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class qiskit.circuit.library.SGate(*args, _force_mutable=False, **kwargs)

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Bases: SingletonGate

Single qubit S gate (Z**0.5).

It induces a π/2\pi/2 phase, and is sometimes called the P gate (phase).

This is a Clifford gate and a square-root of Pauli-Z.

Can be applied to a QuantumCircuit with the s() method.

Matrix Representation:

S=(100i)S = \begin{pmatrix} 1 & 0 \\ 0 & i \end{pmatrix}

Circuit symbol:

q_0: ┤ S ├

Equivalent to a π/2\pi/2 radian rotation about the Z axis.

Create new S gate.



Get the base class of this instruction. This is guaranteed to be in the inheritance tree of self.

The “base class” of an instruction is the lowest class in its inheritance tree that the object should be considered entirely compatible with for _all_ circuit applications. This typically means that the subclass is defined purely to offer some sort of programmer convenience over the base class, and the base class is the “true” class for a behavioural perspective. In particular, you should not override base_class if you are defining a custom version of an instruction that will be implemented differently by hardware, such as an alternative measurement strategy, or a version of a parametrised gate with a particular set of parameters for the purposes of distinguishing it in a Target from the full parametrised gate.

This is often exactly equivalent to type(obj), except in the case of singleton instances of standard-library instructions. These singleton instances are special subclasses of their base class, and this property will return that base. For example:

>>> isinstance(XGate(), XGate)
>>> type(XGate()) is XGate
>>> XGate().base_class is XGate

In general, you should not rely on the precise class of an instruction; within a given circuit, it is expected that should be a more suitable discriminator in most situations.


The classical condition on the instruction.


Get Clbits in condition.


Get the decompositions of the instruction from the SessionEquivalenceLibrary.


Return definition in terms of other basic gates.


Get the duration.


Return instruction label


Is this instance is a mutable unique instance or not.

If this attribute is False the gate instance is a shared singleton and is not mutable.


Return the name.


Return the number of clbits.


Return the number of qubits.


The parameters of this Instruction. Ideally these will be gate angles.


Get the time unit of duration.




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Return inverse of S (SdgGate).


annotated (bool(opens in a new tab)) – when set to True, this is typically used to return an AnnotatedOperation with an inverse modifier set instead of a concrete Gate. However, for this class this argument is ignored as the inverse of this gate is always a SdgGate.


inverse of SGate

Return type



power(exponent, annotated=False)

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Raise this gate to the power of exponent.

Implemented either as a unitary gate (ref. UnitaryGate) or as an annotated operation (ref. AnnotatedOperation). In the case of several standard gates, such as RXGate, when the power of a gate can be expressed in terms of another standard gate that is returned directly.


  • exponent (float(opens in a new tab)) – the power to raise the gate to
  • annotated (bool(opens in a new tab)) – indicates whether the power gate can be implemented as an annotated operation. In the case of several standard gates, such as RXGate, this argument is ignored when the power of a gate can be expressed in terms of another standard gate.


An operation implementing gate^exponent


CircuitError – If gate is not unitary

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