Sub luminal light to super luminal light transition in a double−Λ-system in 87Rb vapor

This paper provides a comprehensive examination of Zeeman Electromagnetically Induced Transparency (EIT) in a closed double$-\Lambda$ system, with a particular emphasis on the $D_2$ transition of ${}^{87}$Rb. We investigate the impact of magnetic field, probe beam ellipticity, and coupling intensity on atomic system properties considering a circularly polarized (${\sigma }^{\pm }$) probe and linearly polarized ($\pi$) coupling beams. The study explores the absorption properties of the system through the peak transmission and EIT width. Furthermore, we also study the dispersive characteristics of the ${}^{87}$Rb atomic medium, including the group index, group velocity, and group delay of the probe beam, in the presence and absence of a magnetic field for a double$-\Lambda$ system. The transmission profile and the rotation of the probe’s polarization are also examined in relation to the probe’s ellipticity and magnetic field. Additionally, the paper emphasizes the process of transitioning from slow light to fast light through the optimization of some parameters including the magnetic field and probe ellipticity considering double$-\Lambda$ system.