Energetics of Forced Thermal Ratchet

TL;DR

This paper challenges the idea that thermal fluctuations enhance the efficiency of molecular ratchets, showing instead that maximum efficiency occurs without thermal noise, raising questions about the role of fluctuations in energy conversion.

Contribution

It clarifies that the maximum efficiency of thermal ratchets is achieved at zero temperature, contradicting previous interpretations that thermal fluctuations facilitate efficiency.

Findings

Maximum efficiency occurs at zero temperature.

Thermal fluctuations do not enhance energy transformation efficiency.

The role of thermal noise in energy conversion remains an open question.

Abstract

Molecular motors are known to have the high efficiency of energy transformation in the presence of thermal fluctuation. Motivated by the surprising fact, recent studies of thermal ratchet models are showing how and when work should be extracted from non-equilibrium fluctuations. One of the important finding was brought by Magnasco where he studied the temperature dependence on the fluctuation-induced current in a ratchet (multistable) system and showed that the current can generically be maximized in a finite temperature. The interesting finding has been interpreted that thermal fluctuation is not harmful for the fluctuation-induced work and even facilitates its efficiency. We show, however, this interpretation turns out to be incorrect as soon as we go into the realm of the energetics [Sekimoto,J.Phys.Soc.Jpn.66,1234-1237(1997)]: the efficiency of energy transformation is not maximized at finite temperature, even in the same system that Magnasco considered. The maximum efficiency is realized in the absence of thermal fluctuation. The result presents an open problem whether thermal fluctuation could facilitate the efficiency of energetic transformation from force-fluctuation into work.