RUI: Measuring Nanoscale Thermal Transport with Trapped Ions

通过热传导的热量传输对于许多日常情况都很重要，从烹饪晚餐或加热和冷却家庭到消除消费电子产品产生的废热。尽管热导率在宏观和日常尺度上被很好地理解，但与今天的现代微电子相关的微小尺度上的热传递——在经典力学与量子力学之间的交叉——一直抵制科学研究。这个项目将模拟纳米级的热导率，使用一个原子系统，这个系统将被电离，被电场捕获，并用激光探测，这是理解量子力学和经典力学交叉的热流的一步。学生将参与实验的各个方面——设计和建造激光、电子和数据采集系统，编写软件，并进行数据收集，为未来的科学职业生涯提供极好的培训。支撑这项工作的核心思想将是共同捕获钙的多种同位素，以创造一个共感冷却的线性离子链。链的末端离子将是44Ca+离子，激光冷却到不同的平均振子数，类似于不同温度的热浴。40Ca+将形成链的中心“主体”。分解边带光谱，单独定位到链中的特定离子，将用于读取每个离子的平均振动数，相当于温度分布。在典型的情况下，振子沿链的输运被认为是弹道的，导致在整体中几乎均匀分布。然而，通过在捕获势中引入局部噪声或在线性到锯齿形结构相变中加强径向-轴向模式耦合来诱导振子减相将使链断裂为热不连通的子系统。这将允许观察扩散热输运的开始，表现为平均振动子数的非均匀梯度。这项工作将很自然地扩展到包括改善线性离子链的交感冷却技术的研究，这是一系列利用捕获离子进行量子信息处理的实验的中心工具。因此，该研究计划有望帮助我们理解纳米尺度的导热性，并为下一代捕获离子量子计算和量子模拟实验提供信息。此外，作为这项工作的一部分，同位素位移测量将有助于理解原子和核理论。

The transport of heat via thermal conduction is important for a host of everyday situations ranging from cooking one's dinner or heating and cooling one's home to removing waste heat produced in consumer electronics. Although thermal conductivity is well understood on macroscopic, everyday scales, heat transport on the tiny size scales relevant for today's modern microelectronics - at the crossover between regimes governed by classical versus quantum mechanics - has resisted scientific study. This project, which will simulate nanoscale thermal conductivity using a system of atoms that will be ionized, trapped with electric fields, and probed using lasers, is a step towards understanding heat flow at the crossover between quantum and classical mechanics. Taking place at an undergraduate institution, students will be involved in all aspects of the experiments - designing and building lasers, electronics, and data acquisition systems, writing software, and carrying out data collection, providing superb training for future careers in the sciences.The central idea underpinning this work will be to co-trap multiple isotopes of calcium to create a sympathetically cooled, linear chain of ions. The end ions of the chain will be 44Ca+ ions, laser cooled to different average vibron numbers, analogous to thermal baths of different temperatures. 40Ca+ will form the central `bulk' of the chain. Resolved sideband spectroscopy, individually addressed to specific ions in the chain, will be used to read out the average number of vibrons at each ion, equivalent to a temperature distribution. Under typical circumstances vibron transport along the chain is expected to be ballistic, leading to a near-uniform distribution in the bulk. However, inducing vibron dephasing by introducing localized noise to the trapping potentials or strengthening radial-axial mode coupling across the linear-to-zig-zag structural phase transition will break the chain into thermally disconnected subsystems. This will allow observation of the onset of diffusive thermal transport, manifested as a non-uniform gradient of the average vibron numbers. This work will extend quite naturally to include study of techniques for improving sympathetic cooling of linear ion chains, a central tool for a wide array of experiments pursuing quantum information processing with trapped ions. This research program is thus expected to aid in our understanding of nanoscale thermal conductivity and also to inform the next generation of experiments in trapped ion quantum computation and quantum simulation. Additionally, isotope shift measurements made as part of this work will contribute to the understanding of atomic and nuclear theory.