本文選題：量子最優(yōu)控制　切入點：半導(dǎo)體量子點　出處：《山東大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：隨著量子力學(xué)理論的發(fā)展和實驗技術(shù)的提高,科學(xué)家們一直希望借由各種手段控制量子系統(tǒng)的動力學(xué)行為,其中激光脈沖是最為有效的手段之一。自20世紀80年代以來,物理學(xué)家、化學(xué)家們利用飛秒激光脈沖和激光整形技術(shù)克服了分子內(nèi)振動遲豫的困難,實現(xiàn)了許多過程和體系的控制,如化學(xué)鍵選擇性的斷裂和生成、分子取向、分子電流的控制、高次諧波生成等等。量子優(yōu)化控制作為一套成熟的理論框架,為探究系統(tǒng)的能控性和設(shè)計優(yōu)化脈沖提供了理論基礎(chǔ)和指導(dǎo)。另一方面,社會科技的發(fā)展對計算機計算能力和速度要求越來越高,科學(xué)家們將目光轉(zhuǎn)向了以量子計算為原理的量子計算機,實現(xiàn)量子計算的關(guān)鍵一步是設(shè)計量子比特(qubit)。量子點作為“人工原子”,性質(zhì)與原子類似,其形狀、尺寸和束縛的電子數(shù)等性質(zhì)很大的可操控性和調(diào)節(jié)性。量子點在量子信息領(lǐng)域廣受關(guān)注,它在信息處理、光源制備等方面具有重要作用。利用量子點的電子自旋或者電子轉(zhuǎn)移過程實現(xiàn)量子比特是很有前途的方案之一。本論文采用量子最優(yōu)控制理論,借由諧振子拋物線模型描述GaAs異質(zhì)結(jié)構(gòu)GaAs半導(dǎo)體雙量子點的限制勢,計算了一維、二維雙量子點模型的基態(tài)和激發(fā)態(tài)能級結(jié)構(gòu),使用優(yōu)化激光脈沖和迭代法模擬了雙量子點中電子由基態(tài)躍遷至第一和第二激發(fā)態(tài)、電子由一側(cè)量子點轉(zhuǎn)移至另外一側(cè)的過程。經(jīng)過計算,我們在50～100次循環(huán)之后得到的激光脈沖可以使控制目標產(chǎn)率達到98%左右。通過分析脈沖和控制過程中的動力學(xué)行為,我們分析了不同脈沖參數(shù)控制效果的差異,研究了采用優(yōu)化激光脈沖時體系的電子密度變化情況。采用優(yōu)化激光脈沖控制量子點中的電子行為具有其它方法不具備的優(yōu)勢,它控制時間短,總脈沖時間尺度在皮秒范圍內(nèi),遠遠低于量子點的退相干時間,可以保持體系的相干性以滿足量子信息和計算的要求。隨著近些年飛秒激光脈沖和高能激光技術(shù)的發(fā)展,我們計算得到的THz頻率的脈沖形式在實驗中也具備可行性,為實驗中脈沖整形和設(shè)計提供了理論指導(dǎo)。
[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.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：O471.1

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本文編號：1638254