Stuttgart 2012 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 38: Quantengase: Optische Gitter 3

Q 38.3: Talk

Thursday, March 15, 2012, 11:15–11:30, V53.01

Observation of a roton-type mode softening in a quantum gas with cavity-mediated long-range interactions — •Renate Landig, Kristian Baumann, Rafael Mottl, Ferdinand Brennecke, Tobias Donner, and Tilman Esslinger — Quantum Optics Group, ETH Zurich, Switzerland

We report on the observation of a characteristic change in the excitation spectrum of a Bose-Einstein condensate due to cavity-mediated long-range interactions. Increasing the strength of the interaction leads to a softening of an excitation mode at a finite momentum, preceding a superfluid to supersolid phase transition. The Bose-Einstein condensate is located inside an ultra-high finesse optical cavity and coupled to the vacuum mode of the cavity, using a non-resonant transverse pump beam. This gives rise to a long-range interaction which couples all particles. The mode softening is spectroscopically studied across the phase transition using a method which excites the system at a specific momentum. At the phase transition a diverging response is measured. The observed behavior is reminiscent of a roton minimum, as predicted for quantum gases with long-range interactions.