Atomic current across an optical lattice
  We devise a microscopic model for the emergence of a collision-induced, fermionic atomic current across a tilted optical lattice. Tuning the - experimentally controllable - parameters of the microscopic dynamics allows to switch from Ohmic to negative differential conductance. 
Alexey V. Ponomarev, Javier Madronero, Andrey R. Kolovsky, and Andreas   Buchleitner