  We propose a simple phenomenological model to estimate the spatial
decoherence time in quantum dots. The dissipative phase space dynamics is
described in terms of the density matrix and the corresponding Wigner function,
which are derived from a master equation with Lindblad operators linear in the
canonical variables. The formalism was initially developed to describe
diffusion and dissipation in deep inelastic heavy ion collisions, but also an
application to quantum dots is possible. It allows us to study the dependence
of the decoherence rate on the dissipation strength, the temperature and an
external magnetic field, which is demonstrated in illustrative calculations on
a circular GaAs one-electron quantum dot.
