# ControlledGate

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

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')
```

## Attributes

### 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

### 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

### 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

### add_decomposition

`add_decomposition(decomposition)`

Add a decomposition of the instruction to the SessionEquivalenceLibrary.

### assemble

`assemble()`

Assemble a QasmQobjInstruction

### broadcast_arguments

`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**

**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**

### c_if

`c_if(classical, val)`

Set a classical equality condition on this instruction between the register or cbit `classical`

and value `val`

.

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

`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**

**Raises**

**QiskitError** – unrecognized mode or invalid ctrl_state

### copy

`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**

### inverse

### is_parameterized

`is_parameterized()`

Return True .IFF. instruction is parameterized else False

### power

`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**

**Raises**

**CircuitError** – If Gate is not unitary

### qasm

`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];`

).

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

`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**

**Raises**

**CircuitError** – If n < 1.

### reverse_ops

`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**

### soft_compare

`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**

### to_matrix

`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.

### validate_parameter

`validate_parameter(parameter)`

Gate parameters should be int, float, or ParameterExpression