Introduction

Almost a century after its birth, quantum theory remains odd and counterintuitive. As Richard Feynman wrote, it seems that nobody really understands it. This is indeed true if by understanding we mean being able to explain it using our common sense and everyday experience. The development of some kind of “quantum common sense” has been very slow even though our everyday life is being continuously influenced by technologies whose roots lie in quantum laws. In recent years the growing field of quantum information and quantum computation became a fruitful playground for physicists, mathematicians, computer scientists, and researchers from other fields who developed new interesting ways of storing, transmitting, and processing information using quantum mechanics at its best. Thus, both theoretical and experimental research on multiparticle entanglement, on the manipulation of individual quantum systems, on decoherence, and on the transition from quantum to classical are subjects of interest not only for their basic relevance but also for their potential practical significance as they might be of help for the development of a real quantum computer. Even though this technology may be far in the future, it is interesting to speculate about what lessons on quantum reality could be learned from quantum computation (eg., what would happen if one could operate a quantum computer).