Observation of Feshbach resonances in 87 Rb

A cloud of ⁸⁷Rb atoms in the |f, m_f>= |1, -1> ground state was evaporatively cooled in a Ioffe-Pritchard trap close to or below the BEC transition temperature. The atoms were then transferred into an optical dipole trap made of an Yb:YAG laser operating at a wavelength of 1030 nm. After turning off the magnetic trap, an RF pulse transferred the atoms to the |1,1> Zeeman state. Subsequently, a homogeneous dc magnetic field was applied. The field range was scanned between 0.5 and 1260 Gauss. Monitoring the atom loss, more than 40 resonances, are observed including the predicted ones. The additional resonances are due to closed channels with rotational quantum number l = 2. The measured resonance positions were included in a fit to obtain an improved set of parameters for the rubidium interatomic potential. Although all resonances are narrow, the magnetic field control should be accurate enough to resolve changes in the elastic scattering length on the broadest resonance at 1007 Gauss.