超导JosephsonF遂道结的制备、性能研究及超导量子比特电路的结构探讨

发布时间：2018-01-17 17:04

本文关键词：超导JosephsonF遂道结的制备、性能研究及超导量子比特电路的结构探讨　出处：《南京大学》2015年硕士论文　论文类型：学位论文

【摘要】：目前作为实现量子计算机的物理系统有很多方案,在诸多方案中,基于Josephson结的超导体方案由于设计和制备的工艺比较成熟、与外界耦合较强、宏观量子系统比一般量子系统大1000倍等优势而备受关注。本文主要研究了超导Al/AlOx/Al隧道结的制备工艺,并通过对隧道结的超导电流密度Jc、面积面积归一化电阻Rc同氧化气压P的关系以及上、下电极的铝薄膜厚度同Rc关系的研究来改善超导隧道结的质量。整个制备工艺简单且能达到构建超导量子比特的要求,同时还制备出三种方案的超导量子比特。本论文的主要研究内容包括以下三个部分：1.超导Al/AlOX/Al隧道结的制备本文利用双层光刻胶经过紫外线曝光制备出悬空掩膜结构,然后采用电子束倾斜角度的原位制备方法制备出Al/AlOX/Al隧道结,该工艺的最大优点在于整个制备过程简单且容易控制。此外,势垒层是通过纯度为99.99%的氧气在下电极铝薄膜的表面直接氧化生成,无污染；结区的长度可以通过调节蒸发角度来控制。目前,该工艺各流程的条件比较稳定,制备出的超导Al/AlOX/Al隧道结的超导电流密度Jc已达到70A/cm2,漏电比可以控制在2%以下,均已达到构建超导量子比特的要求。2.超导Al/AlOx/Al隧道结特性研究由于Jc和能隙电压等参数均需在极低温条件下测量,测量过程周期较长、经济效益低且具有不可预判性,本文系统地研究了影响Jc和Rc的工艺条件,实验结果表明,Rc和Jc有一定的相关性,通过对Rc的测量可以预判Jc,同时在实验中通过对氧化气压P的调节来控制Rc,从而指导实验的进程。此外本论文还针对上、下电极薄膜的厚度同Rc的关系作了系统的分析,结果表明,在其他条件相同的情况下,底电极的膜厚在小于80nm范围内变化时,将显著影响Rc的大小,而上电极的膜厚与Rc关联较小。3.超导量子比特电路的结构探讨本文对三种超导量子比特电路结构的设计进行了尝试,通过在制备过程中不断改善电路的结构以及改变部分重要参数,测出比较理想的qubit信号。
[Abstract]:At present, there are many schemes for the physical system to realize quantum computer. In many schemes, the superconductor scheme based on Josephson junction is more mature in design and fabrication, and has strong coupling with the outside world. The macroscopic quantum system is one thousand times larger than the conventional quantum system, and has attracted much attention. In this paper, the fabrication process of superconducting Al/AlOx/Al tunneling junctions is studied. The relationship between the superconducting current density (Jc), area normalized resistance (RC) and oxidation pressure (P) of the tunnel junction is also discussed. In order to improve the quality of superconducting tunnel junctions, the quality of superconducting tunnel junctions is improved by the study of the relationship between the thickness of aluminum film and RC of the lower electrode. The whole preparation process is simple and can meet the requirements of constructing superconducting quantum bits. At the same time, three kinds of superconducting quantum bits have been prepared. The main contents of this thesis include the following three parts:. 1. Preparation of superconducting Al/AlOX/Al tunnel junctions in this paper, the suspended mask structure was fabricated by UV exposure of double-layer photoresist. Then the Al/AlOX/Al tunnel junctions were prepared by in situ preparation of electron beam tilt angle. The biggest advantage of this process is that the whole preparation process is simple and easy to control. The barrier layer is directly oxidized by oxygen with purity of 99.99% on the surface of the lower electrode aluminum film without pollution. The length of the junction area can be controlled by adjusting the evaporation angle. At present, the conditions of each process are relatively stable. The superconducting current density J _ c of the superconducting Al/AlOX/Al tunnel junction has reached 70 A / cm ~ 2, and the leakage ratio can be controlled below 2%. The characteristics of superconducting Al/AlOx/Al tunnel junctions have been studied because the parameters such as J _ c and gap voltage need to be measured at very low temperature and the measuring process period is longer. The technological conditions affecting JC and RC are studied systematically in this paper. The experimental results show that there is a certain correlation between RC and JC, and JC can be forecasted by the measurement of RC. In addition, the relationship between the thickness of the upper and lower electrode films and RC is analyzed systematically in this paper. Under the same conditions, when the film thickness of the bottom electrode changes in the range of less than 80 nm, the size of RC will be significantly affected. The structure of superconducting quantum bit circuit is discussed. In this paper, we try to design three kinds of superconducting quantum bit circuit structure. The ideal qubit signal is obtained by improving the circuit structure and changing some important parameters.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM26

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