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Originally Posted by nekokami
I get the general idea (I was a physics major for 2 years with an interest in quantum mechanics), but I still haven't worked out how using quantum effects is faster. Is it faster for all sorts of calculations, or for specific tasks such as factoring (as mentioned in the BBC article above)? I know you mentioned search, which is so common that by itself it would be a help, even if regular silicon ICs were faster for other stuff. But I suspect there are broader applications. The only thing that seems analogous to me so far is that if the photons can be in multiple places at once, maybe you can do parallel processing that way?
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Actually no one knows quote what makes quantum computers faster. Superposition (the mathematical name for a photon being in multiple places) definitely plays a role, as does entanglement (which allows for stronger correlations between systems than is possible in classical physics). In fact what makes quantum computers faster and just how much faster is very much an open question.
So far people have only found a handful of algorithms, factoring and search being the two most useful examples where quantum computers show a definite speedup over their classical cousins. In fact, in the case of catoring the speedup is actually exponential!