality(approximate=True)
-class GlobalPhaseOperation(raw_types.Operation):
+@deprecated_class(deadline='v0.16', fix='Use cirq.global_phase_operation')
+class GlobalPhaseOperation(gate_operation.GateOperation):
     def __init__(self, coefficient: value.Scalar, atol: float = 1e-8) -> None:
-        if abs(1 - abs(coefficient)) > atol:
-            raise ValueError(f'Coefficient is not unitary: {coefficient!r}')
-        self.coefficient = coefficient
-
-    @property
-    def qubits(self) -> Tuple['cirq.Qid', ...]:
-        return ()
+        gate = GlobalPhaseGate(coefficient, atol)
+        super().__init__(gate, [])
 
     def with_qubits(self, *new_qubits) -> 'GlobalPhaseOperation':
         if new_qubits:
             raise ValueError(f'{self!r} applies to 0 qubits but new_qubits={new_qubits!r}.')
         return self
 
+    @property
+    def coefficient(self) -> value.Scalar:
+        return self.gate.coefficient  # type: ignore
+
+    @coefficient.setter
+    def coefficient(self, coefficient: value.Scalar):
+        # coverage: ignore
+        self.gate._coefficient = coefficient  # type: ignore
+
+    def __str__(self) -> str:
+        return str(self.coefficient)
+
+    def __repr__(self) -> str:
+        return f'cirq.GlobalPhaseOperation({self.coefficient!r})'
+
+    def _json_dict_(self) -> Dict[str, Any]:
+        return protocols.obj_to_dict_helper(self, ['coefficient'])
+
+
+@value.value_equality(approximate=True)
+class GlobalPhaseGate(raw_types.Gate):
+    def __init__(self, coefficient: value.Scalar, atol: float = 1e-8) -> None:
+        if abs(1 - abs(coefficient)) > atol:
+            raise ValueError(f'Coefficient is not unitary: {coefficient!r}')
+        self._coefficient = coefficient
+
+    @property
+    def coefficient(self) -> value.Scalar:
+        return self._coefficient
+
     def _value_equality_values_(self) -> Any:
         return self.coefficient
 
     def _has_unitary_(self) -> bool:
         return True
 
-    def __pow__(self, power):
+    def __pow__(self, power) -> 'cirq.GlobalPhaseGate':
         if isinstance(power, (int, float)):
-            return GlobalPhaseOperation(self.coefficient ** power)
+            return GlobalPhaseGate(self.coefficient ** power)
         return NotImplemented
 
     def _unitary_(self) -> np.ndarray:
@@ -60,7 +87,7 @@ def _apply_unitary_(self, args) -> np.ndarray:
     def _has_stabilizer_effect_(self) -> bool:
         return True
 
-    def _act_on_(self, args: 'cirq.ActOnArgs'):
+    def _act_on_(self, args: 'cirq.ActOnArgs', qubits):
         from cirq.sim import clifford
 
         if isinstance(args, clifford.ActOnCliffordTableauArgs):
@@ -78,7 +105,17 @@ def __str__(self) -> str:
         return str(self.coefficient)
 
     def __repr__(self) -> str:
-        return f'cirq.GlobalPhaseOperation({self.coefficient!r})'
+        return f'cirq.GlobalPhaseGate({self.coefficient!r})'
+
+    def _op_repr_(self, qubits: Sequence['cirq.Qid']) -> str:
+        return f'cirq.global_phase_operation({self.coefficient!r})'
 
     def _json_dict_(self) -> Dict[str, Any]:
         return protocols.obj_to_dict_helper(self, ['coefficient'])
+
+    def _qid_shape_(self) -> Tuple[int, ...]:
+        return tuple()
+
+
+def global_phase_operation(coefficient: value.Scalar, atol: float = 1e-8) -> 'cirq.GateOperation':
+    return GlobalPhaseGate(coefficient, atol)()