Tunneling dynamics and gauge potentials in optical lattices

We study periodic well-to-well tunneling of Rb-87 atoms on adiabatic potent ial surfaces of a 1D optical lattice. The observed dependence of the lowest -band tunneling period on the depth of the adiabatic potential can only be explained by an additional intensity-independent gauge potential predicted by Dum et al. The experimental data are in excellent agreement with our qua ntum Monte Carlo wavefunction simulations and band structure calculations.