Demon-free quantum Brownian motors

TL;DR

This paper introduces a quantum Smoluchowski equation that accurately models thermal quantum states without violating thermodynamics, and analyzes quantum transport in ratchet potentials influenced by quantum effects.

Contribution

It presents a novel quantum kinetic equation for strong friction regimes that accounts for quantum tunneling and reflection in directed transport.

Findings

Quantum corrections can significantly enhance or suppress transport.

Quantum fluctuations shift the threshold for current reversals.

The model avoids violations of the second law of thermodynamics.

Abstract

A quantum Smoluchowski equation is put forward that consistently describes thermal quantum states. In particular, it notably does not induce a violation of the second law of thermodynamics. This so modified kinetic equation is applied to study {\it analytically} directed quantum transport at strong friction in arbitrarily shaped ratchet potentials that are driven by nonthermal two-state noise. Depending on the mutual interplay of quantum tunneling and quantum reflection these quantum corrections can induce both, either a sizable enhancement or a suppression of transport. Moreover, the threshold for current reversals becomes markedly shifted due to such quantum fluctuations.