Quantum Computer Works Better Shut Off

waimate writes "A New Scientist article relates how its possible to get answers from a quantum computer even when your program isn't running." From the article: "With the right set-up, the theory suggested, the computer would sometimes get an answer out of the computer even though the program did not run. And now researchers from the University of Illinois at Urbana-Champaign have improved on the original design and built a non-running quantum computer that really works."

Comments

You mean like us?

[aliens]

Ever hear the expression "I'll sleep on it" ?

I've read several times how not thinking about a problem will lend itself to a solution.

ie Go take a walk, get a cup of coffee, take a nap.

Interesting, or maybe I just need coffee.

Re:news?

[AbstraktMethodz]

the article is rehashing an idea about resolving certain problems but creating your quantum coherence, but never collapsing that via direct measurement. there are bigger surprises out there than this in quantum computing.

Could someone please explain this?

[Otter]

I've read the linked article, the commentary article in Nature and the Paper itself, and am completely mystified as to what they're claiming. As best as I can tell, they subsetted their data and found that the (rather misleadingly named) "non-running" events were more informative than the set as a whole.

Coming back here, the discussion consists entirely of moronic comments about Windows. Would someone with a clue care to provide some useful commentary?

Re:Could someone please explain this?

[Otter]

Thanks!!! That's very helpful. Two questions, though:

1) In the Elitzur-Vaidman thought experiment, which part corresponds to the on-off switch?

2) Is the "non-running" experiment physically performed differently from the normal method, or is it a refinement made in the data?

Re:Could someone please explain this?

[SirBruce]

>1) In the Elitzur-Vaidman thought experiment,
>which part corresponds to the on-off switch?

The entire computer takes the place of the bomb(s). The "on-off switch" is really whether or not a photon enters the computer (thus running the program).

>2) Is the "non-running" experiment physically
>performed differently from the normal method,
>or is it a refinement made in the data?

The "experiment" only works when it is running. What's "non-running" is the computer, or perhaps more precisely, the computer program. What's physically different between when the program is running and when it isn't is whether or not a photon gets from the "experiment" into the computer. Thanks to QM, you can actually make the probability of the photon entering the computer so small that it never actually runs (or in the bomb-testing case, the bomb is never set off), but you can still infer the result the program would generate.

Bruce

This is an old result

[Expert Determination]

I remember swapping a few emails with the author of a paper on this about ten years ago. Essentially you can get the result of the computation and yet the computer that runs destructively interferes with itself so that it essentially it remains unchanged at the end of the computation.

But this doesn't buy you anything. Quantum computers are reversible meaning they use no energy. And the computer has to spend just as long "doing nothing" as it would have spent doing the computation. And your computer is still tied up "doing nothing". So it's basically useless.

Many Worlds

[jheath314]

Totally OT, but I remember having a (lengthy) debate with a guy who claimed that absolutely nothing is ethically wrong, because according to the Many Worlds interpretation no matter what course of action you choose in this universe, there is some other quantum reality where you did the opposite.

"Gee, don't feel bad about me brutally killing your whole family... according to this completely untestable theory I have, there is another inaccessible parallel universe out there where I didn't! See? It's all good now."

I always hated the Many Worlds interpretation because it's not science, it's religion clothed in science-speek. By it's very nature it is untestable... might as well say invisible purple monkeys (or flying spaghetti monsters) are responsible for how things run "behind the scenes." I subscribe much more strongly to the "shut up and calculate" school of thought.

/off topic

Re:Misleading

[bughunter]

New Scientist's coverage of science is typically horrible. Therefore, it's not surprising that any New Scientist article makes no sense but contains lots of exciting fluff.

There. Fixed it for ya.

Ever since Scientific American went pop-sci in the mid-90's, we've been without a decent, objective layman's science magazine that avoids sensationalising.

Science News weekly is probably the best, but it's written for a 10th grade audience.