class cirq.ZPowGate(*, exponent: Union[cirq.value.symbol.Symbol, float] = 1.0, global_shift: float = 0.0)[source]

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

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

[[1, 0],
 [0, g]]


g = exp(i·π·t).
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 Z axis. See cirq.Rz for rotations without the global
phase. The global phase factor can be adjusted by using the global_shift
parameter when initializing.

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

__init__(*, exponent: Union[cirq.value.symbol.Symbol, float] = 1.0, global_shift: float = 0.0) → None

Initializes the parameters used to compute the gate’s matrix.

The eigenvalue of each eigenspace of a gate is computed by

  1. Starting with an angle in half turns as returned by the gate’s
    _eigen_components method:
  2. Shifting the angle by global_shift:

    θ + s
  3. Scaling the angle by exponent:

    (θ + s) * e
  4. Converting from half turns to a complex number on the unit circle:

    exp(i * pi * (θ + s) * e)
  • 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.


on(*qubits) Returns an application of this gate to the given qubits.
on_each(targets) Returns a list of operations apply this gate to each of the targets.
validate_args(qubits) Checks if this gate can be applied to the given qubits.