Symmetry and size effects on energy and entanglement of an exciton in coupled quantum dots

We study theoretically the essential properties of an exciton in vertically coupled Gaussian quantum dots in the presence of an external magnetic field. The ground state energy of a heavy-hole exciton is split into four energy levels due to the Zeeman effect. For the symmetrical system, the entanglement entropy of the exciton state can reach a value of 1. However, for a system with broken symmetry, it is close to zero. Our results are in good agreement with previous studies.     

用两耦合非线性振子模型研究量子纠缠和相干性

我们研究两耦合非线性振子模型的量子纠缠和量子相干动力学,结果表明在适当条件下,纠缠熵与相干度是正相关的.我们也讨论纠缠熵和相干度与两振子相互作用能的联系.     

用两耦合非线性振子模型研究量子纠缠和相干性

我们研究两耦合非线性振子模型的量子纠缠和量子相干动力学, 结果表明在适当条件下, 纠缠熵与相干度是正相关的. 我们也讨论纠缠熵和相干度与两振子子相互作用能的联系.     

在两个耦合的量子点和腔QED系统中的双模激子的压缩性质(英文)

本文研究了在两个耦合的量子点和腔QED系统中的双模激子的压缩性质.讨论了不同的初始光场对双模激子的正常压缩与和压缩的影响.计算表明,当初始态光场制备在相干态时,双模激子既不存在正常压缩,也不存在和压缩,这说明双模激子振辐的两个正交分量具有相同的量子涨落;然而,当初始腔场处于压缩真空态时,无论是正常压缩还是和压缩,双模激子振辐的两个正交分量总有一个存在压缩.这意味着量子噪声能被有效的得到抑制.此外,两种情形下的最大压缩都由初始腔场的压缩因子r决定.经过比较,我们还发现双模激子的正常压缩比和压缩大.     

圆柱状量子点量子导线复合系统的激子能量和电子概率分布

建立了圆柱状量子点量子导线复合系统中激子满足的方程，用微扰论求出激子能量.以CdS/HgS/CdS/HgS/CdS圆柱状量子点量子导线复合系统为例，研究了系统中电子的概率分布和系统线度对激子能量的影响.结果表明：系统中电子、空穴以及激子的能量均随量子点高度h₀的增大而减小，电子-空穴相互作用对基态激子能量的影响要大于激发态；电子沿径向方向的概率分布呈起伏状，在轴线和表面附近的概率趋于零，而在R/2附近概率最大；在量子点附近电子沿轴向方向的概率分布呈振荡特征 关键词： 量子点 量子导线 激子 能量     

Structure formation of entanglement entropy in a system of two superconducting qubits coupled with an LC-resonator

This paper investigates theoretically the evolutions of the entanglement entropy of a system of two coupled-charge-qubits interacting with an LC-resonator.It is found that when the initial states of the two qubits are prepared in a given superposition excited state,the evolution of the von Neumann entropy of the system depends significantly on the coupling strength between the two Josephson charge qubits.With the variation of the coupling strength,the evolution of the entanglement entropy of the system forms some structures,especially the periodically bistable properties,which are the first discovered for such a system to our knowledge.It is found that the relative entropy entanglement of the system is also sensitive to the variation of the coupling strength between the two charge qubits,some novel ’collective oscillations’ of the relative entropy are found for the system.     

基于InAs单量子点的单光子干涉

利用分子束外延生长 InAs 单量子点样品,测量了温度为 5 K 时单量子点的荧光(PL)光谱.采用时间关联光子强度测量(HBT)验证了 PL 光谱具有单光子发射特性.单光子通过马赫曾德尔 (MZ) 干涉仪,验证了单光子自身具有干涉特性.测量了当 MZ 干涉仪两臂偏振方向的夹角改变时对应的单光子干涉及条纹可见度的变化. 关键词： 量子点单光子源 反群聚效应 马赫曾德尔干涉     

Binding energies of an exciton in a Gaussian potential quantum dot

In this paper, an exciton trapped by a Gaussian confining potential quantum dot has been investigated. Calculations are made by using the method of numerical diagonalization of Hamiltonian in the effective-mass approximation. The dependences of binding energies of the ground state and the first excited state on the size of the confining potential and the strength of the magnetic field are analysed explicitly.     

与腔场耦合的两个量子点中激子的纠缠动力学

利用共生纠缠度研究了单模腔场内两个耦合量子点中激子的纠缠动力学行为.结果表明:无论腔场初始制备于奇相干态还是偶相干态,两个量子点间直接耦合作用均能减弱激子的纠缠度.在腔场初始为奇相干态时,激子的纠缠度随场模强度的增加而减小;偶相干态时,激子的纠缠度呈现一个转折变化.此外,也研究了单模腔场内平均光子数与激子准最大相干纠缠态的关联.     

Optically induced phase transition of excitons in coupled quantum dots

The weak classical light excitations in many semiconductor quantum dots have been chosen as important solid- state quantum systems for processing quantum information and implementing quantum computing. For strong classical light we predict theoretically a novel phase transition as a function of magnitude of this classical light from the deformed to the normal phases in resonance ease, and the essential features of criticality such as the scaling behaviour, critical exponent and universality are also present in this paper.     

三能级原子与耦合腔相互作用系统中的纠缠特性

采用Negativity熵来度量两个子系统间的纠缠,利用数值计算方法研究了简并Λ型三能级原子和简并V型三能级原子与耦合腔共振相互作用系统中原子之间、腔场之间和原子与腔场间的纠缠特性.给出了系统初始激发数为1时系统态矢的演化公式;讨论了腔场间的耦合系数变化对纠缠特性的影响.研究结果表明:随腔场间的耦合系数增大,原子间的纠缠增强,腔场间的纠缠减弱.     

Quantum entanglement in the system of two two-level atoms interacting with a single-mode vacuum field

The entanglement properties of the system of two two-level atoms interacting with a single-mode vacuum field are explored. The quantum entanglement between two two-level atoms and a single-mode vacuum field is investigated by using the quantum reduced entropy; the quantum entanglement between two two-level atoms, and that between a single two-level atom and a single-mode vacuum field are studied in terms of the quantum relative entropy. The influences of the atomic dipole--dipole interaction on the quantum entanglement of the system are also discussed. Our results show that three entangled states of two atoms--field, atom--atom, and atom--field can be prepared via two two-level atoms interacting with a single-mode vacuum field.     

应变纤锌矿ZnO/Mg_xZn_(1-x)O柱形量子点中离子受主束缚激子的光学性质

在有效质量近似下,考虑内建电场效应,采用变分法详细研究了受限于纤锌矿Mg_xZn_(1-x)O/ZnO/Mg_xZn_(1-x)O圆柱形应变量子点中离子受主束缚激子(A~-,X)的带间光跃迁吸收系数随量子点尺寸、Mg含量和离子受主杂质中心位置的变化情况,并和离子施主束缚激子(D~+,X)及自由激子进行了比较.结果表明:随着量子点尺寸的减小,(A~-,X)的光跃迁吸收强度增强,吸收曲线向高能方向移动,出现蓝移现象.随着Mg含量增加,(A~-,X)的光跃迁吸收曲线蓝移,且吸收强度减弱.随着离子受主杂质从量子点的左界面沿材料生长方向移至量子点的右界面,光跃迁吸收曲线向低能方向移动,出现红移现象.此外,与离子施主束缚激子(D~+,X)相比,随着沿材料生长方向掺入杂质位置的变化,光跃迁吸收曲线移动的方向相反.但不管是掺入离子受主杂质还是离子施主杂质,当离子杂质从量子点的左异质界面沿材料生长方向移至右异质界面时,光跃迁吸收峰的移动量大致相同.     

Energy Spectra of Excitons Bound to a Neutral Acceptor in Quantum Dots

The energy spectra of the ground state for an exciton (X) trapped by a neutral acceptor (A⁰) in a quantum dot with a parabolic confinement have been calculated as a function of the electron-to-hole mass ratio σ by using the hyperspherical coordinates. We find that the (A⁰,X) complex confined in a quantum dot has in general a larger binding energy than those in a two-dimensional quantum well and a three-dimensional bulk semiconductor, and the binding energy decreases with the increase of the electron-to-hole mass ratio.     

Kondo transport through a quantum dot coupled with side quantum-dot structures

This paper investigates Kondo transport properties in a quadruple quantum dot (QD) based on the slave-boson mean field theory and the non-equilibrium Green’s function.In the quadruple QD structure one Kondo-type QD sandwiched between two leads is side coupled to two separate QD structures:a single-QD atom and a double-QD molecule.It shows that the conductance valleys and peaks always appear in pairs and by tuning the energy levels in three side QDs,the one-,two-,or three-valley conductance pattern can be obtained.Furthermore,it finds that whether the valley and the peak can appear is closely dependent on the specific values of the interdot couplings and the energy level difference between the two QDs in the molecule.More interestingly,an extra novel conductance peak can be produced by the coexistence of the two different kinds of side QD structures.     

Fano effect of a laterally coupled vertical triple quantum dot system

Using the nonequilibrium Green’s function technique,electron transport through a laterally coupled vertical triple quantum dot is investigated.The conductance as a function of electron energy is numerically calculated.The evolution of the conductance strongly depends on the configuration of dot levels and interdot coupling strengths.     

Visualization of space charge field effect on excitons in a GaAs quantum dot by near-field optical wavefunction mapping

Near-field photoluminescence (PL) imaging spectroscopy was used to investigate multi-exciton and charged-exciton states confined in a single GaAs interface fluctuation quantum dot. We determined the origin of peaks in the PL spectra by employing a wavefunction mapping technique. We observed distortion of the exciton wavefunction due to the electric field produced by an excess electron at a nearby confined state. Near-field wavefunction mapping was demonstrated to be a powerful tool for visualizing the local environment, which affects the emission properties of quantum dots.     

The Electron-Hole Pair in a Single Quantum Dot and That in a Vertically Coupled Quantum Dot

The energy spectra of low-lying states of an exciton in a single and a vertically coupled quantum dots arestudied under the influence of a perpendicularly applied magnetic field. Calculations are made by using the method ofnumerical diagonalization of the Hamiltonian within the effective-mass approximation. We also calculated the bindingenergy of the ground and the excited states of an exciton in a single quantum dot and that in a vertically coupledquantum dot as a function of the dot radius for different values of the distance and the magnetic field strength.     

Quantum control of two interacting electrons in a coupled quantum dot

Quantum-state engineering, i.e. active manipulation over the coherent dynamics of suitable quantum-mechanical systems, has become a fascinating prospect of modern physics. Here we discuss the dynamics of two interacting electrons in a coupled quantum dot driven by an external electric field. The results show that the two quantum dots can be used to prepare a maximally entangled Bell state by changing the strength and duration of an oscillatory electric field. Different from the suggestion made by Loss \textit et al (1998 Phys. Rev. A 57 120, the present entanglement involves the spatial degree of freedom for the two electrons. We also find that the coherent tunnelling suppression discussed by Grossmann \textit et al (1991 Phys. Rev. Lett. 67 516 persists in the two-particle case: i.e. two electrons initially localized in one dot can remain dynamically localized, although the strong Coulomb repulsion prevents them from behaving so. Surprisingly, the interaction enhances the degree of localization to a large extent compared with that in the non-interacting case. This phenomenon is referred to as the Coulomb-enhanced dynamical localization.     

The nonlinear optical properties of a magneto-exciton in a strained Ga0.2In0.sAs/GaAs quantum dot

The magnetic field-dependent heavy hole excitonic states in a strained Gao.2Ino.sAs/GaAs quantum dot are investi- gated by taking into account the anisotropy, non-parabolicity of the conduction band, and the geometrical confinement. The strained quantum dot is considered as a parabolic dot of InAs embedded in a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and the magnetic field strength is numerically measured. The interband optical transition energy as a function of geometrical confinement is computed in the presence of a mag- netic field. The magnetic field-dependent oscillator strength of interband transition under the geometrical confinement is studied. The exchange enhancements as a function of dot radius are observed for various magnetic field strengths in a strained Gao.2Ino.sAs/GaAs quantum dot. Heavy hole excitonic absorption spectra, the changes in refractive index, and the third-order susceptibility of third-order harmonic generation are investigated in the Gao.2Ino.8As/GaAs quantum dot. The result shows that the effect of magnetic field strength is more strongly dependent on the nonlinear optical property in a low-dimensional semiconductor system.