  Using the functional-integral method we investigate the effective dynamics of
a charged particle coupled to a set of two-level systems as a function of
temperature and external electric field. The optical conductivity and the
direct current (dc) resistivity induced by the reservoir are computed. Three
different regimes are found depending on the two-level system spectral
function, which may lead to a non-Drude optical conductivity in a certain range
of parameters. Our results contrast to the behavior found when considering the
usual bath of harmonic oscillators which we are able to recover in the limit of
very low temperatures.
