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H. Schempp, G. Günter, C. Hofmann, S. Sevincli, T. Pohl, T. Amthor, and M. Weidemüller
Coherent population trapping (CPT) and the related phenomenon of a "dark resonance" are paradigms for quantum interference [1]. Intense studies of this phenomenon have lead to intriguing effects like electromagnetically induced transparency [2], lasing without inversion, adiabatic population transfer and subrecoil cooling. Whereas CPT in low-lying atomic states can readily be understood in terms of single-atom dynamics, the situation becomes much more complex when interparticle interactions have to be considered. To gain insight how CPT is affected by interactions we investigate CPT in an ultracold, strongly interacting Rydberg gas [3]. In our experiment we tune the interaction strength by choosing different Rydberg states and control the effects of interactions by varying the density of the cloud. Even in the blockade regime we observe the persistance of 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 observation cannot be explained within a meanfield model. Using a many-body model that includes interparticle correlations we are able to nicely reproduce the observed features. Also a two-atom model is presented, which allows to get a more intuitive understanding, but fails to describe all the features correctly, which again highlights the importance of many-body effects. [1] E. Arimondo, Progress in Optics (Elsevier, New York, 1996), Vol. 35. [2] M. Fleischhauer, A. Imamoglu, and J. P. Marangos, Rev. Mod. Phys. 77, 633 (2005). [3] H. Schempp et al., Phys. Rev. Lett. 104, 173602 (2010). |
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