Optical traps for ultracold quantum gases

The project is a continuation of experimental research which was supported by the Deutsche Forschungsgemeinschaft before the research group moved from Heidelberg (Germany) to Innsbruck. Before, the work on optical traps was carried out in the frame of the Gerhard-Hess-Programm (German analogue to the Austrian START-Programm) under the project title "Novel laser traps for neutral atoms". The purpose of the present application is to facilitate an immediate and effective continuation of the project after its transfer from Heidelberg to Innsbruck, and to develop new research lines in view of a later participation in the Innsbruck-Vienna Spezialforschungsbereich "Measurement and control of coherent quantum systems", which offers an ideal environment for research in this field. The general project goal is to realize new experimental approaches to explore ultracold atomic gases in situations of fundamental interest which are not accessible by standard trapping schemes. For this purpose we use novel optical trapping schemes based on the dipole force in far-detuned laser light. A specific goal is to realize a two- dimensional atomic gas in a trap that is based on evanescent light waves on a dielectric surface. Such a system will represent a unique environment for exploring the physics of ultracold systems in reduced dimensionality. Another goal is to realize a gas of fermions with tunable interactions, which offers interesting features to explore the conditions for Cooper pairing and superfluidiy in an ultracold gas. For this purpose we use a standing-wave trap realized with very high intensity in a build-up resonator. The attainment of these goals will break the ground for a class of new experiments on ultracold quantum matter under conditions not attainable so far.

In the frame of this project two experiments in the field of ultracold atoms and quantum gases were installed at Innsbruck University, which at the occasion of the new appointment of the project leader were transferred from Heidelberg. With FWF funding these experiments could become fully operational again after a few months only, and they are already producing new scientific results. The first experiment deals with trapping of ultracold cesium atoms in a highly anisotropic light trap, created by evanescent waves on the surface of a dielectric prism. The first experiments in Innsbruck yielded temperatures of one-millionth degree above absolute zero and showed exceptionally high atomic number densities, so that the formation of a Bose-Einstein condensate can be expected soon. Moreover successful steps were carried out towards the creation of a two-dimensional quantum gas, which in comparison to three-dimensional systems promise new phenomena and insights in the quantum nature of matter. In the second experiment quantum gases of fermions (lithium-6 isotope) are investigated in high magnetic fields. Of particular interest is the tunability of quantum-mechanical interactions by magnetic fields. In this way the fermionic quantum gas can acquire a strongly repulsive or a strongly attractive character. The latter is of great interest for the realization of Cooper pairs and superfluidity. In the Innsbruck experiment a novel trap is applied which allows for efficient capture and storage or lithium atoms and the studies of their interactions. Very recently, the magnetic tunability and the occurrence of a corresponding "Feshbach resonance" was successfully demonstrated in the experiment. In the frame of the project new laser technologies for mastering ultracold quantum matter could be implemented 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.