Light pulse in $\Lambda$-type cold atomic gases

TL;DR

This paper studies how light pulses behave in Lambda-type cold atomic gases with counterpropagating control lights, revealing conditions for stationary or propagating pulses based on wave packet length and coherence decay rate.

Contribution

It provides a detailed analysis of light pulse dynamics in cold atomic gases, connecting theoretical simulations with experimental observations and identifying key parameters affecting pulse behavior.

Findings

Longer wave packets and higher decay rates produce stationary light pulses.

Shorter wave packets and lower decay rates lead to propagating light pulses.

In the limit of zero decay, light always splits into two propagating pulses.

Abstract

We investigate the behavior of the light pulse in $Lambda$-type cold atomic gases with two counterpropagating control lights with equal strength by directly simulating the dynamic equations and exploring the dispersion relation. Our analysis shows that, depending on the length $L_0$ of the stored wave packet and the decay rate $\gamma$ of ground-spin coherence, the recreated light can behave differently. For long $L_0$ and/or large $\gamma$, a stationary light pulse is produced, while two propagating light pulses appear for short $L_0$ and/or small $\gamma$. In the $\gamma \to 0$ limit, the light always splits into two propagating pulses for sufficiently long time. This scenario agrees with a recent experiment [Y.-W.Lin, et al., Phys. Rev. Lett. 102, 213601(2009)] where two propagating light pulses are generated in laser-cooled cold atomic ensembles.