Theorists Make Quantum Communications Breakthrough

KentuckyFC writes "One of the cornerstones of modern physics is Claude Shannon's theory of communication, which he published in 1948. If you've ever made a phone call, watched TV, or used a computer, you've got Shannon to thank for describing how information can be moved from one place in the universe to another using an idea called the channel capacity. But nobody has been able to develop a quantum version of this theory. So physicists have no idea how much quantum information can be sent from one point to another. Now two American physicists have made an important breakthrough by proving that two quantum channels with zero capacity can carry information when used together. That's interesting because it indicates that physicists may have been barking up the wrong tree with this problem: it implies that the quantum capacity of a channel does not uniquely specify its ability for transmitting quantum information (abstract). And that could be the idea that breaks the logjam in this area."

Comments

quantum mechanics

[edwebdev]

"two quantum channels with zero capacity can carry information"
Feynman once said that nobody understands quantum mechanics, and this is why.

Zero plus Zero equals One for large values of Zero

[LostCluster]

I'm not sure how useful this is. The summaries seem to say that if you take two or more channels that have a signal to noise ratio of zero, there's some potential for binding them into a useful channel, but there's no indication of what kind of recovery rate there can be gained from this. Is this just error-correction applied to an extreme?

Non-peer reviewed

[4D6963]

Am I the only one who's worried that we keep getting 'news' from papers published on ArXiv, which is not a peer-reviewed source?

Just saying, it needs to be taken with a grain of salt.

I think you've got it

[ODBOL]

I think that Khashishi has got the essence of the 0+0>0 thing here. I haven't completely penetrated the noise in the Smith/Yard ArXiv article yet, but I'd bet my money that it boils down to this:

Take two channels in each of which all bits are completely random, and independent of the information that you wish to send. Let each bit of your information determine the correllation or anticorrellation of corresponding bits in the two channels, by introducing a quantum constraint between them before their actual random values are determined. Then, as in Khashishi's description, the xor of the two random channels is the message.

The only difference I detect in Smith/Yard vs. Khashishi is that they use quantum trickery to make the whole thing look symmetric. Neither of the random channels predates the other. Each one, evaluated singly, appears to be completely independent of the encoded message. In Khashishi's description, the time sequence in the construction of the two random sequences makes one of them seem a priori random, and the other to be a one-time pad encoding of the message, while in the Smith/Yard article you can't tell which is which.

It seems more like a meretricious way of telling a causal story about a well-known phenomenon than something truly "essentially quantum."

Re:So 0+0=1!

[tenco]

The zero-point energy of an quantum mechanical harmonic oscillator is 0.5\hbar\omega > 0. Well, spoiled as i am, TFA can't surprise me anymore :)