Quantum Ratchets

We investigate quantum Brownian motion in adiabatically rocked ratchet systems. Above a crossover temperature $T_c$ tunneling events are rare, yet they already substantially enhance the classical particle current. Below $T_c$, quantum tunneling prevails and the classical predictions grossly underestimate the transport. Upon approaching $T=0\mathrm{}$ the quantum current exhibits a tunneling induced reversal, and tends to a finite limit.