Understanding decoherence as an irreversible process

Abstract

If decoherence is an irreversible process, its physical meaning might be clarified by comparing quantum and classical irreversibility. In this work we carry out this comparison, from which a unified view of the emergence of irreversibility arises, applicable both to the classical and to the quantum case. According to this unified view, in the two cases the irreversible macro-level arises from the reversible micro-level as a coarse description that can be understood in terms of the concept of projection. This position supplies an understanding of the phenomenon of decoherence different from that implicit in most presentations: the reduced state is not the quantum state of the open system, but a coarse state of the closed composite system; as a consequence, decoherence should be understood not as a phenomenon resulting from the interaction between an open system and its environment, but rather as a coarse evolution that emerges from disregarding certain degrees of freedom of the whole closed system.