| Dynamic localization (DL) of an electron refers to the return of the electron to its initial quantum state when it is subjected to particular periodic ac electric fields. In this talk, I will examine the conditions for DL of an electron in a spatially-periodic potential in general temporally-periodic ac-dc electric fields. I will show that DL can occur within the nearest-neighbor tight-binding approximation for a wide variety of fields; however for general electron bands, it can only occur when the field has discontinuities in time and satisfies certain very specific conditions. I will also discuss a new type of DL, "Quasi-Bloch Oscillations" (QBOs), that can occur irrespective of the shape and amplitude of the ac part of the field if there is a dc component to the field with the correct amplitude. QBOs occur only for electron bands that are well described by the tight-binding approximation, however QBOs are not restricted to nearest-neighbor tight-binding systems. Finally, I will discuss experiments in waveguide systems where the analog of exact and approximate dynamic localization has been observed and will discuss experiments proposed to observe QBOs for the first time. |
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