Josephson junction arrays with Bose-Einstein condensates

We report on the direct observation of an oscillating atomic current in a o ne-dimensional array of Josephson junctions realized with an atomic Bose-Ei nstein condensate. The array is created by a laser standing wave, with the condensates trapped in the valleys of the periodic potential and weakly cou pled by the interwell barriers. The coherence of multiple tunneling between adjacent welts is continuously probed by atomic interference. The square o f the small-amplitude oscillation frequency is proportional to the microsco pic tunneling rate of each condensate through the barriers and provides a d irect measurement of the Josephson critical current as a function of the in termediate barrier heights. Our superfluid array may allow investigation of phenomena so far inaccessible to superconducting Josephson junctions and l ays a bridge between the condensate dynamics and the physics of discrete no nlinear media.