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Test: Quantum Or Not, Controversial Computer No Faster Than Normal 119

sciencehabit writes The D-Wave computer, marketed as a groundbreaking quantum machine that runs circles around conventional computers, solves problems no faster than an ordinary rival, a new test shows. Some researchers call the test of the controversial device, described in Science, the fairest comparison yet. " test D-Wave’s machine, Matthias Troyer, a physicist at the Swiss Federal Institute of Technology, Zurich, and colleagues didn't just race it against an ordinary computer. Instead, they measured how the time needed to solve a problem increases with the problem's size. That's key because the whole idea behind quantum computing is that the time will grow much more slowly for a quantum computer than for an ordinary one. In particular, a full-fledged 'universal' quantum computer should be able to factor huge numbers ever faster than an ordinary computer as the size of the numbers grow." D-Wave argues that the computations used in the study were too easy to show what its novel chips can do.
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Test: Quantum Or Not, Controversial Computer No Faster Than Normal

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  • by Garfong ( 1815272 ) on Thursday June 19, 2014 @08:44PM (#47277997)

    In this test, both took exponentially longer. So either the d-wave doesn't work, or as the manufacturer has claimed, the problems were not setup to demonstrate the class of problems where the d-wave will show better performance relative to problem complexity growth than a conventional computer.

    Or the maximum problem size handled by the machine is too small so see the sub-exponential growth. Complexity theory deals with performance on very large data sets, and, if I remember correctly, the D-wave machine is limited to a small problem size (max a hundred or so qbits)

  • by HappyPsycho ( 1724746 ) on Thursday June 19, 2014 @10:30PM (#47278569)

    GP is actually correct. This is not even a full quantum computer.

    "The D-Wave machine is not a universal quantum computer, however, but a more limited "quantum annealer."", which according to wikipedia seems to mean some sort of global minimum finder (given how to find all the local minimum solutions, find the lowest one).

    With a mere 512 quibits available on the D-Wave device I'm more than willing to believe they may be still in the area of small inputs where an O(n) algorithm can still beat an O(log n) algorithm (e.g. [] )

  • by quax ( 19371 ) on Friday June 20, 2014 @12:31AM (#47279071)

    Do you know how to use a search engine?

    Are you aware of []?

    It's really not hard to find papers like this [] or this [].

    And yes, the Matthias Troyer who co-authored the first paper is the same guy who conducted the performance study that the /. blurb references.

    That D-Wave performs quantum annealing can be regarded as settled. The only question that remains is how useful this may be.

    Eight years ago everybody (myself included) thought D-Wave was a scam or just crazy. As new facts emerge smart people (such as Matthias) adjust their judgment.

  • by quax ( 19371 ) on Friday June 20, 2014 @12:36AM (#47279091)

    It is not gate based universal quantum computing but special purpose quantum annealing [].

    If you accept this as a valid approach to quantum computing has certainly been the subject of much debate.

  • by quax ( 19371 ) on Friday June 20, 2014 @12:49AM (#47279121)

    .... maybe the slahdot stub should have had a link to hear from the horse's mouth []?

    In this interview Matthias Troyer puts his team's results into the correct context.

  • by hey! ( 33014 ) on Friday June 20, 2014 @12:48PM (#47282625) Homepage Journal

    What we need to know about is the existence or non-existence of unfair comparisons, i.e., problems that favor the putatively "quantum" computer.

    Since I don't expect a quantum computer to be faster at everything, then finding a bunch of solutions to problems that aren't any faster on the "quantum computer" doesn't prove anything, even if the problems look like the kind of problems you'd hope would be quantum-computery. There's not much more you can do than point to the absence of evidence when the burden of proof isn't on you.

    The burden of proof is on the vendor here, and standard of "proof" is conceptually simple at least: demonstrate that for some task this device offers any practical advantage whatsoever over the best available conventional technology. That could be in absolute performance against the best available tech(e.g. ASICs and supercomputers), in relative performance over similarly priced systems, or in some practical measure other than performance, such as power consumption. Any clearly identifiable and verifiable advantage counts as positive proof the vendor has something worth paying attention to.

    Of course even comparable performance by a novel architecture on some class of problems is interesting, because of the huge advantages a mature technology enjoys. Performance of a new design even in the same ballpark as a mature design suggests future improvements might be in the works. But it's only a suggestion.

To write good code is a worthy challenge, and a source of civilized delight. -- stolen and paraphrased from William Safire