Bose-Einstein condensation on a superconducting atom-chip

In atom chip experiments, cold alkali atoms can be trapped at distances as close as a few tens of micrometers from a conducting surface. The dissipation in the surface leads to a fluctuating magnetic field, which can induce Zeeman transitions towards untrapped states. The lifetime of the cloud then decreases as the cloud is brought closer to the surface. One promising solution to circumvent this problem would be to use a chip made of superconducting micro-wires instead of normal conductors. In this thesis, we have obtained the first Bose-Einstein condensate on a superconducting atom chip. Approximately 10⁴ condensed atoms are trapped 50 μm away from the superconducting surface, at a temperature of 100 nK. These results show the feasibility of the achievement of the Bose-Einstein condensation at a distance of a few tens of microns from a superconducting slab. Moreover, we have calculated the near field magnetic noise due to the dynamics of the vortex lattice, and its impact on the trapped cloud. Although the dissipation due to the vortices cannot be neglected, the calculated lifetimes still lies far beyond the values measured in the normal metal case. These theoretical predictions pave the way to applications such as coupling of the cold atoms to mesoscopic superconducting devices, such as stripline cavities or SQUIDs. (author)