Y gate

The Y gate flips a qubit and adds a phase: $\vert 0 \rangle$ becomes $i\vert 1 \rangle$ and $\vert 1 \rangle$ becomes $-i\vert 0 \rangle$. It acts on one qubit and takes no parameters. The Circuit panel draws it as Y. Measured straight after it, a qubit that started as 0 reads 1, the same as after an X; the phase shows only once the qubit meets other gates.

Kets such as $\vert 0 \rangle$ name the basis states and rotations are described on the Bloch sphere; the qubits lesson introduces both.

Call

Matrix

On the Bloch sphere this is a half-turn about the Y axis. It is the same operation as ry(π) up to a global phase.

Effect on basis states

Measured straight away, a basis state flips exactly as it does under X; the phases only matter once the qubit meets other gates.

Inverse

Y is its own inverse. Two Y gates in a row on the same qubit cancel.

Usage

from qiskit import QuantumCircuit

qc = QuantumCircuit(1, 1)
qc.y(0)
qc.measure(0, 0)

import { QuantumCircuit } from 'qiskit';

const circuit = QuantumCircuit(1, 1);
circuit.y(0);
circuit.measure(0, 0);

Every shot reads 1.

On IonQ hardware

Y is exactly GPi(0.25), a native gate with its phase a quarter turn from X, so it costs one physical pulse. See How your circuit is compiled.

Related

• X gate
• Z gate
• CY gate
• Gate reference