A solid-state light–matter interface at the single-photon level

To realize scalable quantum information networks, it will be important to develop techniques for storage and retrieval of light at the single photon level. Quantum interfaces between light and matter have been demonstrated, but mainly with atomic gases that involve sophisticated schemes to trap the atoms. This paper demonstrates a potentially more practical approach; coherent and reversible mapping of a light field with less than one photon per pulse onto an ensemble of ∼107 atoms naturally trapped in a solid state medium. The state of the light is mapped onto collective atomic excitations on an optical transition and stored for a pre-programmed time up of to one microsecond before being retrieved again.