LOCALIZATION EFFECTS IN AC-DRIVEN TIGHT-BINDING LATTICES

We study coherent dynamics of tight-binding systems interacting with s tatic and oscillating external fields. We consider Bloch oscillations and Wannier-Stark localization caused by de fields, and compare these effects to dynamic localization that occurs in the presence of additio nal ac fields. Our analysis relies on quasienergy eigenstates, which t ake over the role of the usual Bloch waves. The widths of the quasiene rgy bands depend non-monotonically on the field parameters. If there i s lattice disorder, the degree of the resulting Anderson localization is determined by the ratio of disorder strength and quasienergy bandwi dth. Therefore the localization lengths can be controlled, within wide ranges, by adjusting the ac amplitude. Experimental realizations of o ur model systems are given by semiconductor superlattices in far-infra red laser fields, or by ultracold atoms in modulated standing light wa ves. In both cases the system parameters, as well as the field amplitu des and frequencies, are readily accessible to experimental control, s uggesting these as highly attractive candidates for systematic study o f localization phenomena.