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A: Fachverband Atomphysik

A 41: Poster: Ultra-cold plasmas and Rydberg systems

A 41.4: Poster

Donnerstag, 15. März 2012, 16:30–19:00, Poster.V

Phase diagram of Rydberg atoms with repulsive van der Waals interaction — •Yaroslav Lutsyshyn and Dieter Bauer — Institut für Physik, Universität Rostock, 18051 Rostock, Germany

Atoms excited to orbitals with high principal quantum number, also known as Rydberg atoms, present rich opportunities for studying strongly correlated quantum many-body effects. Interactions between atoms shift their levels, thus preventing neighboring atoms from being excited simultaneously, an effect called Rydberg blockade. Because of the blockade, excited atoms are spatially correlated and often spaced out to distances where the interaction has the van der Waals C₆/r⁶ form. To understand possible ordering and phase transitions in such situations, we consider a phase diagram of particles with a repulsive van der Waals interaction. The system is studied with quantum and classical Monte Carlo methods, and the harmonic theory. With a proper selection of units, the entire phase diagram may be expressed in terms of just the reduced number density and temperature. This allows to compare phase conditions for considerably different interaction constants. Most present experiments are deeply in the “classical” regime of such a phase diagram, where the solidification would happen at temperature T=0.22ρ² C₆ (C₆ being the interaction constant, and ρ the number density). At zero temperature, the transition occurs at density ρ = 3.9 (ℏ²/m C₆)^3/4. The preferred solid phase is fcc. The findings are reported in ar0.15emχiv:1106.2997 (2011).