Clocking Single Photons

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Science  15 Jan 2010:
Vol. 327, Issue 5963, pp. 251
DOI: 10.1126/science.327.5963.251-b

Quantum information processing requires a protocol for transferring data between memories comprising atomic energy states. Light, in the form of single photons, is the natural candidate for such applications: Photons can couple to the atomic memories, move fast, and remain relatively robust against noise. Though generating single photons is not a big problem, generating them on demand is. Melholt Nielsen et al. demonstrate a technique based on a modification of spontaneous parametric down-conversion, wherein two entangled photons are generated in a nonlinear optical crystal, and one of the photons is heralded by the detection of the other. Although such a process is usually stochastic, the authors show that by pumping an optical parametric oscillator under certain conditions, they can control the generation of single photons deterministically. The quality and properties of the heralded single photons, as well as the inherent tunability of the process, should make it simpler to implement quantum information protocols.

Opt. Lett. 34, 3872 (2009).

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