Computing Library › Quantum Logic Gates
Quantum Logic Gates
Identity Gate (I)
The identity gate leaves a qubit unchanged — the do-nothing operation and the algebraic anchor for every other gate.
Matrix
Unitary matrix
1001
Circuit symbol
Action on basis states
| input | output |
|---|---|
| |0⟩ | |0⟩ |
| |1⟩ | |1⟩ |
How it works
I is the 2×2 identity matrix. It is Hermitian and unitary, its own inverse, and commutes with every gate. In practice it marks an idle time-step on a wire (where a real qubit still decoheres), so compilers track it for timing and error budgeting.
In code (Qiskit)
python
from qiskit import QuantumCircuit
qc = QuantumCircuit(1)
qc.id(0)single-qubitHermitianClifford