Slashdot is powered by your submissions, so send in your scoop

 



Forgot your password?
typodupeerror
Communications Earth Network Networking Transportation Science Hardware Technology

Quantum Teleportation Achieved Over 7km of Cable (sciencealert.com) 189

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.
This discussion has been archived. No new comments can be posted.

Quantum Teleportation Achieved Over 7km of Cable

Comments Filter:
  • by Anonymous Coward on Wednesday September 21, 2016 @06:09AM (#52929795)

    Someone explained this news to me recently, they said the scientists didn't send ~information~ over quantum entanglement, they sent the data across normal networking means and sent and a key to unlock the data via quantum entanglement. The method used has deep implications for security and encryption methods, but not faster than light data transfer. Just wanted to clear that up.

    • by Anonymous Coward on Wednesday September 21, 2016 @06:10AM (#52929799)

      No. This article clearly means we'll be transporting ourselves to Mars before the week is out.

    • by Rei ( 128717 ) on Wednesday September 21, 2016 @06:18AM (#52929817) Homepage

      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: (Score:1, Insightful)

        by Anonymous Coward

        There's no need to be a nerd about it. Some people mistakenly think this news is about fast internet speeds.
        some people see "teleported their information" and skim the rest of the article.

      • by Viol8 ( 599362 )

        If that random message is used as the key then it is transporting information since information is simply data that has a meaning or use.

        • by Rei ( 128717 )

          information since information is simply data that has a meaning or use.

          Data that to an observer is 100% random is not "transmitted information" in a physics context. Or in an information theory context either

          • So basically you are saying that Star Trek style transporting is possible? Exciting news!
          • information since information is simply data that has a meaning or use.

            Data that to an observer is 100% random is not "transmitted information" in a physics context. Or in an information theory context either

            Bullshit. It is transmitted along the fiber optic cable, at a fraction of the speed of light in a vacuum, to yield the same random value at both ends. By being unpredictable, it meets the definition of information.

            • Well, fine, if you want to think of it that way, go ahead, Pretty much every single physicist would say you're wrong, but what do they know, with their "degrees"...

              • Well, fine, if you want to think of it that way, go ahead, Pretty much every single physicist would say you're wrong, but what do they know, with their "degrees"...

                If you want to count the length of the procedure from the time the entities at both end perform and evaluation, then fine. But that's skipping over the time for the entangled photons to get from hither to thon.

                All this yields is a shared private key. Of course some one has already unrolled a reel of fiber optic from hither to thon. You could have just let them transport the key in their pocket.

        • by hey! ( 33014 )

          In a sense you could interpret it that way. But that's quibbling about terminology; it doesn't mean you can send messages that way, which is the important point.

          • In a sense you could interpret it that way. But that's quibbling about terminology; it doesn't mean you can send messages that way, which is the important point.

            Well you can, you just can't choose which message is sent, from the space of all possible messages sendable.

            • by hey! ( 33014 )

              Again it's quibbling about what "sending a message" means.

              To most people "sending a message" implies two roles: the sender knows the content of the message before it is sent, but the recipient does not know the contents until it is received. So if you say "you can use this machine to send a message", that's what they'll picture, but it's not what is happening here.

              And if you say message sending is "faster than light", they simply extend this model, picturing something like the Ansibles of science fiction.

              H

      • by locofungus ( 179280 ) on Wednesday September 21, 2016 @07:25AM (#52930021)

        It's effectively** equivalent to having two identical letters containing a random message

        No. you're describing entanglement.

        Teleportation is subtly different.

        Teleportation consists of transferring the quantum state of one particle to another particle via the use of entangled particles (and a classical channel)

        The beauty of this is that the entangled state can be set up in advance. You then give me a particle that you might or might not know something about its quantum state (but importantly, I do not know what you know about it so cannot measure that quantum state in advance). I can transfer the state of that particle to another particle that Bob has via some entangled particles we exchanged earlier *plus* some standard classical information that goes over classical channels (it's this classical information that limits the teleportation to the speed of light)

        The particle that Bob ends up with is in an identical state the the one you gave me (and which I still have).

        N.B. This is quantum teleportation, not quantum cloning which is not possible. The act of getting the quantum state to Bob affects my particle in a way that means I cannot also extract any information from it about the original state of your particle.

        • I'm very sorry, but I HAVE to steal that signature! :)
        • My education in physics is limited, maybe you could attempt to clarify why the classical channel is required? I thought that once the two ends were entangled they would reflect each others state without any intervening communication.
          • AH never mind , NOW I find the explanation posted later.
          • I don't know what else you saw but basically the entanglement leaves the target (teleportation) end in a superposition of four states, only one of which is the one you want the others are complementary states.

            The sender makes a measurement at their end to determine which one of the four states is the correct one and then transmits it to the receiver. The receiver can then isolate the correct state from the others that would otherwise cancel out all knowledge of the original state.

      • 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.

        It seems to me that they could very well use it for ftl communications. If you can change the state of one particle to a state that represents either a 1 or 0 then the other will change to match it so you just read the state of the recipient and then you have a binary stream. The bandwidth might not be especially great and on an earthly scale you'd probably still get a better data rate over traditional methods. Although I am not a expert in such fields, not even an amateur and there are probably a bunch of

        • It seems to me that they could very well use it for ftl communications. If you can change the state of one particle to a state that represents either a 1 or 0...

          That's just it; you can't do that.

          You can only make measurements; you can't influence the result.

      • The method used has deep implications for security and encryption methods, but not faster than light data transfer. Just wanted to clear that up.

        The parent explicitly says that faster than light data transfer is not possible. It's really sad we are unable to capitalize on the 'spooky action at a distance' phenomena.

        • by tnk1 ( 899206 )

          I think in some sense, the particles are never actually separated, when though their x,y,z coordinates change in 3D space. It may make more sense to think of them as still actually connected in some domain, but that their projection in space has changed so that they seem to now be separated when only looking at spatial coordinates.

    • by Maritz ( 1829006 )
      Yeah. You can send random information faster than the speed of light. Not useful.
      • Yeah. You can send random information faster than the speed of light.

        No. You can't.

        • by Maritz ( 1829006 )
          Amazing rebuttal. Yes, you fucking can.
          • No, you can't, and adding an expletive does not make you correct.

            You cannot send random, or any other kind, of information faster than light. That's just not what entanglement/collapse does.

          • What is being "communicated" FTL, without a non-FTL classical channel, is a random superposition of all the possible quantum states. That is not "random information", it's "no information". Without the classical channel you don't even know whether the holder of the other entangled particle is measuring the same quantum states, so no information is exchanged, not even information about the measured states of the entangled particles.

            But sure, as a trivial special case, it is possible to exchange zero informat

            • NOTHING is being transmitted FTL.
              You entangle particles, separate them at speeds = c, then you measure them.
              The information transfer is in the separation of the particles at speeds = c.

              • Thank you. That is exactly what I said.

                The only part of quantum entanglement that is "instantaneous" (or "FTL") is that when one party performs its measurement, the wave functions for both of the entangled particles collapse out of their superimposed states simultaneously, no matter how far apart they might be. However, this does not communicate any information by itself; for that the two parties still need a classical channel. As you say, nothing is transferred FTL. An observer cannot tell that the wave fu

                • when one party performs its measurement, the wave functions for both of the entangled particles collapse out of their superimposed states simultaneously, no matter how far apart they might be.

                  I'm not sure that can be said to be true. There is no definite "simultaneously" for spatially separated objects.

                  If one person makes a measurement, then the other's state will have been collapsed. But I don't think you can make any statement about when it happened.

                  I know there have been experiments that put an lower limit of so many thousand times the speed of light on it, but I'm not really sure such numbers make proper sense.

    • by Anonymous Coward

      so the key isn't data?

    • A key *is* information.
      • A key is only information if it's a specific key. If you ask me for my key, you're requesting information. If you ask me for a key, then random data suffices.

      • But you can't construct the key without communicating classically to collate your measurements. The key doesn't exist until that is done.

    • by Dunbal ( 464142 ) *

      Uh huh. Tell you what, I just sent you an instantaneous message. I will now send you via snail mail the key to decrypt it.

      Exactly how fucking useful is that?

    • Someone explained this news to me recently, they said the scientists didn't send ~information~ over quantum entanglement, they sent the data across normal networking means and sent and a key to unlock the data via quantum entanglement. The method used has deep implications for security and encryption methods, but not faster than light data transfer. Just wanted to clear that up.

      Quantum Key Distribution: More expensive and less practical that putting the key on a USB stick and driving it to the other end.

  • The data is being send the traditional way. But the information is encrypted by the entangled particles then decrypted by its partner.
    The real trick is to acutely time the communication delay and cache up the states of those times.

  • by Anonymous Coward

    I know there's a black and a white ball in a box. I pick one of them without looking at it and transport it 10km away, then I check what colour it is. Now I also know the colour of the other ball, but is it fair to say that checking the colour "affected" the ball I left in the box over the distance of 10km? Obviously it's absurd. Why would quantum entaglement be any more mysterious than this?

    • by Anonymous Coward on Wednesday September 21, 2016 @06:49AM (#52929909)

      That's not quite the trick.

      You have a box with black and white balls. You take two, X and Y. You throw X without looking at it to Bob. "Hey Bob what's the color of your ball?", Bob says its black. You open your hand and look at your ball,..... amazingly it's black too. No matter what color Bob says, yours is linked to his color!

      The claim: The act of Bob looking at the color *sets* the color of his ball, and because they are linked by a mysterious spooky distance effect, it also sets the color of your ball. The balls normally have no color.

      The reality: You take a photograph of the balls. You throw one, Bob looks at his, you look at yours. The photograph is checked to see if it the balls have the same color? Yes? Then you count the experiment. No? Then you discard the experiment as a failed entanglement.

      EVERY entanglement experiment includes this filtering stage. Since the information on whether the entanglement was a 'success' or 'not' is sent along another line, it follows that you cannot use this "faster than light" communication until the fixup information arrives via normal communications.

      Bob does not know if his ball is a valid entanglement until details of the outcome of the photograph are sent to him.

      For the purposes of this experiment, we downplay the photograph, and we never count the photograph as a "detection". When the ball is measure by Bobs eyes, we count that as a detection, when the ball is photographed, we don't count that as a detection until someone looks at the photograph. I kid you not.

      • So where is Charlie in all this? And the cat? There's a cat in that box too, right?
      • If we can get high reliability, we can encode the detection phase as hamming coding.
    • by Bengie ( 1121981 )
      It gets better than that. You ball may be a wave or a particle, and you can record the state of the ball now, but in a scrambled form. Then send the paired ball to some someone else who may be millions of light years away. And depending on if they observe it or not, will decide if your ball is a wave or a particle. From your point of view, someone possibly measuring the twin ball millions of years in the future decides if your current ball is a particle or wave.

      The issue is that you can't know until data
    • by GuB-42 ( 2483988 )

      I know there's a black and a white ball in a box. I pick one of them without looking at it and transport it 10km away, then I check what colour it is. Now I also know the colour of the other ball, but is it fair to say that checking the colour "affected" the ball I left in the box over the distance of 10km? Obviously it's absurd. Why would quantum entaglement be any more mysterious than this?

      What you describe here it the hidden variable theory, and it has been proven wrong using Bell's theorem.
      Quantum entanglement really is mysterious. Mysterious enough to drive Einstein nuts. And while the maths work, there is currently no satisfactory interpretation.

      • Bell's theorem rules out local hidden variables. There might still be non-local hidden variables, but that's just as weird, if not weirder.

  • by TFlan91 ( 2615727 ) on Wednesday September 21, 2016 @06:25AM (#52929837)

    Can someone spell this out for us lamens?

    How does something teleport across a wire? By that logic, our current communication systems are "teleporting" information.

    I thought Quantum Entanglement is instantaneous and void of any connecting wires, which fits my definition of "teleportation" a little better, but I still don't think of it as teleporting.

    • Re:Confused (Score:5, Informative)

      by Mal-2 ( 675116 ) on Wednesday September 21, 2016 @06:46AM (#52929899) Homepage Journal

      Quantum teleportation is instantaneous, but first the entangled particles must achieve some distance between them, and this is subject to the usual speed-of-light constraints. In this case the photons achieved that separation over a length of fiber, rather than being sent through free space. Fiber is likely to scale considerably better than line-of-sight transmission.

      Entanglement won't survive optical repeaters, so I'm not sure just how well this actually will scale in the real world. Still, 6.2km is a useful distance for some limited applications.

      • I was wondering about that myself. The cool part about entanglement is that it occurs without mediation (like a cable), so I was trying to figure out what the big deal was. I guess I forgot that the entangled particles have to be moved from one place to another first and keeping photons in your pocket is tricky. Easy to get them in, hard to get them to stay.
      • Quantum teleportation requires the use of a classical channel. The entangled particles can be exchanged in advance (provided they can be stored without breaking the entanglement which is difficult in practice but trivial in theory)

        The classical data can only be transferred at the time the teleportation is done - hence that limits the speed of the teleportation to the speed of light.

      • by Dr. Evil ( 3501 )

        "so I'm not sure just how well this actually will scale in the real world. Still, 6.2km is a useful distance for some limited applications."

        FTA, there's another innovation not in the Slashdot headline or summary, except to say " the teams had slightly different set-ups and results."

        One of those results seems to be that the team from China's method allows for quantum repeaters which can relay entangled particles:

        "...it would allow for the creation of quantum repeaters, to propel the signal further along

  • I always thought that it would be apropros to use Bob, Carol, Ted and Alice [wikipedia.org] as example names for sharing.

  • by Anonymous Coward

    "Calgary's fiber optic network that's not regularly in use."
    Yeah no shit it's not in use. ISPs build the network and leave it there for years just to keep getting as much money out of their outdated tech... and when they finally give us fiber, they start with very low speeds (under 100Mbps), at ridiculous pricing, to gouge us even more.

  • ... but if you need a cable, it's not teleportation.

    Just sayin'.

  • Teleportation or teletransportation is the theoretical transfer of matter or energy from one point to another without traversing the physical space between them. It is a common subject in science fiction literature, film, video games, and television.
  • People who scoff at 'memory of water' are going to shit their pants when they read about this!
  • OK, slight background. Basic applied physics knowledge from 20+ years ago.

    How does this qualify as teleportation if you have an optical particle, and a optical transport medium? Isn't this the photon hitting the surface of the fiberoptic transport medium, changing state to an optical waveform, traveling along the transport to the endpoint, exiting and changing state again, and then being detected as a photon?

    Also somewhat confusing as photon's have no mass.

    If this had been a neutron, or some other actual su

  • Alice, Bob, and Charlie show up a LOT in these types of discussions. Mucking around with quantum this and quantum that. Sending encrypted messages. Very suspicious. Why aren't they on some sort of watch list?

  • My favorite way to explain the difference between something "happening" FTL and useful information not being able to travel FTL is this:

    Imagine you've got a powerful laser aimed at a wall a few light-years away. You then sweep the laser beam along the wall's length. The illuminated area changes at several times the speed of light. But this is not information transfer, because each photon travelled a few years in a straigh(ish) line and hit the wall based on the angle of the laser at the time of emission. We "see" a moving spot, but what we're actually seeing is a progression of non-FTL arrivals. The photons carry information, but whatever knowledge is imparted at the point where the wall is illuminated is not transferred to any subsequently illuminated location.

Many people are unenthusiastic about their work.

Working...