Limits and possibilities of refractive index in atomic systems

Manipulation of the refractive index has been of growing interest lately. We consider parameters and possibilities of enhancing the absolute-value limit of the linear index in coherent atomic systems. Starting with a review of how two-level transitions - without and with added coherence effects - do not realistically allow for a significantly enhanced index at fixed atomic density, we discuss a possible way around this using wave mixing. This confirms that the only parameters, besides the medium optical depth/density, that can effectively change the value of the attainable index are the frequencies of the involved transitions.

Automated summary

There has been increasing interest in manipulating the refractive index recently, with a focus on enhancing the absolute-value limit of the linear index in coherent atomic systems. By exploring wave mixing as a possible solution to the limitations posed by two-level transitions, it was found that the frequencies of the involved transitions play a key role in changing the attainable index value, alongside the medium optical depth/density.