定位生长量子点的金字塔形衬底的制备

在理想情况下,单光子是由量子点单光子源发光产生的。量子点单光子发射器件的制作主要利用自组织生长方法在图形衬底上结合光学微腔结构实现。采用金字塔形衬底制备量子点可实现量子点的高定位生长,该方法易于制备和隔离单光子源量子点。利用金字塔形衬底不但可以解决多个量子点占据同一个位置的问题,而且在金字塔形衬底上制备的量子点有利于光子的发射和收集。     

基于腔QED的量子相干能量效应的研究

基于微腔系统与大量二能级原子对组成的非平衡 库相互作用的原子穿腔模型,研究了原子对携带的 量子相干信息对腔场的能量贡献。推导了原子对处于一般态(所有密度矩阵元均为非零参数 )下微腔动力 学演化主方程,并计算了腔场的稳态能量。 展示了能量本征基矢下库中原子对的量子相干 扮演了热力学资 源的角色——能够辅助微腔系统提取更多的能量。同时,分析了所有量子相干元(二能级原 子对密度矩阵 的非对角元)在能量贡献中的不同特征。本研究对设计高效率量子热机具有一定的参考价值 。     

量子点-腔系统耦合强度对非相干抽运的响应

用量子主方程理论研究了量子点-腔耦合系统。为了说明理论模型,分析了一个量子点微柱腔强耦合(SC)实验。经研究发现耦合系统在稳态时抽运产生一个新的强耦合标准,抽运可以抑制或者增强强耦合;腔发射谱双峰结构并不是强耦合的明确特征,它还依赖于非相干抽运。研究表明,强耦合经常出现变相的单峰而弱耦合(WC)出现双峰结构与系统所控制的参数值密切相关。激子抽运增加时,腔发射谱由双峰逐渐变成增宽的单峰最后变成窄的单峰;腔衰减率增加时,均为双峰结构的腔发射光谱经历了从强耦合到弱耦合的转变。量子点腔失谐系统有效耦合强度与非相干抽运密切相关。     

单光子波包与腔-量子点相互作用的动力学研究

对单光子波包与腔-量子点模型相互作用的动力学过程进行了数学推导,并通过数值模拟实现了静态量子比特与飞行光子比特之间的相互转换。结果表明：由腔-量子点系统输出到光纤的光子是一个平滑的波包;通过改变激光脉冲作用时间等系统参数,可实现量子点中的原子和光子的纠缠,在此基础上,即可实现不同量子点中原子的纠缠。研究结果对解决利用腔-量子点系统来构造量子计算机的接口、制备纠缠态以及实现受控量子门等热点问题具有积极意义。     

我国量子点单光子发射器件研究获得重要突破

中科院半导体所超晶格国家重点实验室成功实现了量子点的单光子发射：8K温度下脉冲激光激发InAs单量子点，采用HBT（Hanbury Brown—Twiss）延时复合计数光谱测试系统观察到波长950nm的单光子发射．发射速率大于10kHz。这是国内半导体量子点单光子发射器件研究的重要进展。     

不同基片对单量子点单光子荧光发射的调控

采用时间相关单光子计数原理搭建荧光寿命测量光学系统,实验验证了单量子点发射荧光的单光子性。针对石英玻片、硅片、金膜等不同基片上多处具有单光子荧光发射特性的单量子点,对其发射荧光的寿命进行了测量、对比,计算了不同基片上单量子点发射荧光的衰减速率、量子产率等与量子点到基片有效距离的相关性,解释了实验数据。此外,分析了石英玻片、硅片、金膜上单量子点发射荧光的闪烁行为,结果表明不同基片对单量子点单光子荧光的闪烁与衰减速率具有调控作用。     

量子保密通信的单光子源

光通信中采用量子保密技术,由单光子源发射光量子,加密系统进行光量子编码,单模光纤进行量子 码传输和保偏,实现了信息流的物理加密.单光子源可用双异质结LED或量子阱、量子点激光器经过强衰减得到.     

Er3+-光子强耦合-维微腔的分析与设计

用密度矩阵运动方程计算并分析微腔中原子-光子强耦合的特性，得出一维原子-光子强耦合微腔的临界条件。通过分析Er^3 -光子强耦合-维微腔的掺杂浓度和腔长等参数所应满足的条件，给出实现Er^3 -光子强耦合的-维微腔的设计方法。     

量子保密通信的单光子源

光通信中采用量子保密技术，由单光子源发射光量子，加密系统进行光量子编码，单模光纤进行量子码传输和保偏，实现了信息流的物理加密．单光子源可用双异质结LED或量子阱、量子点激光器经过强衰减得到．     

量子阱垂直腔面发射激光器及其微腔物理

根据发展历史的顺序,对量子阱垂直腔面发射激光器微腔物理进行了概述,其中包括垂直腔面发射激光器、腔量子电动力学和半导体微腔物理。给出半导体垂直腔面发射激光器及其微腔物理思想来源的详细图像。     

Subminiature emitters based on a single (111) In(Ga)As quantum dot and hybrid microcavity

The results of numerical modeling and investigation of a hybrid microcavity based on a semiconductor Bragg reflector and a microlens selectively positioned above a single (111) In(Ga)As quantum dot are presented. Emitters based on the hybrid microcavity demonstrate the effective pumping of a single quantum dot and high emission output efficiency. The microcavity design can be used to implement emitters of polarization- entangled photon pairs based on single semiconductor quantum dots.     

Simulation of the spectroscopic response and electron dynamics in a double quantum dot

We present the results of the numerical simulation of the dependence of the absorption spectrum of a single-electron semiconductor double quantum dot placed in a microcavity on structural parameters and the time dependence of populations of quantum dot states. The investigated physical system can be used for quantum information coding and processing. Initialization and one-qubit operations correspond to the redistribution of populations of localized states of a quantum dot under the action of laser and cavity optical fields.     

Generation and Concentration of Terahertz Radiation in a Microcavity with an Open Quantum Dot

A scheme to generate terahertz radiation by an array of quantum dots localized at the center of a semiconducting heterostructure is developed. Electrons are injected into the active part due to the source and drain Fermi energy difference induced by a dc electric field. The structure is placed inside a microcavity stimulating the electronic transition in the quantum dots accompanied by the emission of a photon to the cavity mode. This process is optimized using the filters formed by the quantum wells, which facilitate the electron density concentration in a quantum dot. The electromagnetic field radiated by the cavity in the waveguide can be used for a local effect on the charge qubits. The parameters of such a source depend on the working characteristics of the quantum dots and cavity.     

Electric-field sensor based on a double quantum dot in a microcavity

A scheme for an optical quantum external-electric-field sensor based on a double quantum dot placed in a high-Q semiconductor microcavity is proposed. A model of the dynamic processes occurring in this system is developed, its spectral characteristics are investigated, and the noise stability of the sensor is examined. It is demonstrated that, owing to design features, the device has a number of advantages, including high sensitivity, the presence of different excitation and measurement channels, and the possibility of accurate determination of the spatial field distribution.     

Photon properties of light in semiconductor microcavities

Properties of atom-like emitters in cavities are successfully described by cavity quantum electrodynamics(cavity-QED).In this work,we focus on the issue of the steady-state and spectral properties of the light emitted by a driven microcavity containing a quantum well (QW) with the excitonic interactions using simulation of fully quantum-mechanical treatment.The system is coherently pumped with laser,and it is found that depending on the relative values of pumping rate of stimulated emission,either one or two peaks close to the excitation energy of the QW or to the natural frequency of the cavity are shown in the emission spectrum.Furthermore,the nonclassical proprieties of the emitted photon have been investigated.This excitonic system presents several dynamical and statistical similarities to the atomic system,in particular for the bad-cavity and good-cavity limits.The results show that the photon emission can be significantly amplified due to the coupling strength between a single emitter and radiation field in the microcavity,and it is concluded that the present semiconductor microcavity system may serve as a QW laser with low threshold.     

Light-emitting tunneling nanostructures based on quantum dots in a Si and GaAs matrix

InGaAs/GaAs and Ge/Si light-emitting heterostructures with active regions consisting of a system of different-size nanoobjects, i.e., quantum dot layers, quantum wells, and a tunneling barrier are studied. The exchange of carriers preceding their radiative recombination is considered in the context of the tunneling interaction of nanoobjects. For the quantum well-InGaAs quantum dot layer system, an exciton tunneling mechanism is established. In such structures with a barrier thinner than 6 nm, anomalously fast carrier (exciton) transfer from the quantum well is observed. The role of the above-barrier resonance of states, which provides “instantaneous” injection into quantum dots, is considered. In Ge/Si structures, Ge quantum dots with heights comparable to the Ge/Si interface broadening are fabricated. The strong luminescence at a wavelength of 1.55 μm in such structures is explained not only by the high island-array density. The model is based on (i) an increase in the exciton oscillator strength due to the tunnel penetration of electrons into the quantum dot core at low temperatures (T < 60 K) and (ii) a redistribution of electronic states in the Δ₂-Δ₄ subbands as the temperature is increased to room temperature. Light-emitting diodes are fabricated based on both types of studied structures. Configuration versions of the active region are tested. It is shown that selective pumping of the injector and the tunnel transfer of “cold” carriers (excitons) are more efficient than their direct trapping by the nanoemitter.     

Controllable growth of GeSi nanostructures by molecular beam epitaxy

We present an overview on the recent progress achieved on the controllable growth of diverse GeSi alloy nanostructures by molecular beam epitaxy. Prevailing theories for controlled growth of Ge nanostructures on patterned as well as inclined Si surfaces are outlined firstly, followed by reviews on the preferential growth of Ge nanoislands on patterned Si substrates, Ge nanowires and high density nanoislands grown on inclined Si surfaces, and the readily tunable Ge nanostructures on Si nanopillars. Ge nanostructures with controlled geometries, spatial distributions and densities, including two-dimensional ordered nanoislands, three-dimensional ordered quantum dot crystals, ordered nanorings, coupled quantum dot molecules, ordered nanowires and nanopillar alloys, are discussed in detail. A single Ge quantum dot-photonic crystal microcavity coupled optical emission device demonstration fabricated by using the preferentially grown Ge nanoisland technique is also introduced. Finally, we summarize the current technology status with a look at the future development trends and application challenges for controllable growth of Ge nanostructures.     

抛物量子点中的二能级体系

采用Pekar类型的变分方法,在抛物量子点中电子与体纵光学声子（LO）强耦合的条件下,得出了电子的基态,第一激发态的能量及相应的波函数。讨论了电子-声子耦合强度,量子点受限长度对电子在基态∣0〉, 激发态∣1〉,叠加态时的概率密度分布的影响。结果显示叠加态时的概率密度随着电子-声子耦合强度的增加而增大,随着量子点受限长度的减小而增大。该结果对以量子点制备量子比特有重要的指导意义。     

Soft‐Lithographed Up‐Converted Distributed Feedback Visible Lasers Based on CdSe–CdZnS–ZnS Quantum Dots

The development of a solution‐deposited up‐converted distributed feedback laser prototype is presented. It employs a sol–gel silica/germania soft‐lithographed microcavity and CdSe–CdZnS–ZnS quantum dot/sol–gel zirconia composites as optical gain material. Characterization of the linear and nonlinear optical properties of quantum dots establishes their high absorption cross‐sections in the one‐ and two‐ photon absorption regimes to be 1 × 10^?14 cm² and 5 × 10⁴ GM, respectively. In addition, ultrafast transient absorption dynamics measurements of the graded seal quantum dots reveal that the Auger recombination lifetime is 220 ps, a value two times higher than that of the corresponding CdSe core. These factors enable the use of such quantum dots as optically pumped gain media, operating in the one‐ and two‐photon absorption regime. The incorporation of CdSe–CdZnS–ZnS quantum dots within a zirconia host matrix affords a quantum‐dot ink that can be directly deposited on our soft‐lithographed distributed feedback grating to form an all‐solution‐processed microcavity laser.     

Obtaining high efficiency at low power using a quantum-dotmicrocavity light-emitting diode

Efficiencies are calculated for quantum-dot apertured-microcavity light-emitting diodes. Although the maximum efficiency depends strongly on the quantum-dot inhomogeneous broadening, greater than 20% efficiency is calculated for a small-sized apertured microcavity, even for an inhomogeneous linewidth as large as 30 meV. The efficiency can be increased to 40% if the inhomogeneous linewidth is reduced to 10 meV and to more than 60% if the inhomogeneous linewidth is eliminated to leave a homogeneous linewidth of 6.6 meV. The maximum output powers are ~40 nW, although a microarray can increase this value. For the case of a single quantum dot, an efficiency >80% is estimated for a submicron apertured-microcavity, with a maximum output power of ~3 nW