qiskit.circuit.library.CXGate

class CXGate(label=None, ctrl_state=None)

Controlled-X gate.

Circuit symbol:

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

Matrix representation:

\[\begin{split}CX\ q_0, q_1 = I \otimes |0\rangle\langle0| + X \otimes |1\rangle\langle1| = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \\ 0 & 1 & 0 & 0 \end{pmatrix}\end{split}\]

Nota

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: ──■──

\[\begin{split}CX\ q_1, q_0 = |0 \rangle\langle 0| \otimes I + |1 \rangle\langle 1| \otimes X = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \end{pmatrix}\end{split}\]

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.

__init__(label=None, ctrl_state=None)

Create new CX gate.

Methods

__init__([label, ctrl_state])	Create new CX gate.
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.
c_if(classical, val)	Add classical condition on register classical and value val.
control([num_ctrl_qubits, label, ctrl_state])	Return a controlled-X gate with more control lines.
copy([name])	Copy of the instruction.
inverse()	Return inverted CX gate (itself).
is_parameterized()	Return True .IFF.
mirror()	DEPRECATED: use instruction.reverse_ops().
power(exponent)	Creates a unitary gate as gate^exponent.
qasm()	Return a default OpenQASM string for the instruction.
repeat(n)	Creates an instruction with gate repeated n amount of times.
reverse_ops()	For a composite instruction, reverse the order of sub-instructions.
to_matrix()	Return a numpy.array for the CX gate.
validate_parameter(parameter)	Gate parameters should be int, float, or ParameterExpression

Attributes

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.
duration	Get the duration.
label	Return gate label
num_ctrl_qubits	Get number of control qubits.
params	Get parameters from base_gate.
unit	Get the time unit of duration.

add_decomposition(decomposition)

Add a decomposition of the instruction to the SessionEquivalenceLibrary.

assemble()

Assemble a QasmQobjInstruction

Tipo de retorno

Instruction

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], ...]
  

Parâmetros

• qargs (List) – List of quantum bit arguments.

• cargs (List) – List of classical bit arguments.

Tipo de retorno

Tuple[List, List]

Retorna

A tuple with single arguments.

Levanta

CircuitError – If the input is not valid. For example, the number of arguments does not match the gate expectation.

c_if(classical, val)

Add classical condition on register classical and value val.

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

Return a controlled-X gate with more control lines.

Parâmetros

• 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.

Retorna

controlled version of this gate.

Tipo de retorno

ControlledGate

copy(name=None)

Copy of the instruction.

Parâmetros

name (str) – name to be given to the copied circuit, if None then the name stays the same.

Retorna

a copy of the current instruction, with the name

updated if it was provided

Tipo de retorno

qiskit.circuit.Instruction

property ctrl_state

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

Tipo de retorno

int

property decompositions

Get the decompositions of the instruction from the SessionEquivalenceLibrary.

property 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.

Tipo de retorno

List

property duration

Get the duration.

inverse()

Return inverted CX gate (itself).

is_parameterized()

Return True .IFF. instruction is parameterized else False

property label

Return gate label

Tipo de retorno

str

mirror()

DEPRECATED: use instruction.reverse_ops().

Retorna

a new instruction with sub-instructions

reversed.

Tipo de retorno

qiskit.circuit.Instruction

property num_ctrl_qubits

Get number of control qubits.

Retorna

The number of control qubits for the gate.

Tipo de retorno

int

property params

Get parameters from base_gate.

Retorna

List of gate parameters.

Tipo de retorno

list

Levanta

CircuitError – Controlled gate does not define a base gate

power(exponent)

Creates a unitary gate as gate^exponent.

Parâmetros

exponent (float) – Gate^exponent

Retorna

To which to_matrix is self.to_matrix^exponent.

Tipo de retorno

qiskit.extensions.UnitaryGate

Levanta

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];).

repeat(n)

Creates an instruction with gate repeated n amount of times.

Parâmetros

n (int) – Number of times to repeat the instruction

Retorna

Containing the definition.

Tipo de retorno

qiskit.circuit.Instruction

Levanta

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.

Retorna

a new instruction with

sub-instructions reversed.

Tipo de retorno

qiskit.circuit.Instruction

to_matrix()

Return a numpy.array for the CX gate.

property unit

Get the time unit of duration.

validate_parameter(parameter)

Gate parameters should be int, float, or ParameterExpression