Fabrication And Properties Of The Superconducting Josephson Junctions And Explore The Structure Of Superconducting Qubit Circuit

Currently,the programs of physical system to achieve the quantum computer are too much,among them, the program based on superconductor Josephson junctions have became on focus due to the design and preparation is relatively mature, strong coupling with the outside world, macroscopic quantum system more 1,000 times than the normal quantum system. This paper is researching on the preparation of superconducting Al/AlOX/Al tunnel junctions, improving the quality of superconducting tunnel junctions through the relation between the superconducting current density Jc, the area normalized resistance Re and the oxidation pressure P. Moreover, we have systematically studied the relationship between the thickness of the upper, bottom electrode and the Re. The whole preparation process is simple and can achieve the requirements of constructing a superconducting quantum bit,at the same time, three programs of superconducting qubit circuit are fabricated. The whole work mainly includes the following three aspects in this thesis:1. Preparation of superconducting Al/AlOX/Al tunnel junctionsWe use the suspended shadow mask which is fabricated by using the double photoresist through the UV exposure and e-beam oblique evaporation to fabricate the Al/AlOX/Al superconducting Josephson tunnel junctions. The biggest advantage of this process is that the whole preparation process is simple and easy to control. In addition, the barrier layer is generated on the surface of the lower electrode aluminum thin film by the purity of 99.99% oxygen, non-polluting; The length of the junction can be controlled by adjusting the angle of evaporation. Every step of the process is stable. The current density Jc can reach 70 A/cm2 and leakage ratio of the superconducting Al/AlOX/Al tunnel junction can be controlled below 2%that have reached the requirements to build superconducting qubits.2. Characteristics of the superconducting Al/AlOX/Al tunnel junctionsJc and the energy gap voltage and other parameters have to be measured on very low temperatures,additional,the measurement period is too long in low economic efficiency and can not be predicted. This paper systematically studied the condition that affect Jc and Re. Results show that, Re and Jc have some relevance.Through the measurement of Re we can predict Jc.While Re is controlled by adjusting the oxidation pressure P in the experiment. In addition, we also have made a systematic analysis on the connection between the Re and thickness of the upper and lower electrode. The results show that under the same other conditions, the thickness of the bottom electrode at less than 80nm will significantly affect Re while the upper electrode thickness and Re have smaller relationship.3. Explore the structure of superconducting qubit circuitThree kinds of superconducting qubit circuit structure are attempted. By improving the structure and changing some important parameters, the ideal qubit signal has been measured at the end.