Finite energy states generation by periodically pulsed nonlinear oscillator

A system comprising an anharmonic oscillator interacting with an external f iled is discussed. The oscillator is assumed to be driven by a series of ul tra-short external coherent pulses, and is initially in the vacuum state. I t is shown that despite strong and permanent external excitations and lack of damping processes, for sufficiently short times between two subsequent p ulses the system's evolution is restricted to a finite set of Fock n-photon states. Consequently, the mean energy of photons remains finite and the sy stem evolves similarly to displaced Kerr states. The dynamics of the mean e nergy of photons is compared to that of its classical counterparts.