--- title: MCXVChain (v1.3) description: API reference for qiskit.circuit.library.MCXVChain in qiskit v1.3 source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/1.3/qiskit.circuit.library.MCXVChain --- # MCXVChain *class* `qiskit.circuit.library.MCXVChain(num_ctrl_qubits=None, dirty_ancillas=False, label=None, ctrl_state=None, *, duration=None, unit='dt', _base_label=None, relative_phase=False, action_only=False)` [GitHub](https://github.com/Qiskit/qiskit/tree/stable/1.3/qiskit/circuit/library/standard_gates/x.py#L1401-L1529) Bases: [`MCXGate`](/docs/api/qiskit/1.3/qiskit.circuit.library.MCXGate "qiskit.circuit.library.standard_gates.x.MCXGate") Implement the multi-controlled X gate using a V-chain of CX gates. > **Deprecated since version 1.3\_pending** > > The class `qiskit.circuit.library.standard_gates.x.MCXVChain` 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. It is recommended to use MCXGate and let HighLevelSynthesis choose the best synthesis method depending on the number of ancilla qubits available. If this specific synthesis method is required, one can specify it using the high-level-synthesis plugins n\_clean\_m15 (using clean ancillas) or n\_dirty\_i15 (using dirty ancillas) for MCX gates. Alternatively, one can use synth\_mcx\_n\_dirty\_i15 and synth\_mcx\_n\_clean\_m15 to construct the gate directly. **Parameters** - **dirty\_ancillas** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – when set to `True`, the method applies an optimized multicontrolled-X gate up to a relative phase using dirty ancillary qubits with the properties of lemmas 7 and 8 from arXiv:1501.06911, with at most 8\*k - 6 CNOT gates. For k within the range \{1, …, ceil(n/2)}. And for n representing the total number of qubits. - **relative\_phase** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – when set to `True`, the method applies the optimized multicontrolled-X gate up to a relative phase, in a way that, by lemma 7 of arXiv:1501.06911, the relative phases of the `action part` cancel out with the phases of the `reset part`. - **action\_only** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – when set to `True`, the method applies only the action part of lemma 8 from arXiv:1501.06911. - **num\_ctrl\_qubits** (*Optional\[*[*int*](https://docs.python.org/3/library/functions.html#int)*]*) – - **label** (*Optional\[*[*str*](https://docs.python.org/3/library/stdtypes.html#str)*]*) – - **ctrl\_state** (*Optional\[Union\[*[*str*](https://docs.python.org/3/library/stdtypes.html#str)*,* [*int*](https://docs.python.org/3/library/functions.html#int)*]]*) – ## 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`](#qiskit.circuit.library.MCXVChain.base_class "qiskit.circuit.library.MCXVChain.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`](/docs/api/qiskit/1.3/qiskit.transpiler.Target "qiskit.transpiler.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: ```python >>> 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. ### condition The classical condition on the instruction. > **Deprecated since version 1.3.0** > > The property `qiskit.circuit.instruction.Instruction.condition` is deprecated as of qiskit 1.3.0. It will be removed in 2.0.0. ### condition\_bits Get Clbits in condition. > **Deprecated since version 1.3.0** > > The property `qiskit.circuit.instruction.Instruction.condition_bits` is deprecated as of qiskit 1.3.0. It will be removed in 2.0.0. ### 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`](#qiskit.circuit.library.MCXVChain.ctrl_state "qiskit.circuit.library.MCXVChain.ctrl_state"), the returned definition is conjugated with X without changing the internal `_definition`. ### duration Get the duration. > **Deprecated since version 1.3.0** > > The property `qiskit.circuit.instruction.Instruction.duration` is deprecated as of qiskit 1.3.0. It will be removed in Qiskit 2.0.0. ### 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: > \ where \ is the gate name for the default case of closed control qubits and \ 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](https://docs.python.org/3/library/functions.html#int) ### num\_qubits Return the number of qubits. ### params Get parameters from base\_gate. **Returns** List of gate parameters. **Return type** [list](https://docs.python.org/3/library/stdtypes.html#list) **Raises** [**CircuitError**](/docs/api/qiskit/1.3/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – Controlled gate does not define a base gate ### unit Get the time unit of duration. > **Deprecated since version 1.3.0** > > The property `qiskit.circuit.instruction.Instruction.unit` is deprecated as of qiskit 1.3.0. It will be removed in Qiskit 2.0.0. ## Methods ### get\_num\_ancilla\_qubits *static* `get_num_ancilla_qubits(num_ctrl_qubits, mode='v-chain')` [GitHub](https://github.com/Qiskit/qiskit/tree/stable/1.3/qiskit/circuit/library/standard_gates/x.py#L1505-L1508) Get the number of required ancilla qubits. **Parameters** - **num\_ctrl\_qubits** ([*int*](https://docs.python.org/3/library/functions.html#int)) – - **mode** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – ### inverse `inverse(annotated=False)` [GitHub](https://github.com/Qiskit/qiskit/tree/stable/1.3/qiskit/circuit/library/standard_gates/x.py#L1485-L1503) Invert this gate. The MCX is its own inverse. **Parameters** **annotated** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – when set to `True`, this is typically used to return an [`AnnotatedOperation`](/docs/api/qiskit/1.3/qiskit.circuit.AnnotatedOperation "qiskit.circuit.AnnotatedOperation") with an inverse modifier set instead of a concrete [`Gate`](/docs/api/qiskit/1.3/qiskit.circuit.Gate "qiskit.circuit.Gate"). However, for this class this argument is ignored as this gate is self-inverse. **Returns** inverse gate (self-inverse). **Return type** [MCXVChain](#qiskit.circuit.library.MCXVChain "qiskit.circuit.library.MCXVChain")