I imagine today’s news about teleportation will create a couple of hollywood blockbusters.
In reality though, how long before the US can use this to send totally secure messages to anywhere on the planet.
Secondly (This might be IMHO though)… how long before they can teleport an object - eg; a grain of sand?
The invention of the transistor could have been reported in an identically sensationalist tone to the article linked to. In that case, it most certainly did change the world we live in. But in ways nobody predicted. And if atomic ‘teleportation’ has the success that is implied in that article, you can guarantee they’re not going to be doing anything as mundane as transporting people from one place to another. They’ll have far more important things to do.
(Hell, if it becomes possible to affect individual atoms with such accuracy, it’d be easier to create an ‘on holiday’ brain and teleport it into your skull, rather than teleport you to Jamaica. Just a thought…)
Using technology in any way resembling this? Never. The use of the word “teleportation” for entanglement phenomena is a big pet peeve of mine: What they’re doing in no way resembles what anyone thinks of as teleportation.
Now, it is conceivable that methods like this could increase security of communications, but there’s no such thing as “totally secure messages”. There are always potential holes in security: If nothing else, you can bribe, extort, or otherwise convince one of the folks who knows the message to tell you.
I think it’s reasonable terminology; a quantum state appears to jump from point A to point B without any quantum information touching any of the points in between. Like all of quantum mechanics, it’s rather spooky: I don’t know what this object’s state is, but I can tell you some information so that you can create it, but you also won’t know what it is when you make it. It’s nothing like Star Trek teleportation, but when has Star Trek terminology ever been scientifically accurate? I know it means that every article on quantum teleportation has to make some sort of Kirk or Spock reference, but I mostly blame unimaginative journalists for that.
Well, of course, but quantum cryptography is pretty different from most classical key-based cryptography schemes in having physical proofs of security (rather than, as in the classical case with DES, RSA, etc., having a belief, based on the apparent difficulty of inverting some mathematical function). And, unlike the classical one-time pad, it doesn’t seem to rely heavily on a secure channel: the classical channel is broadcast, and tapping the quantum channel is detectible. (Man-in-the-middle attacks and capturing the plaintext before encoding or after decoding are always possible, but I wouldn’t call that an insecurity of the cryptosystem so much as an insecurity of the endpoints.)
There are already a few groups out there offering commercial quantum-key-distribution hardware, though as far as I know they currently only allow distribution over short-run fiber optic links. QKD is easier to implement than useful teleportation, though, because no long-term quantum information storage is necessary.
Question: I didn’t read the article carefully, but they made it seem that the teleportation happened instantly. If that is the case, then this could be used to transport information instantly - say, with no time delay when communicating with the rovers on Mars.
Or with probes like Voyager and its sequel, if we every send a similar one.
This could be the big breakthrough here, not something silly like recreating the transporters from Star Trek. I also recall something about instant communication like this being forbidden by some law of physics…another implication here could be trying to rewrite a number of theories to fit it in.
Is this the case, or did I miss the part where the information propagates only at the speed of light?
-Lixi
This is relatively old news, SciAm did a spread about it some years ago. The basic gist is that Einsteins GR is still maintained and information only travels at the speed of light. Only quantum states are transferred immediately but you can’t build an information transfer system out of that because of Heisenberg.
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Cant respond to the OP, but one thing that always has me puzzled is that you often see some new, ground-breaking scientific discovery simultaneously announced by two (or more) independent research groups.
I’m assuming that since what they’re doing is new and therefore difficult, it takes years of work. I also assume that the stakes are high in terms of recognition, so there would be some element of competition. How is it then, that they always (well, often) seem to arrive at the endpoint contemporaneously? Do they coordinate the release of their findings?
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To answer bizzwire’s question, there are a few things at work. First, some discoveries are just “ripe”. A new measuring instrument gets invented, or a new theory is developed, or some combination of many instruments and theories, and multiple groups notice some interesting things they can do with the new tools. Second, a lot of the ground-breaking scientific discoveries you read about aren’t actually the same thing, they just seem like it because of ignorant popular reporting. Then there’s also some collaberation between groups, both formal and informal (I’ve seen cases where two competing groups had members in common, on the one hand, and on the other, you have things like lunchtime conversations at conferences). Finally, results from one group can spur others to release preliminary results earlier than originally planned.
In this instance, the fact that both teams are publishing in Nature is probably much of the explanation for the synchronicity. The reviewing process for both it and Science takes several months, so the editorial staff will be aware if two similar papers are in the pipeline fairly far in advance. Since both magazines are dependent on big splashes, it’s then common for them to arrange for related papers to appear in the same issue to maximise the impact. That one submission may proceed another can be signaled to the readership by placing it first. There will also be the submission dates included, so priority isn’t lost. Similar papers submitted a bit apart will thus tend to appear at the same time.
Nor is this a particularly new practice. The three consecutive papers on the structure of DNA in the April 25th edition of Nature in 1953 were formally all submitted separately. Recognising that they were closely related, the sensible editorial decision was to publish them together.
Of course, while submitted separately, these were not independent. Chronos’ points are similarly sensible explanations of how such parallel papers can be submitted to the same journal at roughly the same time in the first place.
But there are totally secure channels. It’s possible to use a quantum bitstream to code messages so not only can an interloper not read the messages, but that the reciever will be able to tell that someone’s trying to snoop.
As for “teleportation”, what definition do you want? The rationale is that information is transferred from point A to point B and the “original” is destroyed. Leibniz would surely say that for all intents and purposes the thing itself has been sent, since the result is indistinguishable.
Information is NOT transferred from one place to another. The quantum state is. However, due to Heisenberg, no information can get transferred in this manner.
Quantum teleportation certainly does transmit information, because a quantum state does contain information. You might be trying to say that quantum teleportation does not permit “instantaneous” (i.e., faster than light) transfer of information, which is true. The teleportation protocol requires Alice to send classical information to Bob, and Bob can deduce no information about the state being teleported until he receives this information. So no information is transmitted faster than it can be sent from Alice to Bob by “normal” channels. But at the end of the teleportation protocol, the state that Bob has is equivalent to the one Alice started with. If Alice encoded one bit of classical information in the state she teleported to Bob, then Bob can read that bit out when it’s teleported to him (assuming they have agreed on an encoding procedure).
Heisenberg doesn’t prevent reading any information from a quantum state; it just prevents reading all information about the state. (You can’t simultaneously measure “noncommuting observables.”)
Yes, but that’s not what Mathochist means, otherwise, your standard DSL modem would be a teleportation device. No information can be transmitted at FTL speeds.
Ok, but if you set up some kind of test in advance, couldn’t you transmit, in essence, “classical information” at faster than the speed of light? I don’t really understand this stuff, so I’m sure there’s a very obvious problem with what I’m about to throw out, but work with me here…
Alice and Bob set up two isolated “teleportation” systems. Using the BBC article’s terminology, Alice’s Box I contains particles A and B. Bob’s Box I has particle C (the recipient particle, so to speak). Alice’s Box II has particle Z, while Bob’s Box II has particles X and Y. (Particles B and Y are the ones that entangle between both the information-sender and information-recipient particles). Alice then flies to Pluto.
Once she gets there, at a predetermined time, she “teleports” quantum information, so that her particle A information gets tranferred instanteneously to particle C (with Bob). Bob then reads that particle, say, to get the spin rotation. If he gets clockwise, he then sets his particle X to rotate one way, and if he gets counter-clockwise, he sets particle X to rotate the other way. He then “teleports” that information to particle Z (which is with Alice). Therefore, Bob is telling Alice classical information, but without the classical time delay.
Obviously, this presupposes that the B and Y particles can be entangled with other particles at a distance, and instantaneously at that.
So, what did I get wrong?
I’m not sure what you think Mathochist is saying. I don’t read his post as implying that teleportation is FTL. He’s just arguing (or so I read it) that the state Alice started with and the state Bob ended with are, in a philosophical sense, the “same” state. This is distinct from how a standard modem operates, where when I send information over a modem I still may have a copy of it locally; since bits can be copied, it doesn’t make much sense to identify a particular bit as “the” holder of that state; I could make a billion others in the same state. In quantum mechanics I can’t copy states; an unknown quantum state is a unique item which cannot be copied. So Bob really must have the “same” state that Alice started with.
I’m still not sure I understand the distinction you’re trying to make. But at least we agree that there’s no FTL information transfer going on.
It sounds like you’ve forgotten part of the teleportation protocol. For Alice to teleport a state to Bob, she has to make a measurement (of particles A and B, say) and transmit that measurement result to Bob. This measurement is completely random, and uncorrelated with the state being transmitted. In particular, Alice can’t choose what the measurement result will be. Bob also can’t deduce anything about the state being sent by measuring C until he gets the measurement results from Alice. The same holds true for Bob sending information back to Alice; Alice can’t learn anything until she gets the classical information from Bob.
Does that make sense, or am I misunderstanding your proposed protocol?
No, I’m sure it’s me that’s not understanding.
First, if the information-state of a particle can be transmitted, won’t measurements of the same variable on each of the two particles be the same? So if measure the spin rotation of particle A, and it has had its information transmitted to particle C, won’t C have the same measurement? So Bob doesn’t need to know from Alice what Alice measured, he will just “know” since they’re both measuring the same thing on the “same” particle.
Second, my “experiment” is based on the ability for someone to be able to entangle a distant particle (Alice saying “ok, I’m going to entangle my B here on Pluto with Bob’s C back there on earth”), which is probably by itself be impossible, thus rendering my experiment pointless, now that I think about it.
Ah, I see what you’re getting at. No, this won’t work. A quantum-mechanical measurement can be truly random, in that even if you know precisely what the state is you cannot predict the measurement result. That’s the case for the particular measurement whose result Alice has to send to Bob to teleport a state to him. So Bob’s measurement result, of the same state, will not in general be the same as Alice’s.
True, it is impossible to do this. (There’s a theorem that says that you can’t transmit quantum information–i.e., a quantum state–without use of some quantum resources. You can use a quantum channel–just send the state directly–or you can use an entangled pair and teleport the state by sending only classical information. But this uses up that pair; after Alice teleports A to C using B, her particles A and B are worthless for later teleportations.) However, you could imagine that Alice and Bob got together long ago and created a large number of entangled particle pairs to use in their later teleportation experiments, just as spies meet to exchange one-time pads for later use. So this doesn’t itself constrain the speed of the information transfer.
Ok, I see this, sort of. But if measurements are always random, how in the heck can the British/Australian teams ever know that they were successful? I mean, if their measurements of their A and their C are random…maybe it’s just pure luck that A and C matched? And they have to measure to know that the information got transferred.
Also, I think the word “experiment” I used gave the wrong connotation. Bob and Alice are not running a test to see if they can successfully teleport information - the mechanism is assumed to work. So Bob does not even need to know, ever, what Alice measured, he just needs to read the measurement on his particle to receive the transfer of information.
That’s kind of what I was initially thinking, so I’ll expound upon it, and apologize for length. Upon Alice’s departure from Earth, she is given a box with A and B, while Bob has C. B & C are already somehow “entangled” - or B is somehow predisposed to entangle with C. When Alice gets to Pluto, shen then entangles A and B, and since B is predisposed to entangle with C, it does so, and transmits A’s information. Similarly, she has a second box with particle Z, which is predisposed to entangle with Y, and Bob has the box with Y and X.
Now, even assuming this works, all they are doing is just reading states, but not passing any “classical” information per se. However, if somehow a particle could be set to a specific value, they could use this system to transfer “real” information. Let’s say Bob and Alice want to know if Pluto has breathable air. If Alice sets A to “spin-clockwise”, it means “yes, Pluto has breathable air.” Opposite spin means “no.” Upon getting the answer, Bob needs to tell Alice whether to stay there because he’s sending settlers (Pluto has breathable air) or to come home (Pluto doesn’t). (Now, they could’ve decided this ahead of time, but the politics at the time Alice left were volatile, so she needs to know in “real-time” what the answer will be.)
Anyway, this is fascinating, even if I know somehow I’m fundamentally wrong 
No, not all quantum measurements are random. But some are. In an experiment to test teleportation, the experimenters might (for example) know what the state of A is, so they know what the state of C ought to be after the teleportation. It is possible to design a state-verification measurement which will always return “maybe” if the state is the expected state but which will return “no” with some nonzero probability for any other state. It will sometimes return “maybe” as well, but if they do the experiment many times and never see a “no” they can gain confidence that it’s not just a random result. (There are other more complicated experimental tests, but in the end they all involve a measurement which gives statistical information; performing many trials gives high confidence that teleportation is actually happening.)
The measurement Alice makes (whose results she sends to Bob), however, has a purely random result. Each of the possible measurement results occurs with equal probability.
I understand, but Bob does need to know Alice’s measurement result. Remember the teleportation protocol:
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[li]Alice and Bob share an entangled pair B-C.[/li][li]Alice performs a measurement on particles A and B, and throws the particles away.[/li][li]Alice sends the measurement result to Bob.[/li][li]Bob receives the measurement result, and based on this result he performs some quantum operation on his particle C.[/li][/ol]
Before Bob performs the quantum operation in step 4, measurement of particle C won’t give him the right answer. But that means Bob has to wait for step 3 to happen, which means he’s got to wait for Alice’s message “perform operation #3” to arrive before performing the measurement. Otherwise no measurement he can perform will provide any information about Alice’s original state.