Multitask quantum thermal machines and cooperative effects

Abstract

The performance of nonequilibrium work extraction in thermoelectric devices can be enhanced by introducing the phonon-assisted inelastic process. Herein, we study phonon-thermoelectric devices where particle current and phononic heat currents are coupled by dominating phonon-assisted inelastic process and fueled by chemical potential difference and temperature biases and show that inelastic thermoelectric setups have a much richer functionality diagram and can even simultaneously perform multiple tasks, such as heat engines, refrigerators, and heat pumps. From the viewpoint of entropy production, we study the efficiencies and coefficients of performance of multi-task quantum thermal machines by analyzing two typical thermoelectric devices and emphasize the role of the inelastic scattering process and multiple biases in multiterminal setups. In a three-terminal double-quantum-dot setup with a tunable gate, we show that it performs two useful tasks due to the phonon-assisted inelastic process dominating the transport. For four-terminal four-quantum-dot thermoelectric device, we demonstrate that additional thermodynamic affinity furnishes the system with both substantially enriched functionality diagrams and enhanced efficiency. The cooperation between the longitudinal and transverse thermoelectric effects in the three-terminal thermoelectric systems leads to markedly improved performance of the thermal machines. Our work provides insights into optimizing general thermoelectric devices.

Hybrid quantum thermal machines with dynamical couplings

“…III B. The other six operating modes consist of three "pure" ones (engine, refrigerator, heat pump) and three "hybrid" modes [37,68,69]. The existence of the latter implies that a three-terminal device can simultaneously perform multiple thermodynamic tasks, such as employing heat from the hot reservoir to produce power (engine) and simultaneously "lift" heat from the cold reservoir (refrigerator), a possibility out of reach for conventional two-terminal thermal machines [15,36,37,68,69].…”

“…To quantify the performance of a multi-terminal thermal machine in a unified fashion, including also multitasking configurations, it is useful to introduce the so-called input-output exergy efficiency, also known as the second-law efficiency or rational efficiency [37,68,69]. To this end, we split the entropy production rate Ṡ = Ṡ(+) + Ṡ(−) into positive (+) and negative (-) contributions and introduce the exergy efficiency as…”