Magnetic Field Dependence of Ultracold Inelastic Collisions near a Feshbach Resonance

Inelastic collision rates for ultracold ${}^{85}\mathrm{Rb}$ atoms in the $F=2\mathrm{}$, $m_f=-2\mathrm{}$ state have been measured as a function of magnetic field. At 250 gauss (G), the two- and three-body loss rates were measured to be $K_2=(1.87\pm 0.95\pm 0.19)\times {10}^{-14\mathrm{}}{\mathrm{cm}}^3/\mathrm{s}$ and $K_3=({4.24}_{-0.29\mathrm{}}^{+0.70\mathrm{}}\pm 0.85)\times {10}^{-25\mathrm{}}{\mathrm{cm}}^6/\mathrm{s}$, respectively. As the magnetic field is decreased from 250 G towards a Feshbach resonance at 155 G, the inelastic rates decrease to a minimum and then increase dramatically, peaking at the Feshbach resonance. Both two- and three-body losses are important, and individual contributions have been compared with theory.