Reply to post: Re: Lets see it working then

D-Wave promises chip that could search the whole universe


Re: Lets see it working then

No, quantum computers are only known to do better than classical computers in some quite special situations, and NP-complete problems (such as travelling salesman) are not one of those situations (in fact, the belief, although there isn't much evidence, is that they don't gain much for such problems). However some of the problems they are known to do better on are game-changingly important, such as factorisation (read: working quantum computation blows away much of the cryptographic basis for e-commerce).

What D-Wave promise is not a general purpose quantum computer, though - even if it meets their claims, it is not known possible to (and probably it is not possible to) run Shor's algorithm (the factorisation thing). It does some things which are potentially useful, what's maybe more important is that a different design using the same ideas might do more (assuming it works...). What's interesting is they try to sidestep a big problem 'decoherence' with the standard academic approach to building general purpose quantum computers. It's not clear if this is even theoretically possible, but they are going for the try-and-find-out approach rather than trying to work on the theory.

What seems to be clear is that there is something quantum going on in the current versions: there is definitely entanglement, the problem they want to solve definitely gets solved, and it seems reasonable to believe this solution really comes out of a quantum effect. Which is pretty cool. But, there is also (at least for now) quite a lot of reason to believe that this specific quantum effect is something a classical computer can simulate efficiently (there is a known algorithm whose performance appears to be similar, it's not easy to be definite due to a mixture of D-Wave holding trade secrets and that we don't really know how to look at the workings of the chip even if we wanted to). What is certainly true is that the results aren't anything to write home about in terms of computational power. Unless you're reading this on a cheap mobile phone, then you have more computational power in your hands than anything D-Wave demonstrated. Of course, as they point out, you also have more power (by a much greater factor) than the Colossus machines had, and quantum computing today probably should be compared to that.

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