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MCXGate

class qiskit.circuit.library.MCXGate(num_ctrl_qubits=None, label=None, ctrl_state=None, *, _base_label=None)

GitHub

Bases: ControlledGate

The general, multi-controlled X gate.

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

Create new MCX gate.


Attributes

Parameters

  • num_ctrl_qubits (Optional[int]) –
  • label (Optional[str]) –
  • ctrl_state (Optional[Union[str, int]]) –

base_class

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 behavioral 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 parametrized gate with a particular set of parameters for the purposes of distinguishing it in a Target from the full parametrized 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)
True
>>> type(XGate()) is XGate
False
>>> XGate().base_class is XGate
True

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

ctrl_state

Return the control state of the gate as a decimal integer.

decompositions

Get the decompositions of the instruction from the SessionEquivalenceLibrary.

definition

Return definition in terms of other basic gates. If the gate has open controls, as determined from ctrl_state, the returned definition is conjugated with X without changing the internal _definition.

label

Return instruction label

mutable

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.

name

Get name of gate. If the gate has open controls the gate name will become:

<original_name_o<ctrl_state>

where <original_name> is the gate name for the default case of closed control qubits and <ctrl_state> is the integer value of the control state for the gate.

num_ancilla_qubits

The number of ancilla qubits.

num_clbits

Return the number of clbits.

num_ctrl_qubits

Get number of control qubits.

Returns

The number of control qubits for the gate.

Return type

int

num_qubits

Return the number of qubits.

params

Get parameters from base_gate.

Returns

List of gate parameters.

Return type

list

Raises

CircuitError – Controlled gate does not define a base gate


Methods

add_decomposition

add_decomposition(decomposition)

GitHub

Add a decomposition of the instruction to the SessionEquivalenceLibrary.

broadcast_arguments

broadcast_arguments(qargs, cargs)

GitHub

Validation and handling of the arguments and its relationship.

For example, cx([q[0],q[1]], q[2]) means cx(q[0], q[2]); cx(q[1], q[2]). This method yields the arguments in the right grouping. In the given example:

in: [[q[0],q[1]], q[2]],[]
outs: [q[0], q[2]], []
      [q[1], q[2]], []

The general broadcasting rules are:

  • If len(qargs) == 1:

    [q[0], q[1]] -> [q[0]],[q[1]]
  • If len(qargs) == 2:

    [[q[0], q[1]], [r[0], r[1]]] -> [q[0], r[0]], [q[1], r[1]]
    [[q[0]], [r[0], r[1]]]       -> [q[0], r[0]], [q[0], r[1]]
    [[q[0], q[1]], [r[0]]]       -> [q[0], r[0]], [q[1], r[0]]
  • If len(qargs) >= 3:

    [q[0], q[1]], [r[0], r[1]],  ...] -> [q[0], r[0], ...], [q[1], r[1], ...]

Parameters

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

Returns

A tuple with single arguments.

Raises

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

Return type

Iterable[tuple[list, list]]

control

control(num_ctrl_qubits=1, label=None, ctrl_state=None, annotated=False)

GitHub

Return a multi-controlled-X gate with more control lines.

Parameters

  • num_ctrl_qubits (int) – number of control qubits.
  • label (str | None) – An optional label for the gate [Default: None]
  • ctrl_state (str |int | None) – control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s.
  • annotated (bool) – indicates whether the controlled gate should be implemented as an annotated gate.

Returns

controlled version of this gate.

Return type

ControlledGate

copy

copy(name=None)

GitHub

Copy of the instruction.

Parameters

name (str) – name to be given to the copied circuit, if None then the name stays the same.

Returns

a copy of the current instruction, with the name updated if it was provided

Return type

qiskit.circuit.Instruction

get_num_ancilla_qubits

static get_num_ancilla_qubits(num_ctrl_qubits, mode='noancilla')

GitHub

Get the number of required ancilla qubits without instantiating the class.

This staticmethod might be necessary to check the number of ancillas before creating the gate, or to use the number of ancillas in the initialization.

Deprecated since version 1.3_pending

The method qiskit.circuit.library.standard_gates.x.MCXGate.get_num_ancilla_qubits() is pending deprecation as of Qiskit 1.3. It will be marked deprecated in a future release, and then removed no earlier than 3 months after the release date. For an MCXGate it is no longer possible to know the number of ancilla qubits that would be eventually used by the transpiler when the gate is created. Instead, it is recommended to use MCXGate and let HighLevelSynthesis choose the best synthesis method depending on the number of ancilla qubits available. However, if a specific synthesis method using a specific number of ancilla qubits is require, one can create a custom gate by calling the corresponding synthesis function directly.

Parameters

  • num_ctrl_qubits (int) –
  • mode (str) –

Return type

int

inverse

inverse(annotated=False)

GitHub

Invert this gate. The MCX is its own inverse.

Parameters

annotated (bool) – 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 this gate is self-inverse.

Returns

inverse gate (self-inverse).

Return type

MCXGate

is_parameterized

is_parameterized()

GitHub

Return whether the Instruction contains compile-time parameters.

power

power(exponent, annotated=False)

GitHub

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.

Parameters

  • exponent (float) – the power to raise the gate to
  • annotated (bool) – 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.

Returns

An operation implementing gate^exponent

Raises

CircuitError – If gate is not unitary

repeat

repeat(n)

GitHub

Creates an instruction with self repeated :math`n` times.

Parameters

n (int) – Number of times to repeat the instruction

Returns

Containing the definition.

Return type

qiskit.circuit.Instruction

Raises

CircuitError – If n < 1.

reverse_ops

reverse_ops()

GitHub

For a composite instruction, reverse the order of sub-instructions.

This is done by recursively reversing all sub-instructions. It does not invert any gate.

Returns

a new instruction with

sub-instructions reversed.

Return type

qiskit.circuit.Instruction

soft_compare

soft_compare(other)

GitHub

Soft comparison between gates. Their names, number of qubits, and classical bit numbers must match. The number of parameters must match. Each parameter is compared. If one is a ParameterExpression then it is not taken into account.

Parameters

other (instruction) – other instruction.

Returns

are self and other equal up to parameter expressions.

Return type

bool

to_matrix

to_matrix()

GitHub

Return a Numpy.array for the gate unitary matrix.

Returns

if the Gate subclass has a matrix definition.

Return type

np.ndarray

Raises

CircuitError – If a Gate subclass does not implement this method an exception will be raised when this base class method is called.

to_mutable

to_mutable()

GitHub

Return a mutable copy of this gate.

This method will return a new mutable copy of this gate instance. If a singleton instance is being used this will be a new unique instance that can be mutated. If the instance is already mutable it will be a deepcopy of that instance.

validate_parameter

validate_parameter(parameter)

GitHub

Gate parameters should be int, float, or ParameterExpression

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