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Quantum teleportation over 143 kilometres using active feed-forward
- carbocation 14y agoI confess I haven't read the entire article, but from the abstract I was wondering, why 143 kilometers (they answer this: distance to satellites), and why those two islands (except to maybe show off that they were teleporting in the lap of luxury)? I'm guessing it's because there is no physical link between the two, so it will reduce skeptics' abilities to say "this is a hoax, there is a cable connecting the two stations."
- ricardobeat 14y agoBut quantum teleporting does require a link between the two points. From the Wikipedia article: The prerequisites for quantum teleportation are a qubit that is to be teleported, a conventional communication channel capable of transmitting two classical bits (...) There is no teleporting in the classical meaning of the word, just communication between two locations to make a remote qubit match the (unknown) state of the local one. That state is 'teleported'.
- javert 14y agoThere is no teleporting in the classical meaning of the word So isn't it dishonest to call it teleportation? Even if all the scientists working in this area are calling it that?
- chc 14y agoNo? How on earth is it dishonest to use the technical term for the thing? It doesn't seem any more dishonest than calling the constituent parts of matter "atoms" even though they can actually be split.
- javert 14y agoThe discovery that atoms are not atomic (could be split) came after the term was coined. On the other hand, in this case, a bunch of people decided to call something "teleportation" when it isn't teleportation.
- chc 14y agoAFAIK, it is teleportation -- something is going from one place to another without having to move through the space between them -- but it just isn't what you think of when you think of "teleportation".
- rodly 14y agoIf it is moving from A to B via some physical continuous medium, then it is not teleporting.
- tgb 14y ago(Note: my full qualifications are an on-going Coursera course on quantum computing that covers quantum teleportation lightly. FWIW, I recommend the course.) In vague terms, the process of quantum teleportation is the following: * You have a qubit that you want to transmit to a friend and that you don't know anything about. * create an entangled pair of qubits (such as photons) and separate them. Keep one yourself and give another to your friend. * Now you have two qubits; one entangled with your friends and one that you want to transmit. * Send your two bits through a quantum circuit (the main part being a 'controlled NOT gate'). * Your bit is now entangled with the bit that is entangled with your friends bit. * Measure each of your bits, hence 'collapsing' them. Each measurement gives you a classical bit. * Transmit your two classical bits to your friend over any classical connection. * Your friend then performs an operation on his or her qubit depending on what you send him or her. * Your friend's qubit is now in the state that your original qubit was in. Your original qubit is now in a different state. Call it teleporation if you want; it's not that unlike some sci-fi teleportation constructs of 'beaming' things places. Why bother with this? * It lets you send qubits to distant places that you have only classical channels to (and previously close enough contact share two entangled qubits). * It allows more error-resistant computations: if your qubit is difficult to construct and you wish to perform a difficult operation on it, you can actually have your friend perform the difficult operation on his or her bit - prior to teleportation - and, if it succeeds, you can then proceed with the teleportation. If it doesn't succeed, your friend may try again on another entangled qubit without messing up your difficult-to-prepare qubit. After a success and teleportation, you get the same result (up to a commutator which is usually relatively small and risk-free) as performing the difficult operation on the difficult-to-prepare qubit, but with less risk of messing it up.
- Cushman 14y agoDo you also get upset when biologists talk about "cloning" because they don't mean duplicating an adult like in the movies?
- javert 14y agoNo, because the differentia of the definition of cloning does not reference maturity (age).
- johnpmayer 14y agoSo Wikipedia states the following: "Quantum teleportation is unrelated to the common term teleportation – it does not transport the system itself, and does not concern rearranging particles to copy the form of an object." So, in a nutshell, scientists aren't always incredibly creative when conducting nomenclature. Although some people do find subatomic particles quite strange.
- smosher 14y agoNot in any sense is it dishonest to call it quantum teleportation, since the quantum state is precisely (and only) what is subject to the phenomenon. What is dishonest is the claim that F-T-L communication is possible. The quantum state does not undergo travel during the transmission of the classical signal. The only thing that travels is the classical signal, which is needed to tell you how to read the message (and generally preserve causality in the universe.) The quantum state is teleported as though you had two objects with the selfsame quantum state. Poking one pokes the other.
- javert 14y agoTeleportation is teleportation of matter. So AFAIK you can't call it quantum teleportation, for the same reason you can't call travelling along the road "road flying," i.e., flying is travelling above the ground, not on it.
- smosher 14y agoThe human ability to generalize concepts is amazing, watch—I'll swap out your of matter for of quantum information and suddenly you're up to speed on subject of discourse: "The teleportation of quantum information." Magic! Your language gives you away, you've already done this process in reverse to make your case, so I know you have the power to understand this concept.
- javert 14y agoSo we can use any word to mean anything? This kind of abuse of language has serious consequences in the long run. The language of modern physics is already way too muddled. I don't understand what you're trying to say in the last sentence. But it seems like you're being derisive, which is utterly inappropriate.
- Saavedro 14y agoYou know, in a lot of sci-fis its not implied that teleportation is faster-than-light. Quantum teleportation does meet what does seem to be universal about "teleportation" though, which is that the "original" is necessarily destroyed. That is, it takes a thing, and moves it to another location, rather than copying it.
- javert 14y agoAs far as I can tell, it just replicates the state of a particle in a remote location, using another particle of the same kind. So state is being transfered (i.e., information), but not matter, and nothing is being destroyed. I might be wrong about this, but that's what someone who explained it on hn said.
- moondowner 14y agoBeam me up, Scotty! (I couldn't resist...)
- jstalin 14y agoCould someone translate the abstract into English?
- antimora 14y agoHere is another article that tries putting in English. http://www.zmescience.com/science/physics/physicists-quantum-photons-08092012/ http://www.zmescience.com/science/physics/physicists-quantum...
- dandrews 14y agoCareful with this article. They get it wrong, suggesting the possibility of "instantaneous internet connections". No FTL information transfer allowed, kids.
- alecco 14y agoThe author fails to understand the basics of Quantum Teleportation. Think of it this way: Alice has 2 boxes with the same unknown bit, and sends one of those boxes to Bob. When Alice opens her box she can see the value and Bob can see it too. Something like that. Very good for cryptography (think untamperable shared secret keys) and for some cases of parallel computing. Superluminal (FTL) communication would break Special Theory of Relativity. If anybody achieves that it would be an instant Nobel and front page on every newspaper on the planet. Even a mistake like the FTL neutrinos fiasco earlier this year. Tech journalists tend to skim the abstracts and hype it to sell more clicks/ads.
- newhouseb 14y agoI'm trying to think of a physical analogy to better understand this: Image you (Alice) have a randomly shuffled (say, by god) deck of cards. You cut the deck in half and distribute one half to Bob and keep the other half (such that by knowing one half, you would know the other). Until either of you look at your respective half-deck, the distribution of cards is in a superposition of all possible distributions (a la Schrodinger's cat). Where the analogy breaks down (thereby illustration what's special about Quantum Teleportation), is that as soon as Alice flips her cards, Bob's cards flip as well (and visa versa). Thus by the time the cards got to Bob, Bob would be able to detect that someone else could have read the cards and thus the information may have been compromised. (This is kind of how I remember quantum cryptography to work, actually). Does this analogy make sense? My physics background is pretty weak...
- newhouseb 14y agoIs it incorrect to say that, with quantum teleportation - while faster than light travel of _matter_ is impossible, faster than light travel of _information_ is possible provided that you have previously shipped the endpoints of the link?
- alecco 14y agohttp://en.wikipedia.org/wiki/Quantum_teleportation http://en.wikipedia.org/wiki/Quantum_teleportation First paragraph.
- newhouseb 14y agoThanks, the key sentence here is > However, it does not _immediately_ transmit classical information. As I understand it, once you distribute an EPR pair, you can transmit one qubit of quantum information which thereby destroys the pair. Provided you can encode your classical information into quantum information, the amortized rate of classical information communication cannot be faster than light because you need to first distribute the EPR pairs (which you cannot do at FTL), but the _instantaneous_ rate of classical information communication could be faster than light. The biggest assumption here is that you can encode/decode classical information to/from quantum information at a rate (if at all) faster than it would take for matter to travel over the potentially infinite distance between the EPR pair. Some googling reveals that this is possible via means such as time-bin encoding. (Edit: time-bin is only for photons, which I don't know if you can entangle, but it still appears that you might be able to encode classical information in electron spin) What am I missing? Edit - alecco's other answer in this thread make it much more clear what is going on. Thanks again.
- Variance 14y agoIt sounds like you already figured this out, but you can't encode classical information into the system in such a way that would allow for FTL transfer of information. Depending on what you are specifically thinking of as "encoding", there will be an equivalent reason why it won't work; often because you collapse the wave function of your local quantum pair-element when you transfer energy into it, which is a form of observation.
- walrus 14y agoSome previous discussion: https://news.ycombinator.com/item?id=4485347 https://news.ycombinator.com/item?id=4485347
- elorant 14y agoI find it extremely intriguing that although we do not fully understand the fundamentals of the quantum world we are able to exploit it.
- jvdh 14y agoThe full article is also available on Arxiv.org: http://arxiv.org/pdf/1205.3909v1.pdf http://arxiv.org/pdf/1205.3909v1.pdf
- kalmsy 14y ago"... whose location is unknown ..." Wait. Is this the dawn of truly anonymous communication, with no means of tracing the origin or target by wiretap?