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.