qiskit.circuit.library.CXGate¶

class CXGate(label=None, ctrl_state=None)[Quellcode]¶

Controlled-X gate.

Circuit symbol:

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

Matrix representation:

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

Bemerkung

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)[Quellcode]¶: 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

Rückgabetyp: 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], ...]

Parameter

qargs (List) – List of quantum bit arguments.
cargs (List) – List of classical bit arguments.

Rückgabetyp

Tuple[List, List]

Rückgabe

A tuple with single arguments.

Verursacht

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)[Quellcode]¶

Return a controlled-X gate with more control lines.

Parameter

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.

Rückgabe

controlled version of this gate.

Rückgabetyp

ControlledGate

copy(name=None)¶

Copy of the instruction.

Parameter

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

Rückgabe

a copy of the current instruction, with the name: updated if it was provided

Rückgabetyp

qiskit.circuit.Instruction

property ctrl_state¶

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

Rückgabetyp: 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.

Rückgabetyp: List

property duration¶: Get the duration.

inverse()[Quellcode]¶: Return inverted CX gate (itself).

is_parameterized()¶: Return True .IFF. instruction is parameterized else False

property label¶

Return gate label

Rückgabetyp: str

mirror()¶

DEPRECATED: use instruction.reverse_ops().

Rückgabe

a new instruction with sub-instructions: reversed.

Rückgabetyp

qiskit.circuit.Instruction

property num_ctrl_qubits¶

Get number of control qubits.

Rückgabe: The number of control qubits for the gate.
Rückgabetyp: int

property params¶

Get parameters from base_gate.

Rückgabe: List of gate parameters.
Rückgabetyp: list
Verursacht: CircuitError – Controlled gate does not define a base gate

power(exponent)¶

Creates a unitary gate as gate^exponent.

Parameter: exponent (float) – Gate^exponent
Rückgabe: To which to_matrix is self.to_matrix^exponent.
Rückgabetyp: qiskit.extensions.UnitaryGate
Verursacht: 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.

Parameter: n (int) – Number of times to repeat the instruction
Rückgabe: Containing the definition.
Rückgabetyp: qiskit.circuit.Instruction
Verursacht: 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.

Rückgabe

a new instruction with: sub-instructions reversed.

Rückgabetyp

qiskit.circuit.Instruction

to_matrix()[Quellcode]¶: 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