Fabrication And Theoretical Discussion Of Superconducting Quantum Devices

In the thesis, I report our recent research in Nanjing University into superconduct-ing qubits based on Josephson junction systems, especially the rf SQUID flux qubit. These researches include the Josephson junction devices preparation using shadow evaporation method, the theoretical study about the rf SQUID-cavity coupled system.In chapter1,1first introduce the macroscopic quantum phenomena and the Joseph-son physics to help readers understand the following content. And then, I introduce some Josephson circuit qubits, which include phase qubit, flux qubit and charge qubit, and compare their operation modes.In chapter2, I introduce the flux qubit composed by a superconducting loop in-terrupted by single or three Josephson junctions. Although they have similar setups, their operation modes are totally different. I elaborately introduce the theory of three Josephson junctions’flux qubit to clarify the choice of operation point and the energy quantization.In chapter3,1introduce the theory of superconducting microwave cavities. Due to microwave transport in transmission lines, the theory of transmission lines is intro-duced firstly. Then, I introduce the setups which transform a transmission line into a microwave cavity. At last, the microwave field in a cavity is quantized. In chapter4,I introduce the superducting quantum devices preparation methods. Firstly, I briefly review the microfabrication methods used in our experiments. The so called shadow evaporation used in Josephson junction preparation is presented. Then, I give out the process of making Josephson junction devices and superconducting cav-ities. Measured results, such as I-V curves for SQUIDs and transmission spectra for cavities, are presented in this chapter. Further more, these results are compared with theoretical ones.In chapter5,1introduce the theory of a flux qubit coupled to a superconducting cavity, analyze its energy levels and clarify its operation modes. I develop such sys-tems by coupling one flux qubit to two cavities simultaneously. Through study their transmission properties theoretically, I find it can be used as a quantum switch. Based on this property, we can make two remote cavities entangled.In chapter6,1make a conclusion of my thesis and give a prospect of my future work.