  We discuss the problem of the information transfer (exchange of states
configuration) between two interacting quantum systems along their evolution in
time. We consider the specific case of two modes of the electromagnetic field
with rotating wave coupling interaction (up-conversion in a nonlinear crystal).
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), characterising thus pure information flow.
