EFFECT OF THE STATE OF A QUANTIZED ELECTROMAGNETIC-FIELD ON THE INTERACTION WITH AN ATOM WITH ALLOWANCE FOR THE CONTINUUM

This paper studies the effect of a transition into the continuous spec trum on the ''collapse'' and ''revival'' of population oscillations in an atom. It is shown that at large values of the mean number of photo ns in a radiation field and in conditions of weak ionization the pheno mena of collapse and revival can still be observed, but the amplitude of population oscillations decreases exponentially because of the damp ing of the level. The interaction of a quantized electromagnetic field with a Lambda system of an atom when one state is continuous is exami ned. Expressions are derived for the probability of ''survival'' of th e atom when the quantized field was initially in a state with a given number of photons and when it was in a coherent state. An approximate calculation of the sum in averaging over the photon number distributio n in the case of a coherent field leads to expressions for the probabi lities of survival of the atom that transform into expressions, as the mean number of photons tends to infinity, corresponding to the case o f a field in the representation of a fixed number of photons. The poss ibility of a stable state existing in a coherent quantized field is ex amined. It is found that for a Lambda system the condition for the exi stence of a stable state remains valid in the case of a coherent state of the field when the photon number is large. (C) 1998 American Insti tute of Physics.