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Quantum Key Exchange With an Airplane

Posted by samzenpus on from the spooky-flight dept.

submeta writes "Researchers in Munich have successfully performed a quantum key exchange between a moving aircraft and a ground station. Quantum key distribution, which exploits the phenomenon of entanglement, offers theoretically perfect encryption (although it can be vulnerable in practice). This advance is an important step on the way to key exchange with a satellite, which could enable practical usage of the technology."

16 of 44 comments (clear)

  1. This post is relevant to my interests by AikonMGB · · Score: 2, Insightful

    Quantum key exchange via satellite: QEYSSat.

  2. A little unclear on entanglement by msobkow · · Score: 2, Interesting

    Doesn't entanglement also imply faster-than-light communications between the two quantum nodes? Or does the speed of light still apply to the entangled systems?

    If the former, this would eliminate the lag for satellite communications, which would be a major breakthrough in global communications, even if the satellites could only link up to a few ground stations because of the limited number of entangled "transmitters" per satellite.

    --
    I do not fail; I succeed at finding out what does not work.
    1. Re:A little unclear on entanglement by Anonymous Coward · · Score: 5, Insightful

      It does imply faster than light propagation of states, but unfortunately it is not possible to use this effect to communicate information from one place to another. Observing the pair at either end breaks the entanglement immediately (faster than light), but there's no way to tell from one end if the entanglement has been broken, so you could imagine that the universe is talking to itself at faster than light speed, but you can't hear what it's saying.

    2. Re:A little unclear on entanglement by Skillet5151 · · Score: 3, Informative

      No entanglement phenomenon has ever been shown (or really believed) to be capable of transmitting information faster than light. I promise you'll see it right there in the Slashdot headline if a decent experiment ever seems to show any kind of FTL information transfer.

    3. Re:A little unclear on entanglement by kasperd · · Score: 5, Informative

      Doesn't entanglement also imply faster-than-light communications between the two quantum nodes?

      No. It's true that you can have entangled particles far apart and measure the state of both of them at the same time. That does mean you instantaneously know what the other end would read. But that does not imply communication, since you don't have any control over what value comes out. And you can't even find out if the other end was measured or not. In such a situation it doesn't really matter which of the two particles is measured first. Measure particle one first, then the other collapses to a state consistent with the measurement of the first. Measure particle two first, then the first collapses to a state consistent with the measurement of the second. Which of the two happened depends on the viewpoint of the observer.

      And actually quantum key exchange does not need entangled particles at all. There are certain optimizations, that could make use of entangled particles. But in plain quantum key exchange, you send a stream of independent particles where the sender knows the state of each particle he sends. The receiver doesn't know the state of the particles as they are received, but may learn something about the state, depending on how they are measured.

      I have read of some implementations, that produce a particle in a known state by first producing an entangled pair of particles, and then measuring one of them. By the time the other particle leaves the sender it is no longer part of any entanglement. And the fact that it ever was part of an entanglement is just a minor implementation detail, that doesn't actually impact the protocol.

      --

      Do you care about the security of your wireless mouse?
    4. Re:A little unclear on entanglement by gweihir · · Score: 2

      No. It could basically be simulated by both particles agreeing beforehand on a state and then reveal that simultaneously. Cannot be used for FTL communication.

      There are some quantum-physical effects that indicate that this is not what happens and the two particles really sort-of synchronize in an FTL way in real-time, but my impression of the reasoning was that it requires a bit more assumptions than I am comfortable with, i.e. I think it may turn out to be wrong.

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      Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
    5. Re:A little unclear on entanglement by camperdave · · Score: 4, Insightful

      No. It's kind of like flipping a coin. If you know one side is heads, you automatically know that the other side is tails no matter how far apart the sides of the coin are. Quantum Entangling photons is kind of like splitting the coin in half.

      --
      When our name is on the back of your car, we're behind you all the way!
    6. Re:A little unclear on entanglement by Brad1138 · · Score: 2

      I love science and (when I have time) have kept a skeptical eye on quantum entanglement. I haven't studied it a lot, but have problems with a number of its claims. You are saying it works and is faster than light, as long as no one observes the outcome... Really? It sounds less legitimate every time I hear about it.

      --
      If you could reason with religious people, there would be no religious people
    7. Re:A little unclear on entanglement by ikaruga · · Score: 2

      I'm more curious to know how entanglement is even relevant to this study. I'm just an engineer, not a physicist, but from my understand of the article, they basically used an almost standard laser communication. However, in this case with two slightly different beams(different polarization) for transferring the encryption key. The reason they called this "quantum" was simply because they were reading the key signals by directly measuring the photon state due to polarization. That is important because, if someone tried to intercept the signal they'd necessarily use some sort of lens or mirror that would change the signal polarization. This change is measurable and if detected, the keys must be changed. AFAIK, no entanglement phenomena is used in this study. The "New scientist" article mentions entanglement when mentioning that 143km "teleportation" study (sorry, but that hardly looked like any teleportation at all, more like quantum state transfer using laser beams/optical communications). And by mentioning a complete independent Nature study, they can get more clicks. Sorry if there are any mistakes in my post.

    8. Re:A little unclear on entanglement by Anonymous Coward · · Score: 5, Informative
      The mechanism works regardless of if someone observes it or not. The faster than light aspect is just not observable by a person at one end, it can only be noticed when the two ends talk to each other. In other words, the faster than light aspects can not be used in communication, just shows up in patterns that are observed if you compare results from both ends that must be communicated by traditional means.

      I haven't studied it a lot, but have problems with a number of its claims.

      Considering how difficult the field of quantum mechanics is, and how many people fail to grasp basic principles even with extensive studying of pop-sci level material, maybe a little more humility would be called for until you have a chance to read more about it.

    9. Re:A little unclear on entanglement by DriedClexler · · Score: 2

      I always have to wonder about interpretations of quantum mechanics that are able to believe those ideas at the same time:

      "Yes, the information propagates faster than light, but in just the right way that we could never use it for communication" --> isn't that the same thing as "The information doesn't propagate faster than light"?

      --
      Information theory is life. The rest is just the KL divergence.
    10. Re:A little unclear on entanglement by sFurbo · · Score: 2

      I think there exists two kinds of quantum cryptography. The one you describe is the one implemented now. It doesn't require entangled particles. IIRC, the other goes something like this:

      1. Alice creates two sets of entangled particle, and sends one to Bob.
      2. Alice encodes her message into a from that can interact with the entangled particle.
      3. Alice lets her message interact with the entangled particles, creating the coded message. It is now no longer readable.
      4. Alice sends the coded message to Bob. It is not readable, so it can be done over an open channel.
      5. Bob lets the coded message interact with his set of particles, retrieving the original message.

      AFAICT, entanglement creates a one time pad that is guaranteed not to be known by anyone else. The method implemented now creates random, shared information.

      I am not sure whether the coded message created in step 3. is entangled with Bobs particles, or whether step 3. breaks the entanglement.

    11. Re:A little unclear on entanglement by kasperd · · Score: 2

      I am not sure whether the coded message created in step 3. is entangled with Bobs particles, or whether step 3. breaks the entanglement.

      It depends on how you do it. It could come out either way. However the only point in using the second method you describe is, that you can achieve entanglement at that point. I just don't know of any application of that, since usually the data you eventually want to transfer securely, are classical bits.

      If you just want to protect classical bits, then the more complicated and more fragile method you describe doesn't offer any benefits. An ordinary quantum key exchange will in the end produce the same key at both ends, and that key will consist of classical bits, that can easily be stored by the two parties, until they need to communicate.

      --

      Do you care about the security of your wireless mouse?
  3. I will believe it... by kiriath · · Score: 3, Funny

    When Sheldon is excited about it.

  4. BB84 protocol does not use entanglement by Anonymous Coward · · Score: 4, Informative

    This experiment implemented the BB84 protocol with attenuated coherent laser pulses (with a view to use decoy-states to close the photon number splitting attack on attenuated coherent states). The ideal implementation would use single photons (which are highly non-classical states). The protocol does not utilize entanglement. The E91 protocol was the first QKD protocol to propose using entanglement for this purpose.

  5. Solution without a problem by Mathinker · · Score: 2

    QKD is a solution to a non-problem. Even if the current public key algorithms would be broken (via a revolutionary advance in the the field of quantum computing, or in some other, yet unknown way), there exist backup algorithms for which there are no known quantum algorithms which break them.