Subluminal and superluminal light propagation in two kinds of V-type system

TL;DR

This paper investigates how the group velocity of a probe light can be tuned from subluminal to superluminal in two types of V-type three-level systems using coherence effects and incoherent pumping, with analytical and numerical methods.

Contribution

It provides analytical and numerical analysis of light speed control in V-type systems, including application to a real molecular system, highlighting phase and pumping rate effects.

Findings

Group velocity can be switched from subluminal to superluminal.

Phase, pumping rate, and detuning control the group index.

Application demonstrated on LiH molecule.

Abstract

We study the change of the probe field group velocity from subluminal to superluminal range for two kinds of closed three-level V-type system with spontaneously generated coherence and incoherent pumping field. For the first kind of the V-type system we deduce the analytical formula of the group velocity, while for the second kind of the V-type system we solve numerically the density matrix equations system and apply it to a real system from the LiH molecule. We find that the group index of the probe field can be changed from positive to negative within the appropriate choice of the relative phase between the probe and coupling field phases, the incoherent pumping rate and probe detuning.