Rotational diffusion under torque: Microscopic reversibility and excess entropy

TL;DR

This paper investigates rotational diffusion in macrospins and particles on spheres under external torque, revealing how microstates' time-reversal properties affect entropy production and confirming fluctuation theorems through analytical and numerical methods.

Contribution

It introduces a detailed analysis of entropy production differences due to microstate transformations under time-reversal in rotational diffusion systems.

Findings

Total entropy production obeys fluctuation theorems in both systems.

Analytical distribution of entropy production derived for macrospins in the adiabatic limit.

Numerical simulations confirm theoretical predictions of entropy distribution.

Abstract

We consider rotational diffusion for two systems - a macrospin under external magnetic field, and a particle diffusing on the surface of a sphere under external torque. Microstates in the two cases transform differently under time-reversal. This results in Clausius like dependence of stochastic entropy production (EP) for macrospins, and an excess EP for diffusion of particles on sphere. The total EP in both the cases obey fluctuation theorems. For macrospins, we derive analytical expression for probability distribution of total EP in the adiabatic limit. Numerical simulations show that the distribution functions of EP agree well with theoretical predictions.