Reservoir-induced transparency and coherent population trapping

We analytically and numerically investigate the response of an open Lambda-type atomic system to a probe laser field, where one of the atomic transition is coupled with a double-band radiation reservoir and high-Q defect modes formed by atomic doping. This system can be transparent to a weak probe field being two-photon resonant with the frequency of the defect modes or one of the two band edges, and the high-Q defect modes can even induce an atom-field coherent population trapping (CPT) state without involving the excited state of the atom, in spite of the background decay of the excited state of the atom. The steady-state properties of this CPT are independent of the smoothness feature of the density of modes (DOM) at band edges. However, the CPT never occurs in the absence of any defect even if the DOM is singular at both band edges. We also find that the background decay of the second ground state of the atom will destroy the CPT and increase the probe absorption, but the atomic coherence induced by the defect modes is more robust than that induced by the band edges. The transient properties of the CPT are also studied.