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China Communications Security The Internet

Chinese Satellite Breaks Distance Record For Quantum-Key Exchange ( 42

slew writes: Science Magazine reports a team of physicists using the Chinese Micius satellite (launched back in August 2016) have sent quantum-entangled photons from a satellite to ground stations separated by 1200 kilometers, smashing the previous world record. Sending entangled photons through space instead of optical fiber networks with repeaters has long been the dream of those promoting quantum-key exchange for modern cryptography. Don't hold your breath yet, as this is only an experiment. They were only able to recover about 1000 photons out of about 6 billion sent and the two receiving stations were on Tibetan mountains to reduce the amount of air that needed to be traversed. Also the experiment was done at night to minimize interference from the sun. Still, baby steps... Next steps for the program: a bigger satellite for more power and moving to quantum teleportation instead of simple key exchange. The results of the experiment were published in the journal Science.
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Chinese Satellite Breaks Distance Record For Quantum-Key Exchange

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  • by Anonymous Coward

    So they sent entangled photons to ground, and there was a second signal, one that says "entanglement successful, photon is valid", and that was send how exactly? The signal they use to filter out all the other photons detected. That signal, the one that's actually carrying the real information here.... the one any attacker would attack if this was ever used in main stream use.

    Look, I have a space based machine that fires ping pong balls at the earth, it paints them with random paint, and spins them in rando

    • by Anonymous Coward on Saturday June 17, 2017 @04:43AM (#54638229)

      Mods, before modding this up, be aware the poster(s) posts the same misunderstood garbage to nearly every Slashdot story involving anything quantum mechanics related. The poster fundamentally misunderstands entanglement experiments and the variety of possible setups that have been in use for decades now. Yet the poster always disregards any detailed and/or cited reply showing how wrong it is, while taking time to attack others replies that are less intelligent and acting as if that validates their armchair disproof of quantum mechanics. Mean while, those with backgrounds in the subject realize it is a waste of time trying to correct the same mistakes when it gets spammed on so many articles, and yield not because the parent is correct, but because the parent has too much free time and is too dense to argue with.

      • by Anonymous Coward

        Don't play on his level--don't post AC.

    • by rpresser ( 610529 ) <> on Saturday June 17, 2017 @05:08AM (#54638279) Homepage
      RTFA. Or if you can't, I'll summarize.

      The satellite generated entangled photon pairs, sending them down to two separated ground stations in the Himalayas.

      One out of every 6 million pairs was received properly (how they could tell, I don't know. Time codes?). Polarization measured at each ground station and correlated (via normal phone or perhaps Internet). Correlation was nonrandom due to Bell's Inequality, demonstrating that entanglement survived the transmission from space.
    • Getting ahold of the keys to encryption by a man in the middle attack approach is on a short list of 'easy' ways to defeat encryption. A 100% secure method of transmitting the keys globally would be a major advancement. You can then send your message classically with far less worry.
  • Did this include actual communication? How closer is humanity to having a working ansible?

    I'm talking about the so-far science fiction device for instantaneous communication, not the open-source automation engine.

  • is that they're publishing it in Science.

  • Quantum teleportation is the even that's theoretically faster than light by way of being instant, regardless of distance, correct? Am I correct in thinking this is more of that a quantum entangled signal was transmitted in a waveform and they successful read the spin on roughly 1000 of the point resolved photons?
    • Quantum teleportation is the one* that's theoretically faster than light I hate typos :-/ Sorry about that.
      • There are methods of sending information 'faster than light' but essentially the problem is you can only put your signal on top of random states. Untill you measure those and send them at classical light speed, you will have no idea what is sent and therefore sending information (or energy) instantly is by all understanding and experiment, not possible.
  • "They were only able to recover about 1000 photons out of about 6 billion sent"

    My cellphone provider's electrons also only achieve a similar result, judging by the quality of the talks.

  • Are 1000 out 6 billion distinguishable from random chance, or even useful?

  • So they sent them to the space station and now a satellite and I think the space station one blew up on launch but have they determined yet if it's faster than light transmission? The theory is that you had to physically move the particles at least once away from each other so you can't violate causation or something like that. But has it been proven?
  • "Quantum teleportation" is not teleportation. You cannot use entanglement to violate causality. You are not exceeding c.

  • Bell's inequality is incomplete. It does not hold for all possible hidden variables. It holds only for those hidden variables that repeat under different experimental configurations (device orientations). But there are other hidden variables that do not repeat. Hidden variables belonging to the reals do not repeat. Every instance of a real random variable is unique. The probability of two instances being equal is zero, exactly zero. What this means for the Chinese news story is that nothing special h
  • Just a slight pocket loss there kek...

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