Quantum thermochemical engines

TL;DR

This paper investigates quantum thermochemical engines that convert chemical energy into mechanical work, highlighting how quantum effects and statistics can enhance efficiency and power output at the nanoscale.

Contribution

It introduces a finite-time quantum master equation model for these engines and analyzes the impact of quantum degeneracy and Bose-Einstein condensates on performance.

Findings

Quantum degeneracy gases achieve maximum efficiency in reversible engines.

Quantum regime engines outperform classical limits in power and efficiency.

Quantum statistics serve as a resource for improved energy conversion performance.

Abstract

Conversion of chemical energy into mechanical work is the fundamental mechanism of several natural phenomena at the nanoscale, like molecular machines and Brownian motors. Quantum mechanical effects are relevant for optimising these processes and to implement them at the atomic scale. This paper focuses on engines that transform chemical work into mechanical work through energy and particle exchanges with thermal sources at different chemical potentials. Irreversibility is introduced by modelling the engine transformations with finite-time dynamics generated by a time-depending quantum master equation. Quantum degenerate gases provide maximum efficiency for reversible engines, whereas the classical limit implies small efficiency. For irreversible engines, both the output power and the efficiency at maximum power are much larger in the quantum regime than in the classical limit. The analysis of ideal homogeneous gases grasps the impact of quantum statistics on the above performances, which persists in the presence of interactions and more general trapping. The performance dependence on different types of Bose-Einstein Condensates (BECs) is also studied. BECs under considerations are standard BECs with a finite fraction of particles in the ground state, and generalised BECs where eigenstates with parallel momenta, or those with coplanar momenta are macroscopically occupied according to the confinement anisotropy. Quantum statistics is therefore a resource for enhanced performances of converting chemical into mechanical work.