Dephasing of ultracold cesium 80D-Rydberg electromagnetically induced transparency.

We study Rydberg electromagnetically induced transparency (EIT) of a cascade three-level atom involving 80D state in a strong interaction regime employing a cesium ultracold cloud. In our experiment, a strong coupling laser couples 6P to 80D transition, while a weak probe, driving 6S to 6P 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 γ is extracted with optical depth OD = γt. We find that the optical depth linearly increases with time at onset for a fixed probe incident photon number R before saturation. The dephasing rate shows a nonlinear dependence on R. The dephasing mechanism is mainly attributed to the strong dipole-dipole interactions, which leads to state transfer from nD to other Rydberg states. We demonstrate that the typical transfer time τ obtained by the state selective field ionization technique is comparable with the decay time of EIT transmission τ. The presented experiment provides a useful tool for investigating the strong nonlinear optical effects and metastable state in Rydberg many-body systems.