Extreme Tunability of Interactions in a Li7 Bose-Einstein Condensate

We use a Feshbach resonance to tune the scattering length a of a Bose-Einstein condensate of Li7 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. Evidence of the weak anisotropic magnetic dipole interaction is obtained by comparison with different trap geometries for small a.