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I have a college-level understanding of Physics. A recent study from the University of Delft in the Netherlands that seems to suggest that quantum teleportation of information (as in "communication of information") is possible left me confused.

I read:

and the answers in both threads suggest that one cannot use quantum teleportation for superluminal communication in the traditional/practical sense of the word.

The publications in Nature & Science are here and here.

Perhaps more interestingly, the university site (in dutch): http://www.tudelft.nl/nl/actueel/laatste-nieuws/artikel/detail/tu-delft-legt-fundament-voor-quantum-internet/ the statement ends with a quote from the authors saying:

"Ten tweede biedt teleportatie de mogelijkheid om informatie volledig veilig te versturen. Bij teleportatie reist de informatie niet door de tussenliggende ruimte en kan daarom niet worden afgeluisterd".

which can be translated as: "Secondly, teleportation offers the possibility to transmit information in a completely safe way. With teleportation the information does not travel through the space in between thus precluding eaves dropping."

Can these results be understood as a claim that superluminal communication (again, in the traditional/practical sense) is more feasible that previously believed?

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  • $\begingroup$ They want to create the phyisically uncrackable channel. The speeds won't be superluminal. I think you missunderstood only the motivation of the research. It's security and computing, for now at least. $\endgroup$ – WalyKu Jun 6 '14 at 9:53
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    $\begingroup$ The superluminal bit is still to be tested. But as the distance achieved is 10 nanoseconds, we can now accurately measure the actual time the teleportation takes. $\endgroup$ – MSalters Jun 6 '14 at 10:28
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I haven't read the links in any detail, but it might help you to understand that teleportation also requires classical communication to work. (Sorry if you already understood this.) In order to teleport information using entanglement one must also send a physical carrier of information, which is of course limited by Einstein's laws of relativity to travel slower than the speed of light. Perhaps the authors are referring to the fact that intercepting the physical information carrier does not give access to the quantum state that was teleported, because the eavesdropper does not share an entangled pair of systems with the sender.

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    $\begingroup$ Still not convinced it cannot be used. If I can create a pair of devices (receiver and transmiter) even if the transmiter only sends random information to the receiver we can get two states: transmiting/no transmiting and that is enought the create a bit of information $\endgroup$ – jean Jun 6 '14 at 11:45
  • $\begingroup$ @jean The point of quantum teleportation is to send an (unknown) quantum state. In fact, two (classical) bits need to be sent in order to teleport the quantum state of a single qubit. Although you are correct that the physical information carrier can be interpreted as having some information content even for the eavesdropper, there is no way for them to actually reconstruct the quantum state. $\endgroup$ – Mark Mitchison Jun 7 '14 at 12:46
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Entanglement and teleportation do not involve non-local transfer of information. The information that is sent does travel through space and time instantiated in some physical system. The observables of the systems that contain the information depend on the information being sent, but the expectation value of those observables does not depend on the information, see:

http://arxiv.org/abs/quant-ph/9906007

http://arxiv.org/abs/1109.6223.

Since the information is not sent in a non-local manner it can't be used for superluminal communication.

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