On entanglement of quantum states of noninteracting subsystems

Simple models for measuring the characteristics of a system of two atoms that do not interact with each other are used to show that the nonselectivity of measurement, related to the indistinguishability of the quantum subsystems with respect to some general parameter, leads to entanglement of the atomic states of the subsystem selected in such a way. This entanglement is in no way related to some collective process and is only due to the effective measurement in an entangled basis. An analogy between the preparation of entangled states of a system of subsystems that do not interact with each other by a quantum reduction (a measurement) and a quantum evolution is found. (C) 2004 MAIK "Nauka/Interperiodica".