Ultracold chromium: a dipolar quantum gas

Prof.dr. T. Pfau
5th Institute of Physics, University of Stuttgart, Germany

We report on our recent achievement of a Bose-Einstein condensate in a gas of chromium atoms [1]. Peculiar electronic and magnetic properties of chromium require the implementation of novel cooling strategies. We observe up to ~ 105 condensed 52Cr atoms after forced evaporation within a crossed optical dipole trap. Due to its large magnetic moment (6ÁB), the dipole-dipole interaction strength in chromium is comparable with the one of the van der Waals interaction. We prove the anisotropic nature of the dipolar interaction by releasing the condensate from a cigar shaped trap and observe, in time of flight measurements, the change of the aspect-ratio for different in-trap orientations of the atomic dipoles. We also report on the recent observation of 14 Feshbach resonances in elastic collisions between polarized ultra-cold 52Cr atoms [2]. This is the first observation of collisional Feshbach resonances in an atomic species with more than one valence electron. Moreover, such resonances constitute an important tool towards the realization of a purely dipolar interacting gas because they can be used to change strength and sign of the van der Waals interaction. 

1. A. Griesmaier, J. Werner, S. Hensler, J. Stuhler, and T. Pfau, Phys. Rev. Lett. in press (cond-mat/0503044)
2. J. Werner, A. Griesmaier, S. Hensler, J. Stuhler and T. Pfau, Phys. Rev. Lett. in press (cond-mat/0412049)