Amplifying quantum signals with the single-electron transistor

Transistors have continuously reduced in size and increased in switching speed since their invention in 1947. The exponential pace of transistor evolution has led to a revolution in information acquisition, processing and communication technologies. And reigning over most digital applications is a single device structure--the field-effect transistor (FET). But as device dimensions approach the nanometre scale, quantum effects become increasingly important for device operation, and conceptually new transistor structures may need to be adopted. A notable example of such a structure is the single-electron transistor, or SET. Although it is unlikely that SETs will replace FETs in conventional electronics, they should prove useful in ultra-low-noise analog applications. Moreover, because it is not affected by the same technological limitations as the FET, the SET can approach closely the quantum limit of sensitivity. It might also be a useful read-out device for a solid-state quantum computer.     

Slow light between two absorbing resonance in asymmetry double quantum dots

We demonstrate the slow light in double quantum dots (QDs) resonance dispersion material in theory. The slow factor, absorption, and bandwidth are greatly influenced by the energy difference of the two resonance energy. The bandwidth of this system is up to 60 GHz. The 20 ps input signal pulse is delayed by 180 ps (group index of approximately 55) relative to free-space propagation with little broadening in 1 mm dispersion material for the optical communication wavelength. The signal pulse delay can be tuned by the pump pulse.     

Fluorescent immunosensor based on fluorescence resonance energy transfer between CdSe/ZnS quantum dots and Au nanorods for PRRSV detection

An ultrasensitive and selective sandwich-type fluorescent immunosensor based on fluorescence resonance energy transfer (FRET) between CdSe/ZnS quantum dots (QDs) and Au nanorods (AuNRs) was developed for the rapid detection of porcine reproductive and respiratory syndrome virus (PRRSV). Modified CdSe/ZnS QDs and AuNRs were bioconjugated with primary antibodies M and GP5, respectively. When the target antigen was present, a well-known sandwich-type form CdSe/ZnS QDs-M antibody-antigen-GP5 antibody-AuNRs was produced, and thus reducing the distance between the QDs and NRs. As a result, FRET occurred and the fluorescence intensity of CdSe/ZnS QDs decreased, and this decrease was used to determine the antigen concentration. Ultrasensitive detection of PRRSV at low concentrations in swine serum was achieved with a limit of detection of 0.55 TCID₅₀/mL and a linear detection range of 10¹–3.5 ?× ?10⁴ TCID₅₀/mL. Therefore, the fluorescent immunosensor is selective and highly sensitive; specifically, it can detect PRRSV at low concentrations in swine serum over a large concentration range. This proposed detection method can facilitate the development of high-performance fluorescent immunosensors for the detection of PRRSV and other antigens.     

Supercurrent reversal in quantum dots

When two superconductors are electrically connected by a weak link--such as a tunnel barrier--a zero-resistance supercurrent can flow. This supercurrent is carried by Cooper pairs of electrons with a combined charge of twice the elementary charge, e. The 2e charge quantum is clearly visible in the height of voltage steps in Josephson junctions under microwave irradiation, and in the magnetic flux periodicity of h/2e (where h is Planck's constant) in superconducting quantum interference devices. Here we study supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Owing to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This nevertheless can yield a supercurrent when subsequent tunnel events are coherent. These quantum coherent tunnelling processes can result in either a positive or a negative supercurrent, that is, in a normal or a pi-junction, respectively. We demonstrate that the supercurrent reverses sign by adding a single electron spin to the quantum dot. When excited states of the quantum dot are involved in transport, the supercurrent sign also depends on the character of the orbital wavefunctions.     

Synthesis of CdSe quantum dots

Water-soluble CdSe quantum dots（QDs） were synthesized in aqueous solution with thioglycollic acid as stabilizer.CdSe QDswere characterized using Transmission electron microscopy（TEM）,UV-Vis absorption spectrum（UV-Vis） and fluorescence spectra（FL）.The characterization results indicate that as-synthesized CdSe QD was uniform at about 3.5 nm.     

自组织生长Ge量子点材料研究

利用超高真空化学气相淀积设备在Si衬底上生长Ge量子点.通过3因素3水平的正交实验,研究不同的生长参数(衬底温度、GeH4气体流量、生长时间)对Ge量子点生长的影响,从而得到优化的Ge量子点生长参数.透射电镜、X射线双晶衍射测试结果表明,利用优化的生长参数得到的多层Ge量子点材料,具有较好的晶体质量.     

基于半导体量子点的量子通信

光子源和纠缠光子对的制备是量子信息产生和传输过程的源头,是实现量子通信的重要前提条件.半导体量子点固体系统具有可集成性和可扩展性的优点,并且与现有的半导体光电子学技术密切相关,近年来在单光子源和纠缠光子对制备方面取得了重要的进展,是未来全固态量子通信的重要元器件.从量子通信的基本原理出发,阐述了制备单光子源和纠缠光子对的重要性,介绍如何解析推导出圆形常规半导体量子点中的电子结构,描述了圆形拓扑绝缘体量子点中边缘态具有双重简并的电子结构,能级间隔与量子点的具体形状无关,并且具有自旋轨道锁定的特性,总结了实验和理论上在利用这一独特的电子结构制备单光子源和纠缠光子对方面取得的重要进展.     

Quantum computation on gate-defined semiconductor quantum dots

During the past few years, researchers have made significant progress on quantum information processing in gate controlled semiconductor quantum dots. We review the global research efforts, including works by our group, which provides pathways towards applications in quantum computation.     

平行双量点中的Fano-Kondo

通过么正变换得到了平行双量子点有间库仑作用时的Fano—Anderson哈密顿量,并用格林函数运动方程的方法济南市出了与实验观测量密切相关的推迟和量子分布格林函数。借助于新得到的哈密顿量和格林函数,可以研究Kondo和Fano共振的关联效应。     

T型双量子点自旋二极管

用非平衡格林函数理论研究T型耦合的双量子点中自旋二极管效应。量子点与两个电子库或引线相耦合,其中的一个是正常金属,另一个为铁磁材料。由于两个引线铁磁性的不对称,流过系统的电荷流或者点中的电子占据数会在一定情况下出现二极管效应,即在正向电压时电流或占据数的自旋极化有极小值,当电压反向时,其自旋极化有极大值。这种自旋二极管效应与通常电子器件中的电荷二极管现象非常相似,在自旋电子学器件中有实际的应用价值。     

量子点半导体光放大器的自发辐射特性研究

从导带、价带和浸润层的能级跃迁出发,采用分段模型对量子点半导体光放大器的增益和自发辐射进行了数值研究．物理模型包括自发辐射行波方程和各能级栽流子与光子数速率方程．经过大量数值计算,得到基态电子占用概率随注入光脉冲的变化,以及增益动态过程（饱和与恢复）和输出光脉冲的时域波形畸变．进一步研究了量子点光放大器自发辐射谱和增益平坦性,结果表明自发辐射功率随输入信号功率增大而减小,引入合适的钳制光,可在20nm带宽内获得小于0．3dB的增益平坦度,或者40nm带宽内小于1．0dB．     

水溶性硅包CdTe量子点的合成方法研究

本研究成功地合成了水溶性CdTe量子点(QDs).考察温度对回流时间、荧光强度及粒径大小等因素的影响,实验优化合成条件之后确定最佳反应温度为105 ℃.接着,本研究运用改进后的Stober法更为简易地合成了硅包CdTe量子点复合微球,该微球的粒径可通过改变正硅酸乙酯及水的含量控制在160~260 nm之间,同时根据复合微粒的电镜拍摄图初步探讨了SiO₂在CdTe表面的生长模式.为了将来能运用到生物检测中,此实验加入3-氨基丙基三乙氧基硅烷（APTS）,引入氨基团,并优化了 APTS 加入时间,得到的粒子表面氨基含量最高.这种复合微粒具有与原来量子点相当的量子产率,同时具有良好的水溶性、胶体稳定性、化学反应性,为量子点作为荧光标记物的应用打下了基础.     

拓扑绝缘体量子点中的磁交换相互作用

从理论上研究了拓扑绝缘体量子点中的磁交换相互作用.在拓扑绝缘体量子点中,边缘态电子数可以通过量子点的尺寸和外加电场进行调控.当量子点中掺入单个磁离子并且边缘态填充奇数电子时,电子与单个磁离子之间的交换相互作用达到最大值;而边缘态填充偶数电子时,电子与单个磁离子之间的交换相互作用消失.当量子点中掺入2个磁离子时,电子与Mn离子的sp-d相互作用会出现奇偶振荡行为,Mn离子间的相互作用取决于Mn离子间距和量子点壳层中的电子数,表现出典型的Ruderman-Kittel-Kasuya-Yosida型间接交换机制.工作澄清了拓扑绝缘体量子点壳层结构对其磁性的影响,有助于人们设计基于拓扑绝缘体量子点的自旋电子学或量子信息器件.     

双层量子点中的带负电荷激子

利用精确对角化方法,研究了抛物势双层量子点中带负电荷激子的1S态和3P态的关联能与量子点的束缚势大小的变化关系,以及1S态对应几个不同的量子点间点与点的距离的束缚能随束缚势大小的变化关系,计算了电子与空穴质量比为σ=0.677和σ=0.197的缚能随束缚势大小的变化关系.     

Kondo effect in quantum dots and molecular devices

Kondo effect is a very important many-body phenomenon in condensed mailer physics, which explains why the resistance increases as the temperature is lowered （usually 〈10 K） in dilute magnetic alloy, and why the conductance increases as temperature is decreased in quantum dots. This paper simply introduces equilihrium and nonequilibrium Kondo effects in quantum dots together with the Kondo effect in quantum dots with even number of electrons （when the singlet and triplet states are degenerate）. Furthermore, Kondn effect in single aton/molecular transistorss is introduced, which indicates a new way in study Kondo effect.     

ZnO量子点的制备及其条件优化

利用溶胶-凝胶法在乙醇溶液中制备出ZnO量子点。通过紫外-可见吸收光谱(UV-Vis)和荧光光谱对合成量子点的合成条件(反应温度、反应时间、摩尔比)进行了优化。结果表明,在反应温度为40℃、反应时间为1 h、Zn Ac2与Li OH的物质的质量比为1∶2时,得到的ZnO量子点的发光性能最佳,此时能产生明亮的黄绿色荧光。     

PbSe量子点合成路线的探讨

分别采用超声、TOP和NaBH4等三种方法对PbSe量子点的合成路线进行了实验探讨,用IR、XRD、粒度分析和荧光倒置显微技术对三种合成方法制备得到的量子点进行了表征,总结了各种合成方法的操作要点。     

纳米标记材料荧光碳点的制备

以葡萄糖为碳源,以聚乙二醇(PEG)为分散剂和表面修饰剂,采用微波法和水热法2种加热方法,探索了水溶性荧光纳米碳量子点(Carbon Quantum Dots,CQDs)的制备;探讨了碳量子点制备过程中反应温度、反应时间、PEG/葡萄糖摩尔比和p H值对碳量子点荧光性能的影响.实验结果表明,微波法合成碳量子点的影响因素的排列顺序为:反应时间反应物摩尔比反应温度,反应时间为2.5 min、摩尔比n(PEG-200):n(葡萄糖)=6∶1、反应温度为180℃,p H=9为微波法合成荧光碳量子点的最优条件,并在此优化条件下,对微波法和水热法制备的碳量子点的光学性质进行了初步比较,结果显示,水热法制备的荧光碳量子点性能略优于微波法,这2种方法制备的荧光碳量子点都具有较好的荧光性能,均能用于荧光标记领域.     

量子点中电子态的能谱结构

本文研究二维三电子系统的能谱随禁闭势变化的特征，发现禁闭势很强时，能谱成为独立粒子运动谱。当禁闭势较弱时，电子之间的强关联导致了魔角动量的出现，而系统的结构主要由内禀节面决定。