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# CHGate¶

class CHGate(label=None, ctrl_state=None)[source]

Bases : ControlledGate

Applies a Hadamard on the target qubit if the control is in the $$|1\rangle$$ state.

Can be applied to a QuantumCircuit with the ch() method.

Circuit symbol:

q_0: ──■──
┌─┴─┐
q_1: ┤ H ├
└───┘


Matrix Representation:

$\begin{split}CH\ q_0, q_1 = I \otimes |0\rangle\langle 0| + H \otimes |1\rangle\langle 1| = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & \frac{1}{\sqrt{2}} & 0 & \frac{1}{\sqrt{2}} \\ 0 & 0 & 1 & 0 \\ 0 & \frac{1}{\sqrt{2}} & 0 & -\frac{1}{\sqrt{2}} \end{pmatrix}\end{split}$

Note

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: ┤ H ├
└─┬─┘
q_1: ──■──

$\begin{split}CH\ q_1, q_0 = |0\rangle\langle 0| \otimes I + |1\rangle\langle 1| \otimes H = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & \frac{1}{\sqrt{2}} & \frac{1}{\sqrt{2}} \\ 0 & 0 & \frac{1}{\sqrt{2}} & -\frac{1}{\sqrt{2}} \end{pmatrix}\end{split}$

Create new CH gate.

Methods Defined Here

 inverse Return inverted CH gate (itself).

Attributes

condition_bits

Get Clbits in condition.

Type renvoyé

List[Clbit]

ctrl_state

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

Type renvoyé

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.

Type renvoyé

List

duration

Get the duration.

label

Return instruction label

Type renvoyé

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.

Type renvoyé

str

num_clbits

Return the number of clbits.

num_ctrl_qubits

Get number of control qubits.

Renvoie

The number of control qubits for the gate.

Type renvoyé

int

num_qubits

Return the number of qubits.

params

Get parameters from base_gate.

Renvoie

List of gate parameters.

Type renvoyé

list

Lève

CircuitError – Controlled gate does not define a base gate

unit

Get the time unit of duration.