Brownian Carnot engine

TL;DR

This paper reports an experimental realization of a microscopic Carnot engine using a single optically trapped Brownian particle, demonstrating the ability to surpass the Carnot efficiency bound in finite cycles and analyzing the engine's energetics and fluctuations.

Contribution

It provides the first experimental study of a microscopic Carnot engine, exploring efficiency fluctuations and irreversibility at small scales.

Findings

Carnot efficiency can be surpassed in finite-time microscopic cycles.

The energetics of the microscopic engine show properties similar to macroscopic engines.

Efficiency fluctuations follow predictable statistical patterns.

Abstract

The Carnot cycle imposes a fundamental upper limit to the efficiency of a macroscopic motor operating between two thermal baths. However, this bound needs to be reinterpreted at microscopic scales, where molecular bio-motors and some artificial micro-engines operate. As described by stochastic thermodynamics, energy transfers in microscopic systems are random and thermal fluctuations induce transient decreases of entropy, allowing for possible violations of the Carnot limit. Despite its potential relevance for the development of a thermodynamics of small systems, an experimental study of microscopic Carnot engines is still lacking. Here we report on an experimental realization of a Carnot engine with a single optically trapped Brownian particle as working substance. We present an exhaustive study of the energetics of the engine and analyze the fluctuations of the finite-time efficiency, showing that the Carnot bound can be surpassed for a small number of non-equilibrium cycles. As its macroscopic counterpart, the energetics of our Carnot device exhibits basic properties that one would expect to observe in any microscopic energy transducer operating with baths at different temperatures. Our results characterize the sources of irreversibility in the engine and the statistical properties of the efficiency -an insight that could inspire novel strategies in the design of efficient nano-motors.