RUI: Measuring Nanoscale Thermal Transport with Trapped Ions

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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.