Given that various answers here at Physics assert that information isn't transferred (such as this Phys.SE post), and given recent announcements, does this invalidate our understanding of what's happening? Is information actually translated superluminally?


The article is extremely misleading and wrong in many important aspects. Don't read it.

Basically, quantum entanglement means that two particles are inextricably linked, so that measuring the state of one immediately affects the state of the other, no matter how far apart the two are - which led Einstein to call entanglement "spooky action at a distance".

You'll read this statement quite often. Depending on the interpretation it's not completely wrong. If you subscribe to Bohmian mechanics, there is a nonlocal effect (however, it's a randomised effect that cannot be used for signal transmission). If you subscribe to almost any other interpretation, there is no nonlocal effect, hence no "spooky action" at all. Since most people don't subscribe to Bohmian mechanics, this is mostly wrong.

Alice and Bob want to share cryptographic keys, and to do that, they need Charlie's help. Alice sends a particle to Charlie, while Bob entangles two particles and sends just one of them to Charlie.

Charlie then measures the two particles he's received from each of them, so that they can no longer be differentiated - and that results in the quantum state of Alice's particle being transferred to Bob's entangled particle.

So basically, the quantum state of Alice's particle eventually ends up in Bob's particle, via a way station in the form of Charlie.

That's just wrong, that's not how it works. The description is quite imprecise and the crucial step is missing: Charlie needs to send the result of the measurement to Bob, and this is done via telephone or whatever (classical communication). Bob then needs to perform a quantum operation conditioned on the outcome. Only then can he be sure to have Alice's state.


And while many people assume that quantum teleportation would result in faster communication, in reality, decrypting the quantum state of the entangled particle requires a key, which needs to be sent via regular, slow communication - so quantum teleportation wouldn't actually be any faster than the internet we already have, just more secure.

That's also wrong. The whole point is to distribute the key via teleportation (this is called quantum key distribution) not the message. As mentioned above, it does indeed require classical communication. The human message - probably a bitstring - will then be send via the usual channels but encrypted with the quantum key.

If the key was shared via classical communication, the whole protocol would be exactly as secure as the classical key distribution, so we wouldn't have to go through all this trouble.

Finally, that is the most important (and correct) part of the article:

But the fact that both teams were able to use existing telecommunications infrastructure to achieve such long-distance teleportation at all is a huge deal - and something that hasn't been done outside of the lab before.

This experiment doesn't give anything new in terms of physics. It's merely implementing a technology in the real world that so far only existed in the lab (and we can achieve teleportation between labs that are farther apart than that). It's a technological achievement more than a scientific breakthrough. That doesn't make it less of an achievement though.

  • $\begingroup$ Excellent, thank you. The article was suspect, but it's good to have an explanation of exactly why it's wrong from someone who understands it. $\endgroup$ – Don Branson Sep 21 '16 at 19:15

No, nothing has occurred that is not predicted by quantum mechanics theory, and quantum mechanics theory does not predict superluminal information transport. Quantum teleportation is not superluminal, and entanglement cannot be used to transport information.

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    $\begingroup$ Can you expand on this? It seems like the author of the article is claiming superluminal transmission of information. Can you be more specific about what invalidates his assertion? $\endgroup$ – Don Branson Sep 21 '16 at 18:50
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    $\begingroup$ Popular science articles don't make scientific claims, working scientists do. If a scientist publishes a peer-reviewed paper that makes such a claim, then you can worry about their argument. If you see it in a popular science article, it simply means that the non-expert author of the article did not get their story straight, and it's not really worth further analysis. $\endgroup$ – Ken G Sep 21 '16 at 19:14

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