Open-system effects on slow light and electromagnetically induced transparency

The coherence properties of a three-level Λ-system influenced by a Markovian environment are analysed. A coherence vector formalism is used and a vector form of the Lindblad equation is derived. Together with decay channels from the upper state, open-system channels acting on the subspace of the two lower states are investigated, i.e. depolarization, dephasing and amplitude damping channels. We derive an analytic expression for the coherence vector and the concomitant optical susceptibility, and analyse how the different channels influence the optical response. This response depends non-trivially on the type of open-system interaction present, and even gain can be obtained. We also present a geometrical visualization of the coherence vector as an aid to understand the system response.