  We study the lifetime of an atom trapped in an optical vertical lattice in
proximity of a massive surface using a complex scaling approach. We analyze how
the presence of the surface modifies the known lifetimes of Wannier-Stark
states associated to Landau-Zener tunnelling. We also investigate how the
existence of a hypothetical short-distance deviation from Newton's
gravitational law could affect these lifetimes. Our study is relevant in order
to discuss the feasibility of any atomic- interferometry experiment performed
near a surface. Finally, the difficulties encountered in applying the
complex-scaling approach to the atom-surface Casimir-Polder interaction are
addressed.
