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The dynamics of Rydberg atoms excited from an ultracold gas is entirely governed by dipole interactions between the atoms. As an important feature, the strength and the character of the interaction can be tuned by small external fields. This allows one to explore the transition from a weakly coupled two-body system to a strongly coupled many-body system.
We will present experiments on the coherent excitation of Rydberg atoms from an laser-cooled gas of rubidium. Transfer efficiencies beyond 90% have been achieved by applying STIRAP techniques. Dipole interactions lead to resonant energy diffusion within the atomic cloud (Förster processes). Experiments on the Förster transfer dynamics indicate that this process involves the coherent coupling of several atoms. We have demonstrated a local blockade of Rydberg excitation which can be explained by long-range dipole interactions ranging over several micrometers. As a recent result, Rabi oscillations of a mesoscopic Rydberg ensemble are observed which constitutes the first step for the preparation of entangled cluster states. |
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