TwUnaGas · Two-dimensional Uniform Gas with tunable interactions

Two-dimensional Uniform Gas with tunable interactions

This project intended to experimentally study condensed matter physics and many-body effects in an ultra-cold gas of Potassium-39. Particular attention was given to the interface between three- and two-dimensional physics. The project is now at a stage where the role played by the interactions on the Berezinsky-Kosterlitz-Thouless (BKT) transition can be studied in a homogeneous ultracold two-dimensional gas. Cold atom experiments allow to mimic most of the phenomena registered in condensed matter while ensuring almost absolute control over the properties of the system: temperature, density, presence or absence of impurities, inter-particle interaction strength as well as their nature (from contact interactions to long-range interactions for dipolar gases). Nonetheless, studies of homogeneous cold gases are still scarce due to the difficulty of creating “box-potentials”. Indeed within the cold-atom community, most ultra-cold samples are produced in harmonic traps, and therefore the density varies spatially. The possibility to provide, simple and under-control, homogeneous samples is of particular relevance for the condensed matter community where long-standing problems, such as, for instance, the superfluid fraction jump at the BKT transition, can be further investigated and understood. Recent work performed at the hosting institution on creating box potentials led to the first realisation of a 3D homogeneous BEC (see Fig.1), a technique that during this project was applied by the beneficiary to the case of strongly-interacting gases with variable geometries: three- and two-dimensions. The project led to a better understanding of the role played by interactions in cold atomic gases, from weakly-interacting systems all the way up to the unitary regime where interactions are as strong as allowed by quantum mechanics. Furthermore, the beneficiary designed and produced a new uniform two-dimensional potential that allows changing the strong confinement of the potential easily. This new design is currently used to generate, on daily-basis, two-dimensional homogeneous ultra-cold Bose gases with controllable interactions.

Data: CORDIS, © European Union