Dispersion control for matter waves and gap solitons in optical superlattices

We present a numerical study of dispersion manipulation and formation of matter-wave gap solitons in a Bose-Einstein condensate trapped in an optical superlattice. We demonstrate a method for controlled generation of matter-wave gap solitons in a stationary lattice by using an interference pattern of two condensate wave packets, which mimics the structure of the gap soliton near the edge of a spectral band. The efficiency of this method is compared to that of gap soliton generation in a moving lattice recently demonstrated experimentally by Eiermann et al. [ Phys. Rev. Lett. 92 230401 (2004)]. We show that, by changing the relative depths of the superlattice wells, one can fine-tune the effective dispersion of the matter waves at the edges of the minigaps of the superlattice Bloch-wave spectrum and, therefore, effectively control both the peak density and the spatial width of the emerging gap solitons.