# CXGate

*class *`CXGate(label=None, ctrl_state=None)`

Bases: `qiskit.circuit.controlledgate.ControlledGate`

Controlled-X gate.

Can be applied to a `QuantumCircuit`

with the `cx()`

and `cnot()`

methods.

**Circuit symbol:**

```
q_0: ──■──
┌─┴─┐
q_1: ┤ X ├
└───┘
```

**Matrix representation:**

In Qiskit’s convention, higher qubit indices are more significant (little endian convention). In many textbooks, controlled gates are presented with the assumption of more significant qubits as control, which in our case would be q_1. Thus a textbook matrix for this gate will be:

```
┌───┐
q_0: ┤ X ├
└─┬─┘
q_1: ──■──
```

In the computational basis, this gate flips the target qubit if the control qubit is in the $|1\rangle$ state. In this sense it is similar to a classical XOR gate.

$`|a, b\rangle \rightarrow |a, a \oplus b\rangle`$Create new CX gate.

## Methods Defined Here

### control

`CXGate.control(num_ctrl_qubits=1, label=None, ctrl_state=None)`

Return a controlled-X gate with more control lines.

**Parameters**

**num_ctrl_qubits**(*int*) – number of control qubits.**label**(*str or None*) – An optional label for the gate [Default: None]**ctrl_state**(*int or str or None*) – control state expressed as integer, string (e.g. ‘110’), or None. If None, use all 1s.

**Returns**

controlled version of this gate.

**Return type**

### inverse

`CXGate.inverse()`

Return inverted CX gate (itself).

## Attributes

### condition_bits

### ctrl_state

Return the control state of the gate as a decimal integer.

**Return type**

`int`

### 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.

**Return type**

`List`

### duration

Get the duration.

### label

Return instruction label

**Return type**

`str`

### 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.

**Return type**

`str`

### 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.