Quantum dot thermal machines -- a guide to engineering

TL;DR

This paper reviews quantum dot thermal machines, emphasizing how internal dynamics influence their efficiency, power, and stability, and provides engineering guidance to optimize performance beyond basic models.

Contribution

It identifies key parameters of quantum dot dynamics that can be engineered to enhance thermal machine performance beyond simple models.

Findings

Performance depends on conductance and three asymmetries in dynamics.

Optimizing these parameters can surpass basic two-level models.

Quantum dots can approach Carnot efficiency while maintaining practical power and stability.

Abstract

Continuous particle exchange thermal machines require no time-dependent driving, can be realised in solid-state electronic devices, and miniaturised to nanometre scale. Quantum dots, providing a narrow energy filter and allowing to manipulate particle flow between the hot and cold reservoirs are at the heart of such devices. It has been theoretically shown that by mitigating passive heat flow, Carnot efficiency can be approached arbitrarily closely in a quantum dot heat engine, and experimentally, values of 0.7{\eta}C have been reached. However, for practical applications, other parameters of a thermal machine, such as maximum power, efficiency at maximum power, and noise - stability of the power output or heat extraction - take precedence over maximising efficiency. We explore the effect of internal microscopic dynamics of a quantum dot on these quantities and demonstrate that its performance as a thermal machine depends on few parameters - the overall conductance and three inherent asymmetries of the dynamics. These parameters will act as a guide to engineering the quantum states of the quantum dot, allowing to optimise its performance beyond that of the simplest case of a two-fold spin-degenerate transmission level.