Physicists use photons to carry messages from electrons 1.2 miles apart | Hacker News Reader

Physicists use photons to carry messages from electrons 1.2 miles apart

news.stanford.edu

48 pointsjonbaer16 comments

"Quantum supercomputers promise to be exponentially faster and more powerful than traditional computers, Yu said, and can communicate with immunity to hacking or spying. "

Either Yu or the author of this write-up is wrong. I suspect the author...

are you familiar with the potentials of "quantum cryptography"? If not, just do a web search ... that was the reference here.

I'm not a physicist so I can't speak with any authority on the claims but Bruce Schneier in Applied Cryptography claimed that a system which used the principles of quantum cryptography as the transport of the data had already been developed and deployed at great cost between a few key organizations, and this was in a 1996 book.

I'll use this as a basis for a [fallacious] appeal to authority argument here and claim that the "less hackable" claim can't be dismissed outright. But again, I'm not even going to attempt to make any physics claim here --- I simply don't have such credentials.

Those systems afaik currently do not encrypt data but ensure that no one is tapping into the fiber and retransmitting the signal as they cannot reproduce the photons in their original quantum state.

It's pretty standard these days for government point to point links that use existing laid fibers or go through existing metro ducts.

http://www.lanl.gov/projects/feynman-center/technologies/inf...

The quantum part simply allows perfect distribution of keys. So person A can tell person B what key to use, and person B can know with certainty that nobody else saw it. Then they just use regular encryption.

Does asymmetric key exchange handle this problem, or am I missing some attack vector?

Well, I'm not actually sure if there's any problem with asymmetric keys, now.

I think, since asymmetric keys depend on factors of big prime numbers, they are vulnerable to quantum computers actually. Whenever those start working, keys become easily breakable.

https://en.wikipedia.org/wiki/Post-quantum_cryptography

No it doesn't. It depends on the existence of asymmetric algorithms. There's as far as I know, a number of classes of algorithms that have a good potential to satisfy this.

That sounds neat, but we're not using any of those. And I don't see a [0] with a link anywhere in your comment. What I read, cited above, said that all existing asymmetric key algorithms are easily broken with quantum computers.

There are algorithms that can have an exponential speedup on a quantum computer, there are plenty that have a quadratic speedup, for example, searching an unsorted/unindexed database takes O(sqrt(n)) instead of O(n) (with high probability of success). Which means that any optimization problem (with a search tree) can have this quadratic speedup too.

Quantum cryptography has some pretty lovely nature tricks that enable no chance of spying/hacking, measuring the state plays so weirdly with the quantum system.

"Photons from two different sources have different characteristics, like color and wavelength. If they have different wavelengths, they cannot interfere, Yu said"

Can somebody explain why that is the case?

I don't think it's 100% true as stated. https://en.m.wikipedia.org/wiki/Photomixing

That seems like a simple superposition, while I'm going to assume the author meant some sort of quantum interference.

I thought superposition in like was a QM effect.

Here's a link: https://en.wikipedia.org/wiki/Hong%E2%80%93Ou%E2%80%93Mandel...

I can explain that color and wavelength are the same thing, which makes me suspicious of the rest of it.

Why are photons required to "act as the messengers of an electron's spin"? Entanglement works without any communication between the entangled particles, right?

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