Shor, I’ll do it (2007)
>  if you think about quantum computing in terms of “parallel universes” (and whether you do or don’t is up to you)<p>But if you <i>do</i> think of it that way, why not just pick a random number using some quantum process, classically test whether or not it's a divisor of the number you're trying to factor, and kill yourself if it's not? In every universe where you survive (which, for sake of argument, are the only ones you care about) you find a factor on the first try.