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class qiskit.circuit.library.Initialize(params, num_qubits=None, normalize=False)

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Bases: Instruction

Complex amplitude initialization.

Class that initializes some flexible collection of qubit registers, implemented by calling the StatePreparation class. Note that Initialize is an Instruction and not a Gate since it contains a reset instruction, which is not unitary.


  • params (Statevector | Sequence[complex(opens in a new tab)] | str(opens in a new tab) |int(opens in a new tab)) –

    The state to initialize to, can be either of the following.

    • Statevector or vector of complex amplitudes to initialize to.
    • Labels of basis states of the Pauli eigenstates Z, X, Y. See Statevector.from_label(). Notice the order of the labels is reversed with respect to the qubit index to be applied to. Example label ‘01’ initializes the qubit zero to 1|1\rangle and the qubit one to 0|0\rangle.
    • An integer that is used as a bitmap indicating which qubits to initialize to 1|1\rangle. Example: setting params to 5 would initialize qubit 0 and qubit 2 to 1|1\rangle and qubit 1 to 0|0\rangle.
  • num_qubits (int(opens in a new tab) | None) – This parameter is only used if params is an int. Indicates the total number of qubits in the initialize call. Example: initialize covers 5 qubits and params is 3. This allows qubits 0 and 1 to be initialized to 1|1\rangle and the remaining 3 qubits to be initialized to 0|0\rangle.

  • normalize (bool(opens in a new tab)) – Whether to normalize an input array to a unit vector.



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.


Return initialize params.


Get the time unit of duration.



broadcast_arguments(qargs, cargs)

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Validation of the arguments.


  • qargs (List) – List of quantum bit arguments.
  • cargs (List) – List of classical bit arguments.


Tuple(List, List) – A tuple with single arguments.


CircuitError – If the input is not valid. For example, the number of arguments does not match the gate expectation.



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Call to create a circuit with gates that take the desired vector to zero.


Circuit to take self.params vector to 000|{00\ldots0}\rangle

Return type


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