QUANTUM RATCHETS

We investigate quantum Brownian motion in adiabatically rocked ratchet systems. Above a crossover temperature T-c tunnelling events are rare , yet they already substantially enhance the classical particle curren t. Below T-c, quantum tunnelling prevails and the classical prediction s grossly underestimate the transport. Upon approaching T=0 the quantu m current exhibits a tunnelling induced reversal, and tends to a finit e limit.