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D-Wave Systems claim to have produced the first commercial quantum computer:

The company's flagship product, the D-Wave One, is built around a novel type of superconducting processor that uses quantum mechanics to massively accelerate computation. In 2010 Lockheed Martin purchased serial number 1, completing the historic world's first sale of a quantum computer.

However, there have been several articles written that call into question the claim that it is a quantum computer:

IEEE Spectrum Magazine, Jan 2010

But experts are skeptical that D-Wave's quantum computer is really, well, quantum. "If this were the real thing, we would know about it," says Christopher Monroe, a quantum-computing researcher at the University of Maryland, in College Park. He says D-Wave hasn't demonstrated "signatures" believed to be essential to quantum computers, such as entanglement, a coupling between qubits.

ExtremeTech, Match 2013

At a recent computing workshop the company claimed to have also found evidence for entanglement with systems of two and eight qubits. Entanglement is a requirement for its machine to truly operate as a quantum computer, but not proof that it does.

Are D-Wave Systems's claims that their machine is a quantum computer actually true?

please delete me
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    [Welcome to Skeptics!](http://meta.skeptics.stackexchange.com/questions/1505/welcome-to-new-users) What would you consider an acceptable answer? I think this issue has been broadly thrashed out already. The company has been claiming the devices it produces are quantum computers, but by your own reading, has failed to provide independent scientists with verifiable evidence that this is true. I'm wondering what more there is to say... – Oddthinking May 03 '13 at 15:38
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    To reiterate what @Oddthinking said, this is going to be a really tough one to get a good answer for unless you define what you are looking for. From what I read the D-Wave systems are based on [Adiabatic quantum computing](https://en.wikipedia.org/wiki/Adiabatic_quantum_computation) as opposed to [Quantum circuit](https://en.wikipedia.org/wiki/Quantum_circuit) which adds a layer of complication. – rjzii May 03 '13 at 16:03
  • @RobZ You have the beginning of an answer there Rob. I think by comparing the different styles, and possibilities you can give a decent answer that can educate people, and hopefully satisfy the question-asker. Personally I know next to nothing about Quantum Computing, so I would be interested in such an answer. – Wertilq May 03 '13 at 16:05
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    Found the [Nature article](http://www.nature.com/nature/journal/v473/n7346/full/nature10012.html) I was looking for that was published by the company. – rjzii May 03 '13 at 16:06
  • @Wertilq - Let me see if I can get something typed up later today or tomorrow. I've been following D-Wave a bit so I can pull some stuff together. – rjzii May 03 '13 at 16:07
  • @Alexander: Is there a semantic difference between "X is a quantum computer" and "X quantum computes"? If so, please give a definition and find a reference that makes the claim that D-Wave One does it (so we aren't attacking a strawman). If not, why edit the clumsy sentence back into the title? – Oddthinking May 04 '13 at 07:56
  • What do you mean? They claim that it IS a QC here "The company's flagship product, the D-Wave One, is built around a novel type of superconducting processor that uses quantum mechanics to massively accelerate computation." I am just asking whether it actually works on QUANTUM MECHANICS or not. – please delete me May 04 '13 at 08:07
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    @Alexander Jones: any [known] physical process in our universe obeys to quantum mechanics. The question should be whether this computer effectively takes advantage of quantum mechanics effects to accelerate computation... – nico May 04 '13 at 09:55
  • @nico yes, exactly what I mean :) – please delete me May 04 '13 at 10:02
  • @nico - But the question of if the D-wave uses quantum effects for computation is a completely different one that if it is a quantum circuit computer. – rjzii May 04 '13 at 15:12
  • @Rob Z: well, but apparently that is not what the OP is asking. Maybe the question should be clarified. Anyway, if someone has the courage to dig into these, maybe the answer could be there: http://www.dwavesys.com/en/publications.html – nico May 04 '13 at 15:48
  • Related: http://security.stackexchange.com/questions/23085/ and http://physics.stackexchange.com/questions/10496 – BlueRaja - Danny Pflughoeft May 09 '13 at 20:02
  • This discussion is worth noting: http://physics.stackexchange.com/questions/10496/what-can-the-d-wave-quantum-computer-do – Bossliaw May 22 '13 at 17:03

1 Answers1

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Yes in the sense that it uses quantum properties to perform computations, but no in the more general case since it is not a Turing machine (i.e. universal computer).

This answer is somewhat complicated by the fact that what the general public thinks of as a computer and what computer scientists formally define as a Turing machine. Turing machines are interesting from a mathematical standpoint since any computer algorithm can be run on a Turning machine and Turing machines can simulate one another which gives rise to the concept of Turing completeness.

The quantum equivalent to a conventional Turing machine (i.e. a desktop computer) requires the use of quantum circuits that allow for general algorithms to be run on it. In keeping with Turing completeness, conventional computers can actually simulate quantum computers that make use of quantum circuits.

So with that in mind we can now turn to the D-Wave device for closer examination. D-Wave Systems own documentation for developers tells us the following:

The processor in the D-Wave One – codenamed Rainier – is designed to perform a single mathematical operation called discrete optimization.

Along with,

Rainier solves optimization problems using quantum annealing (QA), which is a class of problem solving approaches that use quantum effects to help get better solutions, faster.

Right off the bat we know that the D-Wave is not going to be Turing complete since it can only perform a single mathematical operations which means that it is not a quantum computer in the general sense; however, what about the specific case?

When first introduced there was quite a bit of controversy that D-Wave was not taking advantage of quantum effects to actually solve problems. However, this partly resolved with their 2011 publication of "Quantum annealing with manufactured spins" in Nature which contains the following point of interest in the abstract,

Here we use quantum annealing to find the ground state of an artificial Ising spin system comprising an array of eight superconducting flux quantum bits with programmable spin–spin couplings. We observe a clear signature of quantum annealing, distinguishable from classical thermal annealing through the temperature dependence of the time at which the system dynamics freezes. Our implementation can be configured in situ to realize a wide variety of different spin networks, each of which can be monitored as it moves towards a low-energy configuration

The paper is quite interesting but the mathematics can be quite heavy at times as well though. The key point of the paper is summarized in the conclusion,

This brings us to our main conclusion: a programmable artificial spin system manufactured as an integrated circuit can be used to implement a quantum algorithm. The experiments presented here constitute a step between understanding single-qubit annealing and understanding the multi-qubit processes that could be used to find low-energy configurations in a realistic adiabatic quantum processor. In addition to its problem-solving potential, a system such as this also provides an interesting test bed for investigating the physics of interacting quantum spins, and is an important step in an ongoing investigation into much more complex spin systems realized using this type of architecture. Although our manufactured spin system is not yet a universal quantum computer, by adding a new type of coupler between the qubits, universal quantum computation would become possible.

In short, the paper explains the implementation of a means of doing adiabatic quantum computation. This paper was part of what ultimately lead some of D-Waves critics to back off their previous positions and look more favorably on the company. This in turn has lead to a general warming of the scientific communities options towards the company.

This position that the D-Wave is in fact using quantum effects was further reinforced by the University of Southern California who in 2013 released an article validating the use of quantum effects in the processor,

“Our work seems to show that, from a purely physical point of view, quantum effects play a functional role in information processing in the D-Wave processor,” said Sergio Boixo, first author of the research paper, who conducted the research while he was a computer scientist at ISI and research assistant professor at USC Viterbi

A 2013 pre-print article up titled "Quantum annealing with more than one hundred qubits" also raises a very interesting point,

Considering the pure annealing time, the performance for typical (median) instances matches that of a highly optimised classical annealing code on a high-end Intel CPU.

Meaning that as of right now, there might not be much advantage in using their device over a conventional computer. However, they go on to note that,

Quantum speedup can then be detected by comparing the scaling results of the simulated classical and quantum annealers to experiments, as we discuss in detail in the supplementary material. Going to even larger problem sizes we soon approach the limits of classical computers. Optimistically extrapolating using the observed scaling, the median time to find the best solution for our test problem will increase from milliseconds to minutes for 2048 variables, and months for 4096 variables, and the scaling might be much worse if fat tailed distributions start to dominate, as we had previously observed for other Monte Carlo algorithms [28, 29]. A quantum annealer showing better scaling than classical algorithms for these problem sizes would be an exciting breakthrough, validating the potential of quantum information processing to outperform its classical counterpart.

Meaning that they still feel that for larger data sets their device is likely to be a superior performer over a standard computer for these types of problems.

So to summarize, in the general sense of the D-Wave One being a Turing machine, it is not which means that it is not a quantum computer in the strictest sense of the meaning. However, in the more general sense that the D-Wave One is using quantum effects to perform calculations, the answer appears to be yes.

rjzii
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  • `our test problem will increase from milliseconds to minutes for 2048 variables` -- What's the size of the computer at the moment? And how big do they predict it must be in order to "prove" the concept, i.e. get better performance that "its classical counterpart"? – ChrisW Jun 29 '13 at 00:39
  • @ChrisW - Not sure what you mean, the concept is proven but the performance issue is very complicated since a classical implementation might perform better in some cases but not in others. – rjzii Jun 29 '13 at 01:16
  • "Proof", as in "the proof is in the pudding". The last quote confuses me with units/dimensions: for example, how many is "2048 variables" when it's measured in "qbits" or whatever it is they advertise in their specifications? I thought the implication of the quote was that for some sufficiently large size of problem, the quantum approach would scale better: is large is that large size, and how far is the current implementation from being, therefore, consistently superior? – ChrisW Jun 29 '13 at 01:31
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    Eh, the question of if the D-Wave is faster than a classical computer is still an open question. The big point of contention for a long time was if it really was using quantum effects or not and that's the question that's been solved. – rjzii Jun 29 '13 at 01:35