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

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。目前可用的制冷到低于1 K温度的方法是昂贵的，建造和维护复杂，体积庞大，因此主要限于专门的研究实验室。建立低于1 K的固态制冷将是真正的变革，因为它将影响广泛的新兴高影响力技术，这些技术都取决于超低温低温冷却的紧凑，高效和低成本技术的可用性。高冷却速率和低至100 mK的温度的成功演示将对量子技术（如量子计算）产生巨大影响。此外，亚开尔文固态低温制冷还可以显着改善和简化超灵敏检测器的使用，用于从天体物理学到检测危险材料的许多应用。该项目将建立一种新的固态制冷方法来应对这些挑战。在这个早期概念探索性研究资助（EAGER）项目中，该团队寻求开发基于超导隧道结的固态制冷，该制冷将在没有稀释制冷机的情况下实现从1 K到100 mK的冷却。基于超导隧道结的制冷在原理上与通过超导设备的冷却非常相似，因为它依赖于高能量载流子从一个电极到具有小带隙的第二超导电极的选择性传输。高能载流子的这种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，这阻碍了高冷却功率和所需低温的实现。这项工作的智力价值在于建立固态制冷的全新方法，并组织成旨在理解的推力：1）如何通过经由纳米结构化设计声子态密度或通过在界面处引入分子部分来增加超导隧道结的热侧和冷侧之间的热阻，2）如何设计分子结以提供优异的电子透明度，冷却和热阻，以实现创纪录的冷却速率，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1 K到100 mK的冷却？成功解决这些重要挑战将使超导隧道结为基础的固态制冷和新型制冷设备的发展，可以很容易地与各种量子技术集成。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.