MCXRecursive
class qiskit.circuit.library.MCXRecursive(num_ctrl_qubits=None, label=None, ctrl_state=None, *, duration=None, unit='dt', _base_label=None)
Bases: MCXGate
Implement the multi-controlled X gate using recursion.
Using a single clean ancilla qubit, the multi-controlled X gate is split into four sub-registers, each one of them uses the V-chain method.
The method is based on Lemma 9 of [2], first shown in Lemma 7.3 of [1].
References
- Barenco et al., 1995. https://arxiv.org/pdf/quant-ph/9503016.pdf
- Iten et al., 2015. https://arxiv.org/abs/1501.06911
Create new MCX gate.
Attributes
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
TrueIn 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.
condition
The classical condition on the instruction.
condition_bits
Get Clbits in condition.
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.
duration
Get the duration.
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
num_qubits
Return the number of qubits.
params
Get parameters from base_gate.
Returns
List of gate parameters.
Return type
Raises
CircuitError – Controlled gate does not define a base gate
unit
Get the time unit of duration.
Methods
get_num_ancilla_qubits
static get_num_ancilla_qubits(num_ctrl_qubits, mode='recursion')
Get the number of required ancilla qubits.
inverse
inverse(annotated=False)
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