  We investigate spatial adiabatic passage of a Bose-Einstein condensate in a
triple well potential within the three-mode approximation. By rewriting the
dynamics in the so-called time-dependent dark/dressed basis, we analytically
derive the optimal conditions for the non-linear parameter and the on-site
energies of each well to achieve a highly efficient condensate transport. We
show that the non-linearity yields a high-efficiency plateau for the condensate
transport as a function of the on-site energy difference between the outermost
wells, favoring the robustness of the transport. We also analyze the case of
different non-linearities in each well, which, for certain parameter values,
leads to an increase of the width of this plateau.
