Four-level ‘N-scheme’ in bare and quasi-dressed states pictures

Abstract

In this work, we consider a four-level ‘N-scheme’ (three radiation fields coupling four atomic levels) that has previously been shown to feature different group velocity regimes (sub-luminal, super-luminal, and negative) controlled by the strength of the third interacting field, which is referred to as the control field. Another interesting aspect of the N-scheme is the ‘appearance’ and ‘disappearance’ of an electromagnetically induced transparency (EIT) window at resonance. In this paper, based on a study in the bare states picture, we point out differences and similarities between two settings (different strengths of the acting fields) of this four-level N-scheme. Conclusions are drawn based on a work in a simplified quasi-dressed states picture. We find that the four-level N-scheme under study can be approached as either a one or two three-level lambda-like system(s) that display the same physics regardless of the relative strength between the two fields that form the EIT portion of the system.

Keywords:

• four-level
• N-scheme
• electromagnetically induced transparency
• dressed states
• slow light
• fast light
• negative light

Acknowledgements

Two of the authors (JPD and FAN) would like to acknowledge useful discussions with R.W. Boyd (University of Rochester) and G.R. Welch (Texas A&M University). Two of us (JPD and FAN) gratefully acknowledge the financial support of the Office of Naval Research through an In-House Laboratory Innovative Research Grant.