Actually, refering to item 5, destroying the superposition of states (ie, measuring the final state of your QC) is exact what you so, over and over until you get it right. This requires/implies a few things:
1) QC's are probabilistic computers, that attempt to reduce the probalitity of an incorrect answer by repeating the computation, just like classical probabilistic computer
2) You must be able to able to verify your result in polynomial time in order for your QC computation to be efficient.
What makes a QC so powerful for some problems is not that you can measure all of the states at once, but rather that you can act on them all at once (so long as you don't measure the wave function).
Essentially, QC's bring us a step closer to an nondeterministic automata
AFAIK, the big issue in QC design is dealing with the fact that wave functions have this tendency to evolve on ther own and rather quickly. If a stable superposition of electon spins could be quantumly linked and manipualted, then a QC is likely possible in the near future. This here spintronics stuff sounds like it holds promise to slove this issue.
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1) QC's are probabilistic computers, that attempt to reduce the probalitity of an incorrect answer by repeating the computation, just like classical probabilistic computer
2) You must be able to able to verify your result in polynomial time in order for your QC computation to be efficient.
What makes a QC so powerful for some problems is not that you can measure all of the states at once, but rather that you can act on them all at once (so long as you don't measure the wave function).
Essentially, QC's bring us a step closer to an nondeterministic automata
AFAIK, the big issue in QC design is dealing with the fact that wave functions have this tendency to evolve on ther own and rather quickly. If a stable superposition of electon spins could be quantumly linked and manipualted, then a QC is likely possible in the near future. This here spintronics stuff sounds like it holds promise to slove this issue.