An exact evaluation of memory functions to describe dynamic localization and excitation transfer in a small quantum system is provided to clarify the connection between two recently reported phenomena, one in quantum optics and the other in condensed matter physics. The possibility of quantum control on the basis of the calculation, with relevance to systems as widely different as electrons in a crystal, atoms interacting with light, spins in crossed magnetic fields, and Bose condensates falling in a gravitation field, is briefly mentioned. The connection to the interacting electron-phonon system and to nonlinear Schroedinger equations is pointed out.