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has_stabilizer_effect_protocol.py
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has_stabilizer_effect_protocol.py
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# Copyright 2018 The Cirq Developers
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from typing import (
Any,
Optional,
)
from cirq.ops.clifford_gate import SingleQubitCliffordGate
from cirq import protocols
def has_stabilizer_effect(val: Any) -> bool:
"""
Returns whether the input has a stabilizer effect.
For 1-qubit gates always returns correct result. For other operations relies
on the operation to define whether it has stabilizer effect.
"""
strats = [
_strat_has_stabilizer_effect_from_has_stabilizer_effect,
_strat_has_stabilizer_effect_from_gate,
_strat_has_stabilizer_effect_from_unitary,
]
for strat in strats:
result = strat(val)
if result is not None:
return result
# If you can't determine if it has stabilizer effect, it does not.
return False
def _strat_has_stabilizer_effect_from_has_stabilizer_effect(val: Any) -> Optional[bool]:
"""
Attempts to infer whether val has stabilizer effect via its
_has_stabilizer_effect_ method.
"""
if hasattr(val, '_has_stabilizer_effect_'):
result = val._has_stabilizer_effect_()
if result is not NotImplemented and result is not None:
return result
return None
def _strat_has_stabilizer_effect_from_gate(val: Any) -> Optional[bool]:
"""
Attempts to infer whether val has stabilizer effect via the value of
_has_stabilizer_effect_ method of its constituent gate.
"""
if hasattr(val, 'gate'):
return _strat_has_stabilizer_effect_from_has_stabilizer_effect(val.gate)
return None
def _strat_has_stabilizer_effect_from_unitary(val: Any) -> Optional[bool]:
"""Attempts to infer whether val has stabilizer effect from its unitary.
Returns whether unitary of `val` normalizes the Pauli group. Works only for
2x2 unitaries.
"""
# Do not try this strategy if there is no unitary or if the number of
# qubits is not 1 since that would be expensive.
if not protocols.has_unitary(val) or protocols.num_qubits(val) != 1:
return None
unitary = protocols.unitary(val)
return SingleQubitCliffordGate.from_unitary(unitary) is not None