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C. S. Hofmann, G. Günter, H. Schempp, N. Müller, T. Amthor, and M. Weidemüller
The long-range character of strong Rydberg-Rydberg interactions gives rise to phenomena such as the interaction-induced blockade of Rydberg excitation. The opposite effect, the so-called antiblockade of excitation has recently been proposed for a three-level two-photon Rydberg excitation scheme, in which an Autler-Townes splitting is induced by strong coupling laser at the lower transition [1]. When the coupling energy matches the interaction energy of the long-range Rydberg interactions, the otherwise blocked excitation of close pairs becomes possible. We present the first experimental observation of the antiblockade in an ultracold Rydberg gas [2]. To reveal this effect we use time-resolved ionization detection. In this way we monitor the distribution of excited-pair distances [3], which allows us to clearly observe additional excitation (antiblockade) of pairs at small distances out of a random arrangement of atoms. A model based on a pair interaction Hamiltonian is presented which nicely reproduces our experimental observations and allows to analyze the distribution of nearest neighbor distances. [1] C. Ates et al. Phys. Rev. Lett. 98, 023002 (2007) [2] T. Amthor et al. Phys. Rev. Lett. 104, 013001 (2010) [3] T. Amthor et al. Phys. Rev. Lett. 98, 023004 (2007) |
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