RF-Field-Driven Superconducting Quantum Interference Devices

本研究旨在探讨射频场驱动直流量子干涉仪（RFDS）的特性，并为未来的应用提供理论与实验依据。在模拟中，我们已经获得了器件特性对（i）信号频率、（ii）信号功率、（iii）偏移直流场以及（iv）操作裕度和功率增益的依赖性。然后我们利用YBa_2Cu_3O_<7-δ>晶界约瑟夫森结（YBCO-GBJJ）和H形天线制作了DC-SQUID。在低功率区，计算结果与数值计算结果基本一致。根据这些结果，我们研制了一种共面型谐振腔，用于将射频信号以磁性方式施加到超导量子干涉器件（SQUID）上。我们再次用YBCO-GBJJ制作了DC-SQUID，并将其安装在谐振腔上。通过对SQUID谐振腔施加20 GHz的SF信号，观察到了SQUID的电流-电压特性的Shapiro阶跃。Shapiro台阶对直流偏置场的依赖关系与数值结果一致。与我们以前的设备相比，新方法有三个好处：1。我们可以独立设计一个谐振腔和一个SQUID。2.因此，我们可以通过改变谐振器来利用宽带频率。3.此外，我们可以利用相同的SQUID的宽带频率，这意味着我们可以系统地研究设备的性能对频率的依赖性。最后，我们将器件结构从二结SQUID扩展到三结SQUID。分析和数值计算结果表明，三结SQUID在多相射频信号作用下会产生过零夏皮罗阶跃。因此，扩展的射频场驱动SQUID将适用于可编程约瑟夫森电压标准。

The purpose of this study is to investigate the properties of RF-field-driven DC-SQUID (RFDS) in both simulation and experiments for future possible applications. In simulation, we have obtained the dependence of device properties upon (i) frequency of the signal, (ii) power of the signal, (iii) offset DC field, and (iv) operation margins and power gain. Next we fabricated a DC-SQUID using YBa_2Cu_3O_<7-δ> grain boundary Josephson junctions (YBCO-GBJJs) integrated with an H-shaped antenna. The results agreed with numerical ones at low power region. According to these results, we developed a coplanar-type resonator to apply RF signal to a superconducting quantum interference device (SQUID) magnetically. We fabricated a DC-SQUID using YBCO-GBJJs again, and mounted it on the resonator. By applying SF signal of 20GHz to the resonator, we observed Shapiro steps on ;the current-voltage characteristics of the SQUID. The dependence of Shapiro steps upon DC offset field agreed with the numerical results. In comparison with our previous device, the new method has three benefits: 1. We can design a resonator and a SQUID independently. 2. Hence, we can utilize wide-band frequencies by changing the resonator. 3. Also we can utilize the same SQUID for wide-band frequencies, which means we can systematically investigate the dependence of the device properties upon the frequency. Finally we extended the device configuration from two-junction SQUID to three-junction SQUID. Analytical and numerical results showed that the three-junction SQUID would generate a zero-crossing Shapiro step by applying multi-phase RF signals. Hence, the extended RF-Field-Driven SQUID would be applicable to programmable Josephson voltage standards.