Observation of Low-Field Feshbach Resonances in Collisions of Cesium Atoms

We observe several Feshbach resonances in magnetic fields below 40 G for Cs atoms trapped in a 1D optical lattice. One resonance occurs in the lowest-energy ground state $F=3\mathrm{}$, $m_F=3\mathrm{}$ which is stable against inelastic binary collisions. This opens new possibilities for Bose condensation of Cs. When the elastic collision rate far exceeds the radial vibration frequency, we enter a 2D hydrodynamic regime where the thermalization rate is independent of density and temperature. Other resonances are also observed in the $F=3\mathrm{}$, $m_F=-3\mathrm{}$ state through a dramatic increase in the dipolar relaxation rate.