Some Scientists Question Whether Quantum Computer Really Is Quantum

gbrumfiel writes "Last week, Google and NASA announced a partnership to buy a new quantum computer from Canadian firm D-Wave Systems. But NPR news reports that many scientists are still questioning whether new machine really is quantum. Long-time critic and computer scientist Scott Aaronson has a long post detailing the current state of affairs. At issue is whether the 512 quantum bits at the processor's core are 'entangled' together. Measuring that entanglement directly destroys it, so D-Wave has had a hard time convincing skeptics. As with all things quantum mechanical, the devil is in the details. Still it may not matter: D-Wave's machine appears to be far faster at solving certain kinds of problems (PDF), regardless of how it works."

Comments

D-Wave's Dirty Little Secret

[Greyfox]

Their computer works not by quantum entanglement but by magic.

Re:D-Wave's Dirty Little Secret

[RevDisk]

Is there really any difference between quantum entanglement and magic?

Re:D-Wave's Dirty Little Secret

[JoshuaZ]

Is there really any difference between quantum entanglement and magic?

Yes. There's this tendency to view entanglement as spooky, magical, and hard to understand. But this really isn't the case and is more due to the confusing way that quantum mechanics if often taught, as a series of counterintuitive results tacked on to classical physics. If one adjusts one's perspective to think of quantum mechanics more as the consequences of using a 2-norm and looking then at the structure imposed on vectors by unitary transformations, things make a lot more sense. Scott Aaronson(mentioned in the summary above) has a book out recently on just this subject "Quantum Computing since Democritus" which is aimed at explaining these issues to people outside is field but with a comfortable background in other technical fields- essentially no more than some linear algebra, basic probability and complex numbers. The book is highly readable and Scott is a very funny writer, so there are a lot of amusing asides.

Re:If it works - it works

[Anonymous Coward]

You really need to RTFA. It's slower than an optimized implementation of the same thing on a classical computer (and one that costs a lot less than $10m).

Re:Is any quantum computer really quantum?

[Anonymous Coward]

It is a quantum computer only when no one is looking at it.

it is and it isnt

[nimbius]

the machine is really just a quantum annealer. you still need real computers to do your solving for things like computational quantum thermodynamics but where the D-Wave comes in, its really just there to assist the solver cluster with a more terse or efficient algorythm. Not bashing it, seeing as some of their jobs run months or years if the D-Wave manages to carve 20-30% off the time of a solver run, then you just saved ~80 days of work.

as to naysayers who think D-Wave isnt in a true quantum state, heres a research paper on the matter http://arxiv.org/abs/1304.4595
Simulations of quantum versus classical annealers show that a classical one has a fairly uniform probability of solving a problem correctly; a quantum device should instead have a low probability of success at solving hard problems, and a high probability of success solving easy ones. This is what D-Wave is shown to do.

disclosure: i work for a large engineering firm that handles computational fluid thermodynamic and finite element analysis simulation as a service. Id be speechless to have one of these ajacent to my datacenter.

Re:If it works - it works

[Certhas]

Indeed, the summary is misleading.

Citing from Aaronsons blog:

Among the many interesting comments below, see especially this one by Alex Selby, who says he’s written his own specialist solver for one class of the McGeoch and Wang benchmarks that significantly outperforms the software (and D-Wave machine) tested by McGeoch and Wang on those benchmarks—and who provides the Python code so you can try it yourself.

and

As I said above, at the time McGeoch and Wang’s paper was released to the media (though maybe not at the time it was written?), the “highly tuned implementation” of simulated annealing that they ask for had already been written and tested, and the result was that it outperformed the D-Wave machine on all instance sizes tested. In other words, their comparison to CPLEX had already been superseded by a much more informative comparison—one that gave the “opposite” result—before it ever became public. For obvious reasons, most press reports have simply ignored this fact.

In other words, if it works, it works, except that it doesn't.

Re:It's much cooler if we *don't* know how it work

[gestalt_n_pepper]

Anything can be pushed to the limits of what we know, and on occasion, things work, but not for the reasons you think it did. This is sufficiently close to the cutting edge that it may be operating correctly, but that we only think we understand why.

F'rinstance, for years, we thought about electricity as a liquid. Voltage equaled pressure. Amps equaled volume. The math worked. Nature wiggled it's eyebrows suggestively.

BUT, electricity is NOT a liquid. It works the way it does for completely different reasons. It just took a while for us to figure that out. Yet, even before we understood this, we build practical machinery.