Exciting Calcium BECs
Dr. Sebastian Kraft (Physikalisch-Technische Bundesanstalt)

Ultracold quantum gases of alkaline earth atoms attract attention due to their possible applications in optical clocks, in quantum computing, and in quantum metrology. Recently, we have achieved Bose-Einstein condensation of 40Ca. Due to the large ground state s-wave scattering length and associated large three body losses an optimized loading and cooling scheme was necessary to condense about 2 • 104 atoms. Our cooling scheme consisting of a two-stage magneto-optical trap and subsequent forced evaporation in a optical dipole trap at magic wavelength allows to reach degeneracy within less than 3 s.

In current experiments we excite the ultracold Ca atoms on the intercombination transition with a 1 Hz linewidth diode laser system. We use photoassociation spectroscopy to search for bound molecular states near the 1S0 – 3P1 asymptote. By optically coupling these bound states to the ground state we will be able to generate an optical Feshbach resonance. In contrast to magnetic Feshbach resonances these can be used to modify the scattering length on very small length scales and thus e.g. to produce a disorder potential. By exciting the atoms on resonance we investigate the loss of coherence by collisions. These measurements are a first step towards investigation of superradiant decay of the metastable state.