  We investigate possible ways in which a quantum wavepacket spreads. We show
that in a general class of double kicked rotor systems, a wavepacket may
undergo superballistic spreading; i.e., its variance increases as the cubic of
time. The conditions for the observed superballistic spreading and two related
characteristic time scales are studied. Our results suggest that the symmetry
of the studied model and whether it is a Kolmogorov-Arnold-Moser system are
crucial to its wavepacket spreading behavior. Our study also sheds new light on
the exponential wavepacket spreading phenomenon previously observed in the
double kicked rotor systems.
