Large Scale (Multiphoton) Evolution of Atomic Energy Level's Mean Momentum for Single-Photon Absorption/Emission Process

It is shown that a two-level atom, being initially in general superposition state of ground and excited energy levels with mutually different momentum distributions there, gets a large scale evolution in the energy levels momentum distribution. As a consequence the mean momentum of each individual energy level also gets large scale changes, more than the own momentum hbar k of the photon. Because of not completeness of the literature under the hand, we are not sure that this simple phenomenon isn't known in quantum theory of atom-photon interactions or, particularly, in the interferometry of atomic matter waves. One of main purposes of this article is our request to the leading specialists to respond and if the phenomenon is known, send the corresponding references. Thoroughly is discussed the special case, when the atom's preliminary superposition state is created as a result of interaction of the atom with the resonant standing wave. Also it is pointed that in such conditions the mentioned phenomenon can be presented as a transformation of the resonant Kapitza-Dirac splitting of atomic states into the Stern-Gerlach type splitting.