Rydberg aggregates - Interactions in an ultracold gas of Rydberg atoms
Prof. Dr. Matthias Weidemüller (Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg)

<p> Due to the long-range character of the interaction between highly excited atoms, the dynamics of an ultracold gas of Rydberg atoms is entirely determined by van-der-Waals and dipole-dipole interactions. One outstanding property is the tunability of the strength and the character of the interactions with static electric fields. This allows one to explore the transition from a weakly coupled two-body system to a strongly coupled many-body system. The long-range interaction leads to many-body entanglement and has possible applications in quantum computing. </p> <p> In a recent series of experiments we studied coherent phenomena in an ultracold gas of Rydberg atoms under the influence of dipolar interactions. The Rydberg gas is formed in in a magneto-optical trap via cw two-photon excitation of Rb atoms into states with principal quantum number 30…100 using cw lasers at 780 nm and 480 nm [1]. Our recent results include coherent Rabi oscillations between ground and Rydberg states [2,3] and the observation of the dipole blockade in a mesoscopic sample [4], stimulated rapid adiabatic passage with 90% transfer efficiency into Rydberg states [5], and studies of the many-body character of resonant energy transfer processes [6,7]. Our experiments reveal the role of interaction-induced mechanical forces [8] as well as the influence of black-body radiation on the many-particle motional dynamics of the system [9]. In a recent series of experiments, we have explored coherent population trapping under the influence of long-range van-der-Waals forces [10]. </p>

<p> * Work performed in collaboration with T. Amthor, J. Deiglmayr, J. Denskat, B. dePaola, G. Günter, C. Hofmann, M. Reetz-Lamour, H. Schempp, K. Singer, S. Westermann, A.L. de Oliveira, L.G. Marcassa. </p>

<p> [1] K. Singer, M. Reetz-Lamour, T. Amthor, S. Fölling, M. Tscherneck , M. Weidemüller, J. Phys. B 38, S321 (2005). </p> <p> [2] M. Reetz-Lamour et al., Phys. Rev. Lett. 100, 253001 (2008). </p> <p> [3] M. Reetz-Lamour, J. Deiglmayr, T. Amthor, M. Weidemüller, New J. Phys. 10, 045026 (2008) </p> <p> [4] K. Singer, M. Reetz-Lamour, T. Amthor, L.G. Marcassa, M. Weidemüller, Phys. Rev. Lett. 93, 163001 (2004). </p> <p> [5] J. Deiglmayr, M. Reetz-Lamour, T. Amthor, S. Westermann, A.L. de Oliveira, M. Weidemüller, Opt. Comm. 264, 293 (2006). </p> <p> [6] S. Westermann, T. Amthor, A.L. de Oliveira, J. Deiglmayr, M. Reetz-Lamour, M. Weidemüller, Eur. J. Phys. D 40, 37 (2006). </p> <p> [7] O. Mülken, A. Blumen, T. Amthor, C. Giese, M. Reetz-Lamour, M. Weidemüller, Phys. Rev. Lett. 99, 090601 (2007). </p> <p> [8] T. Amthor, M. Reetz-Lamour, S. Westermann, J. Denskat, M. Weidemüller, Phys. Rev. Lett. 98, 023004 (2007). </p> <p> [9] T. Amthor, M. Reetz-Lamour, C. Giese, M. Weidemüller, Phys. Rev. A 76, 054702 (2007). </p> <p> [10] H. Schempp et al., in preparation. </p>