If Zephod Beeblebrox shows up at the University of Illinois Urbana-Champaign and makes off with the interferometers, don’t say I didn’t warn you.

Not to be a skeptic, but is there really a “disruptive technologies office?” It sounds fishy (much like the rest of quantum mechanics). It’s too early for an April Fool’s joke, though…

c’mon our John. I always get depressed when I see intelligent arts people throwing up their hands in the face of science stuff. Remember these people aren’t demigods; they’re just called “physicists” because they did a physics degree.

It’s not very much more difficult to understand how a photon can simultaneously run and not run an algorithm than to understand how it can simultaneously interfere and not interfere with itself, and you can understand the two-slit experiment from reading the Feynman lectures which are perfectly comprehensible to an intelligent layman who is prepared to apply himself. Being able to perform the actual calculations would be tedious and difficult but the underlying principles are not beyond the ken of man.

The “Disruptive Technologies Office” is the new name for an old agency: ARDA.

It’s worth noting that the computer in question must be turned on, and properly programmed/ready to go, so the savings in labor and energy are pretty minimal. In the past, it was thought that the probability that a final measurement of the system would yield the state |Program not run>|Correct answer obtained> was so small that a random guess would be more likely to succeed. The authors used a neat trick (a “Super Zeno Booster”!) to amplify the “interesting” probability above the random-guess threshold.

Daniel is absolutely right, of course: the calculations needed to explain these results are laborious but straightforward. What is not straightforward is the ingenuity needed to (1) think up paradoxical experiments that will probe the limits of quantum mechanics, and then (2) design and build the experiments themselves. This is why the field of quantum information science is so much fun.

Daniel, from my (physics undergrad) perspective going through the Feynman lectures would seem to be actually harder than learning to calculate some elementary stuff with two-state quantum systems since that’s just linear algebra. Two-state systems allow a fairly rigorous but still easy formulation of quantum mechanics with a simple finite dimensional Hilbert-space and I sometimes wonder why they are not the starting point for teaching QM.

And do you know why I want a cup of tea?

If you use multiverse theory, all this run/not run, simultaneity of position etc becomes perfectly plain. There’s nothing mysterious about it.

I understand the basic physics principle without any problem. But I’m a bit confused about the actual math here–from the newspaper blurb it sounded like they were doing something akin to the double slit, interfere with itself sort of thing, as Daniel points out.

But then it goes on to imply that they also know which state it was in (in this case, the “don’t run the algorithm” state.) And if you’ve measured to determine the particle’s path (in the two slit problem), then it no longer interferes with itself. So there’s something different going on here. I assume it’s explained in the Nature article (or in the references or the references of the references, since high profile physics articles are now constrained to being 3 pages long, which is much too short to actually explain any work starting from basics.), but that’s behind a subscription wall.

This in addition to the general weirdness of quantum computing. Of course, regular computing is pretty weird, too–I can tell you exactly how transistors work, at the electron/semiconductor physics level. But there’s a mysterious “then a miracle occurs” step two in my understanding going from that to an actual chip doing calculations. I have a similar problem transitioning in my mind from well understand prinsiples of quantum mechanics to performing calculations with them.

Just one more in the ever expanding list of fascinating things I don’t have time to learn.

Experimenting with two slits and a chained Zeno effect? Count me in!

I can tell you exactly how transistors work, at the electron/semiconductor physics level. But there’s a mysterious “then a miracle occurs” step two in my understanding going from that to an actual chip doing calculations.

Really? That’s when it gets easy. At that point, it’s boolean logic all the way up.

People who understand this experiment: where would you point us baffled non-physicists to get the hang of it?

Dan, that’s such a good question that I scooted over to the Stanford bookstore to try to find a book that might be a good place to start. Unfortunately, I didn’t find any unambiguously good candidates for you: they were heavy on analogies and hand-waving, and light on the details. For example, I think that the book by Aczel on Entanglement would not be to your liking.

There are probably two reasonable places to start:

1. Wikipedia has a pretty good page on quantum mechanics, and another page on just the basics.

2. Daniel’s suggestion above is actually a pretty good one: try reading the third volume of the Feynman lectures. Feynman doesn’t spend much time on entanglement, but he does an excellent job on the two-slit experiment. There is math, but I bet that you could just skim over it on the first reading. (It’s mostly just algebra — even if it looks more abstract than you saw in high school — and the first year of calculus.)

If I were going to write a book on quantum mechanics for the layman, I think that I’d describe one experiment per chapter, anticipate the result using “classical” intuition, and then describe the actual result. The apparent paradox would then be a vehicle for explaining what seems to be so odd about the universe. (For example, after a discussion of the two-slit experiment and a Bell-inequality experiment, I’d discuss the quantum eraser.) After ten or so chapters, you could probably gain a pretty good understanding of the subject in a general way. I’d forget the history completely; there are enough books on that subject already. Maybe there’s a book available that’s like this, but I didn’t see it at the bookstore.

I’m happy enough with Feynmann’s explanation of the two-slit experiment, and unlike Daniel I also like the multiverse representation.

But I’d like a decent reference on quantum computation focusing on the question implied by the post: can you get something for nothing here, and if so, how and in what sense?

Don’t panic! It’s as simple as…oh, damn, where’s my towel!