  The quantum fidelity was introduced by Peres to study some fingerprints of
classically chaotic behavior in the quantum dynamics of the corresponding
systems. In the present paper the signatures of classical dynamics near
elliptic points and of interactions between particles are characterized for
kicked systems. In particular, the period of the fidelity resulting of the
interactions is found using analytical and numerical calculations. A mechanism
leading to the oscillations with the intermediate period is proposed. It is of
a semiclassical origin and results of the interplay between the oscillations of
the width of the wave packets and the rotation of their center around the
elliptic fixed point.
