Formation of strongly shifted EIT resonances using "forbidden" transitions of Cesium

Abstract

Atomic transitions satisfying $F_e - F_g = \Delta F = \pm 2$ (where $F_e$ stands for excited and $F_g$ stands for ground state) of alkali atoms have zero probability in zero magnetic field (they are so-called "forbidden" transitions) but experience a large probabilty increase in an external magnetic field. These transitions are called magnetically induced (MI) transitions. In this paper, we use for the first time the $\sigma^+$ ($\Delta m_F~=~+1$) MI transitions $F_g = 3 \rightarrow F_e = 5$ of {Cesium} as probe radiation to form EIT resonances in strong magnetic fields (1 - 3 kG) while the coupling radiation frequency is resonant with $F_g=4\rightarrow F_e=5$ $\sigma^+$ transitions. The experiment is performed using a nanometric-thin cell filled with Cs vapor and a strong permanent magnet. The thickness of the vapor column is 852 nm, corresponding to the Cs $D_2$ line transition wavelength. Due to the large frequency shift slope of the MI transitions ($\sim$ 4 MHz/G), it is possible to form contrasted and strongly frequency-shifted EIT resonances. Particularly, a strong 12 GHz frequency shift is observed when applying an external magnetic field of $\sim$ 3 kG. Preliminary calculations performed considering Doppler-broadened three level systems in a nanocell are in reasonable agreement with the experimental measurements.