Enhancing Quantum Otto Engine Performance in Generalized External Potential on Bose-Einstein Condensation Regime

TL;DR

This paper investigates a quantum Otto engine with Bose-Einstein Condensation as the working medium, demonstrating that incomplete thermalization and residual coherence can significantly enhance the engine's efficiency at maximum power.

Contribution

It introduces a model for a quantum Otto engine using BEC in a generalized potential, analyzing the effects of thermal contact time and residual coherence on efficiency and power.

Findings

EMP is higher with BEC than normal Bose gas, exceeding Curzon-Ahlborn efficiency.

Incomplete thermalization can increase EMP by adjusting stroke times.

Residual coherence emerging from incomplete thermalization enhances engine performance.

Abstract

We examine a quantum Otto engine using both Bose-Einstein Condensation (BEC) and normal Bose gas as working medium trapped in generalized external potential. We treated the engine quasi-statically and endoreversibly. Since the expansion and compression in both quasi-static and endoreversible take place isentropic, the expression of efficiency is similar. However, the power output in the quasi-static cycle is zero due to infinite and long stroke time. In contrast, with an endoreversible cycle, thermalization with two reservoirs takes place at a finite time. We use Fourier's law in conduction to formulate the relation between temperature of medium and reservoir, making work depend on heating and cooling stroke time. Moreover, we maximized the power with respect to compression ratio $\kappa$ to obtain efficiency at maximum power (EMP). We found that EMP is significantly higher when using BEC as a working medium, meanwhile EMP with normal Bose gas is just Curzon-Ahlborn efficiency. We also investigate the effect of thermal contact time $\tau$ with hot $(\tau_{h})$ and cold $(\tau_{l})$ reservoir on EMP. We found that when complete thermalization, $\tau_{h}=\tau_{l}$, stroke time occurs, there are no significant differences. Nevertheless, while incomplete thermalization arise, by adjusting various cooling and heating stroke time, provides a significant result on EMP, which is much higher at $\tau_{h}<\tau_{l}$ stroke time whilst lower at $\tau_{h}>\tau_{l}$ stroke time. We conclude this incomplete thermalization leads to the condition where residual coherence emerges which enhances the EMP of the engine.