Coherent control of light field with electromagnetically induced transparency in a dark state Raman coherent tripod system

TL;DR

This paper demonstrates how a dark state Raman tripod system can be used to coherently control light propagation, enabling transitions from absorption to amplification and tuning the group velocity from subluminal to superluminal or negative.

Contribution

It introduces a novel control scheme for light fields using a dark state Raman tripod system with coherent population trapping.

Findings

Probe pulse experiences absorption, transparency, or amplification.

Group velocity of light can be tuned from subluminal to negative.

Propagation behavior is controlled by initial coherent superposition states.

Abstract

The coherent superposition of two-atomic levels induced by coherent population trapping is employed in a standard $\Lambda$ type scheme to form a tripod-like system. A weak probe pulse scanning across the system is shown to experience a crossover from absorption to transparent and then to amplification. Consequently the group velocity of the probe pulse can be controlled to propagate either as a subluminal, a standard, a superluminal or even a negative speed. It is shown that the propagation behavior of the light field is entirely determined and controlled by the initial states of the coherent superposition.