Extreme tunability of interactions in a $^7$Li Bose-Einstein condensate
  We use a Feshbach resonance to tune the scattering length a of a Bose-Einstein condensate of 7Li in the |F = 1, m_F = 1> state. Using the spatial extent of the trapped condensate we extract a over a range spanning 7 decades from small attractive interactions to extremely strong repulsive interactions. The shallow zero-crossing in the wing of the Feshbach resonance enables the determination of a as small as 0.01 Bohr radii. In this regime, evidence of the weak anisotropic magnetic dipole interaction is obtained by comparison with different trap geometries. 
Scott E. Pollack, D. Dries, M. Junker, Y. P. Chen, T. A. Corcovilos,   and R. G. Hulet