Evidently there are computational tasks that are ‘intractable’ if we attempt to perform them using any existing computer, but which would be tractable if we were to use quantum-mechanical objects as special-purpose computers. (Notice that the fact that quantum phenomena can be used to perform computations in this way depends on their not being subject to chaos. If the outcome of computations were an inordinately sensitive function of the initial state, ‘programming’ the device by setting it in a suitable initial state would be an impossibly difficult task.)
