Inelastic collisions and density-dependent excitation suppression in a   ${}^{87}$Sr optical lattice clock
  We observe two-body loss of ${}^3P_0$ ${}^{87}$Sr atoms trapped in a one-dimensional optical lattice. We measure loss rate coefficients for atomic samples between 1 and 6 $\mu$K that are prepared either in a single nuclear-spin-sublevel or with equal populations in two sublevels. The measured temperature and nuclear spin preparation dependence of rate coefficients agree well with calculations and reveal that rate coefficients for distinguishable atoms are only slightly enhanced over those of indistinguishable atoms. We further observe a suppression of excitation and losses during interrogation of the ${}^1S_0$-${}^3P_0$ transition as density increases and Rabi frequency decreases, which suggests the presence of strong interactions in our dynamically driven many-body system. 
Michael Bishof, Michael J Martin, Matthew D. Swallows, Craig Benko,   Yige Lin, Goulven Qu\'em\'ener, Ana Maria Rey, and Jun Ye
physics.atom-ph cond-mat.quant-gas quant-ph