Quantum Teleportation – Quantum Teleportation and the No-Communication Theorem

quantum mechanicsquantum-entanglementquantum-informationquantum-teleportation

According to the Wikipedia article for the No-communication theorem:

In very rough terms, the theorem describes a situation that is analogous to two people, each with a radio receiver, listening to a common radio station: it is impossible for one of the listeners to use their radio receiver to send messages to the other listener. This analogy is imprecise, because quantum entanglement suggests that perhaps a message could have been conveyed; the theorem replies 'no, this is not possible'.

According to the Jet Propulsion's recent article on quantum teleportation: http://www.jpl.nasa.gov/news/news.php?feature=4384

they can effect an entangled photon (B) with another photon (A) to change the state of the other entangled photon.

Doesn't this contradict what the no-communication theorem states ?

Best Answer

Quantum teleportation requires a "classical channel" of information to be communicated between the two experimenters, so it doesn't violate the no-communication theorem because that theorem only rules out the possibility that two experimenters could communicate purely by their choice of measurements on parts of an entangled system. Referring to the schematic diagram of quantum teleportation below (from this page), the first experimenter performs a disruptive measurement on the system to be teleported (A) and also performs a measurement on one half (B) of a larger entangled system, then sends data on her measurements in some ordinary classical way (radio waves, an electrical cable, whatever--this is the "Send Data" arrow in the diagram) to the second experimenter, who then uses that data to perform just the right type of measurement on the other half of the entangled system (C) so that its state becomes identical to original state of A the moment before the disruptive measurement.

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