  The time evolution of a particle, caught in an infinitely deep square well,
displays unexpected features, when one includes tiny relativistic effects.
Indeed, even the smallest corrections to the non-relativistic quadratic
spectrum manifest themselves in a dramatic way. Our theoretical analysis brings
to light a completely new time scale, at which the system exhibits surprisingly
perfect revivals. This longer time scale rules the system dynamics and replaces
the original revival time of the unperturbed system. The early manifestation of
such phenomenon is captured by the sensitivity of sub-Planck structures for
different values of the relativistic corrections.
