cirq.MeasurementGate

A gate that measures qubits in the computational basis.

Inherits From: Gate

cirq.MeasurementGate(
    num_qubits: Optional[int] = None,
    key: Union[str, 'cirq.MeasurementKey'] = '',
    invert_mask: Tuple[bool, ...] = (),
    qid_shape: Optional[Tuple[int, ...]] = None,
    confusion_map: Optional[Dict[Tuple[int, ...], np.ndarray]] = None
) -> None

Used in the notebooks

Used in the tutorials

The measurement gate contains a key that is used to identify results of measurements.

Instead of constructing this directly, consider using the cirq.measure helper method.

num_qubits The number of qubits to act upon.
key The string key of the measurement.
invert_mask A list of values indicating whether the corresponding qubits should be flipped. The list's length must not be longer than the number of qubits, but it is permitted to be shorter. Qubits with indices past the end of the mask are not flipped.
qid_shape Specifies the dimension of each qid the measurement applies to. The default is 2 for every qubit.
confusion_map A map of qubit index sets (using indices in the operation generated from this gate) to the 2D confusion matrix for those qubits. Indices not included use the identity. Applied before invert_mask if both are provided.

ValueError If invert_mask or confusion_map have indices greater than the available qubit indices, or if the length of qid_shape doesn't equal num_qubits.

confusion_map

invert_mask

key

mkey

Methods

controlled

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controlled(
    num_controls: Optional[int] = None,
    control_values: Optional[Union[cv.AbstractControlValues, Sequence[Union[int, Collection[int]]]]
        ] = None,
    control_qid_shape: Optional[Tuple[int, ...]] = None
) -> 'Gate'

Returns a controlled version of this gate. If no arguments are specified, defaults to a single qubit control.

Args
num_controls Total number of control qubits.
control_values Which control computational basis state to apply the sub gate. A sequence of length num_controls where each entry is an integer (or set of integers) corresponding to the computational basis state (or set of possible values) where that control is enabled. When all controls are enabled, the sub gate is applied. If unspecified, control values default to 1.
control_qid_shape The qid shape of the controls. A tuple of the expected dimension of each control qid. Defaults to (2,) * num_controls. Specify this argument when using qudits.

Returns
A cirq.Gate representing self controlled by the given control values and qubits. This is a cirq.ControlledGate in the base implementation, but subclasses may return a different gate type.

full_invert_mask

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full_invert_mask() -> Tuple[bool, ...]

Returns the invert mask for all qubits.

If the user supplies a partial invert_mask, this returns that mask padded by False.

Similarly if no invert_mask is supplies this returns a tuple of size equal to the number of qubits with all entries False.

num_qubits

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num_qubits() -> int

The number of qubits this gate acts on.

on

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on(
    *qubits
) -> 'Operation'

Returns an application of this gate to the given qubits.

Args
*qubits The collection of qubits to potentially apply the gate to.

Returns: a cirq.Operation which is this gate applied to the given qubits.

on_each

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on_each(
    *targets
) -> List['cirq.Operation']

Returns a list of operations applying the gate to all targets.

Args
*targets The qubits to apply this gate to. For single-qubit gates this can be provided as varargs or a combination of nested iterables. For multi-qubit gates this must be provided as an Iterable[Sequence[Qid]], where each sequence has num_qubits qubits.

Returns
Operations applying this gate to the target qubits.

Raises
ValueError If targets are not instances of Qid or Iterable[Qid]. If the gate qubit number is incompatible.
TypeError If a single target is supplied and it is not iterable.

validate_args

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validate_args(
    qubits: Sequence['cirq.Qid']
) -> None

Checks if this gate can be applied to the given qubits.

By default checks that:

  • inputs are of type Qid
  • len(qubits) == num_qubits()
  • qubit_i.dimension == qid_shape[i] for all qubits

Child classes can override. The child implementation should call super().validate_args(qubits) then do custom checks.

Args
qubits The sequence of qubits to potentially apply the gate to.

Raises
ValueError The gate can't be applied to the qubits.

with_bits_flipped

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with_bits_flipped(
    *bit_positions
) -> 'MeasurementGate'

Toggles whether or not the measurement inverts various outputs.

This only affects the invert_mask, which is applied after confusion matrices if any are defined.

with_key

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with_key(
    key: Union[str, 'cirq.MeasurementKey']
) -> 'MeasurementGate'

Creates a measurement gate with a new key but otherwise identical.

with_probability

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with_probability(
    probability: 'cirq.TParamVal'
) -> 'cirq.Gate'

Creates a probabilistic channel with this gate.

Args
probability floating point value between 0 and 1, giving the probability this gate is applied.

Returns
cirq.RandomGateChannel that applies self with probability probability and the identity with probability 1-p.

wrap_in_linear_combination

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wrap_in_linear_combination(
    coefficient: 'cirq.TParamValComplex' = 1
) -> 'cirq.LinearCombinationOfGates'

Returns a LinearCombinationOfGates with this gate.

Args
coefficient number coefficient to use in the resulting cirq.LinearCombinationOfGates object.

Returns
cirq.LinearCombinationOfGates containing self with a coefficient of coefficient.

__add__

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__add__(
    other: Union['Gate', 'cirq.LinearCombinationOfGates']
) -> 'cirq.LinearCombinationOfGates'

__call__

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__call__(
    *qubits, **kwargs
)

Call self as a function.

__eq__

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__eq__(
    other: _SupportsValueEquality
) -> bool

__mul__

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__mul__(
    other: complex
) -> 'cirq.LinearCombinationOfGates'

__ne__

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__ne__(
    other: _SupportsValueEquality
) -> bool

__neg__

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__neg__() -> 'cirq.LinearCombinationOfGates'

__pow__

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__pow__(
    power
)

__rmul__

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__rmul__(
    other: complex
) -> 'cirq.LinearCombinationOfGates'

__sub__

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__sub__(
    other: Union['Gate', 'cirq.LinearCombinationOfGates']
) -> 'cirq.LinearCombinationOfGates'

__truediv__

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__truediv__(
    other: complex
) -> 'cirq.LinearCombinationOfGates'