The influences of lower-level coherence in atomic medium of Ξ-type energy-level scheme on the absorption and dispersion are studied in dressed states. It is found that a weak probe light of a certain frequency can be free of atomic absorption, and at the same time has a large index of refraction.
We study the dispersion-absorption properties in a three-level Λ-type atomic system with two closely lying lower levels. We consider two schemes: in the first, the two lower levels are coupled by decay-induced coherence, and in the second, quantum coherence is created by coupling the two lower levels to each other by a microwave field. We found that due to the decay-induced coherence or microwave-induced coherence, the dispersion-absorption properties can be controlled by the relative phase of applied fields, large index of refraction without absorption always can be obtained just by choosing proper values of the relative phase.
The properties of an optically probed atomic medium can be changed dramatically by coherent interaction with a near-resonant control light field. The authors present experimental results on the elementary case of electromagnetically induced transparency (EIT) with a single neutral atom inside an optical cavity probed by a weak field. The modification of the dispersive and absorptive properties of a single atom by changing the frequency of the control light field in the off-resonant regime is observed.
When the two excited levels in a V-type three-level atom are coupled by a microwave field,the quantum coherence is created by the interference between the atomic coupling transition channels.The probe absorption and dispersion properties can be modulated by adjusting the strength of microwave field,and the phenomenon of the high refractive index without absorption appears at the resonance.Besides,the relative phase control of probe gain can be achieved due to the quantum coherence induced by the microwave field.