Source code for cirq.devices.noise_model

# Copyright 2019 The Cirq Developers
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#     https://www.apache.org/licenses/LICENSE-2.0
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from typing import Any, Dict, Sequence, TYPE_CHECKING, Union

from cirq import ops, protocols, value
from cirq._doc import document

if TYPE_CHECKING:
    from typing import Iterable
    import cirq


[docs]class NoiseModel(metaclass=value.ABCMetaImplementAnyOneOf): """Replaces operations and moments with noisy counterparts. A child class must override *at least one* of the following three methods: noisy_moments noisy_moment noisy_operation The methods that are not overridden will be implemented in terms of the ones that are. Simulators told to use a noise model will use these methods in order to dynamically rewrite the program they are simulating. """
[docs] @classmethod def from_noise_model_like(cls, noise: 'cirq.NOISE_MODEL_LIKE' ) -> 'cirq.NoiseModel': """Transforms an object into a noise model if umambiguously possible. Args: noise: ``None``, a ``cirq.NoiseModel``, or a single qubit operation. Returns: ``cirq.NO_NOISE`` when given ``None``, ``cirq.ConstantQubitNoiseModel(gate)`` when given a single qubit gate, or the given value if it is already a ``cirq.NoiseModel``. Raises: TypeError: The input is not a ``cirq.NOISE_MODE_LIKE``. """ if noise is None: return NO_NOISE if isinstance(noise, NoiseModel): return noise if isinstance(noise, ops.Gate): if noise.num_qubits() != 1: raise ValueError( 'Multi-qubit gates cannot be implicitly wrapped into a ' 'noise model. Please use a single qubit gate (which will ' 'be wrapped with `cirq.ConstantQubitNoiseModel`) or ' 'an instance of `cirq.NoiseModel`.') return ConstantQubitNoiseModel(noise) raise TypeError('Expected a NOISE_MODEL_LIKE (None, a cirq.NoiseModel, ' 'or a single qubit gate). Got {!r}'.format(noise))
[docs] def is_virtual_moment(self, moment: 'cirq.Moment') -> bool: """Returns true iff the given moment is non-empty and all of its operations are virtual. Moments for which this method returns True should not have additional noise applied to them. Args: moment: ``cirq.Moment`` to check for non-virtual operations. Returns: True if "moment" is non-empty and all operations in "moment" are virtual; false otherwise. """ if not moment.operations: return False return all([ isinstance(op, ops.TaggedOperation) and ops.VirtualTag() in op.tags for op in moment.operations ])
def _noisy_moments_impl_moment(self, moments: 'Iterable[cirq.Moment]', system_qubits: Sequence['cirq.Qid'] ) -> Sequence['cirq.OP_TREE']: result = [] for moment in moments: result.append(self.noisy_moment(moment, system_qubits)) return result def _noisy_moments_impl_operation(self, moments: 'Iterable[cirq.Moment]', system_qubits: Sequence['cirq.Qid'] ) -> Sequence['cirq.OP_TREE']: result = [] for moment in moments: result.append([self.noisy_operation(op) for op in moment]) return result
[docs] @value.alternative(requires='noisy_moment', implementation=_noisy_moments_impl_moment) @value.alternative(requires='noisy_operation', implementation=_noisy_moments_impl_operation) def noisy_moments(self, moments: 'Iterable[cirq.Moment]', system_qubits: Sequence['cirq.Qid'] ) -> Sequence['cirq.OP_TREE']: """Adds possibly stateful noise to a series of moments. Args: moments: The moments to add noise to. system_qubits: A list of all qubits in the system. Returns: A sequence of OP_TREEs, with the k'th tree corresponding to the noisy operations for the k'th moment. """
def _noisy_moment_impl_moments(self, moment: 'cirq.Moment', system_qubits: Sequence['cirq.Qid'] ) -> 'cirq.OP_TREE': return self.noisy_moments([moment], system_qubits) def _noisy_moment_impl_operation(self, moment: 'cirq.Moment', system_qubits: Sequence['cirq.Qid'] ) -> 'cirq.OP_TREE': return [self.noisy_operation(op) for op in moment]
[docs] @value.alternative(requires='noisy_moments', implementation=_noisy_moment_impl_moments) @value.alternative(requires='noisy_operation', implementation=_noisy_moment_impl_operation) def noisy_moment(self, moment: 'cirq.Moment', system_qubits: Sequence['cirq.Qid']) -> 'cirq.OP_TREE': """Adds noise to the operations from a moment. Args: moment: The moment to add noise to. system_qubits: A list of all qubits in the system. Returns: An OP_TREE corresponding to the noisy operations for the moment. """
def _noisy_operation_impl_moments(self, operation: 'cirq.Operation' ) -> 'cirq.OP_TREE': return self.noisy_moments([ops.Moment([operation])], operation.qubits) def _noisy_operation_impl_moment(self, operation: 'cirq.Operation' ) -> 'cirq.OP_TREE': return self.noisy_moment(ops.Moment([operation]), operation.qubits)
[docs] @value.alternative(requires='noisy_moments', implementation=_noisy_operation_impl_moments) @value.alternative(requires='noisy_moment', implementation=_noisy_operation_impl_moment) def noisy_operation(self, operation: 'cirq.Operation') -> 'cirq.OP_TREE': """Adds noise to an individual operation. Args: operation: The operation to make noisy. Returns: An OP_TREE corresponding to the noisy operations implementing the noisy version of the given operation. """
@value.value_equality class _NoNoiseModel(NoiseModel): """A default noise model that adds no noise.""" def noisy_moments(self, moments: 'Iterable[cirq.Moment]', system_qubits: Sequence['cirq.Qid']): return list(moments) def noisy_moment(self, moment: 'cirq.Moment', system_qubits: Sequence['cirq.Qid']): return moment def noisy_operation(self, operation: 'cirq.Operation'): return operation def _value_equality_values_(self) -> Any: return None def __str__(self) -> str: return '(no noise)' def __repr__(self) -> str: return 'cirq.NO_NOISE' def _json_dict_(self) -> Dict[str, Any]: return protocols.obj_to_dict_helper(self, [])
[docs]@value.value_equality class ConstantQubitNoiseModel(NoiseModel): """Applies noise to each qubit individually at the start of every moment. This is the noise model that is wrapped around an operation when that operation is given as "the noise to use" for a `NOISE_MODEL_LIKE` parameter. """
[docs] def __init__(self, qubit_noise_gate: 'cirq.Gate'): if qubit_noise_gate.num_qubits() != 1: raise ValueError('noise.num_qubits() != 1') self.qubit_noise_gate = qubit_noise_gate
def _value_equality_values_(self) -> Any: return self.qubit_noise_gate def __repr__(self) -> str: return f'cirq.ConstantQubitNoiseModel({self.qubit_noise_gate!r})'
[docs] def noisy_moment(self, moment: 'cirq.Moment', system_qubits: Sequence['cirq.Qid']): # Noise should not be appended to previously-added noise. if self.is_virtual_moment(moment): return moment return [ moment, ops.Moment([ # TODO: Replace with "VirtualTag" class instance. self.qubit_noise_gate(q).with_tags(ops.VirtualTag()) for q in system_qubits ]) ]
def _json_dict_(self): return protocols.obj_to_dict_helper(self, ['qubit_noise_gate'])
NO_NOISE: 'cirq.NoiseModel' = _NoNoiseModel() document( NO_NOISE, """The trivial noise model with no effects. This is the noise model used when a `NOISE_MODEL_LIKE` noise parameter is set to `None`. """) NOISE_MODEL_LIKE = Union[None, 'cirq.NoiseModel', 'cirq.SingleQubitGate'] document( NOISE_MODEL_LIKE, # type: ignore """A `cirq.NoiseModel` or a value that can be trivially converted into one. `None` is a `NOISE_MODEL_LIKE`. It will be replaced by the `cirq.NO_NOISE` noise model. A single qubit gate is a `NOISE_MODEL_LIKE`. It will be wrapped inside of a `cirq.ConstantQubitNoiseModel`. """)