  We study dynamical recurrences of a Bose-Einstein condensate in an optical
crystal subject to a periodic external driving force. The recurrence behavior
of the condensate is analyzed as a function of time close to nonlinear
resonances occurring in the classical counterpart. Our mathematical formalism
for the recurrence time scales is presented as delicate recurrences, which take
place, for instance, when the lattice is perturbed weakly and robust
recurrences, which may manifest themselves for a sufficiently strong external
driving force. The analysis not only is valid for a dilute condensate, but also
is applicable for the strongly interacting homogeneous condensate provided; the
external modulation causes no significant change in the density profile of the
condensate. We explain the parametric dependence of the dynamical recurrence
times, which can easily be realized in laboratory experiments. In addition, we
find good agreement between the obtained analytical results and the numerical
calculations.
