Switching Light by Vacuum

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Science  02 Sep 2011:
Vol. 333, Issue 6047, pp. 1228-1229
DOI: 10.1126/science.1210104

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When it comes to designing a quantum information network for applications such as computing or cryptography, photons have almost everything: They are fast, cheap, easy to guide and manipulate, and they can even be stored in quantum memories. However, building a switch or shutter that is sensitive to the quantum state of a single photon (in other words, that allows the creation of an all-optical quantum logic gate) is a long-standing and still unsolved problem. The experimental breakthrough reported on page 1266 of this issue by Tanji-Suzuki et al. (1) has brought us substantially closer to a solution. Their method changes the optical transparency of a cloud of cold atoms by using what might appear to be “nothing”—the electric field produced by a small empty cavity that can trap photons. The method causes the cloud to go from opaque to transparent (and back again) with just 10 photons.