A gate that measures qubits in the computational basis.

Inherits From: Gate

Used in the notebooks

Used in the tutorials

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

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.

ValueError If the length of invert_mask is greater than num_qubits. or if the length of qid_shape doesn't equal num_qubits.






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

num_controls: Total number of control qubits. control_values: For which control qubit values to apply the sub gate. A sequence of length num_controls where each entry is an integer (or set of integers) corresponding to the qubit value (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.


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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.


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The number of qubits this gate acts on.


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Returns an application of this gate to the given qubits.

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


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

*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.

Operations applying this gate to the target qubits.

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.


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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.

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


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


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Toggles whether or not the measurement inverts various outputs.


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


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Call self as a function.


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