  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.
