With all the disscussion about classical computing issues on Daniweb, I thought it was time for an explanation of quantum computing. As I'm sure most of you are aware, a conventional CPU performs operations by switching transistors on and off in order to manipulate values stored on registers. The registors are of course collections of transistors themselves. Most of the groundwork needed to develop the transistor required an understanding of quantum mechanics, in order to understand how electrons behave on small distance scales in semiconductors.
What quantum mechanics says about electrons is that on small scales they behave more like waves than particles. By small scales I am referring to distances comparable to the width of atoms. This wave like behavior can include commonly understood effects like diffraction, refraction and interference. It also includes a rather less well understood concept called entanglement. Quantum entanglement basically means that once two particles (or waves) have interacted in a particular way, they will behave as if they are a single system across which information can propagate instantaneously.
Some people might say "Doesn't this violate relativity?". The answer is "Kind of. Research the EPR paradox if you're interested.". Anyway, how do you build a quantum computer? First, put a few atoms close together to use as your quantum bits (qbits). This is your computers "register". Then, cool the system to under 1K (-273 C) and entangle the atom's electrons (making sure they stay entangled for a while). This last step is extremely difficult because entanglement is very fragile.
Now, remember I said that electrons are waves? Well, they're actually a superposition of an infinite number of wave functions. I could explain this bit, but I don't want to bore you. What this means for our computer is that it can potentially perform billions of operations in parallel. So, it could solve billions of simultaneous linear equations in a matter of minutes. This would make cracking a 128-bit encryption system like SSL a five minute job. For this reason various government and military types are keeping a close eye on this subject.
This technology is in an early stage of development and the best way to implement it has not yet been decided, which is why I've been a bit sketchy with the details. Oh, I don't really understand it either, that's another reason.