Quantum Teleportation

Entire quantum particles can be "sent" from one place to another over any distance. The process starts with a sender and a receiver, Alice and Bob. The pair are on opposite sides of the universe but are in possession of photons A and B, respectively, which are entangled. Alice also holds photon C, which is in a state that she wants to teleport to Bob. Entangled particles have the property that a measurement on one immediately determines the state of the other. If Alice performs a procedure that entangles photons A and C, photon B, held by Bob, is forced to adopt the original state, a particular polarization, say, of photon C. Bob can only measure this state if Alice sends him details of the type of experiment he must do to get the message, and this can only be done at or below the speed of light. Although only the quantum state of photon C is teleported, when photon B adopts this state, it cannot be distinguished from photon C. To all intents and purposes, it has become photon C. This is what physicists mean when they say photon C has been teleported from Alice to Bob.

Teleportation was first demonstrated by a group of researchers at the University of Innsbruck using the experimental setup shown here. Pairs of entangled photons, with polarization orthogonal to each other, are generated by splitting an ultraviolet laser pulse using a crystal called a parametric down-coverter. One of the pair (photon A) is sent to Alice while the other (photon B) is sent to Bob. Meanwhile, a message photon (C) is prepared in a state that is to be teleported to Bob-- in this case, 45-degree polarization. This is sent to Alice and arrives coincidentally with photon A at a beam-splitter. If the photons leave the splitter and strike both detectors, they have become entangled, and Alice sends notice of the entanglement to Bob. Bob can then carry out a measurement on photon B to confirm that it is in the 45-degree polarization state that the message photon C started off in.

 Alıntı: http://www.spectrum.ieee.org/WEBONLY/publicfeature/feb01/quantsb2.html

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