We demonstrate the operation of an atom interferometer based on a weakly interacting Bose-Einstein condensate. We strongly reduce the interaction induced decoherence that usually limits interferometers based on trapped condensates by tuning the $s$-wave scattering length almost to zero via a magnetic Feshbach resonance. We employ a ${}^{39}\mathrm{K}$ condensate trapped in an optical lattice, where Bloch oscillations are forced by gravity. The fine-tuning of the scattering length down to $0.1a_0$ and the micrometric sizes of the atomic sample make our system a very promising candidate for measuring forces with high spatial resolution. Our technique can be in principle extended to other measurement schemes opening new possibilities in the field of trapped atom interferometry.

• Received 26 October 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.080405