  We investigate fusion cross section of a nucleus with a valence neutron,
using the time-dependent wave-packet method. For a stable projectile, in which
the valence neutron is tightly bound (e_n < -3 MeV), the neutron could enhance
the fusion probability when the matching condition of orbital energies are
satisfied. In contrast, for a halo nucleus, in which the binding energy of the
neutron is very small (e_n>-1 MeV), the fusion probability is hindered by the
presence of the weakly bound neutron.
