Inelastic Collisions in Optically Trapped Ultracold Metastable Ytterbium
  We report measurement of inelastic loss in dense and cold metastable ytterbium (Yb[$^3P_2$]). Use of an optical far-off-resonance trap enables us to trap atoms in all magnetic sublevels, removing multichannel collisional trap loss from the system. Trapped samples of Yb[$^3P_2$] are produced at a density of 2$\times10^{13}$ cm$^{-3}$ and temperature of 2 $\mu$K. We observe rapid two-body trap loss of Yb[$^3P_2$] and measure the inelastic collision rate constant 1.0(3)$\times10^{-11}$ cm$^3$s$^{-1}$. The existence of the fine-structure changing collisions between atoms in the $^3P_2$ state is strongly suggested. 
A. Yamaguchi, S. Uetake, D. Hashimoto, J. M. Doyle, Y. Takahashi