cirq.ops.XPowGate

A gate that rotates around the X axis of the Bloch sphere.

Inherits From: EigenGate, SingleQubitGate, Gate

The unitary matrix of XPowGate(exponent=t) is:

[[g·c, -i·g·s],
[-i·g·s, g·c]]

where:

c = cos(π·t/2)
s = sin(π·t/2)
g = exp(i·π·t/2).

Note in particular that this gate has a global phase factor of e^{i·π·t/2} vs the traditionally defined rotation matrices about the Pauli X axis. See cirq.rx for rotations without the global phase. The global phase factor can be adjusted by using the global_shift parameter when initializing.

cirq.X, the Pauli X gate, is an instance of this gate at exponent=1.

exponent The t in gate**t. Determines how much the eigenvalues of the gate are scaled by. For example, eigenvectors phased by -1 when gate**1 is applied will gain a relative phase of e^{i pi exponent} when gate**exponent is applied (relative to eigenvectors unaffected by gate**1).
global_shift Offsets the eigenvalues of the gate at exponent=1. In effect, this controls a global phase factor on the gate's unitary matrix. The factor is:

exp(i * pi * global_shift * exponent)

For example, cirq.X**t uses a global_shift of 0 but cirq.rx(t) uses a global_shift of -0.5, which is why cirq.unitary(cirq.rx(pi)) equals -iX instead of X.

exponent

global_shift

phase_exponent

Methods

controlled

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Returns a controlled XPowGate, using a CXPowGate where possible.

The controlled method of the Gate class, of which this class is a child, returns a ControlledGate. This method overrides this behavior to return a CXPowGate or a ControlledGate of a CXPowGate, when this is possible.

The conditions for the override to occur are:

* The `global_shift` of the `XPowGate` is 0.
* The `control_values` and `control_qid_shape` are compatible with
the `CXPowGate`:
* The last value of `control_qid_shape` is a qubit.
* The last value of `control_values` corresponds to the
control being satisfied if that last qubit is 1 and
not satisfied if the last qubit is 0.

If these conditions are met, then the returned object is a CXPowGate or, in the case that there is more than one controlled qudit, a ControlledGate with the Gate being a CXPowGate. In the latter case the ControlledGate is controlled by one less qudit than specified in control_values and control_qid_shape (since one of these, the last qubit, is used as the control for the CXPowGate).

If the above conditions are not met, a ControlledGate of this gate will be returned.

in_su2

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Returns an equal-up-global-phase gate from the group SU2.

num_qubits

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The number of qubits this gate acts on.

on

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Returns an application of this gate to the given qubits.

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

on_each

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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.

validate_args

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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.

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

Throws:

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

with_canonical_global_phase

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Returns an equal-up-global-phase standardized form of the gate.

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__call__

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Call self as a function.

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__truediv__

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