Information transfer in the course of a quantum interaction

We discuss the problem of information transfer (exchange of states configur ation) between two interacting quantum systems along their evolution in tim e. We consider the specific case of two modes of an electromagnetic field w ith a rotating wave coupling interaction (up-conversion in a nonlinear crys tal). We verify that for certain initial states of the fields the swapping of state configuration occurs with conservation of the mean energy of each mode (without energy transfer), thus characterizing pure information flow.