A Solace for Quantum Computing

A year on from a spectacular controversy in quantum computing, it looks like rationality is breaking out.

Last year, D-Wave Systems, the only commercial start-up in the highly demonstrated a 16 qubit quantum computer. Or not, as the case may be.

The problem was that quantum computing is still at an early stage in the labs. It's rare to get two qubits, and to persuade them to exist long enough to do anything. D-Wave claimed its "adiabatic" approach got round the problem and performed a demo. But it was effectively a demo on a "black box" - and was criticised by academic quantum computing specialists, because D-Wave did not actually do the measurements which would have proved whether it really WAS a quantum computer or not.

Scott Aaronson, whose marvellous Shtetl-Optimised blog is required and delicious nerd reading, said D-Wave's Orion system was "as useful as a roast-beef sandwich". This didn't stop D-Wave from promising great things - earlier in 2007, it was talking about having a 1024-qubit system available by the end of 2008.

One year on, things seems a bit less confrontational. Geordie Rose - maverick founder of D-Wave - actually visited MIT, to talk with Aaronson, and Seth Lloyd, the co-inventor of the theory of adiabatic quantum computing. There are write-ups in MIT Technology Review from Lloyd and Aaronson. Aaronson says, in his blog: "The people at D-Wave are not conscious frauds; they genuinely believe in what they’re doing. On the other hand, much of the publicity surrounding D-Wave can be safely rejected."

For its part, D-Wave seems to be turning down the hype. It does expect to manufacture its next step - a claimed 128-qubit quantum computer sometime in the next couple of weeks (see Geordie Rose's blog), still way beyond anything in the peer-reviewed literature, but a step down from the 1024 qubits we were promised last year.

And Rose is now very circumspect, explaining to me that there are no plans for a big demo, and that this is still very much a prototype: "No demonstration is planned and hopefully there are no such reports. We are about to go to glass with the first rev of a 128-qubit design."

And meanwhile, if quantum computing is still a bit opaque to you - Scott Aaronson has written an article for Scientific American on the limits of quantum computing. I've yet to get hold of the final published version but Aaronson's early draft is beautiful.