EAGER: CRYO: Engineering Charge and Energy Transfer in Superconducting Tunnel Junctions to Achieve Solid-State Refrigeration to Sub-Kelvin Temperatures

获得亚开尔文温度对于探索有趣的量子现象以及开发新的量子计算和基于量子光学的技术至关重要。目前可用的制冷到1摄氏度以下的方法昂贵，建造和维护复杂，而且体积大，因此主要局限于专门的研究实验室。在1K以下建立固态制冷将具有真正的变革性，因为它将影响广泛的新兴、高影响技术，这些技术都取决于能否获得紧凑、高效和低成本的超低温冷却技术。成功展示高冷却速度和低至100MK的温度将对量子技术产生巨大影响，如量子计算。此外，亚开尔文固态低温制冷还可以极大地改进和简化超灵敏探测器的使用，应用范围从天体物理学到危险材料检测。该项目将建立一种新的固态制冷方法来应对这些挑战。在这个探索性研究早期概念补助金(AGERGE)项目中，该团队寻求开发基于超导隧道结的固态制冷，使其能够在不稀释冰箱的情况下从1K冷却到100MK。基于超导隧道结的制冷原理上与通过热电子装置制冷非常相似，因为它依赖于高能载流子从一个电极到具有小带隙的第二个超导电极的选择性传输。这种高能载流子的选择性传输导致半导体/正常金属的冷却和超导体中的加热。实现基于超导隧道结的制冷的一个关键挑战是热端和冷端之间通过声子的热耦合，这阻碍了实现高冷却功率和所需的低温。这项工作的智力价值在于建立了全新的固态制冷方法，并被组织为旨在了解以下内容的推进：1)如何通过纳米结构或通过在界面引入分子部分来设计声子密度来增加超导隧道结热端和冷端之间的热阻；2)如何设计分子结以提供良好的电子透明度、冷却和热阻以达到创纪录的冷却速度；以及3)如何级联基于不同材料和结构的超导隧道结，以实现从1K到100MK的一路冷却？成功解决这些重要挑战将使基于超导隧道结的固态制冷和可容易与各种量子技术集成的新型制冷设备的开发成为可能。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Accessing sub-Kelvin temperatures is critical for exploring interesting quantum phenomena as well as for the development of novel quantum computing and quantum optics-based technologies. Currently available approaches to refrigeration to sub-1 K temperatures are expensive, complicated to build and maintain as well as bulky, and therefore are restricted largely to specialized research labs. Establishing solid-state refrigeration below 1K will be truly transformative, because it will impact a broad range of emerging, high-impact technologies that all hinge on the availability of compact, efficient and low-cost technologies for ultra-low temperature cryogenic cooling. Successful demonstration of high cooling rates and temperatures as low as 100 mK will have a dramatic impact on quantum technologies, such as quantum computing. Further, the sub-Kelvin solid-state low temperature refrigeration can also dramatically improve and simplify the use of ultrasensitive detectors for a number of applications ranging from astrophysics to detection of hazardous materials. This project will establish a novel approach to solid state refrigeration to address these challenges. In this EArly-concept Grant for Exploratory Research (EAGER) project the team seeks to develop superconducting tunnel junction-based solid-state refrigeration that will enable cooling from 1 K to 100 mK without a dilution refrigerator. Superconducting tunnel junction-based refrigeration is, in principle, very similar to cooling via a thermionic device as it relies on the selective transmission of high energy carriers from one electrode to a second superconducting electrode featuring a small bandgap. Such selective transmission of high energy carriers results in cooling of the semiconductor/normal metal and heating in the superconductor. A key challenge to achieve superconducting tunnel junction-based refrigeration is the thermal coupling between the hot and cold sides, via phonons, which prevents realization of high cooling powers and the required low temperatures. The intellectual merit of this work is in establishing completely novel approaches to solid-state refrigeration and is organized into thrusts aimed at understanding: 1) How the thermal resistance between the hot and the cold sides of the superconducting tunnel junction can be increased by engineering the phonon density of states via nanostructuring or by introducing molecular moieties at interfaces, 2) How molecular junctions can be engineered to provide excellent electronic transparency, cooling and thermal resistance to achieve record cooling rates, and 3) How superconducting tunnel junctions based on different materials and structures can be cascaded to achieve cooling all the way from 1 K to 100 mK? Successfully addressing these important challenges will enable development of both superconducting tunnel junction based solid-state refrigeration and novel refrigeration devices that can be readily integrated with various quantum technologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.