Information Transfer in the Course of a Quantum Interaction

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.