Quantum Computing, Finally!! (or maybe not)

Today's New York Times has an article hailing the arrival of superfast practical quantum computers (weird thing pictured above), courtesy of Lockheed Martin who purchased one from a company called D-Wave Systems. As the article notes,

... a powerful new type of computer that is about to be commercially deployed by a major American military contractor is taking computing into the strange, subatomic realm of quantum mechanics. In that infinitesimal neighborhood, common sense logic no longer seems to apply. A one can be a one, or it can be a one and a zero and everything in between — all at the same time. ...  Lockheed Martin — which bought an early version of such a computer from the Canadian company D-Wave Systems two years ago — is confident enough in the technology to upgrade it to commercial scale, becoming the first company to use quantum computing as part of its business.

The article does mention that there are some skeptics. So beware.

Ten to fifteen years ago, I used to write frequently, mostly for New Scientist magazine, about research progress towards quantum computing. For anyone who hasn't read something about this, quantum computing would exploit the peculiar properties of quantum physics to do computation in a totally new way. It could potentially solve some problems very quickly that computers running on classical physics, as today's computers do, would never be able to solve. Without getting into any detail, the essential thing about quantum processes is their ability to explore many paths in parallel, rather than just doing one specific thing, which would give a quantum computer unprecedented processing power. Here's an article giving some basic information about the idea.

I stopped writing about quantum computing because I got bored with it, not the ideas, but the achingly slow progress in bringing the idea into reality. To make a really useful quantum computer you need to harness quantum degrees of freedom, "qubits," in single ions, photons, the spins of atoms, etc., and have the ability to carry out controlled logic operations on them. You would need lots of them, say hundreds and more, to do really valuable calculations, but to date no one has managed to create and control more than about 2 or 3. I wrote several articles a year noting major advances in quantum information storage, in error correction, in ways to transmit quantum information (which is more delicate than classical information) from one place to another and so on. Every article at some point had a weasel phrase like ".... this could be a major step towards practical quantum computing." They weren't. All of this was perfectly good, valuable physics work, but the practical computer receded into the future just as quickly as people made advances towards it. That seems to be true today.... except for one D-Wave Systems.

Around five years ago, this company started claiming that it was producing and achieving quantum computing and had built functioning devices with 128 qubits. It used superconducting technology. Everyone else in the field was aghast by such a claim, given this sudden staggering advance over what anyone else in the world had achieved. Oh, and D-Wave didn't release sufficient information for the claim to be judged. Here is the skeptical judgement of IEEE Spectrum magazine as of 2010. But more up to date, and not quite so negative, is this assessment by quantum information expert Scott Aaronson just over a year ago. The most important point he makes is about the failure of D-Wave to really demonstrate that its computer is really doing something essentially quantum, which is why it would be interesting. This would mean demonstrating so-called quantum entanglement in the machine, or really carrying out some calculation that was so vastly superior to anything achievable by classical computers that one would have to infer quantum performance. Aaronson asks the obvious question:

... rather than constantly adding more qubits and issuing more hard-to-evaluate announcements, while leaving the scientific characterization of its devices in a state of limbo, why doesn’t D-Wave just focus all its efforts on demonstrating entanglement, or otherwise getting stronger evidence for a quantum role in the apparent speedup?  When I put this question to Mohammad Amin, he said that, if D-Wave had followed my suggestion, it would have published some interesting research papers and then gone out of business—since the fundraising pressure is always for more qubits and more dramatic announcements, not for clearer understanding of its systems.  So, let me try to get a message out to the pointy-haired bosses of the world: a single qubit that you understand is better than a thousand qubits that you don’t.  There’s a reason why academic quantum computing groups focus on pushing down decoherence and demonstrating entanglement in 2, 3, or 4 qubits: because that way, at least you know that the qubits are qubits!  Once you’ve shown that the foundation is solid, then you try to scale up.   

So there's a finance and publicity angle here as well as the science. The NYT article doesn't really get into any of the specific claims of D-Wave, but I recommend Aaronson's comments as a good counterpoint to the hype.

Quantum thinking

I just had a feature article for New Scientist magazine covering research showing some rather peculiar connections between the mathematics of quantum theory and patterns of human decision making. I don't want to say too much more here, but would like to clarify one very important point and give some links.

I was inspired to write this article a couple years ago at a brain storming session held by the European Commission. Participants were supposed to be bold and propose radical visions about where the most promising avenues for research lay in the near future (this was in the context of information and computing technology). One Belgian researcher gave a fascinating talk on the application of quantum mathematics to human decision making, claiming that quantum logic fits actual human behaviour more closely than does classical logic. There are many famous "anomalies" -- such as the Ellsberg Paradox -- where people systematically violate the laws of classical logic and probability when making decisions of economic importance. The Belgian researcher explained that the quantum formalism is able to accommodate such behaviour, and was therefore surprisingly useful in understanding how people organize and use concepts.

What struck me then was the derision with which several other scientists (physicists) greeted this suggestion, while completely mis-understanding what the man had said. One physicist came close to screaming that this was "embarrassing mumbo jumbo" somehow linked to the idea that quantum physics underlies brain function (the idea proposed over a decade ago by Roger Penrose in his profound book Shadows of the Mind). He had dismissed the idea so quickly that he hadn't listened. The Belgian physicist had actually pointed out that he wasn't at all suggesting that quantum physics plays a role in the brain, only that the mathematics of quantum physics is useful in describing human behaviour.

This is a very important point -- the mathematics of quantum theory (the mathematics of Hilbert spaces) isn't identical with the theory and somehow owned by it, but stands quite independent of that theory and existed for at least a century before quantum theory was invented. The Belgian was saying -- this mathematics which turned out to be so useful for quantum physics is now turning out to be profoundly useful in quite another setting.

The New Scientist article is just a very brief introduction to some of the work. A few other things I found utterly fascinating while researching the article are:

1. This research paper called A Quantum Logic of Down Below which falls somewhere in between philosophy, psychology and computer science. The second author Dominic Widdows is a computer scientist at Google working on information retrieval. The paper essentially argues that philosophers historically devised classical logic and then took it as a model for what human logic must be or at least should be. They suggest this was the wrong way around. Pure logic isn't our best example of reasoning. The best example of reasoning systems is people, and so a logic of what reasoning is and can be ought to start with people rather than mathematics. This is a powerful idea. As the authors put it:

... what reasoning is (or should be) can only be read off from what reasoners are (and can be). Such a view one finds, for example in [Gabbay and Woods, 2001] and [Gabbay and Woods, 2003b], among logicians, and, also in the social scientific literature [Simon, 1957, Stanovich, 1999, Gigerenzer and Selten, 2001b]. Here the leading idea of the “new logic” is twofold. First, that logic’s original mission as a theory of human reasoning should be re-affirmed. Second, that a theory of human reasoning must take empirical account of what human reasoners are like – what they are interested in and what they are capable of.

 They then go on to argue that whatever the accurate logic of human reasoning is, it is more similar to quantum logic than to classical.

2. A second fascinating paper is more technical and describes some applications of this in computer science and information retrieval. Here the idea is that if people create concepts and texts and organize them using a quantum-style logic, then search methods based on classical logic aren't likely to search such conceptual spaces very effectively. This paper describes applications in which literature search can be improved by using quantum logic operations. Most interesting (and I did mention this in the New Scientist piece) is the use of quantum operations to generate what might be closely akin to "hunches" or "guesses" about where in a mass of textual data interesting ideas might be found -- guesses not based on logical deduction, but on something less tightly constrained and ultimately more powerful.