Bose-Einstein condensation of cesium in a CO2 laser trap

The goal of the project is to attain a Bose-Einstein condensate (BEC) of cesium atoms as a macroscopic quantum state of matter with tunable interactions. Our new approach to atom trapping and evaporative cooling is based on far-infrared light generated with CO2 lasers. This optical trapping approach overcomes loss problems inherent to cesium trapped in magnetic fields, which have so far prevented conventional approaches to reach BEC for this species. Because of the unusual quantum-mechanical scattering properties of cesium and the tunable interatomic interaction, a cesium BEC will constitute a macroscopic quantum state of matter with new and intriguing properties and will strongly increase our understanding of the physical behavior of ultracold quantum matter. The intermediate goals of the project on the way towards BEC of cesium are of major scientific interest in itself: The realization of a CO2-trap for atoms in selectable spin states, the implementation of radio-frequency induced evaporation in this trap, and the measurement of two-body and three-body loss for different spin states will yield important results of great relevance for the research field.

In this project technological developments were carried out for the attainment of a Bose-Einstein condensate of cesium based on a new optical method that uses powerful CO2 lasers. Such a condensate of cesium, which has not been realized yet, is of great interest as a macroscopic quantum state of matter with magnetically tunable interactions. The heart of the new optical method is an optical atom trap realized in the crossing region of two intense laser beams. The perturbing influence of gravity is overcome by a magnetic levitation field, where gravity is exactly compensated by a magnetic force. In such a trap particular loss processes occuring for cesium are suppressed, which have so far prevented the attainment of a Bose-Einstein condensate with conventional methods. Because of the very unusual quantum-mechanical interaction properties of ultracold cesium atoms a Bose-Einstein condensate of this species will considerable extend our experimental possibilities and widen our understanding of quantum matter at extremely low temperatures. The intermediate steps on the way towards Bose-Einstein condensation are of great scientific interest: The successful steps of the Innsbruck experiments to realize a CO2 laser trap for atoms in selectable spin states and to implement radio-frequency induced cooling therein will be very useful also for other experiments on ultracold quantum gases. Measurements of three-body collisions under unambiguous experimental conditions will be important to understand quantum-mechanical interactions and extremely low energies. In the frame of this project a new laser technology for mastering ultracold quantum matter by using the far-infrared light of CO2 laser could be implemented for the first time in Austria. This fosters the introduction of new laser technologies in general, and in particular contributes to create a scientific fundament for future quantum technologies.