  We study an atomic quantum dot representing a single hyperfine "impurity"
atom which is coherently coupled to two well-separated Bose-Einstein
condensates, in the limit when the coupling between the dot and the condensates
dominates the inter-condensate tunneling coupling. It is demonstrated that the
quantum dot by itself can induce large-amplitude Josephson-like oscillations of
the particle imbalance between the condensates, which display a two-frequency
behavior. For noninteracting condensates, we provide an approximate solution to
the coupled nonlinear equations of motion which allows us to obtain these two
frequencies analytically.
