Measurement Based Quantum Heat Engine with Coupled Working Medium

TL;DR

This paper analyzes a measurement-based quantum heat engine with a coupled spin-1/2 Heisenberg model, showing that coupling can enhance efficiency and lead to negative efficiency in higher spin and asymmetric cases, revealing complex relationships between coupling and performance.

Contribution

It extends the quantum heat engine model to coupled spin systems, exploring higher spins and asymmetry, and uncovers conditions where coupling improves efficiency or results in negative efficiency.

Findings

Coupling can increase engine efficiency compared to uncoupled systems.

Higher spins can lead to negative efficiency under certain conditions.

Asymmetric spin systems exhibit unique efficiency behaviors.

Abstract

We consider measurement based single temperature quantum heat engine without feedback control, introduced recently by Yi, Talkner and Kim [Phys. Rev. E 96, 022108 (2017)]. Taking the working medium of the engine to be a one-dimensional Heisenberg model of two spins, we calculate the efficiency of the engine undergoing a cyclic process. Starting with two spin-1/2 particles, we investigate the scenario of higher spins also. We show that, for this model of coupled working medium, efficiency can be higher than that of an uncoupled one. However, the relationship between the coupling constant and the efficiency of the engine is rather involved. We find that in the higher spin scenario efficiency can sometimes be negative (this means work has to be done to run the engine cycle) for certain range of coupling constants, in contrast to the aforesaid work of Yi, Talkner and Kim, where they showed that the extracted work is always positive in the absence of coupling. We provide arguments for this negative efficiency in higher spin scenarios. Interestingly, this happens only in the asymmetric scenarios, where the two spins are different. Given these facts, for judiciously chosen conditions, an engine with coupled working medium gives advantage for the efficiency over the uncoupled one.