标题： 超导微波振荡器作为电子顺磁共振光谱的探测器 显示英文标题

标题： Superconducting microwave oscillators as detectors for ESR spectroscopy

摘要： 微波超导谐振器在量子计算和电子自旋共振（ESR）光谱学等领域得到了广泛研究。然而，将超导谐振器与反馈机制结合以创建超低噪声振荡器是一个相对未被探索的领域，此类振荡器在ESR光谱学中的应用尚未得到展示。在本工作中，我们报告了基于超导谐振器的微波振荡器的设计、制造和应用，展示了改进基于振荡器的ESR传感器性能的一种替代方法。具体而言，通过测量施加静态磁场时由ESR效应引起的振荡器频率偏移来获得ESR光谱。这些振荡器由单个异质结双极晶体管（HBT）或高电子迁移率晶体管（HEMT）与NbTi或YBa$_2$Cu$_3$O$_7$（YBCO）超导谐振器组成。制造的振荡器工作频率为0.6和1.7 GHz，温度高达80 K（对于YBCO谐振器）和8 K（对于NbTi谐振器）。 测量到的最低频率噪声约为9 mHz/Hz$^{1/2}$ (-139 dBc/Hz)，最佳自旋灵敏度约为$1\times10^{10}$ 自旋/Hz$^{1/2}$，最佳浓度灵敏度约为$3\times10^{18}$ 自旋/Hz$^{1/2}$米$^3$。本文提出的方法应该允许在正常导体可实现的运行频率、磁场和温度范围内，显著提高自旋和浓度灵敏度，这些范围内的超导体表现出比正常导体低得多的有效微波电阻。 显示英文摘要

摘要： Microwave superconducting resonators are extensively studied in fields such as quantum computing and electron spin resonance (ESR) spectroscopy. However, the integration of superconducting resonators with feedback mechanisms to create ultra-low noise oscillators is a relatively unexplored area, and the application of such oscillators in ESR spectroscopy has not yet been demonstrated. In this work, we report the design, fabrication, and application of microwave oscillators based on superconducting resonators for ESR spectroscopy, illustrating an alternative way for the improvement of the performance of oscillator based ESR sensors. Specifically, ESR spectra are obtained by measuring the oscillator's frequency shift induced by the ESR effect as a function of the applied static magnetic field. The oscillators are composed of a single heterojunction bipolar transistor (HBT) or high electron mobility transistor (HEMT) coupled with NbTi or YBa$_2$Cu$_3$O$_7$ (YBCO) superconducting resonators. The fabricated oscillators operate at frequencies of 0.6 and 1.7 GHz and temperatures up to 80 K (for YBCO resonators) and 8 K (for NbTi resonators). The lowest measured frequency noise is about 9 mHz/Hz$^{1/2}$ (-139 dBc/Hz), the best spin sensitivity is about $1\times10^{10}$ spins/Hz$^{1/2}$, and the best concentration sensitivity is about $3\times10^{18}$ spins/Hz$^{1/2}$m$^3$. The approach proposed in this work should allow for significantly better spin and concentration sensitivities compared to those achievable with normal conductors, up to operating frequencies, magnetic fields, and temperatures where superconductors exhibit substantially lower effective microwave resistance than normal conductors.