Cheap Quantum Computer

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!