  In this talk we present a model to demonstrate how time-periodic potential
can be used to manipulate quantum metastability of a system. We study
metastability of a particle trapped in a well with a time-periodically
oscillating barrier in the Floquet formalism. It is shown that the oscillating
barrier causes the system to decay faster in general. However, avoided
crossings of metastable states can occur with the less stable states crossing
over to the more stable ones. If in the static well there exists a bound state,
then it is possible to stabilize a metastable state by adiabatically increasing
the oscillating frequency of the barrier so that the unstable state eventually
cross-over to the stable bound state. It is also found that increasing the
amplitude of the oscillating field may change a direct crossing of states into
an avoided one. Hence, one can manipulate the stability of different states in
a quantum potential by a combination of adiabatic changes of the frequency and
the amplitude of the oscillating barrier.
