Theoretical Breakthrough For Quantum Cryptography

KentuckyFC writes "Quantum cryptography uses the quantum properties of photons to guarantee perfect secrecy. But one of its lesser known limitations is that it only works if Alice and Bob are perfectly aligned so that they can carry out well-defined polarization measurements on the photons as they arrive. Physicists say that Alice and Bob must share the same reference frame. That's OK if Alice and Bob are in their own ground-based labs, but it's a problem in many other applications, such as ground-to-satellite communications or even in chip-to-chip communications, because it's hard to keep chips still over distances of the order of the wavelength of light. Now a group of UK physicists have developed a way of doing quantum cryptography without sharing a reference frame. The trick is to use entangled triplets of photons, so-called qutrits, rather than entangled pairs. This solves the problem by embedding it in an extra abstract dimension, which is independent of space. So, as long as both Alice and Bob know the way in which all these abstract dimensions are related, the third provides a reference against which measurements of the other two can be made. That allows Alice and Bob to make any measurements they need without having to agree ahead of time on a frame of reference. That could be an important advance enabling the widespread use of quantum cryptography."

Re:qutrits?

[Nadaka]

Especially when dealing with entangled triplets.

Engineering

[SEWilco]

I think this is engineering, not theory. Theory was the original idea of using entanglement for cryptography. Now they're applying the technology to make it practical, and that's engineering. They're adding a bit of steel or another entanglement to make it more usable. If nobody has built this device yet, it's theoretical engineering.

Re:Quantum Communications

[Threni]

Would this system still allow alice/bob to know if someone's evesdropped? What's the difference between a hostile evesdropper and just some other part of the infrastructure for getting data from alice to bob? Without that, quantum cryptography is just another encryption system, and there are nothing wrong with the current ones. Right? (It would arouse me if replies to this post started simply "Wrong.")

Re:You lost me at hello...

[Anonymous Coward]

No car analogy, but I think I summarize it a little simpler (though I am no expert).
In Quantum Cryptography it's possible to detect the presence of an eavesdropper. The eavesdropper, by the act of listening changes the transmission of the signal and is provably unable to put it right again. This is possible because of some physics mumbo-jumbo and is highly sensitive to the distances between the people involved.
As best I can make out, this research used more physics mumbo-jumbo to encode the distances between the involved parties inside the communication so that they can move about (instead of being tethered together by a fixed length line of fiber-optic cable).