Researchers Build an All-Optical Transistor
A team of MIT, Harvard, and the Vienna University of Technology scientists built an all-optical transistor. Using ultracold atoms researchers were able to demonstrate that a single gate photon can control the transmission of hundreds of signal photons.
For more information, see the Science article(1) and the MIT Press Release(2).
(1) W. Chen, K.M. Beck, R. Bücker, M. Gullans, M. D. Lukin, H.a Tanji-Suzuki, and V. Vuletić, "All-Optical Switch and Transistor Gated by One Stored Photon," Science, 341:6147, pp. 768-770 (16 August 2013), DOI: 10.1126/science.1238169).
(2) L. Hardesty, "Researchers build an all-optical transistor," MIT News, 4 July 2013.