Torsten Scholak, University of Toronto
Rydberg atoms are highly excited neutral atoms with exceptional properties. Not long ago, interest in Rydberg atoms was limited to their spectroscopic properties. However, in recent years, Rydberg science has become increasingly interdisciplinary. It is now a rapidly progressing research area at the crossroads of atomic, optical, condensed matter physics, and quantum information science with a host of possible applications. Groundbreaking experiments demonstrate the promise of Rydberg systems not only for quantum information processing, but also for exploring the long-range nature of the strong Rydberg-Rydberg interaction that gives rise to many-particle correlations and excitation energy transfer (EET).
After an introduction to Rydberg physics, I will focus on our theoretical research work on the quantum-coherent EET through "frozen" Rydberg gas clouds, in which the atoms have been slowed down almost to a full stop. For these systems, I reveal how the nature of EET can be controlled via the dipole blockade . This effect is known to lead to a proximity-dependent suppression of Rydberg excitations and the emergence of ordered excitation structures from a disordered gas. For weak blockade, we predict the transient localization of EET on small clusters of two or more atoms. For stronger blockade, however, EET will be significantly faster, since the excitations are efficiently migrated by delocalized states. I will illustrate this with our results on the spectral and eigenvector structure of the Rydberg gas ensemble. My talk is concluded by an outline of upcoming milestones and their challenges.
 T. Scholak, T. Wellens, and A. Buchleitner, Phys. Rev. A , in press (2014), arXiv:1409.5625.
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