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

If it works - it works

[telchine]

Does it really matter so long as it does what it says on the tin? It works faster, surely that's all that matters?

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:If it works - it works

[RDW]

You may say that now, but wait until PETA find out about the number of cats and flasks of cyanide their prototype gets through every month...

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 In other words, their comparison to CPLEX had already been superseded by a much more informative comparison—one that gave the “opposite” result—before it ever became public.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:If it works - it works

[alexander_686]

Here is a link to a good article.
      There were 3 tests with D-Wave going against a generic algorithm.
      It tied on 2 or the 3 tests, but beat the generic algorithm running 3,600 times faster.
      However, if it went against a specialized algorithm it was just as fast.

http://www.economist.com/news/science-and-technology/21578027-first-real-world-contests-between-quantum-computers-and-standard-ones-faster

Re:If it works - it works

[ceoyoyo]

Maybe you can't, but when I was in university we had to wire up transistors to make gates, then wire up gates to make adders, then wire up adders to make ALUs, then wire up ALUs to make computers. Then we went and wrote assemblers and compilers to run on those. They were simple and limited, yes, but the concepts are just the same. The problem with D-Wave is that nobody is really sure how their computers work, on any level.

Re:If it works - it works

[justthinkit]

Thanks for the link. In trying to confirm this from other sources, which I did to my own satisfaction anyway, I was shocked to see zero mention of PETA's hipocrasy on Wikipedia. No "controversy" section (on either Ingrid Newkirk's or PETA's page, no mention of the 14,000+ animals PETA have killed over the years. Truly sickening.

Heisenberg Uncertainty principle is intact...

[Stolpskott]

So they know where the D-Wave system is, but they cannot definitively measure whether it is actually a quantum computer or not...

Re:Heisenberg Uncertainty principle is intact...

[plover]

Its amazing to watch the confusion among scientists as the entire structure of the machine goes into a state of superposition with being real and not real all at the same time.

All quantum computers are real, unless declared integer.

Re:Heisenberg Uncertainty principle is intact...

[blue trane]

The difference between classical probability and quantum superposition is that if you flip one coin many times you will get a binomial distribution, but if you send one photon at two slits you will get a wave-like multinomial distribution.

Quoting Dirac (quoted in http://en.wikipedia.org/wiki/Quantum_superposition):

The original state must be regarded as the result of a kind of superposition of the two or more new states, in a way that cannot be conceived on classical ideas.

Is any quantum computer really quantum?

[dingen]

A real quantum computer both is and isn't at the same time.

Re:Is any quantum computer really quantum?

[Anonymous Coward]

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

Re:Is any quantum computer really quantum?

[K. S. Kyosuke]

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

That sounds like the invasion of Weeping Turings...

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

[Anonymous Coward]

Is there really any difference between quantum entanglement and magic?

You may have to ritually sacrifice the occasional intern to keep magic working, but otherwise, no.

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:D-Wave's Dirty Little Secret

[plover]

Any insufficiently advanced magic is just technology.

Re:D-Wave's Dirty Little Secret

[Anonymous Coward]

>using a 2-norm and looking then at the structure imposed on vectors by unitary transformations

Like, obviously!

Re:D-Wave's Dirty Little Secret

[Anonymous Coward]

" 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."

Which means absolutely nothing to the vast majority of people; hence spooky, magical and hard to understand.

Re:D-Wave's Dirty Little Secret

[flayzernax]

One is a bunch of mathematical equations modeling a universe.

Math is not real. The models are not real. They are virtual.

Not saying that quantum mechanics doesn't have some robust models. But it is not "real" in an empirical sense. It is also not complete.

Re:D-Wave's Dirty Little Secret

[flayzernax]

Simply put any math we use only defines a simulation. You only get real when you observe things. Which QM takes extreme issue with =p

Re:D-Wave's Dirty Little Secret

[Comrade Ogilvy]

I think my mathematics and quantum physics are not bad (although it were genuinely strong, perhaps I would have gone further than ABD), and I have trouble making "a lot more sense" of "using a 2-norm". Yes, I understand that the wave functions are complex, but that is not enlightening without a lot of math.

Most "spooky" results are simply the result of not accepting that everything is a wave form, and waves cannot understand that they are not supposed to be stretched across space. Which is another way of saying that JoshuaZ is correct about QM, unfortunately, being taught as "a series of counterintuitive results tacked on to classical physics". Pity.

(I would note that the QM as variance from Classical Physics can be sensible, but only if you deeply understand statistical physics at a level that is not usual even for physics PhDs.)

Our brains have evolved to feel comfortable with classical physics. When friends/family ask about exotic physics (QM or Relativity), I tell them: "The reason you are finding it implausible is your brain is working correctly; the sense comes from building up abstractions carefully with mathematics, motivated by precise experiments, that is completely outside everyday experience."

Read the blog post

[oGMo]

The problem is that it's not faster, and while there's a study that concludes it is, the blog post specifically invalidates this:

Namely, the same USC paper that reported the quantum annealing behavior of the D-Wave One, also showed no speed advantage whatsoever for quantum annealing over classical simulated annealing. In more detail, Matthias Troyer’s group spent a few months carefully studying the D-Wave problem—after which, they were able to write optimized simulated annealing code that solves the D-Wave problem on a normal, off-the-shelf classical computer, about 15 times faster than the D-Wave machine itself solves the D-Wave problem! Of course, if you wanted even more classical speedup than that, then you could simply add more processors to your classical computer, for only a tiny fraction of the ~$10 million that a D-Wave One would set you back.

About the paper claiming it's faster:

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.

Re:Read the blog post

[MozeeToby]

Because if it is quantum it's a generation 0 (barely out of prototype) implementation going up against a generation... oh I don't know... 30+ classical computer. If it's not quantum, if it's basically an ASIC chip designed to solve simulated annealing problems (intentionally or not), it's worthless even as research. What they are selling is a research and training system, so that engineers can learn what kinds of problems can be solved on the hardware that will, presumably, get much more powerful going forward.

Look at it this way, the current D-wave machine has 512 qbits and a modern PC can match it's speed. Double the qbits and you end up with a simulation space several million times larger, the 15x faster is going to seem laughable when the problem you are solving is trillions of times larger and the D-Wave solves in constant time while your PC runs an algorithm that's O(n^2). If, if, what D-wave is selling is using quantum affects.

Re: Read the blog post

[Anonymous Coward]

But what if I build a standard internal combustion engine, wrap it in a sheet of tin foil, and proclaim that I have created a portable cold fusion generator? Is that worth $10m for advancing cold fusion technology, despite the fact that it's not actually cold fusion?

The issue with D-Wave isn't that it's not as good as classical methods, it's that it probably isn't what it claims to be.

Re:Read the blog post

[ceoyoyo]

That's the problem - nobody is sure if it really IS a quantum computer. If it were just a slow quantum computer, it would be interesting. If it's a slow classical computer, it's not. Some people would like to know which it is before they buy one and their engineers invest a lot of time "learn[ing] what kinds of problems can be solved on the hardware."

Also the "get much more powerful going forward" is in doubt. There's a lot of expert criticism that D-Wave's approach cannot be easily scaled up because they've neglected error correction and some other things. In fact, that's where much of the suggestion that D-Wave's machines are not quantum computers comes from - they've already managed to scale WAY past what other people can do, and the suggestion is that in so doing they've lost the quantum part of the quantum computer.

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:it is and it isnt

[JoshuaZ]

This is the sort of thing where it helps to read Scott's post. He specifically discusses the primary claim here:

Namely, the same USC paper that reported the quantum annealing behavior of the D-Wave One, also showed no speed advantage whatsoever for quantum annealing over classical simulated annealing. In more detail, Matthias Troyer’s group spent a few months carefully studying the D-Wave problem—after which, they were able to write optimized simulated annealing code that solves the D-Wave problem on a normal, off-the-shelf classical computer, about 15 times faster than the D-Wave machine itself solves the D-Wave problem! Of course, if you wanted even more classical speedup than that, then you could simply add more processors to your classical computer, for only a tiny fraction of the ~$10 million that a D-Wave One would set you back.

Re:Not General Purpose

[gestalt_n_pepper]

But doesn't this suggest that arrays of narrow domain analog computers of this type might be constructed in such a way as to produce a *really* fast general purpose supercomputer? For example, sorting routines are built into most software frameworks. Could we not hybridize a system wherein np hard problems are called from the framework that transfers the sort to an quantum adiabatic solver and returns an answer?

Entanglement isn't the only issue

[JoshuaZ]

Scott's blog post and the comment thread there are really worth reading. Entanglement isn't the only issue. A major part of this also is whether the process that the D-Wave machine is doing is anything that is even faster (either in practice or asymptotically) than a classical computer. Right now, the answer for the first is clearly no. Scott describes mildly optimized systems which have been shown to effectively outperform D-Wave at its own problem. The second question- of asymptotic performance is a little trickier but the answer looks like "probably not". It is also worth noting that the D-Wave machines do a very specific optimization problem, of unclear usefulness, and cannot be used at all for many of things that we think of as what one wants a quantum computer for, like Shor's algorithm http://en.wikipedia.org/wiki/Shor's_algorithm to factor integers.

In fairness to D-Wave though if one thinks of this as essentially a research machine, then not doing as well as conventional systems isn't that much of mark against it any more than very early cars being slower than horses. However, D-Wave is trying to sell these machines commercially. And Scott expresses worry that there's going to be a serious backlash against quantum computing as a whole when the the D-Wave hype bubble bursts. Apparently, D-Wave has now gotten about 100 million in funding, so at least, this is an extremely suboptimal allocation to resources when much more promising academic quantum computer research projects are getting much less money.

Re:Entanglement isn't the only issue

[MozeeToby]

However, D-Wave is trying to sell these machines commercially. And Scott expresses worry that there's going to be a serious backlash against quantum computing as a whole when the the D-Wave hype bubble bursts.

No one with the money to afford one of their machines is stupid enough to buy them as anything other than a research machine. Even if someone hadn't come up with a way to match their speed with a classical computer (which has already happened) a 10,000x speed increase on a very narrow problem set at a cost of more than 100,000x just buying the additional hardware (not to mention the cost in learning how to use this new and exotic machine) makes obvious that it is not yet an economical solution for anyone.

Re:Entanglement isn't the only issue

[Anonymous Coward]

I would argue that we should be open-minded at first and see what they can actually do. Maybe analog computers are in fact not as outdated as some people claim. Maybe we could build some sort of "analog FPGA" and do massively useful things with that. I still remember an HP computer graphics subsystem using analog computers !

Surely digital computers have the advantage of simple control of temperature, aging and general error margin issues, but it comes at a massive cost in the number of transisitors to perform a certain function. less than ten transistors can perform an analog multiplication while you need tens of thousands if not hundreds of thousands of transistors to perform a floating point multiplication. Also, the analog multiplier will be operating at much higher speed (easily 10x). Again, if we could control temperature and aging-related issues and have high integration and programmability (FPGA-style), maybe we could do massively useful things at very low power levels or with massive parallelity. I do NOT think that analog computers are dead forever. It might be more of a cultural thing we currently don't use them much ("digital is always better", "digital is modern" and similar semi-truths.

If you put one seasoned computer scientists and one seasoned electrical engineer in one room and task them to do what I described, if you give them massive funding (say 3 million dollars), I am sure they could come up with something massively useful. For example, digital circuits could periodically calibrate the analog circuits to compensate for all kinds of drift and aging. Software could automate the drudgery of manual circuit synthesis, it could model crosstalk and similar things.

Well, maybe Analog Devices already has this kind of thing.....

Proved the Market

[bill_mcgonigle]

Whether this thing turns out to be the real McCoy (dammit Jim, I'm a quantum annealer) or not, one thing D-Wave has done is proven that there are customers who will pay $10M to be on the cutting edge of quantum computing for a few years. This should help boost investment and entrepreneurship in other companies. Eventually, one of them will revolutionize everything.

Re:Proved the Market

[oh_my_080980980]

The only thing they proved is there's a sucker born every minute. It has not helped the field of quantum computing. In fact it set it back because now people are going to distrust something that's called a quantum computer.

I need more evidence!

[FilmedInNoir]

D-Wave is probably a scam, but I work in IT, almost the entire industry is built on scams.
Scott Aaronson comes off as an egotistical man-child that is just angry he's not directly involved in all this.
It's still love - love in this match.

Re:Not General Purpose

[JoshuaZ]

There are a lot of problems wit this idea. Among other issues, quantum computers, even general purposes quantum computers, cannot as far as it is known solve any NP-hard problem in polynomial time. It is strongly suspected by people in the field that BQP (roughly speaking the set of problems easily solvable on a quantum computer http://en.wikipedia.org/wiki/BQP) does not contain NP. There are also a variety of problems which are conjectured to be intermediate between P and NP which do not have known BQP algorithms. The set of things where a quantum computer can provide a lot of speed up is as of right now, highly specialized. That said, the long-term plan isn't that far off of what you are talking about, using general purpose classical machines to do most computations and only call the quantum computer when one has a problem of a specific type that substantially benefits from it (either from a drop into polynomial time from worse than polynomial time, or just a massive polynomial speedup).

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.

Stupid Question of the Day!!!!

[Xaedalus]

Now that I've RTFA and through the commentary threads, as a dumb ignorant layperson I get why Scott Aaronsen is right to call out D-Wave. I also get the counter-argument that there needs to be some sort of hype in order to sustain interest in QC. And, the damn thing's got to work eventually. What I'm wondering though is this: Are we (as a society) making an error in trying to use QC to solve problems that are particular to classical computing?

The reason I ask is that a while back on /. I was educated about the nature of Base-10 computing. Prior to this, I'd spent my entire life thinking that Base-10 WAS mathematics, and I'd had no reason to assume or even imagine that there could be any other type of mathematics than Base-10. Base-10 was the pinnacle of mathematics to me. Then I find out that Base-10 is probably the most efficient to date for our society, but that it is not the only way to count; and that Pi is only Pi because of Base-10. Which led me to look at mathematics in a whole new light. Similar with Quantum mechanics--the more I understand about Quantum Mechanics, the more I realize that I have to set aside everything I know about Newtonian physics, because trying to understand quantum physics from a newtonian perspective will always result in failure--while there is a bridge between the two, if I don't take that "bridge" into account then I'm metaphorically trying to judge apples based on my prior experience in dog shows.

Given this, is it fair to hold QC to the same standards as Classical Computing, or should we be looking at entirely new applications of computing? And, is there anyone out there who's staring into the vast unknown and saying "What happens if we do THIS with a QC?"

Re:Stupid Question of the Day!!!!

[JoshuaZ]

he reason I ask is that a while back on /. I was educated about the nature of Base-10 computing. Prior to this, I'd spent my entire life thinking that Base-10 WAS mathematics, and I'd had no reason to assume or even imagine that there could be any other type of mathematics than Base-10. Base-10 was the pinnacle of mathematics to me. Then I find out that Base-10 is probably the most efficient to date for our society, but that it is not the only way to count; and that Pi is only Pi because of Base-10.

No. Pi will be the same regardless of base. The digits of Pi will be different if you write it in a different base, but this is simply a representation, not a change in what the number is. If you do calculations involving Pi in one base and do the same thing with another base and then convert the answer from one to the other you will get the same thing.

Your general question is a good one. In fact, one of the major things people want to use quantum computers for is to do simulations of quantum systems, which they can do, but which are extremely inefficient (both in terms of time and memory) on a classical computer. So people are looking at problems which are practically not doable on a classical computer. At the same time though, we know that a quantum computer can be simulated on a classical computer with massive resource overhead (essentially exponential slowdown), so we know that anything you can do on a quantum computer you can do on a classical computer if one is patient enough.

Re:Stupid Question of the Day!!!!

[arth1]

Pi will be the same regardless of base.

Most bases. Not base 1 (unary), base 0 or base -1.

What?

[jones_supa]

They can build these things already? I thought that quantum computers would be only a theoretical idea for many coming years.

No really, READ IT ALL

[oGMo]

It's pretty obvious who is and who is not reading the article here:

In short, there seems to be no evidence, at present, that the D-Wave machine is going to overtake simulated annealing for any instance size.

The author concedes that it is possible that this may happen, but:

Well, I concede that almost anything is possible in the future—but “these experiments, while not supporting D-Wave’s claims about the usefulness of its devices, also don’t conclusively disprove those claims” is a very different message than what’s currently making it into the press.

Additionally the author wants this to succeed because of possible results of its failure:

Academic QC programs will be decimated, despite the slow but genuine progress that they’d been making the entire time in a “parallel universe” from D-Wave. People’s contempt for academia is such that, while a D-Wave success would be trumpeted as its alone, a D-Wave failure would be blamed on the entire QC community.

Seriously, read the whole damn article.