Energy flow between two hydrodynamically coupled particles kept at different effective temperatures

TL;DR

This study investigates energy exchange between two hydrodynamically coupled particles at different effective temperatures, demonstrating measurable energy flow and correlations driven by external forcing, with results matching theoretical models.

Contribution

It introduces an experimental setup to measure energy flow between coupled particles at different effective temperatures, validated by a hydrodynamic coupling model.

Findings

Energy flow is observed between particles with different effective temperatures.

Cross-correlation functions depend on the temperature difference.

Experimental results agree with hydrodynamic coupling theory.

Abstract

We measure the energy exchanged between two hydrodynamically coupled micron-sized Brownian particles trapped in water by two optical tweezers. The system is driven out of equilibrium by random forcing the position of one of the two particles. The forced particle behaves as it has an "effective temperature" higher than that of the other bead. This driving modifies the equilibrium variances and cross-correlation functions of the bead positions: we measure an energy flow between the particles and an instantaneous cross-correlation, proportional to the effective temperature difference between the two particles. A model of the interaction which is based on classical hydrodynamic coupling tensors is proposed. The theoretical and experimental results are in excellent agreement.