  The effects of decoherence for quantum system coupled with a bosonic field
are investigated. An application of the stochastic golden rule shows that in
the stochastic limit the dynamics of such a system is described by a quantum
stochastic differential equation. The corresponding master equation describes
convergence of a system to equilibrium. In particular it predicts exponential
damping for off-diagonal matrix elements of the system density matrix, moreover
these elements for a generic system will decay at least as
\exp(-tN{kT\over\hbar}), where N is a number of particles in the system. As an
application of the described technique a derivation from first principles (i.e.
starting from a Hamiltonian description) of a quantum extension of the Glauber
dynamics for systems of spins is given.
