Observation of sub-Doppler temperatures in bosonic magnesium
T. E. Mehlst\"{a}ubler, K. Moldenhauer, M. Riedmann, N. Rehbein, J. Friebe, E. M. Rasel, and W. Ertmer

For the first time temperatures below the Doppler limit of 1.9 mK have been observed in magnesium. The strong cooling transition was modified by a coherent two-color excitation exploiting the longer lifetime of an upper level. We developed a theoretical model to describe light forces and cooling originating from the induced quantum interference in a three-level-system. Time-of-flight measurements verified temperatures of 500~$\mu$K in a 1D molasses in accordance with our theoretical model. By implementing this scheme in a 3D MOT with a single IR beam temperatures as low as 1~mK could be realized. For ideal conditions we extrapolate temperatures of 50~$\mu$K. With cooling times of about 1~ms a fast and efficient cooling scheme was realized, particularly attractive for optical frequency standards.

© 2008 The American Physical Society.