  We develop a method to determine spatial configurations to realize
decoherence-free subspaces for spatially extended multi-particle systems. We
have assumed normal reservoir behavior including translational invariance of
the reservoir and preparation in stationary states or mixture thereof and weak
Markovian system-reservoir coupling that requires energy transfer. One
important outcome of our method is a proof that there does not exist a
multi-particle decoherence-free subspace in such systems except in the limit
that the spatial extent of the system becomes infinitesimal.
