Evanescent-wave trapping of Cs at the crossover to two-dimensionality

Summary form only given. Our experiment aims at investigating a two-dimensional degenerate quantum gas of cesium atoms. For this purpose, we exploit a double evanescent-wave trap (DEW trap) consisting of a repulsive and an attractive evanescent wave and providing a highly anisotropic dipole potential. Efficient loading is accomplished by a multi-stage sequence. Cesium atoms are laser cooled in a MOT and then transferred into a gravito-optical dipole trap that serves as a surface reservoir. In the next stage, the phase-space density is enhanced by creating a dimple in the potential with a far-detuned, attractive laser beam that is focused to the center of the reservoir. Finally, we transfer the atoms into the DEW trap. The vertical dipole potential provides a well close to the surface, and depends on the power of the attractive evanescent wave. Ramping down the power of the attractive evanescent wave leads to efficient evaporation. A situation at the crossover to two-dimensionality is reached when the thermal energy of k_B × 100 nK equals the level spacing hν; thus the vertical ground state is populated by over 60 percent. Since the final phase-space density is as high as 0.1, the creation of a degenerate two-dimensional quantum gas of Cs comes into experimental reach. In present experiments we polarize the atoms into the F = 3, m_F = 3 state. As a consequence of the resonant interaction properties of cesium, the scattering length can be tuned in a wide range by applying a magnetic field. We use the tunability of interactions to optimize the evaporation efficiency on the way to a two-dimensional degenerate quantum gas of cesium.