In my view it's useless to argue about interpretations. Last I checked they had the same predictions.
Not true at all. If the superposition in the QM formalism merely represents our ignorance about the system's state, rather than an objective reality, then QC loses the massive parallelism which is supposed to make it so much more efficient than classical computation.
Well nobody argues the wave function represents our ignorance about the system's state. It's certainly not in the Copenhagen interpretation anyway. The wave function sacrifices realism.
In the Copenhagen interpretation, the wave function represents our ignorance of what the system's state will become when observed, but it's taken as an accurate description of the system's actual state prior to observation. That is the point of the "Schroedinger's cat" paradox: that under the Copenhagen interpretation, the cat actually is in a superposition of alive and dead states, until someone looks in the box. Quantum computation crucially depends on the objective reality of this superposition. It seems likely to me that the superposition in the formalism actually just represents our ignorance of the system's state, not the state itself.
