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Single Photons Bounced Off Orbiting Satellite

Posted by CmdrTaco on Mon Mar 17, 2008 10:00 AM
from the pling-pling-pling dept.
Communications Science
KentuckyFC writes "If we're ever going to benefit from the perfect security of quantum communication, we're going to need ways of transmitting entangled photons around the globe and certainly further than the current record of 144km through the atmosphere. Anton Zeilinger at the University of Vienna and colleagues have taken an important step towards this by bouncing individual photons off the Ajisai geodetic satellite (essentially a space-based disco ball) which is orbiting at 1400km. The group says the experiment is an important proof of principle for satellite-based quantum communications."
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Submission: Single photons bounced off orbiting satellite by KentuckyFC (1144503)
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  • Anton Zeilinger at the University of Vienna and colleagues have taken an important step towards this by bouncing individual photons off the Ajisai geodetic satellite (essentially a space-based disco ball) which is orbiting at 1400km.
    Big deal. Drunken frat boys at sports games bounce millions of "single photons" off of the opposing team members with pen lasers. *snort* You're a few zeptometers short of the goal.

    Not to mention photons are like words: you shouldn't use those you don't understand. Is it a wave or is it matter? Huh, Mr. Smarty Pants? Oh, what's that you say? A boson followed by a long explanation, how utterly predictable! Ha, you would say that. No. I want answers and I wanted them back when the church would persecute you for publishing them!

    We need something smaller. Go back to the lab, anything larger than a Planck Length [wikipedia.org] is unacceptable. And only 1400km? So help me god, if you can't express the distance it travels in double up arrow notation [wikipedia.org] or tetration [wikipedia.org], I don't want to hear about it. Come on people, this is real science, not some religious mumbo jumbo (6,000 years? Is that the absolute limit of your imagination!?) ... and if there's one thing I rely on from real science, it's announcements of experiments with inconceivable units performed in a totally contrived and intangible environment. The fact that I understood this experiment speaks libraries of congress about its complexity (or lack thereof). I'm encouraging you to go the extra yottameter here.

  • essentially a space-based disco ball
    Shiny disco balls anyone?
    • For some reason, I picture the giant space disco ball playing "get down tonight" by KC and the Sunshine Band. Disco Stu bounces protons back to you!

      • Re:Shiny Disco Balls? (Score:5, Funny)

        by HTH NE1 (675604) on Monday March 17 2008, @11:37AM (#22774312)
        Ah, ha, ha. ha, staying entangled, staying entangled
        Ah, ha, ha, ha, staying entaaa-aaaan-gleeee-eeeed, oh yeah!

        Well, you can tell by the way that I've been spun,
        I'm either a zero, or eyther a one.
        Quantum entangled far and long.
        I've been a qubit since I was born.

        And now it's all right, it's O.K.
        But you must look the other way.
        'Cos if you look, you'll understand
        A quantum state's effect on man.

        Whether you're a top or whether you're a bottom
        You're quantumly entangled, quantumly entangled
        Though we're separated, our states are identicated
        We're staying entangled, staying entangled

        Ah, ha, ha, ha, staying entangled, staying entangled
        Ah, ha, ha, ha, staying entaaa-aaaan-gleeee-eeeed, oh yeah!

        Light goin' nowhere
        Quanta probability
        Someone observe me now
        Light goin' nowhere
        Someone observe me now
        I'm stayin' entangled
    • Most Expensive Disco Ball...Ever!

    • essentially a space-based disco ball

      Shiny disco balls anyone?

      You laugh, but this was a tricky achievement. The satellite doesn't have an infinite number of reflecting surfaces. Therefore, a single photon fired at it must not only hit the satellite accurately, but it must be lucky enough to strike a reflecting surface that happens to be at the precisely correct angle. If the angle of incidence is not 90.000 degrees, or whatever exact precision, then the photon will miss the receiving antenna back on the

  • Come clean (Score:5, Funny)

    by sleeponthemic (1253494) on Monday March 17 2008, @10:06AM (#22773376) Homepage
    This is just an elaborate game of pong, isn't it...

    • This is just an elaborate game of pong, isn't it...
      It was factored into the defense budget after televised fear mongering [wikipedia.org] of an invading alien race hailing from planet Nintendu 64.
  • Ah, from some angles, this experiment proves the opposite. You need the photons to be "entangled". That means effectively in their own little world, not intereacting with the universe in any way. Shooting them up through 10^38 atoms of the atmosphere and bouncing them off a satellite is the exact opposite of entanglement.

    • Re: (Score:3, Informative)

      by Romancer (19668)
      "You need the photons to be "entangled". That means effectively in their own little world, not intereacting with the universe in any way."

      What are you smoking? Where did you get that definition of entanglement?
      Read up on the topic. [wikipedia.org]
      Pay special attention to the "faster than light discussion" parts to see why they need to send the photon.
  • Call me Old School, but when I was a kid, we had this thing called Heisenberg Uncertainty. Obviously, with the advent of Dark Matter, Quantum Entanglement and a Beowulf Cluster of XBox 360's, we don't need to worry about that.

    Humor your old man... tell me how we got around that?
    • The Heisenberg Uncertainty Principle is not a physical "law" rather it is a summation of other observations and it has been "short-cutted"

      Imagine, you May have a quantum entangled pair in a box. How do you know if the box is full? If you shine anything in you will disturb the pair. So you send a single photon through a beam spliter. One path is clear the other goes through the box. The beams then recombine to create an interference pattern. Since you slit the single photon, it has a 50/50 shot of send
      • Ok, I can buy this.

        I think we are talking about two different parts of the HUP. While you did a fine job describing the "state" of the photon, I guess I was referring to specifying the "position" of the photon. If specified tight enough to hit the mirror, the HUP effect on momentum was enough to make the error cone bigger than the mirror.

        But I was also taught that the Universe was going to re-collapse and that moon craters were volcanos.

        Now, either get off my lawn or help me with this Beowulf Cluster
  • If the photon has to get from point A to point B, then what is the advantage to quantum communications? Is it because the photon can be sent _before_ the data, which will then be sent by entanglement? Can someone explain it so my dumb mechanical engineering ass will understand it? I'm sure I'm not the only one who'd love to hear it. Thanks.
    • What is sent is a qubit, which is a whole lot different than a bit.

      The photon could also be sent before the data, and then you would use quantum teleportation to send the information on this photon. However, this is not what they have done here. They're pretty much just sending a photon, and that's it.

      However, in this case, what is really interesting is that they were able to detect a single photon, which is a lot harder to do than detecting normal pulse of light (or radio for that matter) containing
    • They're not faster, they're more secure. The quantum communication gear tells you if someone else is listening to your conversation.

  • In other news... (Score:4, Funny)

    by JCSoRocks (1142053) on Monday March 17 2008, @10:39AM (#22773694)
    People are still puzzling over how the world's largest rave got started. It seems that once a light show started from what appeared to be a giant disco ball in space people everywhere got out their glow sticks, drugs and pacifiers and started dancing.
  • We got a decent firing photon cannon.
  • How can they possibly align the mirror so that a single photon bounces back to the detector? Surely a single-atom imperfection would be enough to deflect it across the room, and a few atoms would deflect it to the next country

    I am expecting some quantum genius to tell me that it doesn't matter if it misses the detector because one from a parallel universe will hit it anyway!
    • Well, a single photon can't have a direction. So it doesn't do much bouncing.

    • A photon isn't like a very small rock. It has both wave and particle properties. The photon generally won't notice an imperfection that's much smaller than its wavelength.

    • Re: (Score:3, Informative)

      by Overzeetop (214511)
      The satellite is covered with retroreflectors, aka corner cubes. It is a property of three perpendicular planes that any light is returned along its incident path. Reflectors are used on bikes and cars, and highway signs (and high-gain front projection screens).

      http://www.af.ca/halifax/sciences/gim/LAGEOS-NASA.jpg [www.af.ca]

      The sphere, LAGEOS, is covered with corner cubes. For scale, I think it's about 60cm in diameter. To send a single photon up and receive it is amazingly accurate, and lucky. Divergence of a laser r
  • People have been bouncing single photon's off of the Moon for almost 40 years, using Lunar Laser Ranging [nasa.gov], or LLR.

    Typically, with LLR a dense "pancake" of photons (maybe 1 meter across and a few mm deep) is shot at the LLR site on the Moon, and one photon returns per shot.

    Ajisai [www.jaxa.jp] is a relatively large Japanese satellite intended for Satellite Laser Ranging (SLR). Even though the SLR return is typically many photons, not just one, the ratio of (photons received back / photons sent) is still extremely ti

  • Hemisphere-wide disco dance party everybody!!!!

    \o
    |>
    /\

    • Re:Other than supposed security improvements... (Score:5, Informative)

      by OzPeter (195038) on Monday March 17 2008, @10:24AM (#22773542)
      From my understanding it does serve a practical purpose in that intercepting the message changes it. Thus while you can't stop people from tapping into your message, you do have instant feedback about when that happens.

      • From my understanding it does serve a practical purpose in that intercepting the message changes it. Thus while you can't stop people from tapping into your message, you do have instant feedback about when that happens.

        That is correct.

        Except that practically, you can stop people from intercepting the communications, by the very aspect you point out.

        While the connection is sending data merrily along its way, upon the first bit being intercepted, both ends know this, thus naturally should be programmed to stop communicating at that point.
        Once communication is stopped, the interception of useful data has been prevented.

        Granted, this is vulnerable to a pretty bad DoS attack, but that was never its goal to prevent, only to pr

    • Why so cynical, Viol8? This sort of research will often net us other technologies that can be used in all facets of our lives. I would agree that nothing is unbreakable. I would think that another quantum computer would eventually break some quantum encrypted packets.

    • Not "supposed" security improvements... (Score:4, Informative)

      by Chrisq (894406) on Monday March 17 2008, @10:37AM (#22773670)
      Real security improvements. There is no proof that there is not a trivial way to factorise multiples of large prime numbers, which is the basis of most current encryption standards. There are alternatives, but again there is no proof that these cannot be cracked quickly.

      Even though it is unlikely that someone will have a mathematical breakthrough that would allow your PDA to break 2kb keys, we know that a lot (maybe all) of these algorithms could be cracked with a quantum computer. It is possible that the US NSA already has such a computer, maybe together with Russia, China and Bill Gates ;-)

      Quantum encryption is proven to be uncrackable without showing that someone is listening. With a preamble of two-way communications you can have a connection that is proven to be absolutely secure, and no breakthrough in mathematics or technology will break it.

    • Re:Other than supposed security improvements... (Score:5, Informative)

      by kmac06 (608921) on Monday March 17 2008, @10:39AM (#22773696)
      Breaking quantum cryptography is not hard, it is impossible. The security is guaranteed by the laws of physics. Unless quantum mechanics is flat out wrong, it can never be broken, period. And saying quantum mechanics could be wrong is like saying gravity could be wrong.

      About quantum computing, it's actually closer to providing new computational powers than you might think. In terms of a powerful, programmable computer that can factor large numbers, we are a long way off. But in terms of being able to simulate certain quantum systems that current supercomputers cannot, we are fairly close.

      • Re: (Score:2, Interesting)

        by BrentH (1154987)
        Intercepting (and breaking) quantum crypto is very much so possible. If Charlie intercepts Bob's fotons on their way to Alice, and Charlie can transmit the very same fotons he just recieved, he can intercept the message succesfully without Alice or Bob ever noticing (perhaps a lag because Charlie has to do some work before he transmits). What Charlie cannot do is old style wiretapping: every foton is a carier of one bit and reading it causes the bit to flip and thus Alice knowing the line is tapped. Reading

        • Re: (Score:3, Interesting)

          by kmac06 (608921)
          I refer you to the no cloning theorem [wikipedia.org]. And you are correct, that in practice there is a probability that there can be more than one photon per bit sent. However, there are ways of correcting for this such as privacy amplification [wikipedia.org]. The guys who are doing this stuff are smart. They know what they're doing. Physicists don't throw around terms like "provably secure" lightly.

        • Re: (Score:3, Informative)

          by JohnFluxx (413620)
          Hi,

          I am a theoretical particle physicist, and I understand what you are trying to say, and I understand what the replies are saying as well.

          You are correct that the 'basic' quantum cryptography that is taught can be hacked. This is just because a simplified version is used in books, because it's confusing enough.

          Others who point out the no cloning principle are exactly right. You cannot read and then reemit a photon with the same polarization (for example). Ba

          • Re:Other than supposed security improvements... (Score:5, Interesting)

            by kelpless (712072) on Monday March 17 2008, @01:08PM (#22775412)

            no cloning principle are exactly right. You cannot read and then reemit a photon with the same polarization
            Hmm. I think you meant you cannot read and reemit with 100% fidelity. http://www.icfo.es/images/publications/J05-055.pdf [www.icfo.es], "Quantum Cloning", Valerio Scarani, Sofyan Iblisdir, and Nicolas Gisin. This is a late 2005 review and of eavesdropping techniques for QKD. Much of the terminology of quantum physics is unfamiliar to me but I think the paper states that Eve could theoretically get 5/6 of the bits through cloning and to keep this from happening, Alice and Bob have to assume an eavesdropper if more than 11% of the bits have errors. When dealing with single photons, read errors will happen. There is also work at the University of Tokyo, the Japan Science and Technology Agency, and the University of York (Sam Braunstein and Akira Furusawa) on telecloning (combined quantum teleportation and quantum cloning) that I have a reference to an experiment done two years ago where they cloned 58% of the photons successfully out of a theoretical 66%.

            Others have created quantum crypto systems that take the possibility of cloning into account, http://w3.antd.nist.gov/pubs/Mink-SPIE-One-Time-Pad-6244_22.pdf [nist.gov]

            'basic' quantum cryptography that is taught can be hacked
            This is true but I think not for the reasons you believe. Basic quantum crypto provides confidentiality only. To keep from being hacked, you must provide authentication as well (Alice must be able to prove she is communicating with Bob and not Eve). I haven't heard of a way to do this without falling back onto more conventional cryptographic techniques such as RSA signatures - at least when doing quantum crypto over fiber. Maybe sending photons through the atmosphere means you can actually just see if somebody is acting as a man-in-the-middle.
      • Quantum cryptography isn't actually cryptography. It's a tamper-resistant method of transmission. In other words, it will tell you when someone is reading your message enroute. It does not encrypt the message. You do that with the same old cryptography routines, quite likely prime number based. As you pointed out, these are quite crackable. The difference is, you KNOW when someone read your message.

        Nobody has yet proven that you can do non-trivial things with quantum computing that you can't do with n
    • Existing cryptography is based on difficult mathematics. RSA, for example, is equivalent to finding a prime factorization of a very large number. By "equivalent" I mean that factoring the number is sufficient to break the encryption, and breaking the encryption (even if you managed to do it without actually attempting to factor the number) tells you the prime factors, so you can't do one without also doing the other. If you developed an incredibly fast, novel way of breaking RSA, you would also have deve
      • The German Enigma machine from WWII was fairly uncrackable, even for the decoders at Betchley Park, but the German operators got lazy, and weren't following proper procedures, which allowed Turning et. al. to get a toehold into the crack.

        The One Time Pad is provably unbreakable, but the British were able to decypher Soviet OTPs, because they had reused the pads after a year, thinking no-one would go back that far. One of our Admirals did the same thing, but there's no evidence he got caught.

        The obvio
      • Oh great...

        I can't wait until someone at the RIAA figures out how to protect music with quantum DRM. You get to listen to a song ONCE, then it doesn't exist anymore.
        They will charge PER listening.
    • With quantum computer I'd assume would come quantum cracking. This is the whole seemingly apparent dualistic nature of this universe in that either one side or the other will be ahead (encryption vs crackers, good vs bad, etc), and that will not last forever. Very wavelike all things can be when you see the binary facts to be merely the expression of the relative positions of two observed events. The crest and trough of waves are two of the three distinct points in waves that can be observed, the third bein
    • I would gather that this is another medium of long-distance communication that uses less energy than current ones do. You do know how saturated the spectrum of communication is, so why nay-say a possibly useful advancement that is in testing and research stages. Innovation is always welcome as long as it serves some sort of purpose, but your skepticism is most likely warranted.
      Although is it particle communication or wave communication? If it were a wave then it would just be another wavelength of radiatio
      • i'm not sure it would use less energy, i think it would actually use more, because quantum communication can only work together with a classical communication channel.

        you cant actually send information using the quantum channel, because you cant control it. you can only compare it to the classical channel. the quantum channel gives you random bits, and the classical channel tells you whether each bit is correct or the opposite of what it should be.
    • And yet again the moderators on here prove that anyone who dares to question the prevailing "wisdom" on /. gets marked as a troll.
    • I am not a particle physicist, nor do I possess anything other than an ameteur's grasp of how this stuff works.

      One potential use for quantum entanglement is to use a whole slew of entangled photons that can be used to transmit binary information at an arbitrary bit-width. While transmitting via the quantum channel, you also transmit via a classical channel some minimal information to discern the clock and parity for decoding the quantum information at the other end.

      The reciever continually records the info

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