Entropy production in an elementary, light driven micro-machine

TL;DR

This paper investigates the thermodynamic behavior of a light-driven micro-propeller at colloidal scales, demonstrating fluctuation theorem compliance and exploring entropy production in microscopic systems.

Contribution

It provides the first detailed analysis of entropy production and fluctuation theorems in a carefully designed, light-driven micro-machine operating at colloidal scales.

Findings

The micro-propeller satisfies a fluctuation theorem.

Entropy decreases can occur temporarily in individual trajectories.

The second law holds on average, not necessarily in single trajectories.

Abstract

We consider the basic, thermodynamic properties of an elementary micro-machine operating at colloidal length scales. In particular, we track and analyse the driven stochastic motion of a carefully designed micro-propeller rotating unevenly in an optical tweezers, in water. In this intermediate regime, the second law of macroscopic thermodynamics is satisfied only as an ensemble average, and individual trajectories can be temporarily associated with decreases in entropy. We show that our light driven micro-propeller satisfies an appropriate fluctuation theorem that constrains the probability with which these apparent violations of the second law occur. Implications for the development of more complex micro-machines are discussed.