GaAs双量子点中电子激发和转移过程的量子最优控制

发布时间：2018-03-20 08:19

本文选题：量子最优控制　切入点：半导体量子点　出处：《山东大学》2015年硕士论文　论文类型：学位论文

【摘要】：随着量子力学理论的发展和实验技术的提高,科学家们一直希望借由各种手段控制量子系统的动力学行为,其中激光脉冲是最为有效的手段之一。自20世纪80年代以来,物理学家、化学家们利用飞秒激光脉冲和激光整形技术克服了分子内振动迟豫的困难,实现了许多过程和体系的控制,如化学键选择性的断裂和生成、分子取向、分子电流的控制、高次谐波生成等等。量子优化控制作为一套成熟的理论框架,为探究系统的能控性和设计优化脉冲提供了理论基础和指导。另一方面,社会科技的发展对计算机计算能力和速度要求越来越高,科学家们将目光转向了以量子计算为原理的量子计算机,实现量子计算的关键一步是设计量子比特(qubit)。量子点作为“人工原子”,性质与原子类似,其形状、尺寸和束缚的电子数等性质很大的可操控性和调节性。量子点在量子信息领域广受关注,它在信息处理、光源制备等方面具有重要作用。利用量子点的电子自旋或者电子转移过程实现量子比特是很有前途的方案之一。本论文采用量子最优控制理论,借由谐振子抛物线模型描述GaAs异质结构GaAs半导体双量子点的限制势,计算了一维、二维双量子点模型的基态和激发态能级结构,使用优化激光脉冲和迭代法模拟了双量子点中电子由基态跃迁至第一和第二激发态、电子由一侧量子点转移至另外一侧的过程。经过计算,我们在50～100次循环之后得到的激光脉冲可以使控制目标产率达到98%左右。通过分析脉冲和控制过程中的动力学行为,我们分析了不同脉冲参数控制效果的差异,研究了采用优化激光脉冲时体系的电子密度变化情况。采用优化激光脉冲控制量子点中的电子行为具有其它方法不具备的优势,它控制时间短,总脉冲时间尺度在皮秒范围内,远远低于量子点的退相干时间,可以保持体系的相干性以满足量子信息和计算的要求。随着近些年飞秒激光脉冲和高能激光技术的发展,我们计算得到的THz频率的脉冲形式在实验中也具备可行性,为实验中脉冲整形和设计提供了理论指导。
[Abstract]:With the development of quantum mechanics theory and the improvement of experimental technology, scientists have always wanted to control the dynamic behavior of quantum system by various means, among which laser pulse is one of the most effective methods. Physicists and chemists use femtosecond laser pulses and laser shaping techniques to overcome the difficulties of intramolecular vibration and to control many processes and systems, such as selective fracture and formation of chemical bonds, molecular orientation, Quantum optimal control, as a mature theoretical framework, provides a theoretical basis and guidance for exploring the controllability of the system and designing optimal pulses. With the development of social science and technology, the demands of computer computing ability and speed are becoming higher and higher, so scientists turn their attention to quantum computers based on the principle of quantum computing. A key step in quantum computing is the design of a quantum bit qubit.Quantum dots, as "artificial atoms," are similar in shape to atoms. The size and the number of bound electrons are very controllable and adjustable. Quantum dots are widely concerned in the field of quantum information, and they are used in information processing. The preparation of light source plays an important role. It is one of the promising schemes to realize quantum bit by using the electron spin or electron transfer process of quantum dot. In this paper, the quantum optimal control theory is adopted. By using the parabola model of harmonic oscillator to describe the confinement potential of GaAs heterostructure GaAs semiconductor double quantum dots, the ground state and excited state energy levels of one and two dimensional double quantum dot models are calculated. The process of electron transition from ground state to first and second excited state and electron transfer from one side of quantum dot to the other side in double quantum dot are simulated by using the optimized laser pulse and iterative method. The laser pulse obtained after 100 cycles can make the control target yield reach about 98%. By analyzing the dynamic behavior of the pulse and the control process, we analyze the difference of the control effect of different pulse parameters. The changes of electron density in the system with optimized laser pulses are studied. The optimized laser pulses have advantages over other methods in controlling the electron behavior in quantum dots. The control time is short and the total pulse time scale is in the picosecond range. With the development of femtosecond laser pulse and high-energy laser technology in recent years, the coherence of the system can be maintained to meet the requirements of quantum information and computation. The pulse form of the calculated THz frequency is also feasible in the experiment, which provides theoretical guidance for the pulse shaping and design in the experiment.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O471.1

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