A quantum computer only needs one universe

The nature of quantum computation is discussed. It is argued that, in terms of the amount of information manipulated in a given time, quantum and classical computation are equally efficient. Quantum superposition does not permit quantum computers to “perform many computations simultaneously” except in a highly qualified and to some extent misleading sense. Quantum computation is therefore not well described by interpretations of quantum mechanics which invoke the concept of vast numbers of parallel universes. Rather, entanglement makes available types of computation process which, while not exponentially larger than classical ones, are unavailable to classical systems. The essence of quantum computation is that it uses entanglement to generate and manipulate a physical representation of the correlations between logical entities, without the need to completely represent the logical entities themselves. The main purpose of this article is to improve our insight into what is going on in any quantum computation. Although I have no new quantum algorithms or methods to offer, I hope this type of contribution may still be of some help towards a better grasp of quantum computation, and therefore towards future insights and new methods.