Another Update (Feb. 7): I have a new piece up at IEEE Spectrum, explaining why I made this bet. Thanks to Rachel Courtland for soliciting the piece and for her suggestions improving it.

Update: My $100,000 offer for disproving scalable quantum computing has been Slashdotted. Reading through the comments was amusing as always. The top comment suggested that winning my prize was trivial: “Just point a gun at his head and ask him ‘Convinced?'” (For the record: no, I wouldn’t be, even as I handed over my money. And if you want to be a street thug, why limit yourself to victims who happen to have made public bets about quantum computing?) Many people assumed I was a QC skeptic, and was offering the prize because I hoped to spur research aimed at disproving QC. (Which is actually an interesting misreading: I wonder how much “pro-paranormal” research has been spurred by James Randi’s million-dollar prize?) Other people said the bet was irrelevant since D-Wave has already built scalable QCs. (Oh, how I wish I could put the D-Wave boosters and the QC deniers in the same room, and let them duke it out with each other while leaving me alone for a while!) One person argued that it would be easy to prove the impossibility of scalable QCs, just like it would’ve been easy to prove the impossibility of scalable classical computers in 1946: the only problem is that both proofs would then be invalidated by advances in technology. (I think he understands the word “proof” differently than I do.) Then, buried deep in the comments, with a score of 2 out of 5, was one person who understood precisely:

I think he’s saying that while a general quantum computer might be a very long way off, the underlying theory that allows such a thing to exist is on very solid ground (which is why he’s putting up the money). Of course this prize might still cost him since if the news of the prize goes viral he’s going to spend the next decade getting spammed by kooks.

OK, two people:

There’s some needed context. Aaronson himself works on quantum complexity theory. Much of his work deals with quantum computers (at a conceptual level–what is and isn’t possible). Yet there are some people who reject the idea the quantum computers can scale to “useful” sizes–including some very smart people like Leonid Levin (of Cook-Levin Theorem fame)–and some of them send him email, questions, comments on his blog, etc. saying so. These people are essentially asserting that Aaronson’s career is rooted in things that can’t exist. Thus, Aaronson essentially said “prove it.” It’s true that proving such a statement would be very difficult … But the context is that Aaronson gets mail and questions all the time from people who simply assert that scalable QC is impossible, and he’s challenging them to be more formal about it. He also mentions, in fairness, that if he does have to pay out, he’d consider it an honor, because it would be a great scientific advance.

For better or worse, I’m now offering a US$100,000 award for a demonstration, convincing to me, that scalable quantum computing is impossible in the physical world. This award has no time limit other than my death, and is entirely at my discretion (though if you want to convince me, a good approach would be to convince most of the physics community first). I might, also at my discretion, decide to split the award among several people or groups, or give a smaller award for a discovery that dramatically weakens the possibility of scalable QC while still leaving it open. I don’t promise to read every claimed refutation of QC that’s emailed to me. Indeed, you needn’t even bother to send me your refutation directly: just convince most of the physics community, and believe me, I’ll hear about it! The prize amount will not be adjusted for inflation.

The impetus for this prize was a post on Dick Lipton’s blog, entitled “Perpetual Motion of the 21st Century?” (See also this followup post.) The post consists of a debate between well-known quantum-computing skeptic Gil Kalai and well-known quantum-computing researcher Aram Harrow (Shtetl-Optimized commenters both), about the assumptions behind the Quantum Fault-Tolerance Theorem. So far, the debate covers well-trodden ground, but I understand that it will continue for a while longer. Anyway, in the comments section of the post, I pointed out that a refutation of scalable QC would require, not merely poking this or that hole in the Fault-Tolerance Theorem, but the construction of a dramatically-new, classically-efficiently-simulable picture of physical reality: something I don’t expect but would welcome as the scientific thrill of my life. Gil more-or-less dared me to put a large cash prize behind my words—as I’m now, apparently, known for doing!—and I accepted his dare.

To clarify: no, I don’t expect ever to have to pay the prize, but that’s not, by itself, a sufficient reason for offering it. After all, I also don’t expect Newt to win the Republican primary, but I’m not ready to put $100,000 on the line for that belief. The real reason to offer this prize is that, if I did have to pay, at least doing so would be an honor: for I’d then (presumably) simply be adding a little to the well-deserved Nobel Prize coffers of one of the greatest revolutionaries in the history of physics.

Over on Lipton’s blog, my offer was criticized for being “like offering $100,000 to anyone who can prove that Bigfoot doesn’t exist.” To me, though, that completely misses the point. As I wrote there, whether Bigfoot exists is a question about the contingent history of evolution on Earth. By contrast, whether scalable quantum computing is possible is a question about the laws of physics. It’s perfectly conceivable that future developments in physics would conflict with scalable quantum computing, in the same way that relativity conflicts with faster-than-light communication, and the Second Law of Thermodynamics conflicts with perpetuum mobiles. It’s for such a development in physics that I’m offering this prize.

Update: If anyone wants to offer a counterpart prize for a demonstration that scalable quantum computing is possible, I’ll be happy for that—as I’m sure, will many experimental QC groups around the world. I’m certainly not offering such a prize.