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Australian Researchers Demo Random Access Quantum Optical Memory
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.
But it could be fast enough that it doesn't matter. Perhaps someone that read the brief could chime in?
Unfortunately from the description it would appear that the memory is not quantum addressable ... that is, you can't use a set of qubits as the address of which qubit to read. For a fully general-purpose quantum computer, we will probably need quantum addressable memory.
While light can be bounced around, absorbed and re-emitted fairly well in a classical sense, it gets tricky when you start trying to store single photons that have been intentionally "dicked with" to encode quantum information. (i.e. Quantum bits, or qubits) What this paper is talking about is one way of implementing quantum memory for successfully storing and recalling photonic qubits. (i.e. light)
Now, the computer geeks out there probably heard "qubits" and immediately thought "OooOOOooo... Quantum Computers!". Not so fast. Photonic qubits are generally too quick to decohere (even when stored in memory such as this) and difficult to interact with to be good candidates for quantum computing. It's certainly not impossible, and perhaps even probable in the long-run, but atomic qubits are currently more promising and more widely being looked at for quantum computing. What a photonic quantum memory is immediately useful for is communications. i.e. Quantum cryptography. More specifically, building quantum repeater networks.
If you know a little about computer networks, you know that signals traveling over long distances have to be boosted by repeaters every so often or loss humps your data. Optical networks are exactly the same. After a few hundred kilometers of fiber you have a lot of loss. Unfortunately, unlike classical bits, which can simply be copied, qubits cannot be reliably copied. (Google the "no cloning" theorem if you care.) The work around is a little complex to explain (it's essentially a daisy chain of entanglement swapping), but requires quantum memory to work.
The short of it is, this sort of quantum memory will allow us to build longer distance quantum encryption networks than currently exist. (Quantum crypto is currently being used by some European banks.) At first, this might allow banks in North America to jump on the Quantum bandwagon. It's hideously expensive at the moment, naturally, and probably less economical than running volkswagen's full of hard-drives with one-time-pads on them back and forth, but in principle nothing about this tech is any more expensive than the repeaters the internet currently runs on. Economy of scale should eventually kick in, and these quantum crypto networks will be pretty handy if quantum computers manage to toast public key encryption. (Authentication, of course, is another issue entirely...)
Now, I haven't had a chance to read the Nature paper yet. I've read this groups past papers though, and they really are world leaders in experimental CRIB implementation. Last I checked, they still didn't have adequate efficiency to make their tech useable (must be greater than 50% recall to be practical). Still, CRIB is one of the more promising methods out there.