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Communications Science

Single Photons Bounced Off Orbiting Satellite 131

Posted by CmdrTaco from the pling-pling-pling dept.
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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Single Photons Bounced Off Orbiting Satellite More

Single Photons Bounced Off Orbiting Satellite

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  • Complicatedly Unacceptable (Score:5, Funny)

    by eldavojohn ( 898314 ) * <eldavojohn@noSpAM.gmail.com> on Monday March 17, 2008 @11:02AM (#22773324) Journal

    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 @12:37PM (#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

      • OK, but how did they know the received photon was the one they fired, and not one received from a far-away star?

      • Re: (Score:2)

        by HTH NE1 ( 675604 )

        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 ground.

        Are you sure it's not just covered in triangular corner reflectors [wikipedia.org]? That's how I'd design it.

  • Come clean (Score:5, Funny)

    by sleeponthemic ( 1253494 ) on Monday March 17, 2008 @11:06AM (#22773376) Homepage
    This is just an elaborate game of pong, isn't it...

  • well, no (Score:2, Insightful)

    by Ancient_Hacker ( 751168 )
    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.
      • Thanks, I've read many books on the subject.

        Please explain how the entanglement survives the photon's many interactions with the atmosphere and the mirror.

        AFAIK entanglement won't survive any non-unitary interaction, like scattering or reflection.

        • Re: (Score:2)

          by Romancer ( 19668 )
          No, you cite where entanglement id destroyed by any interaction with the universe. as in:
          " That means effectively in their own little world, not intereacting with the universe in any way."

          For the proof of actual entanglement you have to interact with the pair in some way to test it. Which means that they must be effected by the universe to have any use or proof of existance. And for all I can remember tachions are the closest to non interactive as we've been able to imagine. If you were to actually read the
  • 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
      • No you haven't violated the HUP. Your experiment has something to do with observer effect but I have no clue what it is supposed to prove. However, you haven't measured the position and velocity of the particle, so you havn't violated uncertainty principle.

        • Re: (Score:2)

          by clonan ( 64380 )
          The observer effect is a direct result of the connection between position and velocity.

          My design has determined the position of an object (within the box) without effecting the speed whatso ever since I haven't interacted with it.
      • Most people confuse the difficulty of measurement with the uncertainty principle. The difficulty of measurement has to do with the fact that you can't measure something without affecting it. The uncertainty principle is actually a direct consequence of the fundamental postulates of quantum mechanics. You cannot, even in principle, even as a thought experiment, construct a quantum mechanical state which violates the uncertainty principle (or any of the uncertainty principles). This is a mathematical cert

        • Re: (Score:2)

          by clonan ( 64380 )
          Actually, if you review the uncertainty principle, you find that uncertainty includes more than just position and velocity but in the quantum world it also includes entanglement with the environment. Having entangled particles adds a great deal of uncertainty since you don't know what the other particel in the pair is experienceing.

          This is actually Bohr's solution to one of Einstein's thought experiments, although phrased differently. (Read up on the light in the box)

          Therefore, you are partially correct.
  • Scientists later found that the photon had been Photoshopped [slashdot.org].
  • 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

    • Re: (Score:2)

      by ceoyoyo ( 59147 )
      They're not faster, they're more secure. The quantum communication gear tells you if someone else is listening to your conversation.
      • But what if the entanglement is in the router...?

        • Re: (Score:2)

          by ceoyoyo ( 59147 )
          You mean inside the router? I don't see what the point would be. It's unlikely someone is going to tap into your router to read your message. Quantum communication protects the transmission it's used on. If you use it on your LAN it protects your LAN. If you use it between your router and the ISP then it protects that.
          • Sorry, that was meant to be a joke!

            Typically when someone says "the Internet treats censorship as damage, and routes around it," the standard reply is "but what if the censorship is in the router"?

  • In other news... (Score:4, Funny)

    by JCSoRocks ( 1142053 ) on Monday March 17, 2008 @11:39AM (#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.

      • On second thoughts, if you had a wide enough 'beam' with this one photon in it, it should work okay.

    • Re: (Score:2)

      by ceoyoyo ( 59147 )
      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.

    • They use Corner reflectors [wikipedia.org] looking like this [wikipedia.org].

      Even then the photon will be greatly diffracted, meaning you need a large detector - a 1.5m telescope in this case. With this setup the article reports a detection rate of roughly one in 3000.

    • 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
    • You can partially answer your question just by thinking about what you yourself said. When you look in a mirror, you're using photons to view yourself. If photons were as sensitive to single atom imperfections as you suggest, you'd see bits of features all the way across the room rather than your own face in the mirror. So it should be completely obvious that photons, at least photons of visible light, aren't terribly sensitive to single atom imperfections.
  • 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
  • Would make for an interesting game of pong!
  • I misread both the title and the summary. I got:

    Simpletons bounced off orbiting satellite.

    ....
    at the University of Vienna and colleagues have taken an important step fowards by bouncing this individual Anton Zeilinger off the Ajisai geodetic satellite
    ...

    It's been a long Monday.

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

    \o
    |>
    /\
  • W3 h4v3 ur ph070n. F u 3v3r w4n7 70 s33 17 4g41n, u mus7 ...
  • The FCC is already making plans to auction off the entire spectrum of quantum communications for billions of dollars.
  • Comment removed based on user account deletion

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