Dynamics of spin systems in rapidly oscillating external fields

Abstract

This paper investigates the dynamics of spin systems with a rapidly oscillating Hamiltonian. The Floquet-Liapounoff theorem is used to solve the Liouville equation, the expansion in powers of the small parameter being constructed from the very beginning in such a say as to separate the slow time dependence from the fast. It is shown that the expansion obtained in this manner is equivalent to the one obtained earlier on the basis of the Krylov-Bogolyubov-Mitropol'skii method of averaging.