I have a feeling that quantum computing is like those perpetual motion machines people keep trying to make with complicated arrangements with magnets. No matter how much you try to iron out the errors you never actually get there. I suspect there is, like the laws of thermodynamics, a deeper truth in there somewhere. Something like: there is no way to find out things any faster than it is possible through normal means, because it is not possible to access other universes, even if they do exist.