All-Optical Switch and Transistor Gated by One Stored Photon

The realization of an all-optical transistor where one 'gate' photon controls
a 'source' light beam, is a long-standing goal in optics. By stopping a light
pulse in an atomic ensemble contained inside an optical resonator, we realize a
device in which one stored gate photon controls the resonator transmission of
subsequently applied source photons. A weak gate pulse induces bimodal
transmission distribution, corresponding to zero and one gate photons. One
stored gate photon produces fivefold source attenuation, and can be retrieved
from the atomic ensemble after switching more than one source photon. Without
retrieval, one stored gate photon can switch several hundred source photons.
With improved storage and retrieval efficiency, our work may enable various new
applications, including photonic quantum gates, and deterministic multiphoton
entanglement.