# Coherence

Quantum coherence is a desired property for a qubit. Its coherence time – the duration of the qubit coherence – is used to make quality comparisons between qubits. Coherence tells us something about how long a qubit retains its information, and thus dictates some sort of lifetime. In this video, Ph.D. student Jonas Helsen (QuTech) introduces this concept and its meaning.

## Prerequisite knowledge

## Further thinking

What do you think can improve the coherence of a qubit? Can you think of what decoheres a qubit?

## Further reading

For an extensive overview of quantum coherence and how a qubit loses its information to the environment, we recommend taking a look at the Wikipedia page on quantum decoherence. That page does an excellent job of explaining all the low-level details.

For those looking for an expert insight in quantum coherence, take a look at this insights issue of Nature on Quantum coherence (Vol. 453, No. 7198 pp 1003–1049)