An Information-Theoretic Bound on Thermodynamic Efficiency and the Generalized Carnot's Theorem

TL;DR

This paper derives a new, sharper efficiency bound for thermal engines based on information theory, applicable to classical and quantum systems, and demonstrates its attainability in quantum dot engines.

Contribution

It introduces an information-theoretic efficiency bound that surpasses Carnot's limit and applies to finite-time, multi-bath engines, with practical design implications.

Findings

The bound can be saturated in finite-time cycles.

Quantum dot engines can achieve the derived efficiency bound.

The bound applies to both classical and quantum thermal engines.

Abstract

We derive a bound on the efficiency of thermal engines that can be sharper than Carnot's limit. It is a function of statistical correlations between the engine internal state and Hamiltonian, can be saturated even in finite-time cycles, and applies to both classical and quantum engines. Specifically, the bound establishes the exact maximal efficiency of engines operating with multiple baths, tightening the upper limit set by Carnot's theorem. Then, we show that an engine made of a quantum dot coupled with fermionic baths can achieve the bound, even when operating beyond the quasistatic regime. The result provides a design principle for realistic energy harvesting machines.