All-Optical Switch and Transistor Gated by One Stored Photon

A Single-Photon Gate A long-standing goal in optics is to produce an all-optical transistor, in which the transmission of a light beam can be controlled by a single photon. Using a system in which a cloud of cesium atoms is coupled to an optical cavity, Chen et al. (p. 768, published online 4 July; see the Perspective by Volz and Rauschenbeutel) were able to control transmission through the optical cavity by exciting the atomic ensemble using a “gate” laser pulse. Just one gate photon stored was sufficient to detune the system and switch the transmission of source photons through the cavity. Optical transmission through a cesium-filled cavity can be controlled by a single stored photon. [Also see Perspective by Volz and Rauschenbeutel] The realization of an all-optical transistor, in which 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 realized 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.