Electromagnetically induced transparency in strongly interacting Rydberg gases

We develop an efficient Monte Carlo approach to describe the optical response of cold three-level atoms in the presence of electromagnetically induced transparency (EIT) and strong atomic interactions. In particular, we consider a Rydberg-EIT medium where one involved level is subject to large shifts due to strong van der Waals interactions with surrounding Rydberg atoms. Agreement with much more involved quantum calculations is excellent, demonstrating its applicability over a wide range of densities and interaction strengths. The calculations show that nonlinear absorption due to Rydberg-Rydberg atom interactions exhibits universal behavior.