Experimental evidence of dynamical localization and delocalization in a quasi-periodic driven system

This paper presents the first experimental evidence of the transition from dynamical localization to delocalization under the influence of a quasi-periodic driving on a quantum system. A quantum kicked rotator is realized by placing cold atoms in a pulsed, far-detuned, standing wave. If the standing wave is periodically pulsed, one observes the suppression of the classical chaotic diffusion, i.e. dynamical localization. If the standing wave is pulsed quasi-periodically with two different frequencies, dynamical localization is observed or not, depending on the two frequencies being commensurable or incommensurable. One can thus study the transition from the localized to the delocalized case as a function of the effective dimensionality of the system.