  Nanoscopic rings pierced by external magnetic fields and asymmetrically
connected to wires behave in sharp contrast with classical expectations. By
studying the real-time evolution of tight-binding models in different
geometries, we show that the creation of a magnetic dipole by a bias-induced
current is a process that can be reversed: connected rings excited by an
internal ac flux produce ballistic currents in the external wires. In
particular we point out that, by employing suitable flux protocols,
single-parameter nonadiabatic pumping can be achieved, and an arbitrary amount
of charge can be transferred from one side to the other. We also propose a set
up that could serve a memory device, in which both the operations of {\it
writing} and {\it erasing} can be efficiently performed.
