Cyclical heat engines are a paradigm of classical thermodynamics, but are impractical for miniaturization because they rely on moving parts. A more recent concept is particle-exchange (PE) heat engines, which uses energy filtering to control a thermally driven particle flow between two heat reservoirs^1,2. As they do not require moving parts and can be realized in solid-state materials, they are suitable for low-power applications and miniaturization. It was predicted that PE engines could reach the same thermodynamically ideal efficiency limits as those accessible to cyclical engines^3,4,5,6, but this prediction has not been verified experimentally. Here, we demonstrate a PE heat engine based on a quantum dot (QD) embedded into a semiconductor nanowire. We directly measure the engine’s steady-state electric power output and combine it with the calculated electronic heat flow to determine the electronic efficiency η. We find that at the maximum power conditions, η is in agreement with the Curzon–Ahlborn efficiency^6,7,8,9 and that the overall maximum η is in excess of 70% of the Carnot efficiency while maintaining a finite power output. Our results demonstrate that thermoelectric power conversion can, in principle, be achieved close to the thermodynamic limits, with direct relevance for future hot-carrier photovoltaics¹⁰, on-chip coolers or energy harvesters for quantum technologies.

循环热机是经典热力学的范例，但是由于其依赖于运动部件，因此对于小型化是不切实际的。最近的概念是颗粒交换（PE）热机，它使用能量过滤来控制两个储热器^1,2之间的热驱动颗粒流。由于它们不需要活动部件并且可以用固态材料实现，因此它们适合于低功率应用和小型化。据预测，PE发动机可以达到与周期性发动机可达到的相同的热力学理想效率极限^3,4,5,6，但是该预测尚未通过实验验证。在这里，我们演示了一种基于嵌入半导体纳米线中的量子点（QD）的PE热机。我们直接测量发动机的稳态电功率输出，并将其与计算出的电子热流结合起来，以确定电子效率η。我们发现，在最大功率条件下，η与Curzon-Ahlborn效率^{6,7,8,9一致}，总的最大η超过卡诺效率的70％，同时保持有限的功率输出。我们的结果表明，原则上可以实现热电功率转换，使其接近热力学极限，这与未来的热载光伏发电有直接关系¹⁰，用于量子技术的片上冷却器或能量收集器。