Quantum heat engines

热机是热力学的核心原理之一。在循环热机中，工作气体通过可逆循环在冷热蓄热池之间传递热量，并执行有用的功。蒸汽机和内燃机是循环热机的两个著名例子。粒子交换热机也将热能转化为有用的功，然而，热量通过有限能量范围内的粒子(例如电子)的交换从热库转移到冷库。在电子热机的特殊情况下，电子在外加电场的作用下流动以产生电力。电子热机的典型实施例包括热电和光伏器件，其中半导体带隙充当能量过滤器，导致净电荷从热库流向冷库。电子热机的热力学效率取决于能量过滤器的确切细节，以及由核振动或声子介导的热导。近年来，纳米结构热电材料的发展大大提高了热电发电机和制冷器的效率。然而，还有很大的改进空间：传统的热电设备只在卡诺效率的一小部分下运行，卡诺效率是任何经典发动机将热量转化为功所能达到的上限。量子点热机有可能在接近热力学极限的情况下运行。它们的离散光谱提供了理想的能量过滤器，它们的核振动可以通过巧妙的分子设计来控制。然而，到目前为止，石墨烯量子点中的热电转换实验证据很少。此外，已知的量子效应在石墨烯量子点的电荷传输中发挥作用，并可以提高量子点热机的效率。然而，在单个分子的层面上，量子力学和热力学之间的联系在很大程度上仍未得到探索。该项目将开发一个用于研究量子点热电设备的综合实验工具包，并探索纳米级热电能量转换的最终效率极限，以建立纳米级热力学中的量子点热机范式。

Heat engines are one of the central tenets of thermodynamics. In cyclical heat engines, a working gas moves through a reversible cycle to transfer heat between a hot and a cold reservoir and perform useful work. The steam engine and the internal combustion engine are two well-known examples of cyclical heat engines. Particle-exchange heat engines also convert thermal energy into useful work, however heat is transferred from a hot to a cold reservoir via the exchange of particles, for example electrons, in a finite energy range. In the particular case of electron heat engines, electrons flow against an applied electric field to generate power. Typical embodiments of electron heat engines include thermoelectric and photovoltaic devices, where a semiconductor bandgap acts as an energy filter that results in a net charge flow from the hot to the cold reservoir. The thermodynamic efficiency of an electron heat engine depends on exact details of the energy filter and on the heat conductance mediated by nuclear vibrations, or phonons. In recent years the development of nanostructured thermoelectric materials has led to a significant increase in the efficiency of thermoelectric generators and coolers. Yet there is still plenty of room for improvement: conventional thermoelectric devices operate only at a fraction of the Carnot efficiency that is the upper limit that any classical engine can achieve in converting heat to work.Quantum dot heat engines have the potential to operate close to the thermodynamic limit. Their discrete spectrum of provides an ideal energy filter, and their nuclear vibrations could be controlled through clever molecular design. To date there is however sparse experimental evidence of heat- to-electricity conversion in graphene quantum dots. Moreover, quantum effects that are known to play a role in charge transport through graphene quantum dots, and could enhance the efficiency of quantum dot heat engines. Yet, the link between quantum mechanics and thermodynamics on the level of an individual molecule has remained largely unexplored. This project will develop a comprehensive experimental toolkit for investigating quantum dot thermoelectric devices and explore the ultimate efficiency limits of nano-scale thermoelectric energy conversion to establish the paradigm of quantum dot heat engines in nanoscale thermodynamics.