用于超导器件的普通金属中的声子下转换
Phonon down-conversion by normal metals for superconducting devices
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中文总结 AI 辅助
研究超导器件中因准粒子导致的配对破坏声子中毒机制，通过基于动力学方程的模型，研究普通金属膜下转换缓解该机制，发现下转换效率在有限金属厚度范围接近最优，最小近最优厚度约为微米量级。
中文摘要 AI 辅助
由于低损耗，超导器件在诸如探测器和量子计算实现等许多应用中很有前景。然而，它们的工作会受到准粒子的不利影响，因此所谓的准粒子中毒机制及其缓解方法正在深入研究。本文聚焦于一种中毒机制，即配对破坏声子，以及通过普通金属膜下转换来缓解它的方法——高能声子被电子散射使前者能量降低到配对破坏阈值以下的过程。为研究下转换，我们引入基于动力学方程的模型，在稳态下进行解析（近似）和数值求解。我们用解来估计一个适当定义的下转换效率，它取决于材料参数（如电子 - 声子相互作用强度和界面处的声子传输系数）以及薄膜和衬底厚度。有趣的是，我们发现效率在金属厚度的有限范围内接近最优，最小近最优厚度通常为微米量级。
英文摘要
Thanks to low dissipation, superconducting devices are promising for a number of applications, such as detectors and implementations of quantum computation. However, their working can be adversely impacted by quasiparticles, which is why so-called quasiparticle poisoning mechanisms and their mitigation are under intense investigation. Here we focus on one poisoning mechanism, namely pair-breaking phonons, and its mitigation through down-conversion by a normal-metal film - the process in which scattering of high-energy phonons by electrons lowers the energy of the former below the pair-breaking threshold. To study the down-conversion, we introduce a model based on kinetic equations, which we solve both analytically (approximately) and numerically in the steady state. We use the solution the estimate a properly-defined down-conversion efficiency which depends on material parameters (such as the strength of electron-phonon interaction and the phonon transmission coefficient at interfaces) and film and substrate thicknesses. Interestingly, we find that the efficiency is nearly optimal over a finite range of metal thicknesses, with the minimum near-optimal thickness being typically of the order of a micron.
