# Universal trade-off between power, efficiency, and constancy in steady-state heat engines

## TL;DR

This paper proves a universal trade-off in steady-state heat engines showing that achieving high power, efficiency, and constancy simultaneously is impossible, unifying recent ideas to overcome this limitation.

## Contribution

It establishes a fundamental bound linking power, efficiency, and constancy in steady-state heat engines, unifying previous approaches.

## Key findings

- Constancy constrains the power-efficiency trade-off.
- Universal bound applies to quantum dot solar cells.
- Bound also holds for Brownian gyrators.

## Abstract

Heat engines should ideally have large power output, operate close to Carnot efficiency and show constancy, i.e., exhibit only small fluctuations in this output. For steady-state heat engines, driven by a constant temperature difference between the two heat baths, we prove that out of these three requirements only two are compatible. Constancy enters quantitatively the conventional trade-off between power and efficiency. Thus, we rationalize and unify recent suggestions for overcoming this simple trade-off. Our universal bound is illustrated for a paradigmatic model of a quantum dot solar cell and for a Brownian gyrator delivering mechanical work against an external force.