激子自旋弛豫对简并量子点发射光子对纠缠度的影响

利用粒子数运动方程和量子回归理论，计算了单个半导体量子点双激子体系脉冲激发下粒子在各能级间辐射跃迁的二阶交叉相关函数以及系统发射光子对的偏振密度矩阵.分析了激子态能级简并量子点体系发射光子对偏振纠缠特性，讨论了纠缠度随激子态间自旋弛豫的变化关系.研究表明，激子自旋弛豫会破坏该系统发射光子对的纠缠度. 关键词： 纠缠光子对 半导体量子点 二阶相关函数     

半导体InAs量子点单光子发射器件

文章概述了量子点单光子源的研究现状,综述了微腔量子点耦合单光子发射器件制备中关键的低密度InAs量子点外延技术,单量子点单光子发射二阶关联函数HBT检测方法,分布布拉格反馈微腔结构的制备以及实现液氮温度下电驱动微腔量子点单光子发射器件等研究结果.     

微腔增强发射的半导体量子点单光子源

单光子源是实现量子密匙分配、线性光学量子计算的基本单元。作者回顾了单光子源在量子信息科学发展中的作用,讨论了光子的统计特性,分析了具有类似原子二能级结构的半导体量子点作为单光子发射源的特点,介绍了微腔与二能级系统的耦合以及微腔量子电动力学基本原理。在弱耦合区,Purcell效应导致微腔中量子点激子复合寿命降低,因此可用微腔来改善量子点单光子发射效率。文章总结了近年来在半导体微腔增强量子点单光子发射领域的进展,探讨了分布式布拉格反射微腔、柱状微腔和光子晶体微腔等结构对改善半导体量子点单光子发射和收集效率、光子极化以及光子全同性等方面的作用,并对未来半导体量子点单光子源的发展进行了展望。     

各向异性量子点单光子发射的高偏振度特性

研究了线偏振脉冲光场激发下,单个各向异性InGaAs量子点的高偏振光发射. 给出其偏振因子与两个正交本征态之间的交叉弛豫之间的关系式. 分析表明，交叉弛豫随激发场强度增大，并导致偏振因子随激发场入射脉冲面积减小. 关键词： 量子点 单光子发射 偏振度     

单量子点在双脉冲激发下偏振光子发射的统计特性

用产生函数(generating function)方法对单个半导体量子点系统在外加双脉冲场作用下发射偏振(x偏振和y偏振)光子的统计性质进行了研究. 研究结果表明,量子相干对单量子点系统的吸收线型、Mandel参数Q与x偏振光子和y偏振光子之间的高阶交叉关联具有显著的影响. 关键词： 量子点 三能级体系 产生函数 双脉冲     

门控下InGaAs/InP单光子探测器用于符合测量的时域滤波特性研究

基于砷化镓/磷化铟雪崩光电二极管(InGaAs/InP APD)的半导体单光子探测器因工作在通信波段,且具有体积小、成本低、操作方便等优势,在实用化量子通信技术中发挥了重要作用.为尽可能避免暗计数和后脉冲对单光子探测的影响,InGaAs/InP单光子探测器广泛采用门控技术来快速触发和淬灭雪崩效应,有效门宽通常在纳秒量级.本文研究揭示了门控下单光子探测器可测量的最大符合时间宽度受限于门控脉冲的宽度,理论分析与实验结果良好拟合.该研究表明,门控下InGaAs/InP单光子探测器用于双光子符合测量具有显著的时域滤波特性,限制了其在基于双光子时间关联测量的量子信息技术中的应用.     

基于色散位移光纤的高宣布式窄带单光子源

文章利用脉冲激光抽运色散位移光纤,通过自发四波混频过程产生的关联光子对,实验演示了一种光通讯波段的窄带宣布式单光子源. 实验测得-3 dB带宽为1.1 nm单光子场的二阶关联函数g⁽²⁾(0)=0.09±0.01,宣布效率可达0.5以上. 这种单光子源在量子通信中有潜在的应用前景. 关键词： 宣布式单光子 光纤 自发四波混频 量子通信     

基于微型光学偶极阱中单个铯原子俘获与操控的852 nm触发式单光子源

基于单原子操控的单光子源具有窄带宽、可与同类原子吸收线匹配、基本不受外界环境因素的影响等特点,在量子光学基本问题研究及量子信息处理等方面具有重要价值.本文研究了强聚焦1064 nm基模高斯光束形成的光学偶极阱中铯原子6S_(1/2)|F_g=4,mF=+4-6P_(3/2)|F_e=5,m_F=+5循环跃迁的光频移,并在实验上进行了测量.基于共振脉冲光激发俘获在远失谐微型光学偶极阱中的单个铯原子,实验演示了10 MHz重复频率的触发式852 nm单光子源.采用基于单光子探测器的Hanbry Brown-Twiss实验系统,对单光子源的二阶相干度进行了测量,零延时处符合计数值为0.09,实验显示单光子源呈现显著的光子反群聚特性.     

单光子源及在量子信息领域的应用

光量子比特是量子计算和量子通信的理想候选体系之一。高效率、高品质、确定性的单光子源是实现光学量子计算和绝对安全量子通信的重要前提条件。自组装半导体量子点,又称“人造原子”,具有优良的单光子性和光子全同性,是理想的单光子源。此外,量子点可以通过外加电场,囚禁单个原子或空穴,作为光子-自旋比特的界面,构建可扩展光量子网络。微柱腔耦合的量子点,拥有很强的Purcell效应,在保持单光子性和光子全同性的同时,大大地提高了提取效率,且具有很好的相干性,可用于大规模量子计算。近年来,人们在二维单原子层材料中发现了非经典的单光子发射,使二维材料和量子光学领域得到了结合,开辟了新的研究路线：探索单原子层材料在量子技术的潜在应用。和传统固态单光子源系统相比,二维材料更易于与其他光电平台结合,可人为控制缺陷位置,有利于推动高品质、低成本单光子源的发展,得到了科学家的广泛关注。本报告首先从量子计算和量子通信两方面提出发展单光子源的意义,接着介绍单光子源的性质和产生原理,然后介绍单光子源在自组装半导体量子点和二维单原子层材料中的实现和发展,最后从光子-自旋量子隐形传态和玻色采样实验中讨论单光子源在量子计算和量子网络方面的应用前景。     

半导体自组织量子点量子发光机理与器件

介绍了自组织量子点单光子发光机理及器件研究进展.主要内容包括：半导体液滴自催化外延GaAs纳米线中InAs量子点和GaAs量子点的单光子发光效应、自组织InAs/GaAs量子点与分布布拉格平面微腔耦合结构的单光子发光效应和器件制备,单量子点发光的共振荧光测量方法、量子点单光子参量下转换实现的纠缠光子发射、单光子的量子存储效应以及量子点单光子发光的光纤耦合输出芯片制备等.     

Cross-Polarized Single Photon Emission from Single Semiconductor Quantum Dots with V-Type Level Driven by Pulse Field

The statistic properties of photon emissions from single semiconductor quantum dots with V-type level driven by pulses are investigated theoretically. Based on quantum regression theorem and master equations, the dynamic equations of the second-order correlation function of the photon emissions are deduced. The calculated results reveal that the efficiency of single photon emissions from two orthogonal polarization eigenstates |x〉and |y〉) reaches the maximum when the input pulses area is about π, and the probability of the cross-polarized single photon emission from |x 〉 and |y 〉decreases with increasing of pulse width.     

Second-Order Correlation Function of the Photon Emission from a Single Quantum Dot

The photon correlation of photon emission from a single quantum dot with cw excitation and pulsed excitation is investigated in details. To calculate the second-order correlation function for optical pumping, we deduce rate equations with a simplified two-level model under cw excitation and present the master equation approach in the interaction picture to the study of evolution of a three-level system under pulsed excitation. In addition, we report photon correlation measurements on a single self-assembled In0.5Ga0.5As quantum dot, which show strong antibunching behaviour under both the conditions of cw and pulsed excitations. The calculated results are in agreement with the experimental measurements.     

Single-Photon Emission at Liquid Nitrogen Temperature from a Single InAs/GaAs Quantum Dot

We report on the single photon emission from single InAs/GaAs self-assembled Stranski-Krastanow quantum dots up to 80 K under pulsed and continuous wave excitations. At temperature 8OK, the second-order correlation function at zero time delay, g^（2）（0）, is measured to be 0.422 for pulsed excitation. At the same temperature under continuous wave excitation, the photon antibunching effect is observed. Thus, our experimental results demonstrate a promising potential application of self-assembled InAs/GaAs quantum dots in single photon emission at liquid nitrogen temperature.     

Nonlinear behavior of the population dynamics of three-level systems in the presence of single photon absorption

We numerically investigate the population dynamics in a single photon resonant three-level cascade and non-cascade energy level molecules at 532-nm wavelength. The time-dependent population in the energy levels in the presence of 100 ps(pico-second) and 100 ns(nano-second) laser pulses is described in the form of rate equations. We provide a brief idea of how the optical energy transfer takes place in the light-matter interaction and we also discuss the absorption as a function of pulse width and repetition rate. We also plot the z-scan transmittance curve as a function of number of excitation pulses participating in the absorption.     

Single-Photon Emission from a Single InAs Quantum Dot

Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions, whose photoluminescence intensities have linear and quadratic excitation power dependences, respectively, are identified. Under pulsed laser excitation, the zero time delay peak of second order correlation function corresponding to exciton emission is well suppressed, which is a clear evidence of single photon emission.     

Switching Dynamic Analysis for Twin-Core Fibre Coupler Using Supermode Theory

Characteristics of optical switching in a twin-core fibre coupler are numerically analysed under short pulse input by using supermode theory. The dynamic nonlinear coupled superlnode equations are derived, The numerical results show that the input pulse width determines the power transfer and the pulse temporal profile in the output ports. The optimal switching characteristics can be obtained by selecting an appropriate initial pulse width. In addition, the switching characteristic curves are insensitive to the input pulse shape for either fundamental soliton pulse or Gaussian pulse input, but sensitive to pulse sharpness. A reduced switching power and a sharper switching transition can be obtained by using the sharp super-Gaussian pulse.     

Charge-state populations for the neon-XFEL system

The interaction between neon and x-ray free-electron lasers with different laser parameters is systematically studied by solving a set of coupled rate equations. As an example, the evolution of 1s~12 s~22 p~6 configuration is given under different incident photon numbers, pulse widths, and photon energies. We have also determined all of the charge-state populations as a function of three laser pulse parameters by averaging over time. The result shows that the variations of these charge-state populations demonstrate a pattern when the pulse width is shorter than 10 fs: some of the charge-states decrease rapidly,while the others rise but remain relatively constant for pulse width larger than 10 fs. The variation of the average charge with three parameters has also obtained. The average charge decreases for a pulse width shorter than 10 fs but remains basically unchanged for a pulse width longer than 10 fs.     

Amplified spontaneous emission in dye-laser systems for single photon amplification

A longitudinally pumped dye-laser amplifier is numerically investigated for the amplification of a very low intensity signal (as low as one photon per pulse), which is easily hindered by the simultaneous amplification of spontaneous emission. From the relevant set of coupled rate equations for population and photon fluxes the spatial dependence of these quantities is accounted for. The equations are solved numerically in some significant practical situations. The results describe the dependence of the amplified-spontaneous-emission (ASE) output flux on the pumping rate, on the spectral narrowing process and on the total spontaneous emission for a pulse in the selected angular width. The performance of dye-laser amplifiers is described by the same set of equations, and the gain characteristics of such systems are analyzed as functions of the pumping rate.     

Correlated photons from multi-carrier complexes in GaAs quantum dots

We have studied micro-photoluminescence spectra of a self-assembled single GaAs quantum dot under 8 K. With strong pulsed excitation, the micro-photoluminescence spectrum shows bright emission lines originated from an exciton, a positively charged exciton, and a biexciton, together with weak lower energy emissions reflecting multi-excitonic structures with more carriers. We have identified the origins of these weak emission lines, and showed the existence of charged biexciton states, through single photon correlation measurements and excitation power dependence of the photoluminescence intensity. In addition, investigating the radiative recombination process of the charged biexciton, we have determined the electron–hole exchange energy in the GaAs quantum dot.