All-optical Realization of Quantum Ratchets
  A theoretical realization of an all-optical quantum ratchet is proposed in a medium composed of an array of coupled waveguides. By coupling light into two adjacent waveguides, and calculating the expectation value for the position space operator, we demonstrate the quantum ratchet like behavior of this optical system. 
Clinton Thompson, Gautam Vemuri, and G.S. Agarwal
quant-ph physics.optics