A chaotic 'turnstile' for atoms in periodic potentials
  Using a new type of chaotic ratchet generated by pulsed standing waves of light, we propose a mechanism which would allow packets of atoms travelling through a pulsed optical lattice in one direction to pass almost undisturbed, while strongly heating atoms drifting through in the opposite direction. An analytical formula for the diffusive energy growth is derived and shown to give good agreement with numerical calculations. 
M.R. Isherwood and T.S. Monteiro