Ultracold Chromium: a dipolar quantum gas

We report on experiments using a Bose-Einstein condensate of chromium atoms [1]. We produce up to $\sim $ 10$^{5}$ condensed $^{52}$Cr atoms after forced evaporation within a crossed optical dipole trap. Due to its large magnetic moment (6$\mu _{B})$, 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 [2]. This is the first experimental observation of mechanical dipolar effects in a quantum gas. We also report on the observation of 14 Feshbach resonances in elastic collisions between polarized ultra-cold $^{52}$Cr atoms [3]. 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 as they can be used to change strength and sign of the van der Waals interaction. \newline \newline \textbf{References} \newline 1. A. Griesmaier, J. Werner, S. Hensler, J. Stuhler, and T. Pfau, \textit{Phys. Rev. Lett. }\textbf{\textit{94}}\textit{, 160401 (2005)} \newline 2. J. Stuhler, A. Griesmaier, T. Koch, M. Fattori, T. Pfau, S. Giovanazzi, P. Pedri, and L. Santos, \textit{Phys. Rev. Lett. }\textbf{\textit{95}}\textit{, 150406 (2005)} \newline 3. J. Werner, A. Griesmaier, S. Hensler, J. Stuhler and T. Pfau, \textit{Phys. Rev. Lett. }\textbf{\textit{94}}\textit{, 183201 (2005)}