# 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*(opens in a new tab)) – The name of the gate.**num_qubits**(*int*(opens in a new tab)) – The number of qubits the gate acts on.**params**(*list*(opens in a new tab)) – A list of parameters for the gate.**label**(*Optional[**str*(opens in a new tab)*]*) – An optional label for the gate.**num_ctrl_qubits**(*Optional[**int*(opens in a new tab)*]*) – 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*(opens in a new tab)*,**str*(opens in a new tab)*]]*) – 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

### 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**

### 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**

**qargs**(*list*(opens in a new tab)) – List of quantum bit arguments.**cargs**(*list*(opens in a new tab)) – 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*(opens in a new tab)[tuple(opens in a new tab)[list(opens in a new tab), list(opens in a new tab)]]

### 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*(opens in a new tab)) – number of controls to add to gate (default:`1`

)**label**(*str*(opens in a new tab)*| None*) – optional gate label**ctrl_state**(*int*(opens in a new tab)*|**str*(opens in a new tab)*| 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*(opens in a new tab)) – 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*(opens in a new tab)) – Gate^exponent

**Returns**

To which to_matrix is self.to_matrix^exponent.

**Return type**

.library.UnitaryGate

**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*(opens in a new tab)) – 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.

### to_mutable

`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

`validate_parameter(parameter)`

Gate parameters should be int, float, or ParameterExpression