Dephasing of ultracold cesium 80D_5/2-Rydberg Electromagnetically Induced Transparency

We study Rydberg electromagnetically induced transparency (EIT) of a cascade three-level atom involving 80D_5/2 state in a strong interaction regime employing a cesium

ultracold cloud. In our experiment, a strong coupling laser couples 6P_3/2 to 80D_5/2 transition, while a weak probe, driving 6S_1/2 to 6P_3/2 transition, probes the coupling induced EIT signal. At the two-photon resonance, we observe that the EIT transmission decreases slowly with time, which is a signature of interaction induced metastability. The dephasing rate r_OD is extracted with optical depth OD = r_OD. We find that the optical depth linearly increases with time at onset for a

fixed probe incident photon number R_in before saturation. The dephasing rate shows a nonlinear dependence on R_in. The dephasing mechanism is mainly attributed to the strong Rydberg interactions and simulated with density matrix equation.