Pumping of matter wave solitons in one-dimensional optical superlattices

We study the pumping of matter-wave solitons formed in Bose-Einstein condensates with attractive atomic interactions that are loaded into optical superlattices, in which one of the lattices is moving with respect to the other. We find that the matter-wave solitons exhibit lattice-parameter-dependent nonlinear integer (fractional) pumping and trapping. Different from the perspective of linear band Chern numbers, treating solitons as effective classical particles provides a good understanding of the quantized pumping or trapping. This reveals an unexpected insight: the nonlinear adiabatic pumping may be classical, and the quantization may be accidental, as dictated by the spatial period of the sliding sublattice. This alternative perspective on understanding soliton pumping highlights the parameter-dependent transition between soliton quantized pumping and trapping, and it exposes the nonlinear transition from a trapped soliton to a pumped soliton with increasing nonlinearity, which has never been reported before.