Assume PhasedXPowGate is different from XPowGate and YPowGate (#7070)

* Assume PhasedXPowGate is different from XPowGate and YPowGate for value_equality protocol.

A similar change was done for PhasedISwapPowGate. This addresses issue #6528.

* Remove _value_equality_values_cls_ and update tests.

* Explicitly test that Pauli gates differ from equal-effect PhasedXPowGate

* Change engine tests to compare circuit unitaries

Adjust for unequality between X and equal-effect PhasedXPowGate.

* Fix unintentionally empty Moment in the test

* eject_phased_paulis - replace PhasedXPowGate with equivalent X or Y

This mostly restores the eject_phased_paulis unit tests to their
initial form with a few `cirq.Y` replacements sparkled around.

* phase_by for X and Y - replace PhasedXPowGate with equivalent X or Y

This mostly restores `eject_z_test.py` to its initial form.

---------

Co-authored-by: Michael Hucka <[email protected]>
Co-authored-by: Pavol Juhas <[email protected]>

Author: 3 people

cirq-core/cirq/ops/common_gates.py

@@ -289,9 +289,7 @@ def phase_exponent(self):
 
     def _phase_by_(self, phase_turns, qubit_index):
         """See `cirq.SupportsPhase`."""
-        return cirq.ops.phased_x_gate.PhasedXPowGate(
-            exponent=self._exponent, phase_exponent=phase_turns * 2
-        )
+        return _phased_x_or_pauli_gate(exponent=self._exponent, phase_exponent=phase_turns * 2)
 
     def _has_stabilizer_effect_(self) -> Optional[bool]:
         if self._is_parameterized_() or self._dimension != 2:
@@ -484,7 +482,7 @@ def phase_exponent(self):
 
     def _phase_by_(self, phase_turns, qubit_index):
         """See `cirq.SupportsPhase`."""
-        return cirq.ops.phased_x_gate.PhasedXPowGate(
+        return _phased_x_or_pauli_gate(
             exponent=self._exponent, phase_exponent=0.5 + phase_turns * 2
         )
 
@@ -1542,3 +1540,17 @@ def cphase(rads: value.TParamVal) -> CZPowGate:
     $$
     """,
 )
+
+
+def _phased_x_or_pauli_gate(
+    exponent: Union[float, sympy.Expr], phase_exponent: Union[float, sympy.Expr]
+) -> Union['cirq.PhasedXPowGate', 'cirq.XPowGate', 'cirq.YPowGate']:
+    """Return PhasedXPowGate or X or Y gate if equivalent at the given phase_exponent."""
+    if not isinstance(phase_exponent, sympy.Expr) or phase_exponent.is_constant():
+        half_turns = value.canonicalize_half_turns(float(phase_exponent))
+        match half_turns:
+            case 0.0:
+                return XPowGate(exponent=exponent)
+            case 0.5:
+                return YPowGate(exponent=exponent)
+    return cirq.ops.PhasedXPowGate(exponent=exponent, phase_exponent=phase_exponent)

cirq-core/cirq/ops/phased_x_gate.py

@@ -24,10 +24,10 @@
 import cirq
 from cirq import protocols, value
 from cirq._compat import proper_repr
-from cirq.ops import common_gates, raw_types
+from cirq.ops import raw_types
 
 
-@value.value_equality(manual_cls=True, approximate=True)
+@value.value_equality(approximate=True)
 class PhasedXPowGate(raw_types.Gate):
     r"""A gate equivalent to $Z^{-p} X^t Z^{p}$ (in time order).
 
@@ -241,22 +241,7 @@ def _canonical_exponent(self):
 
         return self._exponent % period
 
-    def _value_equality_values_cls_(self):
-        if self.phase_exponent == 0:
-            return common_gates.XPowGate
-        if self.phase_exponent == 0.5:
-            return common_gates.YPowGate
-        return PhasedXPowGate
-
     def _value_equality_values_(self):
-        if self.phase_exponent == 0:
-            return common_gates.XPowGate(
-                exponent=self._exponent, global_shift=self._global_shift
-            )._value_equality_values_()
-        if self.phase_exponent == 0.5:
-            return common_gates.YPowGate(
-                exponent=self._exponent, global_shift=self._global_shift
-            )._value_equality_values_()
         return self.phase_exponent, self._canonical_exponent, self._global_shift
 
     def _json_dict_(self) -> Dict[str, Any]:

cirq-core/cirq/ops/phased_x_gate_test.py

@@ -79,16 +79,17 @@ def test_eq():
         cirq.PhasedXPowGate(exponent=1, phase_exponent=0),
         cirq.PhasedXPowGate(exponent=1, phase_exponent=2),
         cirq.PhasedXPowGate(exponent=1, phase_exponent=-2),
-        cirq.X,
     )
+    eq.add_equality_group(cirq.X)
     eq.add_equality_group(cirq.PhasedXPowGate(exponent=1, phase_exponent=2, global_shift=0.1))
 
     eq.add_equality_group(
         cirq.PhasedXPowGate(phase_exponent=0.5, exponent=1),
         cirq.PhasedXPowGate(phase_exponent=2.5, exponent=3),
-        cirq.Y,
     )
-    eq.add_equality_group(cirq.PhasedXPowGate(phase_exponent=0.5, exponent=0.25), cirq.Y**0.25)
+    eq.add_equality_group(cirq.Y)
+    eq.add_equality_group(cirq.PhasedXPowGate(phase_exponent=0.5, exponent=0.25))
+    eq.add_equality_group(cirq.Y**0.25)
 
     eq.add_equality_group(cirq.PhasedXPowGate(phase_exponent=0.25, exponent=0.25, global_shift=0.1))
     eq.add_equality_group(cirq.PhasedXPowGate(phase_exponent=2.25, exponent=0.25, global_shift=0.2))
@@ -266,3 +267,18 @@ def test_exponent_consistency(exponent, phase_exponent):
     u = cirq.protocols.unitary(g)
     u2 = cirq.protocols.unitary(g2)
     assert np.all(u == u2)
+
+
+def test_approx_eq_for_close_phase_exponents():
+    gate1 = cirq.PhasedXPowGate(phase_exponent=0)
+    gate2 = cirq.PhasedXPowGate(phase_exponent=1e-12)
+    gate3 = cirq.PhasedXPowGate(phase_exponent=2e-12)
+    gate4 = cirq.PhasedXPowGate(phase_exponent=0.345)
+
+    assert cirq.approx_eq(gate2, gate3)
+    assert cirq.approx_eq(gate2, gate1)
+    assert not cirq.approx_eq(gate2, gate4)
+
+    assert cirq.equal_up_to_global_phase(gate2, gate3)
+    assert cirq.equal_up_to_global_phase(gate2, gate1)
+    assert not cirq.equal_up_to_global_phase(gate2, gate4)

cirq-core/cirq/transformers/eject_phased_paulis.py

@@ -14,7 +14,7 @@
 
 """Transformer pass that pushes 180° rotations around axes in the XY plane later in the circuit."""
 
-from typing import cast, Dict, Iterable, Iterator, Optional, Tuple, TYPE_CHECKING
+from typing import cast, Dict, Iterable, Iterator, Optional, Tuple, TYPE_CHECKING, Union
 
 import numpy as np
 import sympy
@@ -63,15 +63,15 @@ def eject_phased_paulis(
     def map_func(op: 'cirq.Operation', _: int) -> 'cirq.OP_TREE':
         # Dump if `op` marked with a no compile tag.
         if set(op.tags) & tags_to_ignore:
-            return [_dump_held(op.qubits, held_w_phases), op]
+            return [_dump_held(op.qubits, held_w_phases, atol), op]
 
         # Collect, phase, and merge Ws.
         w = _try_get_known_phased_pauli(op, no_symbolic=not eject_parameterized)
         if w is not None:
             return (
                 _potential_cross_whole_w(op, atol, held_w_phases)
                 if single_qubit_decompositions.is_negligible_turn((w[0] - 1) / 2, atol)
-                else _potential_cross_partial_w(op, held_w_phases)
+                else _potential_cross_partial_w(op, held_w_phases, atol)
             )
 
         affected = [q for q in op.qubits if q in held_w_phases]
@@ -96,12 +96,12 @@ def map_func(op: 'cirq.Operation', _: int) -> 'cirq.OP_TREE':
             )
 
         # Don't know how to handle this situation. Dump the gates.
-        return [_dump_held(op.qubits, held_w_phases), op]
+        return [_dump_held(op.qubits, held_w_phases, atol), op]
 
     # Map operations and put anything that's still held at the end of the circuit.
     return circuits.Circuit(
         transformer_primitives.map_operations_and_unroll(circuit, map_func),
-        _dump_held(held_w_phases.keys(), held_w_phases),
+        _dump_held(held_w_phases.keys(), held_w_phases, atol),
     )
 
 
@@ -127,14 +127,14 @@ def _absorb_z_into_w(
 
 
 def _dump_held(
-    qubits: Iterable[ops.Qid], held_w_phases: Dict[ops.Qid, value.TParamVal]
+    qubits: Iterable[ops.Qid], held_w_phases: Dict[ops.Qid, value.TParamVal], atol: float
 ) -> Iterator['cirq.OP_TREE']:
     # Note: sorting is to avoid non-determinism in the insertion order.
     for q in sorted(qubits):
         p = held_w_phases.get(q)
         if p is not None:
-            dump_op = ops.PhasedXPowGate(phase_exponent=p).on(q)
-            yield dump_op
+            gate = _phased_x_or_pauli_gate(exponent=1.0, phase_exponent=p, atol=atol)
+            yield gate.on(q)
         held_w_phases.pop(q, None)
 
 
@@ -184,7 +184,7 @@ def _potential_cross_whole_w(
 
 
 def _potential_cross_partial_w(
-    op: ops.Operation, held_w_phases: Dict[ops.Qid, value.TParamVal]
+    op: ops.Operation, held_w_phases: Dict[ops.Qid, value.TParamVal], atol: float
 ) -> 'cirq.OP_TREE':
     """Cross the held W over a partial W gate.
 
@@ -204,10 +204,10 @@ def _potential_cross_partial_w(
     exponent, phase_exponent = cast(
         Tuple[value.TParamVal, value.TParamVal], _try_get_known_phased_pauli(op)
     )
-    new_op = ops.PhasedXPowGate(exponent=exponent, phase_exponent=2 * a - phase_exponent).on(
-        op.qubits[0]
+    gate = _phased_x_or_pauli_gate(
+        exponent=exponent, phase_exponent=2 * a - phase_exponent, atol=atol
     )
-    return new_op
+    return gate.on(op.qubits[0])
 
 
 def _single_cross_over_cz(op: ops.Operation, qubit_with_w: 'cirq.Qid') -> 'cirq.OP_TREE':
@@ -351,3 +351,16 @@ def _try_get_known_z_half_turns(
     if no_symbolic and isinstance(h, sympy.Basic):
         return None
     return h
+
+
+def _phased_x_or_pauli_gate(
+    exponent: Union[float, sympy.Expr], phase_exponent: Union[float, sympy.Expr], atol: float
+) -> Union['cirq.PhasedXPowGate', 'cirq.XPowGate', 'cirq.YPowGate']:
+    """Return PhasedXPowGate or X or Y gate if equivalent within atol in z-axis turns."""
+    if not isinstance(phase_exponent, sympy.Expr) or phase_exponent.is_constant():
+        half_turns = value.canonicalize_half_turns(float(phase_exponent))
+        if abs(half_turns / 2) <= atol:
+            return ops.XPowGate(exponent=exponent)
+        if abs((half_turns - 0.5) / 2) <= atol:
+            return ops.YPowGate(exponent=exponent)
+    return ops.PhasedXPowGate(exponent=exponent, phase_exponent=phase_exponent)

cirq-core/cirq/transformers/eject_phased_paulis_test.py

@@ -212,11 +212,7 @@ def test_crosses_czs():
             [cirq.CZ(a, b) ** 0.25],
         ),
         expected=quick_circuit(
-            [cirq.CZ(a, b) ** 0.25],
-            [
-                cirq.PhasedXPowGate(phase_exponent=0.5).on(b),
-                cirq.PhasedXPowGate(phase_exponent=0.25).on(a),
-            ],
+            [cirq.CZ(a, b) ** 0.25], [cirq.Y(b), cirq.PhasedXPowGate(phase_exponent=0.25).on(a)]
         ),
     )
     assert_optimizes(
@@ -387,8 +383,7 @@ def test_phases_partial_ws():
     assert_optimizes(
         before=quick_circuit([cirq.PhasedXPowGate(phase_exponent=0.25).on(q)], [cirq.X(q) ** 0.5]),
         expected=quick_circuit(
-            [cirq.PhasedXPowGate(phase_exponent=0.5, exponent=0.5).on(q)],
-            [cirq.PhasedXPowGate(phase_exponent=0.25).on(q)],
+            [cirq.Y(q) ** 0.5], [cirq.PhasedXPowGate(phase_exponent=0.25).on(q)]
         ),
     )
 

cirq-core/cirq/transformers/eject_z_test.py

@@ -51,10 +51,10 @@ def assert_optimizes(
         cirq.Moment(cirq.CircuitOperation(before.freeze()).repeat(3).with_tags("preserve_tag")),
     )
     c_expected = cirq.Circuit(
-        cirq.PhasedXPowGate(phase_exponent=0, exponent=0.25).on_each(*q),
+        (cirq.X**0.25).on_each(*q),
         (cirq.Z**0.5).on_each(*q),
         cirq.Moment(cirq.CircuitOperation(before.freeze()).repeat(2).with_tags("ignore")),
-        cirq.PhasedXPowGate(phase_exponent=0, exponent=0.25).on_each(*q),
+        (cirq.X**0.25).on_each(*q),
         (cirq.Z**0.5).on_each(*q),
         cirq.Moment(cirq.CircuitOperation(expected.freeze()).repeat(3).with_tags("preserve_tag")),
     )

cirq-core/cirq/transformers/merge_single_qubit_gates_test.py

@@ -45,7 +45,7 @@ def test_merge_single_qubit_gates_to_phased_x_and_z():
         optimized=cirq.merge_single_qubit_gates_to_phased_x_and_z(c),
         expected=cirq.Circuit(
             cirq.PhasedXPowGate(phase_exponent=1)(a),
-            cirq.Y(b) ** 0.5,
+            cirq.PhasedXPowGate(phase_exponent=0.5)(b) ** 0.5,
             cirq.CZ(a, b),
             (cirq.PhasedXPowGate(phase_exponent=-0.5)(a)) ** 0.5,
             cirq.measure(b, key="m"),

cirq-google/cirq_google/api/v1/programs_test.py

@@ -15,31 +15,27 @@
 import pytest
 import sympy
 
-import cirq
+import cirq.testing
 import cirq_google.api.v1.programs as programs
 from cirq_google.api.v1 import operations_pb2
 
 
 def assert_proto_dict_convert(gate: cirq.Gate, proto: operations_pb2.Operation, *qubits: cirq.Qid):
     assert programs.gate_to_proto(gate, qubits, delay=0) == proto
-    assert programs.xmon_op_from_proto(proto) == gate(*qubits)
+    xmon_op = programs.xmon_op_from_proto(proto)
+    assert xmon_op.qubits == qubits
+    assert xmon_op.gate == gate or np.allclose(cirq.unitary(xmon_op.gate), cirq.unitary(gate))
 
 
 def test_protobuf_round_trip():
     qubits = cirq.GridQubit.rect(1, 5)
     circuit = cirq.Circuit(
-        [cirq.X(q) ** 0.5 for q in qubits],
-        [
-            cirq.CZ(q, q2)
-            for q in [cirq.GridQubit(0, 0)]
-            for q, q2 in zip(qubits, qubits)
-            if q != q2
-        ],
+        [cirq.X(q) ** 0.5 for q in qubits], [cirq.CZ(qubits[0], q1) for q1 in qubits[1:]]
     )
 
     protos = list(programs.circuit_as_schedule_to_protos(circuit))
     s2 = programs.circuit_from_schedule_from_protos(protos)
-    assert s2 == circuit
+    cirq.testing.assert_circuits_with_terminal_measurements_are_equivalent(s2, circuit)
 
 
 def make_bytes(s: str) -> bytes:

cirq-google/cirq_google/engine/engine_program_test.py

@@ -20,7 +20,7 @@
 from google.protobuf import any_pb2, timestamp_pb2
 from google.protobuf.text_format import Merge
 
-import cirq
+import cirq.testing
 import cirq_google as cg
 from cirq_google.api import v1, v2
 from cirq_google.cloud import quantum
@@ -304,7 +304,9 @@ def test_get_circuit_v2(get_program_async):
 
     program = cg.EngineProgram('a', 'b', EngineContext())
     get_program_async.return_value = quantum.QuantumProgram(code=_PROGRAM_V2)
-    assert program.get_circuit() == circuit
+    cirq.testing.assert_circuits_with_terminal_measurements_are_equivalent(
+        program.get_circuit(), circuit
+    )
     get_program_async.assert_called_once_with('a', 'b', True)