Gravity-induced Wannier-Stark ladder in an optical lattice
  We discuss the dynamics of ultracold atoms in an optical potential accelerated by gravity. The positions and widths of the Wannier-Stark ladder of resonances are obtained as metastable states. The metastable Wannier-Bloch states oscillate in a single band with the Bloch period. The width of the resonance gives the rate transition to the continuum. 
J. Zapata, A. M.Guzman, M. G. Moore and P. Meystre