ControlledGate

class ControlledGate(name, num_qubits, params, label=None, num_ctrl_qubits=1, definition=None, ctrl_state=None)

Controlled unitary gate.

Create a new ControlledGate. In the new gate the first num_ctrl_qubits of the gate are the controls.

Parameters

• name (str) – The name of the gate.

• num_qubits (int) – The number of qubits the gate acts on.

• params (List) – A list of parameters for the gate.

• label (Optional[str]) – An optional label for the gate.

• num_ctrl_qubits (Optional[int]) – Number of control qubits.

• definition (Optional[List[Tuple[Gate, List[Qubit], List[Clbit]]]]) – A list of gate rules for implementing this gate. The elements of the list are tuples of (Gate(), [qubit_list], [clbit_list]).

• ctrl_state (Union[int, str, None]) – The control state in decimal or as a bitstring (e.g. ‘111’). If specified as a bitstring the length must equal num_ctrl_qubits, MSB on left. If None, use 2**num_ctrl_qubits-1.

Raises

• CircuitError – If num_ctrl_qubits >= num_qubits.

• CircuitError – ctrl_state < 0 or ctrl_state > 2**num_ctrl_qubits.

Examples:

Create a controlled standard gate and apply it to a circuit.

from qiskit import QuantumCircuit, QuantumRegister
from qiskit.circuit.library.standard_gates import HGate

qr = QuantumRegister(3)
qc = QuantumCircuit(qr)
c3h_gate = HGate().control(2)
qc.append(c3h_gate, qr)
qc.draw()

           
q0_0: ──■──
        │  
q0_1: ──■──
      ┌─┴─┐
q0_2: ┤ H ├
      └───┘

Create a controlled custom gate and apply it to a circuit.

from qiskit import QuantumCircuit, QuantumRegister
from qiskit.circuit.library.standard_gates import HGate

qc1 = QuantumCircuit(2)
qc1.x(0)
qc1.h(1)
custom = qc1.to_gate().control(2)

qc2 = QuantumCircuit(4)
qc2.append(custom, [0, 3, 1, 2])
qc2.draw()

                   
q_0: ──────■───────
     ┌─────┴──────┐
q_1: ┤0           ├
     │  circuit12 │
q_2: ┤1           ├
     └─────┬──────┘
q_3: ──────■───────
                   

Attributes

ControlledGate.ctrl_state	Return the control state of the gate as a decimal integer.
ControlledGate.decompositions	Get the decompositions of the instruction from the SessionEquivalenceLibrary.
ControlledGate.definition	Return definition in terms of other basic gates.
ControlledGate.label	Return gate label
ControlledGate.params	return instruction params.

Methods

ControlledGate.add_decomposition(decomposition)	Add a decomposition of the instruction to the SessionEquivalenceLibrary.
ControlledGate.assemble()	Assemble a QasmQobjInstruction
ControlledGate.broadcast_arguments(qargs, cargs)	Validation and handling of the arguments and its relationship.
ControlledGate.c_if(classical, val)	Add classical condition on register classical and value val.
ControlledGate.control([num_ctrl_qubits, …])	Return controlled version of gate.
ControlledGate.copy([name])	Copy of the instruction.
ControlledGate.inverse()	Invert this gate by calling inverse on the base gate.
ControlledGate.is_parameterized()	Return True .IFF.
ControlledGate.mirror()	For a composite instruction, reverse the order of sub-gates.
ControlledGate.power(exponent)	Creates a unitary gate as gate^exponent.
ControlledGate.qasm()	Return a default OpenQASM string for the instruction.
ControlledGate.repeat(n)	Creates an instruction with gate repeated n amount of times.
ControlledGate.to_matrix()	Return a Numpy.array for the gate unitary matrix.