Minimal universal quantum heat machine

TL;DR

This paper introduces a minimal quantum heat machine model using a single two-level system with periodic modulation, capable of functioning as an engine or refrigerator, and analyzes its efficiency and performance limits.

Contribution

It presents the first minimal quantum heat machine model that operates at Carnot efficiency with finite power, expanding understanding of quantum thermodynamics.

Findings

Achieves Carnot efficiency at zero power.

Can operate as engine or refrigerator depending on modulation.

Provides conditions for finite-time optimal performance.

Abstract

In traditional thermodynamics the Carnot cycle yields the ideal performance bound of heat engines and refrigerators. We propose and analyze a minimal model of a heat machine that can play a similar role in quantum regimes. The minimal model consists of a single two-level system with periodically modulated energy splitting that is permanently, weakly, coupled to two spectrally-separated heat baths at different temperatures. The equation of motion allows to compute the stationary power and heat currents in the machine consistently with the second-law of thermodynamics. This dual-purpose machine can act as either an engine or a refrigerator (heat pump) depending on the modulation rate. In both modes of operation the maximal Carnot efficiency is reached at zero power. We study the conditions for finite-time optimal performance for several variants of the model. Possible realizations of the model are discussed.