Berlin 2001 – wissenschaftliches Programm

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A: Atomphysik

A 16: Cooling and Trapping V (joint session A and Q)

A 16.3: Vortrag

Donnerstag, 5. April 2001, 18:00–18:15, H104

Levitated atoms in a CO₂-laser trap — •Tino Weber, Jens Herbig, Hanns-Christoph Nägerl, and Rudi Grimm — Institut für Experimentalphysik, Universität Innsbruck, A-6020 Innsbruck

We are exploring a novel concept for trapping and cooling cesium towards BEC. In an optical dipole trap formed by the crossed beams of two 100-W CO₂ lasers focused to w₀=500 µm, a trap depth of ∼20 µK can be achieved. In order to compensate the gravitational force of k_B×1.6 mK/cm, which is much stronger than the trapping potential in this large and shallow trap, a magnetic field gradient of 31 G/cm along the vertical axis is applied. This counterbalances gravitation for the internal ground state of Cs (F=3, m_F=3), effectively levitating those atoms. Other spin states are expelled from the trap, opening up a path for rf evaporation. In previous experiments, we have successfully demonstrated transfer of cesium into a CO₂ laser trap and long-term storage with extremely low trap heating [1]. The new trap design is optimized for efficient transfer of a pre-cooled atom cloud from a MOT. Our approach to trap the lowest spin state excludes two-body losses, and the relatively low density in the shallow potential well (trap frequency ∼30 Hz) reduces three-body collisions. The free choice of a magnetic bias field allows exploration of Feshbach resonances to tune scattering properties.

[1] H. Engler et al., Phys. Rev. A 62, 031402(R) (2000)