ControlledGate

class qiskit.circuit.ControlledGate(name, num_qubits, params, label=None, num_ctrl_qubits=1, definition=None, ctrl_state=None, base_gate=None, duration=None, unit=None, *, _base_label=None)

Bases: Gate

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['QuantumCircuit']) – A list of gate rules for implementing this gate. The elements of the list are tuples of (Gate(), [qubit_list], [clbit_list]).

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

• base_gate (Optional[Gate]) – Gate object to be controlled.

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('mpl')

(Source code)

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('mpl')

(Source code)

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 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)
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.

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 self.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_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

unit

Get the time unit of duration.

Methods

add_decomposition(decomposition)

Add a decomposition of the instruction to the SessionEquivalenceLibrary.

assemble()

Assemble a QasmQobjInstruction

broadcast_arguments(qargs, cargs)

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]]

c_if(classical, val)

Set a classical equality condition on this instruction between the register or cbit classical and value val.

Note

This is a setter method, not an additive one. Calling this multiple times will silently override any previously set condition; it does not stack.

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

Return controlled version of gate. See ControlledGate for usage.

Parameters:

• num_ctrl_qubits (int) – number of controls to add to gate (default: 1)

• label (str | None) – optional gate label

• ctrl_state (int | str | None) – The control state in decimal or as a bitstring (e.g. '111'). If None, use 2**num_ctrl_qubits-1.

Returns:

Controlled version of gate. This default algorithm uses num_ctrl_qubits-1 ancilla qubits so returns a gate of size num_qubits + 2*num_ctrl_qubits - 1.

Return type:

qiskit.circuit.ControlledGate

Raises:

QiskitError – unrecognized mode or invalid ctrl_state

copy(name=None)

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

inverse()

Invert this gate by calling inverse on the base gate.

Return type:

ControlledGate

is_parameterized()

Return True .IFF. instruction is parameterized else False

power(exponent)

Creates a unitary gate as gate^exponent.

Parameters:

exponent (float) – Gate^exponent

Returns:

To which to_matrix is self.to_matrix^exponent.

Return type:

.library.UnitaryGate

Raises:

CircuitError – If Gate is not unitary

qasm()

Return a default OpenQASM string for the instruction.

Derived instructions may override this to print in a different format (e.g. measure q[0] -> c[0];).

Deprecated since version 0.25.0: The method qiskit.circuit.instruction.Instruction.qasm() is deprecated as of qiskit-terra 0.25.0. It will be removed no earlier than 3 months after the release date. Correct exporting to OpenQASM 2 is the responsibility of a larger exporter; it cannot safely be done on an object-by-object basis without context. No replacement will be provided, because the premise is wrong.

repeat(n)

Creates an instruction with gate repeated n amount of 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()

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(other)

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()

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()

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(parameter)

Gate parameters should be int, float, or ParameterExpression