Quantum ratchet

We propose two models of quantum ratchet, in which particles obeying quantu m mechanics produce net flow under a spatially asymmetric periodic potentia l and an unbiased external perturbation. One is a quantum mechanical analog ue of the thermal ratchet and the other is that of the mechanical ratchet. In both models the finite net flow emerges, which is a manifestation of the new quantum effects resulting from the interaction with the heat bath. (C) 2000 Elsevier Science B.V. All rights reserved.