We introduce power-law tail quantum wave packets. We show that they can be
seen as eigenfunctions of a Hamiltonian with a physical potential. We prove
that the free evolution of these packets presents an asymptotic decay of t
he maximum of the wave packets which is anomalous for an interval of the ch
aracterizing power-law exponent. We also prove that the number of finite mo
ments of the wave packets is a conserved quantity during the evolution of t
he wave packet in the free space.