Spectral shift and dephasing of electromagnetically induced transparency   in an interacting Rydberg gas
  We perform spectroscopic measurements of electromagnetically induced transparency (EIT) in a strongly interacting Rydberg gas, and observe a significant spectral shift of the transparency from the single-atom EIT resonance as well as a spectral dephasing of the same order. We characterize the shift and dephasing as a function of atomic density, probe Rabi frequency, and principal quantum number of Rydberg states, and demonstrate that the observed spectral shift and dephasing are reduced if the size of a Gaussian atomic cloud is increased. We simulate our experiment with a semi-analytical model, which gives results in good agreement with our experimental data. 
Jingshan Han, Thibault Vogt, and Wenhui Li
physics.atom-ph cond-mat.quant-gas quant-ph