Quantum Teleportation Achieved Over 7km of Cable (sciencealert.com)

An anonymous reader quotes a report from ScienceAlert: Quantum teleportation just moved out of the lab and into the real world, with two independent teams of scientists successfully sending quantum information across several kilometers of optical fiber networks in Calgary, Canada, and Hefei, China. Quantum teleportation relies on a strange phenomenon called quantum entanglement. 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." In the latest experiments, both published in Nature Photonics (here and here), the teams had slightly different set-ups and results. But what they both had in common is the fact that they teleported their information across existing optical fiber networks -- which is important if we ever want to build useable quantum communication systems. To understand the experiments, Anil Ananthaswamy over at New Scientist nicely breaks it down like this: picture three people involved -- Alice, Bob, and Charlie. 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. The Canadian experiment followed this same process, and was able to send quantum information over 6.2 km of Calgary's fiber optic network that's not regularly in use.

Comments

Re:I Think this article might be a bit misleading.

[Rei]

Given that none of the articles, as far as I saw, said anything about faster than light communication, and one explicitly disavowed the concept, I think you're projecting your own mistaken conceptions here.

And your friend is correct - quantum teleportation has nothing to do with faster than light communication, as you can neither determine to what form the waveform has collapsed, nor whether one side has already collapsed it. It's effectively** equivalent to having two identical letters containing a random message sealed in an envelope, taking them to different locations, and opening them at the same time. Both sides will get the same random message at the same time, but it provides no means for conveying information faster than light. It is however useful for keysharing.

** In the real world, what is written inside the "envelopes" isn't determined until it's actually observed. But it works out to the same net effect.

Re:Explaining FTL non-information travel

[wonkey_monkey]

One could easily sweep the spot of a laser across the surface of the moon faster than a light-speed signal would do so.