The idea of quantum computing (for those of us that spent the last seven years under a rock or so) consists in exploiting the fact that quantum systems remain in a state of simultaneous superposition of their potential actualities until they are actually observed (that is, until they interact with the observing part of the universe). Thereby, you can have a computer with a register that does not store just one value, but that holds all potential values in simultaneous superposition, and what's more, you can run algorithms these values simultaneously. If you were to use a decryption algorithm that checks if the result is a proper English text, you could try all possible encryption keys at once and have the system stop in a state where it finds a valid text and thereby a solution for the key, before you observe it. Some people have actually built such quantum computers with incredibly expensive and tricky arrangements of extremely cooled particles in extremely strong fields that where manipulated with extremely expensive laser beams, and while they have shown that the principle is sound, the particles store extremely few bits and most of the time they interact too early with the outside world (thereby losing their precious superposition state) or get lost altogether.

I want to propose building such a system using simple rays of light traveling through switchable cascades of double slits. By tuning this down to the level of individual photons to avoid stray interactions, we should be able to realize temporary registers nicely. In theory, a further simplification could be made: use an indeterministic source in a classical system that does the testing, and isolate this system in such a way that no interaction with the outside world is possible (hey, I know that it won't be trivial, a bit of heat and noise insulation will hardly suffice). The properties of the quantum source will then be inherited by the whole classical system, and viola! We got a reliable, easy-to-program large scale quantum computer!
-- TeaInTheAfternoon, Feb 03 2004

tmxxine software and hardware http://en.wikipedia.org/wiki/User:Tmxxine
Software for Open Source Quantum computer [tmxxine, Oct 04 2004]

IEEE Spectrum: “Can Quantum Dots Compute?” http://www.spectrum...aug04/0804ndot.html
“4 August 2004—Researchers have long been trying to develop quantum computers based on the same semiconductor technologies that have so successfully powered conventional computers. Now, after years of exploration, two groups have begun to connect the dots—literally.” [bristolz, Oct 04 2004]

Them quantums ain't cheap.
-- 2 fries shy of a happy meal, Feb 03 2004


Cheap?. Quantum? = How much?!.
-- gnomethang, Feb 04 2004


//If you were to use a decryption algorithm that checks if the result is a proper English text//

Could you do that to the first sentence of the first paragraph?
-- thumbwax, Feb 04 2004


// Them quantums ain't cheap. //

Surely they cost no more than the quantum of money, which is the cent or penny.
-- kropotkin, Feb 04 2004


Add a microflux field to the external vombeyer chamber this will polarize the warp field and allow us to make safe retreat captain.
-- grippit, Feb 04 2004


[marked-for-deletion], Do I even have to say it out loud? MAGIC!
-- zigness, Apr 18 2004


Why is it magic? It may be implausible but not magic. The author makes a valid attempt to describe the mechanism.
-- bristolz, Apr 18 2004


Like Einstein, zig just doesn’t buy into that quantum stuff.
-- ldischler, Apr 19 2004


May I suggest that the use of 'could', 'should' and 'extremely' may well prejudice the case.
'Tricky' doesn't help, either.
Nevertheless, it will be great when this is fully developed.
-- gnomethang, Apr 19 2004


How about impossible and interesting, simultaneously?
-- bristolz, Apr 19 2004


I can sort of see how this might work... would you do it one photon at a time???
-- xaviergisz, Apr 20 2004


I love it. Of course, since it is only probably there, it is a little dicey to back up.
-- grecosartre, Apr 20 2004


How do you plan on "tuning" the double-slit down to the level of individual photons? I think this is where the "magic" comes in. Any submicroscopic tuning of this nature is probably not going to be cheap.
-- GenYus, Apr 20 2004


I don't think it's possible to do Toffoli or Fredkin gates with light, only controlled not.

Controlled not is not universal. So no factoring million digit numbers with it.

You can calculate any sequence of controlled not operations in reasonable time with a matrix, making the quantum computer rather unnecessary for calculations involving it.
-- Bad Jim, May 26 2008



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