Australian Researchers Demo Random Access Quantum Optical Memory 74
nuur writes "Researchers at the Australian National University have developed a new form of optical memory that allows random access to stored optical quantum information. Pulses of light are stored on a kind of 'optical conveyor-belt' that is controlled with a magnetic field. By manipulating the magnetic field, the conveyor-belt can be moved, allowing the recall of any part of the stored optical information. The research is published in Nature." You'll probably know after reading the abstract linked whether you'd be in the market to pay for the whole thing.
meh (Score:3, Informative)
Re:Why this could be useful: (Score:5, Informative)
Here's the principle on which quantum repeater networks will operate:
Alice (----- Entangled Photon Pair Source -----) Bell State Measurement (------ Entangled Photon Pair Source -----) Bob
What we want is for Alice and Bob to each wind up holding half of an entangled pair of photons. The two sources create two pairs of entangled photons and send the halves in opposite directions. Alice and Bob initially receive photons that have nothing to do with each other. However, when the other halves of Alice and Bob's pairs are annihilated together in the Bell State Measurement in the middle, the entanglement of the annihilated photons is swapped to Alice and Bob's photons such that they wind up being entangled together. The nice thing about this is that Alice and Bob can verify that they share entangled pairs and there's no way for anyone in the middle to fool them, provided Alice and Bob authenticate each other and there are no real-world deficiencies in their apparatus. In essence, Alice and Bob don't have to trust the man in the middle even though he's handling their photons.
To build a quantum repeater network, you just expand this out in a giant daisy chain with many many steps. Quantum memory is necessary for caching photons at each node in the chain so that you can wait for all nodes to be ready before proceeding with the bell state measurements. Caching is necessary because the probability of photons reaching each of the stations in the network simultaneously is no better than the probability of one photon going from end-to-end. i.e. Not bloody likely over long distances.
P.S. Funny aside: The first BB84 system built by Bennett and Brassard (the first quantum crypto system ever built), had some rather noisy pockel cell's controlling measurement bases such that you could tell what basis Alice was measuring in from the sound of the cell. Additionally, Alice and Bob were on the same lab bench, so an eavesdropper in between them would necessarily be inside the room. It was therefore famously joked that the first quantum crypto system was only secure if any potential eavesdropper was stone deaf! This is an example of a side-channel attack that can occur when reality doesn't quite live up to theory, and is the sort of thing people building any kind of crypto system, quantum or otherwise, have to worry about.