Two-level system in the field of two intense waves

The problem of a two-level system in the field of two intense monochromatic waves is reduced to the problem of a two-level system in the field of a nonmonochromatic but periodic (in time) wave, which makes it possible to introduce quasienergy states. An investigation is made by the method proposed in [1, 2]. For the quasienergy an analytic expression is obtained that is valid in the complete range of variation of the frequencies at all values of one of the intensity parameters and moderate values of the other. The quasienergy is also calculated in the case of asymptotically large values of the parameters of both intensities when one of the frequencies of the external field is equal to the resonance frequency. The Fourier components of the density matrix at the frequencies of the external field are also calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 23–25, August, 1980.We thank M. L. Ter-Mikaelyan for interest in the work.