A master equation approach for the description of dark-state polaritons in
coherently driven atomic media is presented. This technique provides a
description of light-matter interactions under conditions of
electromagnetically induced transparency (EIT) that is well suited for the
treatment of polariton losses. The master equation approach allows us to
describe general polariton-polariton interactions that may be conservative,
dissipative or a mixture of both. In particular, it enables us to study
dissipation-induced correlations as a means for the creation of strongly
correlated polariton systems. Our technique reveals a loss mechanism for
stationary-light polaritons that has not been discussed so far. We find that
polariton losses in level configurations with non-degenerate ground states can
be a multiple of those in level schemes with degenerate ground states