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Comment by leeoniya | Hacker News Reader

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 :)

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>> i dont think you can keep them entangled while transporting them that kind of distance.

The main reason for this is decoherence (the pair of entangled photons interact with other photons, or particles along the way) ... and lose their connection because they have to share it with the other particles [1].

People have come up with clever tricks to fight that. It's called distillation of entanglement [2]. You share 1000 pairs of particles, all weakly entangled because they have travelled a long distance and rubbed with the wrong particles along the way. Then each party at each end combines the particles with some measurements and classical communications (phone or internet) and ends up with a single pair, far away, highly entangled.

[1] http://www.quantiki.org/wiki/Monogamy_of_entanglement

[2] https://en.wikipedia.org/wiki/Entanglement_distillation

>>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.

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?

Sure. Last year, they stopped a photon for a solid minute. 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.

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.

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.

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

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