5 ms·

When two network quantum chips can communicate instantly (not at speed of light--instantly) over infinite distances, using entangled atoms, then we can ditch th

When two network quantum chips can communicate instantly (not at speed of light--instantly) over infinite distances, using entangled atoms, then we can ditch the tecos. I'm so looking forward to that.

thangalin 13y ago
Chances are FTL communication is not possible. http://curious.astro.cornell.edu/question.php?number=612 http://curious.astro.cornell.edu/question.php?number=612 http://en.wikipedia.org/wiki/Superluminal_communication http://en.wikipedia.org/wiki/Superluminal_communication The book, "Why E=mc^2" is an exceptional read. If I recall correctly, it explains why light-speed is a universal limit: http://www.amazon.co.uk/Why-Does-mc2-Brian-Cox/dp/0306819112 http://www.amazon.co.uk/Why-Does-mc2-Brian-Cox/dp/0306819112
- deleted 13y ago
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- leoc 13y ago
  Mind you, this would imply that the telcos probably can't send data FTL either, so it's all good. :)
- jerf 13y ago
  Stating whether FTL communication is possible at all may require hedging. Stating that it can't occur over quantum superposition does not, as I understand it. The math is clear; there's no information traveling. It does not matter how sophisticated our quantum computers get, there will not be any FTL communication coming out of them. If we could do that at all, we'd almost certainly be able to to it today, anyhow. We have multi-q-bit QM computers, they just aren't of a practical size for computation. But if FTL communication was possible, it would have been done with them already.
leeoniya 13y ago
how would you entangle the photons in the first place? from what i understand they have to be in close proximity or even emitted from the same source. once entangled, they need to be maintained in this state very very carefully. i think a few hours is the record currently. to really reap the benefits of entanglement for anything other than microsecond HFT algos, like for human telecommunication, you would need to physically separate these photons by hundreds of thousands to millions of miles. i dont think you can keep them entangled while transporting them that kind of distance. i could be really really wrong on all of this :)
- chris_mahan 13y ago
  Yeah, not saying this was possible now. But in 10, 20 years? Perhaps they can be entangled at the factory in the "special room" then kept stable over the next 10 years. That would be enough, no?
  - sp332 13y ago
    Sure. Last year, they stopped a photon for a solid minute. http://www.extremetech.com/extreme/162289-light-stopped-completely-for-a-minute-inside-a-crystal-the-basis-of-quantum-memory http://www.extremetech.com/extreme/162289-light-stopped-comp... Note this preserves the quantum state of the photon - it's not just storing the energy and then re-emitting a different photon.
    - devilshaircut 13y ago
      It is my limited understanding that the idea of "a different photon" would be sort of irrelevant here as quantum state is the only thing that differentiates objects such as photons from one another. Outside of that, photons are essentially fungible. I don't really understand the finer points of the experiment however and I could be totally wrong in my understanding.
      - sp332 13y ago
        Oh yeah, I think the current model is that it gets stuck in an electron somehow. But since it preserves the quantum state, it's still usable for quantum crypto and quantum computing.
      - knodi123 13y ago
        I can imagine a world where they're more than just fungible- They could even be literally the same object. See http://en.wikipedia.org/wiki/One-electron_universe http://en.wikipedia.org/wiki/One-electron_universe
- frozenport 13y ago
  >>to really reap the benefits of entanglement for anything other than microsecond HFT algos These systems are high latency as they often are supplemented by classical communication and post processing. They are used by banks (in Switzerland) to do secure point-to-point communication. But they only protect the channel and not the copy of Windows 2000 running on either end.
Strilanc 13y ago
Quantum mechanics doesn't allow instantaneous communication. QM does allow some additional forms of spontaneous coordination, like in quantum pseudo telepathy games [1], but there is no communication. There is no back-and-forth decision making, just after-the-fact correspondence. Unfortunately, the distinction between classical communication and quantum coordination is kind of hard to explain. It has to do with the difference between stochastic and unitary matrices [2]. 1: http://en.wikipedia.org/wiki/Quantum_pseudo-telepathy http://en.wikipedia.org/wiki/Quantum_pseudo-telepathy 2: http://en.wikipedia.org/wiki/Unitary_matrix http://en.wikipedia.org/wiki/Unitary_matrix
- alphydan 13y ago
  I'll bite the bullet and try to explain it in layman's terms (with not attempt at rigor): When you measure particle A, something happens to particle B. Unfortunately, particle B always has 2 potential outcomes (let's say, with 50% chance of being RED and 50% chance of being BLUE). So when you measure B, you find "B is red", or "B is blue". Now when you measure particle A, imagine you change the probabilities for B remotely to 90%/10%. But when you're the guy at B, and you machine say "RED!" ... did that just happen because A changed the likelyhood, or did it happen because, well, there was a 50/50 chance of it happening? It is more subtle than that, but that's the gist of why you can't send information. (yes when you repeat the experiment and A and B compare their results, the probabilities have changed, but for a single measurement you never know if you got it by chance or if you got it because A did something).
  - hackuser 13y ago
    >When you measure particle A, something happens to particle B. Couldn't that be the signal? For example, one person could tell the other: "When B resolves, press the button!" It wouldn't matter if B resolved to red or blue. Is it that we cannot detect whether B is in a superposition state without observing it and therefore resolving its state to one 'position' or the other? (I hope I'm not the only one on HN with an incomplete understanding of current quantum theory.)
    - 13y ago
michael_nielsen 13y ago
Faster-than-light communication using entanglement is not possible, according to the standard rules of quantum mechanics. (Dropping some credentials doesn't seem inappropriate here: I worked professionally as a researcher on quantum computing and quantum information for 13 years.)
- deleted 13y ago
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bashinator 13y ago
If at any point in the future of human history FTL travel or communications gets invented, we would already know about it.
- wlievens 13y ago
  As far as I understand, faster-than-light communication violates causality in some reference frames but not in all. FTL communication without arbitrary tims travel might be possiblem

thangalin 13y ago

Chances are FTL communication is not possible. http://curious.astro.cornell.edu/question.php?number=612 http://curious.astro.cornell.edu/question.php?number=612 http://en.wikipedia.org/wiki/Superluminal_communication http://en.wikipedia.org/wiki/Superluminal_communication The book, "Why E=mc^2" is an exceptional read. If I recall correctly, it explains why light-speed is a universal limit: http://www.amazon.co.uk/Why-Does-mc2-Brian-Cox/dp/0306819112 http://www.amazon.co.uk/Why-Does-mc2-Brian-Cox/dp/0306819112

deleted 13y ago
[deleted]
leoc 13y ago
Mind you, this would imply that the telcos probably can't send data FTL either, so it's all good. :)
jerf 13y ago
Stating whether FTL communication is possible at all may require hedging. Stating that it can't occur over quantum superposition does not, as I understand it. The math is clear; there's no information traveling. It does not matter how sophisticated our quantum computers get, there will not be any FTL communication coming out of them. If we could do that at all, we'd almost certainly be able to to it today, anyhow. We have multi-q-bit QM computers, they just aren't of a practical size for computation. But if FTL communication was possible, it would have been done with them already.

leeoniya 13y ago

how would you entangle the photons in the first place? from what i understand they have to be in close proximity or even emitted from the same source. once entangled, they need to be maintained in this state very very carefully. i think a few hours is the record currently. to really reap the benefits of entanglement for anything other than microsecond HFT algos, like for human telecommunication, you would need to physically separate these photons by hundreds of thousands to millions of miles. i dont think you can keep them entangled while transporting them that kind of distance. i could be really really wrong on all of this :)

chris_mahan 13y ago
Yeah, not saying this was possible now. But in 10, 20 years? Perhaps they can be entangled at the factory in the "special room" then kept stable over the next 10 years. That would be enough, no?
- sp332 13y ago
  Sure. Last year, they stopped a photon for a solid minute. http://www.extremetech.com/extreme/162289-light-stopped-completely-for-a-minute-inside-a-crystal-the-basis-of-quantum-memory http://www.extremetech.com/extreme/162289-light-stopped-comp... Note this preserves the quantum state of the photon - it's not just storing the energy and then re-emitting a different photon.
  - devilshaircut 13y ago
    It is my limited understanding that the idea of "a different photon" would be sort of irrelevant here as quantum state is the only thing that differentiates objects such as photons from one another. Outside of that, photons are essentially fungible. I don't really understand the finer points of the experiment however and I could be totally wrong in my understanding.
    - sp332 13y ago
      Oh yeah, I think the current model is that it gets stuck in an electron somehow. But since it preserves the quantum state, it's still usable for quantum crypto and quantum computing.
    - knodi123 13y ago
      I can imagine a world where they're more than just fungible- They could even be literally the same object. See http://en.wikipedia.org/wiki/One-electron_universe http://en.wikipedia.org/wiki/One-electron_universe
frozenport 13y ago
>>to really reap the benefits of entanglement for anything other than microsecond HFT algos These systems are high latency as they often are supplemented by classical communication and post processing. They are used by banks (in Switzerland) to do secure point-to-point communication. But they only protect the channel and not the copy of Windows 2000 running on either end.

Strilanc 13y ago

Quantum mechanics doesn't allow instantaneous communication. QM does allow some additional forms of spontaneous coordination, like in quantum pseudo telepathy games [1], but there is no communication. There is no back-and-forth decision making, just after-the-fact correspondence. Unfortunately, the distinction between classical communication and quantum coordination is kind of hard to explain. It has to do with the difference between stochastic and unitary matrices [2]. 1: http://en.wikipedia.org/wiki/Quantum_pseudo-telepathy http://en.wikipedia.org/wiki/Quantum_pseudo-telepathy 2: http://en.wikipedia.org/wiki/Unitary_matrix http://en.wikipedia.org/wiki/Unitary_matrix

alphydan 13y ago
I'll bite the bullet and try to explain it in layman's terms (with not attempt at rigor): When you measure particle A, something happens to particle B. Unfortunately, particle B always has 2 potential outcomes (let's say, with 50% chance of being RED and 50% chance of being BLUE). So when you measure B, you find "B is red", or "B is blue". Now when you measure particle A, imagine you change the probabilities for B remotely to 90%/10%. But when you're the guy at B, and you machine say "RED!" ... did that just happen because A changed the likelyhood, or did it happen because, well, there was a 50/50 chance of it happening? It is more subtle than that, but that's the gist of why you can't send information. (yes when you repeat the experiment and A and B compare their results, the probabilities have changed, but for a single measurement you never know if you got it by chance or if you got it because A did something).
- hackuser 13y ago
  >When you measure particle A, something happens to particle B. Couldn't that be the signal? For example, one person could tell the other: "When B resolves, press the button!" It wouldn't matter if B resolved to red or blue. Is it that we cannot detect whether B is in a superposition state without observing it and therefore resolving its state to one 'position' or the other? (I hope I'm not the only one on HN with an incomplete understanding of current quantum theory.)
  - 13y ago

michael_nielsen 13y ago

Faster-than-light communication using entanglement is not possible, according to the standard rules of quantum mechanics. (Dropping some credentials doesn't seem inappropriate here: I worked professionally as a researcher on quantum computing and quantum information for 13 years.)

deleted 13y ago
[deleted]

bashinator 13y ago

If at any point in the future of human history FTL travel or communications gets invented, we would already know about it.

wlievens 13y ago
As far as I understand, faster-than-light communication violates causality in some reference frames but not in all. FTL communication without arbitrary tims travel might be possiblem