Skip to content

Identity (I)

Identity gate tile from the Operations catalog

The identity gate does nothing to the qubit's state. It exists so a wire can have an explicit, visible gate - for example to pad a circuit's timing/layout - without changing what the qubit represents.
Qubits 1
Parameters None
Inverse Itself (I is its own inverse)
Also called Identity, No-op

What it does

Applying I leaves every amplitude exactly as it was. It's a genuine gate in the mathematical sense (a valid 1-qubit unitary), it's simply the unitary that changes nothing.

Matrix

\[ I = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix} \]

Action on basis states

  • \( |0\rangle \rightarrow |0\rangle \)
  • \( |1\rangle \rightarrow |1\rangle \)

Example

Placing I on q[0] leaves its state unchanged - useful mainly for visually marking a time step on a wire, or as a starting point before editing a gate's parameters.

Other notations

Naming conventions across ecosystems; exact syntax can vary by library version, and this does not claim to be Qompile's generated output unless otherwise noted.

Language Typical form
OpenQASM 2.0 id q[0];
Qiskit circuit.id[q[0]]
Cirq cirq.I(q[0])
Q# I(q[0]);