Superluminal light propagation in a bi-chromatically Raman-driven and Doppler-broadened N-type 4-level atomic system

TL;DR

This paper demonstrates superluminal light pulse propagation in a Doppler-broadened N-type atomic system using double Raman gain, achieving larger negative group indices and undistorted pulses compared to previous experiments.

Contribution

It introduces a novel scheme for superluminal light propagation with enhanced advance time and minimal distortion in a controllable four-level atomic system.

Findings

Achieved larger negative group index of 7.32×10^8.

Pulse leaves the medium 76.12 ms earlier than previous experiments.

Gaussian pulse remains almost undistorted at output.

Abstract

We investigate the behavior of fast light pulse propagation in an N-type Doppler-broadened 4-level atomic system using double Raman gain processes. This system displays novel and interesting results of two controllable pairs of the double gain lines profile with a control field. The detailed physics of the processes are explored having multiple controllable anomalous regions in the medium. In this set up, the system exhibits significant enhancement in the probing Gaussian pulse through the medium as compared with Ref. [L. J. Wang, A. Kuzmich, and A. Dogariu, Nature \textbf{406}, 227(2000)]. The advance time of the retrieved Gaussian pulse is always greater than the advance time studied in the above said experiment. We analyzed that the pulse propagating through the medium with larger negative group index, $7.32\times10^8$, leaves the medium almost undistorted and sooner by time $76.12 \ ms$ than the pulse which leaves the medium of Wang \emph{et al.}. The Gaussian pulse always remains almost undistorted at output due to lossless characteristic of the medium. We also underlined the ways to suppress incoherences generated by the Doppler-broadening effect in the system. The limitations of the recently developed applications require to explore mechanisms for ultimate speed of a superluminal probe light pulse. In this connection, the proposed scheme may be helpful and can be easily adjusted with the current technology.