量子点中的自旋量子比特

发布时间：2018-01-07 19:16

本文关键词：量子点中的自旋量子比特　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：半导体量子点中的自旋量子比特所具有的长相干时间以及易于集成的特点使其受到了广泛的关注。本论文致力于GaAs双量子点中自旋量子比特的研究,主要内容包括:1、简要介绍了量子计算的背景和概念。利用常相互作用模型对量子点中的一些基本现象作了解释,包括单量子点中的库伦振荡,库伦阻塞,双量子点中的三相点,偏压三角形等。2、对单电子自旋量子比特作了简单的原理分析。详细介绍了两电子自旋单态三重态量子比特的哈密顿量,以及实验细节,包括观测自旋阻塞的两种方式以及表征系统的方法,最后介绍了两个经典的实验以及我们的实验结果。3、利用双量子点的不对称性在三电子(1,2)-(2,1)电荷跃迁区域观测到了四重态的自旋阻塞。利用这种自旋阻塞我们实现了自旋四重态和两重态之间的Landau-Zener-Stuckelberg干涉和交换振荡。最后补充了我们另外两个奇数电子区(1,2)-(0,3)和(1,6)-(0,7)的实验结果。4、在偶数电子区(1,3)-(0,4)区域的交换振荡实验中发现了一种信号放大机制。分析并且实验验证该机制。设计了一种控制放大过程的方法,并利用此方法提取出不同自旋态的隧穿速率。5、对双量子点进行输运研究。在五个连续的电荷跃迁区域观察到了自旋阻塞现象。通过分析数据确定了每个区域的阻塞自旋态。本文的主要创新点有:1、首次在双量子点(1,2)-(2,1)区域观察到了自旋阻塞现象,并利用该现象实现了自旋态的读取,以及演示了相干操作。利用在此区域发展的方法,我们对其他奇数区进行了探索,并得到了类似的结果。我们的结果和实验方法将对未来探索多电子自旋量子比特编码具有启发意义。2、发现了一种新的自旋到电荷转换机制。该机制在用来读取自旋量子比特的状态时产生比传统的基于自旋阻塞的方法更强的信号。在实验中我们实现了两倍的放大。我们阐明了如何用一个简单的方案实现放大倍数的显著提升。3、首次在连续的多个电荷跃迁区域观察到自旋阻塞现象。尤其是奇数电子区自旋阻塞,结合平面双量子点强大的可控性,为研究电子自旋与核自旋相互作用提供了新的有力的工具。
[Abstract]:Spin quantum bits in semiconductor quantum dots have attracted wide attention due to their long dry time and easy integration. This thesis is devoted to the research of spin quantum bits in GaAs double quantum dots. The main contents include: 1. The background and concept of quantum computation are briefly introduced. Some basic phenomena in quantum dots are explained by using the constant interaction model, including Coulomb oscillation and Coulomb blocking in single quantum dots. In this paper, the simple principle of single-electron spin quantum bit is analyzed, and the Hamiltonian of two-electron spin triplet quantum bit is introduced in detail. And the details of the experiment, including the two ways of observing spin blocking and the method of characterizing the system. Finally, two classical experiments and our experimental results are introduced. The asymmetry of the double quantum dots is used in the three-electron system. 1). In the charge transition region, the spin blocking of the quaternary states is observed. Using this spin blocking, we have realized the Landau-Zener-Stuckelberg interference between the spin quadruple states and the double states. And exchange oscillations. Finally, we add two other odd electron regions. 1. The experimental results of 2 ~ (-0) ~ (3) and 1 ~ (1) ~ (6) ~ (~ (0) ~ (7))) are found in the even number electron region of ~ (1) ~ (3) ~ (-) ~ (0). 4) A signal amplification mechanism is found in the region switching oscillation experiment. The mechanism is analyzed and verified experimentally. A method to control the amplification process is designed. The tunneling rate of different spin states is extracted by this method. In this paper, the spin blocking phenomenon is observed in five continuous charge transition regions. The blocking spin states of each region are determined by analyzing the data. The main innovation point of this paper is: 1. Spin blocking has been observed for the first time in the region of double quantum dots (TQDs), and the reading of spin states has been realized by using this phenomenon, and the coherent operation has been demonstrated. The method developed in this region has been used. We have explored other odd regions and obtained similar results. Our results and experimental methods will be instructive for exploring multi-electron spin quantum bit coding in the future. A new spin to charge conversion mechanism is found, which produces stronger signals than the traditional spin-blocking method when used to read states from spin quantum bits. In the experiment, we achieve double amplification. We illustrate how to achieve a significant increase in magnification by 3. 3 using a simple scheme. Spin blocking is observed for the first time in successive charge transition regions, especially in odd electron regions, combined with the strong controllability of planar double quantum dots. It provides a new powerful tool for studying the interaction between electron spin and nuclear spin.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O471.1

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