  We analyze a microscopic decoherence model in which the total system is
described as a spin gas. A spin gas consists of N classically moving particles
with additional, interacting quantum degrees of freedom (e.g. spins). For
various multipartite entangled probe states, we analyze the decoherence induced
by interactions between the probe- and environmental spins in such spin gases.
We can treat mesoscopic environments (10^5 particles). We present results for a
lattice gas, which could be realized by neutral atoms hopping in an optical
lattice, and show the effects of non-Markovian and correlated noise, as well as
finite size effects.
