First Evidence That Google's Quantum Computer May Not Be Quantum After All 224
KentuckyFC writes "In May last year, Google and NASA paid a reported $15 million for a quantum computer from the controversial Canadian start up D-Wave Systems. One question mark over the device is whether it really is quantum or just a conventional computer in disguise. That's harder to answer than it sounds, not least because any direct measurement of a quantum state destroys it. So physicists have to take an indirect approach. They assume the computer is a black box in which they can input data and receive an output. Given this input and output, the question is whether this computing behavior can be best reproduced by a classical or a quantum algorithm. Last summer, an international team of scientists compared a number of classical algorithms against an algorithm that relies on a process called quantum annealing. Their conclusion was that quantum annealing best reproduces the D-Wave computer's behavior, a result that was a huge boon for the company. Now a group from UC Berkeley and IBM's Watson Research Lab says it has a found a classical algorithm that explains the results just as well, or even better, than quantum annealing. In other words, the results from the D-Wave machine could just as easily be explained if it was entirely classical. That comes on the back of mounting evidence that the D-Wave computer may not cut the quantum mustard in other ways too. Could it be that Google and NASA have forked out millions for a classical calculator?"
Re:Quantum Cash! (Score:5, Informative)
Before this research, it was demonstrably faster at some things, and slower at things a quantum computer is not good at. So they did exactly what you expect.
Re:Quantum Cash! (Score:5, Informative)
Why buy something that isn't demonstratively faster than the old stuff...
I mean if the difference is so small that there is some sort of debate about if it is effectively working or not, then it seems to me at that point cost should be the deciding factor. I doubt these D Wave machines are any cheaper than the old stuff.
Part of the problem has been D-Wave's confusing abuse of terminology:
1) They claim their device is a computer, but it's not according to the usual definition (a Turing machine with bounded tape (RAM)). It's more similar to an ASIC (application-specific integrated circuit).
2) They claim their device is a quantum computer, but it's not according to the usual definition (a device which requires quantum phenomena to operate). There is some evidence it uses quantum effects, but they don't appear fundamental to its operation (otherwise we wouldn't be having this quantum-or-not merry-go-round).
3) They claim their device solves its (application-specific) problem 35,000x faster than a classical machine, but in fact they had programmed the classical machine with a much harder problem (finding an exact solution, rather than an approximate one). When a classical computer was programmed to solve the same problem as D-Wave's machine, the classical machine was faster.
4) They consistently conflate quantum algorithms (algorithms inspired by quantum mechanics) with quantum computing (which requires quantum mechanics to operate). Their machine implements a 'quantum simulated annealing' algorithm, but this doesn't require a quantum computer to run. Likewise, a regular 'simulated annealing' algorithm doesn't require a heat engine to run. Likewise a 'genetic algorithm' doesn't require a DNA-based computer to run.
5) They keep moving the goalposts to remain as impressive-but-vague as possible. Rather than showing definitive results to back up their claims, they keep making claims then weakening them afterwards when researchers show them to be false. This is like an inverse No-True-Scotsman; academics have a clear definition of what a quantum computer is, and D-Wave keep trying to expand that definition it to include their machines.
In short, Google and NASA bought their machines when there were claims bouncing around about 35,000x speedups, but these were subsequently found to be flawed.
I'm all for investing in basic research, but it often looks like D-Wave's research output is coming from their marketing department rather than their scientists and engineers :(
Nonsense (Score:4, Informative)
D-Wave has Josephson junction qubits on their chip and couple them. Yet, somehow they are supposed to end up with a machine that is a classical annealer? Although the behavior of the box is exactly what you'd expect from a quantum annealer?
Seems rather far fetched.
I wished before anybody was writing about D-Wave they'd watch this video form the last Q+ hang-out where the Troyer et. al. research into the characteristics of the D-Wave machine was presented. [wavewatching.net]