# Hannover 2010 – wissenschaftliches Programm

## Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

# Q: Fachverband Quantenoptik und Photonik

## Q 9: Ultracold Atoms: Rydberg Gases / Miscellaneous (with A)

### Q 9.5: Vortrag

### Montag, 8. März 2010, 17:45–18:00, A 320

**Antiblockade of Rydberg excitation in an ultracold gas** — •Christoph S. Hofmann^{1}, Thomas Amthor^{1}, Christian Giese^{2}, Georg Günter^{1}, Hanna Schempp^{1}, Nele Müller^{1}, and Matthias Weidemüller^{1} — ^{1}Physikalisches Institut, Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg — ^{2}Physikalisches Institut, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg

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, 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., arXiv:0909.0837v1