Coherent control of dense Rydberg gases
We report on coherent interaction effects involving Rydberg atoms in a dense gas. Their long-range strong interaction is responsible for novel many-body physics. Universal scaling behaviour due to an underlying quantum phase transition is observed . Also the coherence properties of Förster resonances giving rise to resonant dipolar interactions were investigated using a pair state interferometer . When leaving the frozen gas regime the admixture of Rydberg states to the ground state atoms in a quantum gas can change the character of their mutual interaction . We report first evidence for this Rydberg dressing. Finally we report on our effort to realize mesoscopic quantum ensembles based on thermal microscopic vapour cells .
 R. Löw, H. Weimer, U. Raitzsch, R. Heidemann, V. Bendkowsky, B. Butscher, H. P. Büchler, and T. Pfau, Phys. Rev. A 80, 033422 (2009), H. Weimer, R. Löw, T. Pfau, and H. P. Büchler, Phys. Rev. Lett. 101 250601 (2008).
 J. Nipper, J. B. Balewski, A. T. Krupp, B. Butscher, R. Löw, T. Pfau, Phys. Rev. Lett. 108, 113001 (2012), J. Nipper, J.B. Balewski, A.T. Krupp, S. Hofferberth, R. Löw, T. Pfau, accepted in Phys. Rev. X.
 J. Honer, H. Weimer, T. Pfau, and H. P. Büchler, Phys. Rev. Lett. 105, 160404 (2010).
 H. Kübler, J. P. Shaffer, T. Baluktsian, R. Löw, and T. Pfau, Nature Photonics 4, 112 (2010). B. Huber, T. Baluktsian, M. Schlagmüller, A. Kölle, H. Kübler, R. Löw, T. Pfau, Phys. Rev. Lett. 107, 243001 (2011).