AI 中文总结
该研究针对低损耗grAl谐振器，发现其最低温度下谐振频率随温度和读取功率升高而增加的异常行为，提出空间非均匀能隙超导准粒子机制解释部分数据，为量子器件损耗机制研究提供新参考。
AI 中文摘要
超导高动力学电感材料如颗粒铝（grAl）是电路量子电动力学（cQED）工具箱中的通用组成部分，前提是它们在微波频率下的损耗足够低。为进一步推进grAl在量子器件中的应用，识别主导损耗机制至关重要。标准方法是将谐振器几何结构的电磁模拟与测量得到的谐振频率及损耗率的温度和功率依赖关系相结合。大多数材料在低温下遵循双能级系统（TLS）的唯象理论，导致谐振频率随温度升高初始降低。在本研究中，我们在最低温度下观察到相反的行为：谐振频率随温度和读取功率的升高而初始增加，这与标准TLS模型的预测相矛盾。我们能够通过与具有空间非均匀能隙的颗粒系统中超导准粒子效应相关的替代机制解释部分数据。然而，观察到的谐振频率随温度的变化与损耗率的比例变化不匹配。我们还观察到高能事件后的异常正频率响应，其特征为多个时间尺度。尽管之前已有grAl中异常行为的报道，但由于我们的器件具有极低的损耗率，与标准模型的不一致在我们的器件中尤为明显。
英文摘要
Superconducting high-kinetic inductance materials like granular aluminum (grAl) are a versatile part of the circuit quantum electrodynamics (cQED) toolbox, provided their losses at microwave frequencies are low enough. To further advance the use of grAl in quantum devices, it is indispensable to identify the dominant loss mechanisms. The standard approach pairs electromagnetic simulations of resonator geometry with measured temperature and power dependence of resonance frequency and loss rate. Most materials follow the phenomenological theory of two-level systems (TLSs) at low temperatures, resulting in an initial decrease of the resonance frequency with increasing temperature. In our work, we observe an opposite behavior at the lowest temperatures: The resonance frequency initially increases with both temperature and readout power, contradicting the standard TLS model predictions. We are able to explain a part of the data by an alternative mechanism associated with the effect of superconducting quasiparticles in a granular system with spatially-nonuniform gap. Yet, the observed change in the resonance frequency with temperature is not matched by a proportional change in the loss rate. We also observe anomalous positive frequency responses following high-energy events, characterized by several time scales. While anomalous behavior has been reported previously in grAl, the disagreement with standard models is particularly visible in our devices thanks to their exceptionally low loss rates.
Comments10 pages, 8 figures (main text) and 11 pages, 7 figures (supplementary material)
