Argh it's been a while. The question is whether an n-qbit system actually can contain arbitrary (k <= 2^n^) amounts of n-bit states for arbitrary values of n and k: Such a system might work up to a certain number, but then lose coherence once you try to exceed what the universe can actually compute. As far as I know we simply don't know because noone has yet built a system that actually pushes boundaries in earnest. The limiting factor is more n than k I think but then I'm not a quantum physicist.

It would still mean ludicrously miniaturised computing, in fact, minimised to a maximum extent, but it would not give the asymptotic speedup cryptologists are having nightmares about.