The influence functional approach for the descrition of multilevel quantum systems dynamics in strong laser fields

We describe multilevel quantum systems dynamics in electromagnetic fields using the influence functional approach in path integration formalism. We obtain equations for the statistical density matrix and the probability of transitions of quantum systems induced by the electromagnetic field. The explicit form of the quantized electromagnetic field influence functional is concretized. Spontaneous transition of the quantum systems, the Rabi oscillations and their fluctuations are obtained. The two#photon photoelectric effect is explained.