Influence of the counter-rotating terms on the spontaneous emission from a two-level hydrogenic atom: non-Markovian solution for atomic population-inversion expectation value and the radiative line shape

By using a new projection-operator method, developed recently by one of the present authors (J.S.), the counter-rotating terms are self-consistently included into the interaction of a two-level hydrogenic atom with a vacuum radiation field. A non-Markovian solution for the atomic population inversion showing new features is derived by a rigorous mathematical method. Moreover, the radiative line shape with some new characteristics is calculated within the scope of the model.