Identity channel

In quantum information theory, the identity channel is a noise-free quantum channel. That is, the channel outputs exactly what was put in.^[1]

The identity channel is commonly denoted as $I$, $\mathsf{id}$ or $\mathbb{I}$.

References

1. Wilde, Mark (2013), Quantum Information Theory, Cambridge University Press, p. 618, ISBN 9781107034259.