Resonance fluorescence spectra near a photonic bandgap

Optical radiation properties of a single atom have been among the most popular research problems in quantum optics since the early years. In contrast to classical intuition, the quantum theory asserts that the optical radiation properties are not wholly determined by the intrinsic characteristics of the atom but also depend on the electromagnetic mode structure seen by the atom even when these modes are empty (i.e., vacuum states). The emission frequency will be slightly modified through the interaction with these vacuum states (the Lamb shift), and the spontaneous emission rate can be enhancedwhen the atom is placed inside a resonant cavity (the Purcell effect). These are the two well-known examples dated back to the 1940s. Another fundamental example is the resonance fluorescence from a two-level atom. If the twolevel atom is excited on resonance by an intense optical field, the fluorescence spectrum can exhibit three peaks (the Mollow triplet), which was theoretically predicted in 1969 [1] and experimentally observed in 1975 by using the sodium atoms [2]. The coupling of the optical pump field with the two atomic levels produces Rabi oscillation in the time domain or equivalently the energy level splitting in the frequency domain. From such a dressed atom picture, it is easy to understand that the down transition from the upper two sublevels to the lower two sub-levels will exhibit three transmission frequencies since the frequency splitting of ω