低损耗超导谐振电路用带隙电容器
Vacuum-Gap Capacitors for Low-Loss Superconducting Resonant Circuits
摘要：
从低温探测器阵列的多路复用读出到量子比特，许多超导谐振电路中都使用了低损耗微波元件。非晶介电材料中的二能级系统缺陷会引起能量的过度损耗。在努力改善电容器组件，我们已经使用光学光刻和微机械加工技术，以开发超导平行板电容器，其中有损耗的电容器被真空间隙取代。在50 mK下对集成了这些真空间隙电容器（VGC）的集总LC电路进行的谐振测量显示，在低功率下的损耗角正切低至4 × 10 ^{-5}，显著低于使用非晶双极晶体的电容器。VGC结构坚固、体积小，并且容易扩展到100 pF以上的电容值。
英文摘要：
Low-loss microwave components are used in many superconducting resonant circuits from multiplexed readouts of low-temperature detector arrays to quantum bits. Two-level system defects in amorphous dielectric materials cause excess energy loss. In an effort to improve capacitor components, we have used optical lithography and micromachining techniques to develop superconducting parallel-plate capacitors in which lossy dielectrics are replaced by vacuum gaps. Resonance measurements at 50 mK on lumped LC circuits that incorporate these vacuum-gap capacitors (VGCs) reveal loss tangents at low powers as low as 4x10^{-5}, significantly lower than with capacitors using amorphous dielectrics. VGCs are structurally robust, small, and easily scaled to capacitance values above 100 pF.
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