Observation of Density-Induced Tunneling
  We study the dynamics of bosonic atoms in a tilted one-dimensional optical lattice and report on the first direct observation of density-induced tunneling. We show that the interaction affects the time evolution of the doublon oscillation via density-induced tunneling and pinpoint its density- and interaction-dependence. The experimental data for different lattice depths are in good agreement with our theoretical model. Furthermore, resonances caused by second-order tunneling processes are studied, where the density-induced tunneling breaks the symmetric behavior for attractive and repulsive interactions predicted by the Hubbard model. 
Ole J\"urgensen, Florian Meinert, Manfred J. Mark, Hanns-Christoph   N\"agerl, Dirk-S\"oren L\"uhmann
cond-mat.quant-gas