 Deutsch (1997) has argued that the exponential speed-up in quantum computation, and in general the way a quantum system processes information, can only be properly understood within the framework of Everett’s ‘many-worlds’ interpretation (see the entries on  Everett’s relative-state formulation of quantum mechanics  and the  many-worlds interpretation of quantum mechanics).  The idea, roughly, is that an entangled state of the sort that arises in the quantum computation of a function, which represents a linear superposition over all possible arguments and corresponding values of the function, should be understood as something like a massively parallel classical computation, for all possible values of a function, in parallel worlds. For an insightful critique of this idea of ‘quantum parallelism’ as explanatory, see Steane 2003.