Abstract
We have investigated the effect of the counter-rotating terms on the field quantum entropy and the entanglement of the atom-field in the two-photon process, taking into account the level shifts produced by the Stark effect, with an additional Kerr-like medium for one mode. A factorization of the initial density operator is assumed, with the privileged field mode being in a coherent state. We invoke the mathematical notion of the maximum variation of a function to construct a measure for entropy fluctuations. The effects of both the Stark shift and a Kerr-like medium on the entropy and the presence of the counter-rotating terms are analyzed.