Density wave packets of ultracold atoms in an optical lattice with the adaptive t-DMRG

We investigate the propagation of wave packets in systems of ultracold atoms in an optical lattice with the help of the adaptive time-dependent density-matrix renormalization-group method (adaptive t-DMRG). We discuss the dependence of the velocity, in particular of the sound velocity, on the interaction strength and the height of the perturbation in a quasiexact calculation.