# cirq.phase_by¶

cirq.phase_by(val: Any, phase_turns: float, qubit_index: int, default: TDefault = ([], ))[source]

Returns a phased version of the effect.

For example, an X gate phased by 90 degrees would be a Y gate.
This works by calling val’s phase_by method and returning
the result.
Parameters: val – The value to describe with a unitary matrix. phase_turns – The amount to phase the gate, in fractions of a whole turn. Divide by 2pi to get radians. qubit_index – The index of the target qubit the phasing applies to. For operations this is the index of the qubit within the operation’s qubit list. For gates it’s the index of the qubit within the tuple of qubits taken by the gate’s on method. default – The default value to return if val can’t be phased. If not specified, an error is raised when val can’t be phased. If val has a _phase_by_ method and its result is not NotImplemented, that result is returned. Otherwise, the function will return the default value provided or raise a TypeError if none was provided. TypeError – val doesn’t have a _phase_by_ method (or that method returned NotImplemented) and no default was specified.