One photon stored in four places at once
Quantum physics: Entangled quartet
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When light passes through two slits to hit a distant screen, a periodic light pattern emerges that is associated with the interference of the waves emanating from the two sources. Some of quantum physics’ deepest mysteries – or, according to the iconic Richard Feynman, its only mystery – arise when that observation is made with a single particle that, although indivisible, must have passed simultaneously through both slits. Recent advances in the storage of single photons in atomic gases  have now enabled a tour-de-force experiment that investigates interference with light stored simultaneously in four spatially distinct atom clouds, as reported on p. xxx of this issue. Chou et al. demonstrate stronger-than-classical correlations (entanglement) in this composite matter-light system, and study how the entanglement gives way to weaker and weaker, and ultimately only classical, correlations.
DepartmentMassachusetts Institute of Technology. Department of Physics
Nature Publishing Group
Vuletic, Vladan. “Quantum physics: Entangled quartet.” Nature 468.7322 (2010): 384-385.
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