Scientists Dubious of Quantum Computing Claims

Dollaz wrote with a link to the International Business Times, which questions the authenticity of D-Wave's Quantum computing. We discussed the 'Sudoku playing' computer yesterday, but scientists in the field have expressed a lot of distrust of the company's findings. The machine was not available for inspection during or after the demo, and even if the technology was working as intended there is some doubt that it can be scaled. The article points out that "notwithstanding lofty claims in the company's press release about creating the world's first commercial quantum computer, D-Wave Chief Executive Herb Martin emphasized that the machine is not a true quantum computer and is instead a kind of special-purpose machine that uses some quantum mechanics to solve problems." Good to see people in the field questioning 'breakthroughs'.

How to verify their claims?

[stratjakt]

How would you?

I'm legitimately curious. Such a device has never been built, how do these guys prove they have one? They say themselves they aren't certain if it's quantum-ing up the sudoku.

Good blog responses

[Ambitwistor]

Quantum computing researcher Scott Aaronson wrote some good anti-hype pieces about the D-Wave PR here [scottaaronson.com] and here [scottaaronson.com], focusing on their incorrect marketing claims to be able to solve NP-complete problems in polynomial time. The first link also has an update with comments from Lawrence Ip of Google, who clarifies what the D-Wave people are really claiming.

Marketing department at work...

[viking2000]

Let me guess: It is a regular computer that solves a regular problem the regular way. One function needed is a number generator.

You could pick any device that returns different numbers at different times. It could be a microphone, a geiger counter, a clock og a quantum device

Now pick the quantum device, and call the whole device a "Quantum computer"

This is normal in marketing departments. The only unusual thing here is that they got the engineering department to go with them.

I've been saying for ages it's a scam

[exp(pi*sqrt(163))]

It's the electronic equivalent of using soap bubbles to solve the traveling salesman problem. For simple problems you really can use soap bubbles because soap bubbles like to form minimal surfaces. This 'quantum' computer does something similar - it uses a form of annealing to find the minimum of some function with the energy representing the function you're trying to minimise. Cool the system and you find what that minimum energy is. But soap bubbles don't scale.

So the first part of the scam is this: even if this device wasn't a quantum device at all it would still work to some extent because when you allow systems to cool they fall into lower energy states. If the 'quantum' aspect of things works then it might find that state faster, but without careful monitoring there's no way of telling if the 'quantumness' had anything to do with what it did. In fact, for large systems we know that it won't be very 'quantum' at all because it will interact with its environment and decohere. But it's a perfect strategy for designing a machine that you can claim is quantum, when it isn't. It stinks of scam.

Secondly: suppose you want to solve a challenging problem with this device. For example you want to search some space for a miniumum of some sort. For this machine to be effective the state space must be pretty large or else you could use a regular classical computer. Consider a billion state problem (quite small really for combinatorial problems). You have to be able to get a system to settle into the minimum energy state despite the fact that there are a billion states nearby all of which have almost the same energy. Just the tiniest input of energy and it'll jump up from that minimum. There is absolutely no way that they can search a large enough state space and still have the minimum energy state sufficiently far from other states.

BTW This device is quite different from what is conventionally meant by a 'quantum computer', it's more like a quantum, analog computer.

Real and useful 'digital' quantum computers are a long way off. I expect that the size of quantum computers will grow by a bit or so per year at the most. (When I say 'bit' I mean total memory, not the size of the bus.)

Article makes things seems worse

[aditi]

Scientists are skeptical because it hasn't been submitted for peer review. Yes, but that's true for any new scientific discovery. It's not entirely fair to spin that into "this quantum computer might not really work".
Also, while the article claims it might not be a "true quantum computer", it never really says how that's different from a "computer that uses quantum mechanics to solve certain problems", and given its audience, can't possibly expect its readers to know. To me, this just sounds like journalists looking for something to hype about.

Re:Sudoku

[austior]

I thought they already had a conventional algorithm that could solve Sudoku without utilizing quantum effects?

Quantum computers can only solve problems that conventional algorithms can solve. Potentially, they could solve them faster.

Nature doesn't seem to have utilized the method

There are a lot of useful things nature hasn't discovered, like wheels (macro sized) and transistors. The nervous system doesn't take advantage of ANY molecular scale computation, so how could it build a quantum computer?

Re:He kind of has a point...

[Sam Nitzberg]

Direct test for a quantum computer:
Solve any problem polynomially reducable to SAT/3-SAT (http://en.wikipedia.org/wiki/Boolean_satisfiabili ty_problem)
without the use of heuristic algorithms. Further, show it being done in polynomial-time with respect to the problem size.

Naturally, the machine and program would also have to be subject to inspection to show that it wasn't just spitting out a canned response to a problem already worked on and answered by a team of supercomputers elsewhere....

Fortunately, checking the result won't take too long. The check should be calculable on a conventional computer in polynomial-time.

Reply button missing

[dangitman]

Good to see people in the field questioning 'breakthroughs'.

This is an odd statement, because that's generally what people "in the field" do. The author says this as though it's unusual to see anybody questioning lofty claims. In fact, it's very common. The first slashdot article about this was met mostly with skepticism.

Note: Replying to this post, because I am not getting a "reply" button for the story itself. Anybody else experiencing this bug?

Re:Well DUH

[Anonymous Coward]

here is a longer cut of D:wave's presentation..

Link 1 http://video.google.com/videoplay?docid=8033280380 582597891&hl=en/ [google.com]

Link 2 http://video.google.com/videoplay?docid=-687784917 8932916346&hl=en/ [google.com]

Misconceptions about NP-Completeness

[et764]

Depending on what you mean by "solve," I think you are a little mistaken on what it means for a problem to be NP-Complete. NP-Complete problems are actually relatively easy to solve. For example, take 3SAT, were you have a bunch of boolean variables, x[1] through x[n], and then a bunch of string of clauses ANDed together, as in (x[1] OR x[2] OR NOT x[3]) AND (x[24] OR NOT x[37] OR x[42]) ... To solve 3SAT you just have to tell me whether there exists some combination of variables such that the expression is true. You can just enumerate all 2^n possible combinations of variable assignments and see if any of them work out to be true. The problem is, it doesn't take very large values of n before it will take you longer than the time civilization has been around to try all the combinations. 3SAT is easy to solve, if you just want an answer. What's still an open question is whether we can come up with an algorithm that can solve it efficiently, where efficiently means in O(n^k) time for some k, rather than O(2^n).

For a problem that actually can't be solved, try the Halting Problem.

Now, the cool thing about NP-Complete problems is that any other problem that's known to be in NP (meaning we can solve them, just some instances will take a ridiculous amount of time to do so) can be efficiently transormed, meaning transformed in polynomial time, into an NP-Complete problem. This means if you can really solve general instances of Sudoku in polynomial time, you can take an instance of the 3SAT problem, efficiently transform it into an instance of Sudoku, then efficiently solve the Sudoku problem and then transform the answer into a solution to the 3SAT problem. If they have really built such a machine, this is a big deal.

They didn't hire me so they must know something

[Jay 78]

I actually interviewed with these guys a few months back. I can tell you I was quite impressed with the facility and they came off as very bright. I also got a tour of the facility so I'll share what I know. The chip core is stored in a large tank roughly 2m tall and cooled to very very near absolute zero. That is then held inside what is in essence a very large faraday cage. All the refrigeration and electronic equipment is kept outside with only passive sensors allowed in the room wherever possible. Apparently electrical noise and stray heat has been a huge hurdle. From what I understood they saw themselves as building chips that would be housed on site and used remotely so it doesn't surprise me that they didn't have a setup that was available for public viewing. The company culture was essentially work till you drop and hope the stock options make you rich.

Re:He kind of has a point...

[cpeikert]

Solve any problem polynomially reducable to SAT/3-SAT

You have your reducibility direction mixed up: even really easy problems (like sorting, or outputting "2") are reducible to SAT. It's the hard problems that SAT reduces to.

Not that this matters, because quantum computing is very unlikely to be able to solve NP-complete problems. It does seem to help with very structured problems like factoring, though. No, factoring is (almost definitely) not NP-complete.

Further, show it being done in polynomial-time with respect to the problem size.

Polynomial-time is an asymptotic notion. It can't be verified for a particular problem size (or finite set of problem sizes). It is purely an analytical concept, not an experimental/testable one.

Re:They didn't hire me so they must know something

[Mock]

I was at the Vancouver showing.
I've done a lot of smoke and mirror shows myself, and this demo did not smell funny at all.

The headline "Scientists Dubious of Quantum Claims" is rather sensationalist for what they're actually saying in the article.
Can you really fault them for not wanting to move a computer that has to be housed in a special chamber, cooled to near absolute zero, and be havily shielded from any outside interference?
Besides, judging by the questions people asked, not a single person in the audience could have verified that it was a computer and not a big refrigerator.

What I saw were a group of really smart people who are onto something real, and need to drum up enthusiasm for a later release of their product.
Their machine appeared to do what they claimed it did, and while it is quite easy to fake it, I didn't get such an impression at the demo.