Abstract

Coherent population trapping (CPT) and the related phenomenon of Electromagnetically Induced Transparency (EIT) are paradigms for quantum interference effects and have been studied intensely over the last decade [1]. Only recently, EIT involving Rydberg states has attracted much interest, with regard to nonlinear optics [2] as well as in the context of quantum information processing [3]. Whereas CPT and EIT are generally described within a single-atom framework, the situation becomes more involved when interparticle interactions have to be considered. To address the effect of interactions, we investigate CPT in a strongly interacting ultracold Rydberg gas [4]. In our experiment we tune the interaction strength by choosing different Rydberg states and control interactions effects by varying the ground state atom density. Even in the blockade regime we observe a resonance with sub-natural linewidth at the single-particle resonance frequency despite the strong van der Waals interactions among Rydberg atoms. Due to the correlations among the atoms the experimental observations cannot be explained within a meanfield model. A theoretical model that includes interparticle correlations is presented and nicely reproduces the observed features.

© 2011 IEEE