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Often “why”-questions are interpreted as criticism. I would like to ask one, just because I am curious: why are people interested in this for communication? With current technology we can communicate with within the limits of the speed of light. We can also encrypt communication. So, what makes this technology so interesting, that people may want to use it in the future? Will it be cheaper? Faster? More secure/better encrypted?



From the article:

Teleportation can also securely transmit quantum information even when Alice does not know where Bob is. Bob can take his entangled particle wherever he pleases, and Alice can broadcast her instructions for how to ungarble the teleported state over whatever conventional channels — radio waves, the Internet — she pleases. That information would be useless to an eavesdropper without an entangled link to Alice.

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As far as I can tell, this just seems like an obscenely overcomplicated one time pad. Instead of Alice giving Bob a string of bits that are known in advance, she gives Bob an entangled particle that can be collapsed to determine a string of bits at a later date. I can't see any security benefit.

This is very neat from a purely scientific perspective. It seems pointless and misleading to try to present it as having direct practical value.

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For one thing, AFAIK, Alice can be sure that Bob's 'pad' is the only copy in existence because no one can copy Bob's 'pad' without destroying the entanglement.

For a 'regular' one time pad this is not the case. Someone could have copied it and both Alice and Bob would be none the wiser until it's too late.

One-time pad based encryption schemes are theoretically unbreakable - one of the things (the thing?) holding back wide spread adoption is the difficulty of proper key management. This has the potential to solve that issue.

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Basically, the advantage is that you're creating the same one time pad in two faraway places at the same time, so there's no risk of it being intercepted. If Eve tries to mess with the stream of entangled photons all that will happen is that Alice and Bob will see garbage when they try to decrypt their message. If the one-time pad had been sent via traditional means, Eve would be able to read the message without Alice and Bob knowing.

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The difference is that the quantum version of the "one time pad" can't be copied. So if someone stole Bob's quantum states he would realize. (Anyway for practical applications this is still overcomplicated and http://xkcd.com/538/ apply.)

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This is very neat from a purely scientific perspective. It seems pointless and misleading to try to present it as having direct practical value.

If I had a buck for every time this was said about a scientific discovery, I would be quite well off...

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So a VERY advanced version of this could be used for things like:

* underground/underwater communication systems where wires and radio waves faulter

* interstellar communication without antennae and without bouncing the signal off satellites

* radiowave-less espionage

* etc?

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Maybe even something crazy like teleportation!

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With current technology we can communicate with within the limits of the speed of light.

Despite knowing close to nothing about this field, I'd hope that error-correction code would be somewhat simpler, resulting in less padding and more data going through. Think about the problems with dial-up telephones alone, lots of noisy lines and so you have to pad the data with enough error detection that it's still recoverable at the other end of the line.

It's been nearly two decades since I last studied this, but something about parity check matrices is screaming away in my head. Could be very wrong about that though.

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It allows sending quantum information over a classical channel, at 2 bits per qbit.

Of course you have to have already prepared and sent the same amount of qbits... maybe sending qbits "as needed" is harder than sending them in bulk in advance?

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