Correlation and Entanglement in Elliptically Deformed Two-Electron Quantum Dots

We study quantum correlation in a two-dimensional system of two Coulombically interacting electrons trapped in an anisotropic harmonic potential in dependence on the interaction strength. The linear entropy and von Neumann entropy that measure the entanglement between the electrons are compared with the correlation energy and the statistical correlation coefficient. We observe that the entanglement properties are dramatically influenced by the anisotropy of the confining potential.     

Ground State of a Two-Electron Quantum Dot with a Gaussian Confining Potential

We investigate the ground-state properties of a two-dimensional two-electron quantum dot with a Gaussian confining potential under the influence of perpendicular homogeneous magnetic field. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. A ground-state behaviour （singlet→triplet state transitions） as a function of the strength of a magnetic field has been found. It is found that the dot radius R of the Gaussian potential is important for the ground-state transition and the feature of ground-state for the Gaussian potential quantum dot （QD）, and the parabolic potential QDs are similar when R is larger. The larger the quantum dot radius, the smaller the magnetic field for the singlet-triplet transition of the ground-state of two interacting electrons in the Gaussian quantum dot.     

介电限域效应对PbSe量子点禁带宽度计算的影响研究

考虑了PbSe量子点介电限域效应对激子的影响,引入了修正因子,提出了一种新的量子点禁带宽度的计算模型．与实验数据比较,两者具有良好的一致性．尤其是在小尺寸量子点的情况下,修正后的模型与实验值表现出更好的一致性．通过调整受限势垒的大小,分析不同溶剂条件下PbSe禁带宽度的计算模型,说明采用的修正模型对溶剂的变化是不敏感的,与实验的结论是一致的.     

Nodal Quantum Numbers for Two-Electron States in Solids

The problem of construction and physical labelling of singlet and triplet zero total momentum two-electron states in solids is considered. It is shown that the wavefunctions belonging to repeating multi-dimensional irreducible representations can be labelled making use of theorem of induction transitivity. The intermediate group in this classification can be chosen depending on experimental nodal structure of superconducting order parameter. The application of the results to unconventional superconductors is discussed.     

Efimov Resonances in Ultracold Quantum Gases

Ultracold atomic gases have developed into prime systems for experimental studies of Efimov three-body physics and related few-body phenomena, which occur in the universal regime of resonant interactions. In the last few years, many important breakthroughs have been achieved, confirming basic predictions of universal few-body theory and deepening our understanding of such systems. We review the basic ideas along with the fast experimental developments of the field, focussing on ultracold cesium gases as a well-investigated model system. Triatomic Efimov resonances, atom-dimer Efimov resonances, and related four-body resonances are discussed as central observables. We also present some new observations of such resonances, supporting and complementing the set of available data.     

Charged-Exciton Complexes in Quantum Dots

It is known experimentally that stable charged-exciton complexes can exist in low-dimensional semiconductor nanostructures. Much less is known about the properties of such charged-exciton complexes since three-body problems are very difficult to be solved, even numerically. Here we introduce the correlated hyperspherical harmonics as basis functions to solve the hyperangular equation for negatively and positively charged excitons (trions) in a harmonic quantum dot. By using this method, we have calculated the energy spectra of the low-lying states of a charged exciton as a function of the radius of quantum dot. Based on symmetry analysis, the level crossover as the dot radius increases can be fully explained as the results of symmetry constraint.``     

上转换发光量子点

光子上转换是一种重要的非线性反斯托克斯发光现象,在激光、显示、光伏、信息安全以及生物成像与诊疗等领域具有应用前景.与研究较多的有机分子三重态-三重态湮灭和稀土掺杂纳米颗粒上转换发光材料相比,上转换量子点可以在宽光谱激发范围内实现上转换发光,具有频谱吸收宽、发光效率高、近红外可吸收、能带可调、尺寸小以及稳定性高等特点,引...     

Electron Spins in Quantum Dots as Quantum Bits

The creation, coherent manipulation, and measurement of spins in nanostructures open up completely new possibilities for electronics and information processing, among them quantum computing and quantum communication. We review our theoretical proposal for using electron spins in quantum dots as quantum bits, explaining why this scheme satisfies all the essential requirements for quantum computing. We include a discussion of the recent measurements of surprisingly long spin coherence times in semiconductors. Quantum gate mechanisms in laterally and vertically tunnel-coupled quantum dots and methods for single-spin measurements are introduced. We discuss detection and transport of electronic EPR pairs in normal and superconducting systems.     

Charged-Exciton Complexes in Quantum Dots

It is known experimentally that stable charged-exciton complexes can exist in low-dimensional semiconductor nanostructures. Much less is known about the properties of such charged-exciton complexes since three-body problems are very difficult to be solved, even numerically. Here we introduce the correlated hyperspherical harmonics as basis functions to solve the hyperangular equation for negatively and positively charged excitons (trions) in a harmonic quantum dot. By using this method, we have calculated the energy spectra of the low-lying states of a charged exciton as a function of the radius of quantum dot. Based on symmetry analysis, the level crossover as the dot radius increases can be fully explained as the results of symmetry constraint.     

Stark Splitting of the Energy Spectrum in a Two-Electron Quantum Dot

A two-electron quantum dot model assuming the existence of the image charge is formulated in the present paper. Based on this model, the effective electron confinement potential is calculated by the self-consistent method. It is established that the electron confinement potential in the quantum dot has both symmetric and antisymmetric parts. An analysis of this potential demonstrates that the tunnel electron transition in the quantum dot can occur only in the direction perpendicular to the film plane. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 9–20, May, 2005.     

Feshbach共振下BCS-BEC渡越量子分析

考虑一个涵盖分子间相互作用的多体模型,给出一种半解析计算模型中费米原子对转化成玻色分子转化率的有效方法.这种方法主要使用独立交叉近似,并在平均场理论下推导出一个精确计算转化率的解析公式.对比分析证明,该解析公式的计算结果得到多体模型的数值分析的支持,并与Rice小组的⁶Li实验能够很好的吻合.     

On Exciton Decoherence in Quantum Dots

The effects resulting due to dressing of an exciton with phonons are analyzed as the source of unavoidable decoherence of orbital degrees of freedom in quantum dots. The dressing with longitudinal optical phonons results in energetic shift of order of a few meV even of the ground state of exciton in a state-of-the-art InAs/GaAs dot and the mediating role of longitudinal acoustical phonons is essential in this process. The characteristic time needed for dressing of the exciton with optical phonons is of a picosecond order. That time can be regarded as the lower limit for decoherence for optically driven quantum gates employing self-assembled quantum dot structures.     

g-Factor Calculation in Small Quantum Dots

It is shown that the effective Lande splitting factor or g-factor of electrons localized on heterostructures such as small quantum dots is always formed as a difference of two values. The first of themrelates to thematerial of the dot itself and critically depends on its sizes and shape; the second one relates to the barriermaterial (surrounding matrix); therewith, the dependence on the latter does not disappear at any dot sizes. The known (k, p) Kane theory defining the renormalization of electron mass and g-factor in bulk semiconductors, is modified for small quantum dots with “incomplete” band structure. Specific calculations of the electron ground state energy and g-factor are performed for the covariant InAs/AlSb heterostructure not localizing holes and, hence, capable of forming pure one-electron states (prototypes of solid-state qubits).     

利用AAO模板制备银量子点

阳极氧化铝模板(Anodic Aluminum oxide,AAO)是一种具有纳米孔径的透明模板,其孔径在5-200nm范围内可控,孔径大小一致并且分布高度有序。利用阳极氧化铝模板制备量子点具有简单易行,能大规模生产的特点,同时能制备出尺寸大小可控的高度有序的量子点阵,这是其它方法很难做到的,有利于纳米材料及纳米器件的研究与合成。     

Versatile Graphene Quantum Dots with Tunable Nitrogen Doping

This paper reports a facile fabrication of N‐doped graphene quantum dots (N‐GQDs) showing controllable chemical properties through a hydrothermal treatment. The N‐GQDs have a uniform size of 3.06 ± 0.78 nm and prefer the equilibrium shapes of circle and ellipse due to the minimization of edge free energy. The N/C atomic ratio in N‐GQDs can be precisely tailored in a range from 8.3 at% to 15.8 at% by simply controlling the concentration of N source (ammonium hydroxide). One order of magnitude quantum yield of 34.5% is achieved by N‐GQDs, compared with the N‐free GQDs, as the substitutional N has an essential role in more effective radiative emission. Excessive N dopants in N‐GQDs can lead to photoluminescence quenching, through nonradiative transition back to the ground state. The N‐GQDs are further found to be suitable as photocurrent conversion materials due to benign energy matching with anatase nanofibers, the ultrafast electron injection at their interface, and efficient electron transfer. This work provides an efficient and inspiring approach to engineering both chemical components and physical properties of N‐GQDs, and will therefore promote their basic research and applications in energy conversion.