Dresden 2011 – wissenschaftliches Programm
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Q: Fachverband Quantenoptik und Photonik
Q 24: Quantum Gases: Opt. Lattice 1
Q 24.9: Vortrag
Mittwoch, 16. März 2011, 12:30–12:45, HSZ 02
The Dicke quantum phase transition in an optical cavity QED system — •Rafael Mottl1, Kristian Baumann1, Ferdinand Brennecke1, Tobias Donner1, Christine Guerlin2, and Tilman Esslinger1 — 1Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland — 2Thales Research and Technology, 91767 Palaiseau Cedex, France
The collective interaction of an ensemble of atoms with an electromagnetic field mode is of fundamental interest. A conceptually important model describing such a system is the Dicke model for which the existence of a quantum phase transition was predicted years ago. We have achieved its first experimental realization in an open system in which a Bose-Einstein condensate is coupled to an optical high-finesse cavity. The interaction between the condensate atoms is mediated by the field of the optical cavity and is of infinite range. Starting in a superfluid state, the self-organized phase which emerges at the phase transition is of supersolid character.
We map out the phase diagram which agrees quantitatively with the Dicke model prediction. The spontaneous symmetry breaking occuring at the quantum phase transition leads to the development of two initially degenerate ground states which are observed by a phase-sensitive detection of light leaking out of the cavity. Investigating the excitation spectrum below threshold by Bragg spectroscopy, we identify a vanishing energy gap when approaching the critical point - a precursor of the quantum phase transition.