  A small quantum system is studied which is a superposition of states
localized in different positions in a static gravitational field. The time
evolution of the correlation between different positions is investigated, and
it is seen that there are two time scales for such an evolution (decoherence).
Both time scales are inversely proportional to the red shift difference between
the two points. These time scales correspond to decoherences which are linear
and quadratic, respectively, in time.
