InGaAsSb/AlGaAsSb长波长多量子阱激光器有源区的优化设计

系统地研究了波长为2.7μm的InGaAsSb/AlGaAsSb多量子阱激光器中有源区的优化设计.分别用含应变势的6带KP模型和抛物带模型计算价带和导带的能带结构，并得到薛定谔方程和泊松方程的自洽解，由此计算量子阱在载流子注入时的增益谱.研究表明制约量子阱增益的主要因素不是跃迁矩阵元，而是粒子数反转程度，尤其是空穴填充HH1子带的概率.增加压应变或减小阱宽都会提高量子阱增益.前者降低了价带HH1子带空穴的平面内有效质量；后者拉大了价带子带间距，尽管它同时略微增加了空穴有效质量.这两种因素都导致价带顶空穴态     

Bose-Einstein condensation in interacting gases

We study the occurrence of a Bose-Einstein transition in a dilute gas with repulsive interactions, starting from temperatures above the transition temperature. The formalism, based on the use of Ursell operators, allows us to evaluate the one-particle density operator with more flexibility than in mean-field theories, since it does not necessarily coincide with that of an ideal gas with adjustable parameters (chemical potential, etc.). In a first step, a simple approximation is used (Ursell-Dyson approximation), which allow us to recover results which are similar to those of the usual mean-field theories. In a second step, a more precise treatment of the correlations and velocity dependence of the populations in the system is elaborated. This introduces new physical effects, such as a change of the velocity profile just above the transition: the proportion of atoms with low velocities is higher than in an ideal gas. A consequence of this distortion is an increase of the critical temperature (at constant density) of the Bose gas, in agreement with those of recent path integral Monte-Carlo calculations for hard spheres. Received 13 November 1998     

量子非破坏性测量

介绍了量子光学中的量子非破坏性（QND）测量,并列举了两个实例,指出QND测量是很重要的。     

非均匀外磁场下海森堡自旋链的热纠缠

研究了两量子比特海森堡XXX自旋链处于x方向的非均匀磁场时系统的纠缠特性,并用负度N来度量.得到N的解析表达式,并在此基础上进行数值计算.仔细讨论了均匀磁场B、非均匀磁场b、温度T和自旋耦合系数J对纠缠度N的影响.结果表明:N会随着■和T的增大而减小,但会随着J的增大而增大.同时,增大的J和b还会使临界磁场■和临界温度T_th变大,从而使系统中热纠缠存在的磁场范围和温度范围都变大.这一点在较大磁场和较高温度下需要纠缠具有实际意义.由此,我们可以通过调节B、b、T和J来控制热纠缠,这对固态系统中通过构建和选择参数调整系统的纠缠度具有一定的作用和意义.     

Quantum entanglement generation on magnons assisted with microwave cavities coupled to a superconducting qubit

We present protocols to generate quantum entanglement on nonlocal magnons in hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled to respective microwave cavities in resonant way, and the SC qubit is placed at the center of the cavities, which interacts with the cavities simultaneously. By exchanging the virtual photon, the cavities can indirectly interact in the far-detuning regime. Detailed protocols are presented to establish entanglement for two, three and arbitrary N magnons with reasonable fidelities.     

太赫兹量子级联激光器研究进展

太赫兹技术涉及电磁学、光电子学、半导体物理学、材料科学以及微加工技术等多个学科,它在信息科学、生物学、医学、天文学、环境科学等领域有重要的应用价值.太赫兹辐射源是太赫兹频段应用的关键器件.本文简要介绍了太赫兹电磁波的研究背景、重要特点以及潜在应用,重点讨论了太赫兹半导体量子级联激光器的工作原理和研究进展等.     

Quantum Correlations in Infinite XY Spin-1/2 Chains and Quantum Phase Transition

We examine the ability of quantum discord (QD) and entanglements (concurrence, EoF and negativity) to detect the critical points associated to quantum phase transitions (QPTs) for XY models, i.e., the isotropic XY model with three-spin interactions at zero temperature, and the anisotropic XY model in a transverse magnetic field h at finite temperatures. For the case of zero temperature, we found that both entanglements and QD can spotlight the critical points of QPTs for these two models. Moreover, QD versus distance M exhibits the long-range behavior of quantum correlation for the anisotropic XY model, while entanglement is short-ranged. For the case of finite temperatures, we found that negativity has the same behaviors with concurrence at or near transition points. Moreover, QD for the anisotropic XY model can increase with temperature even in the absence of a magnetic field.     

High sensitivity Hall devices with AlSb/InAs quantum well structures

AlSb/InAs quantum well (QW) structures and InAs films on GaAs (001) substrates were grown by molecular beam epitaxy (MBE). We investigated the dependence of electron mobility and two-dimensional electron gas (2DEG) concentration on the thickness of an InAs channel. It is found that electron mobility as high as 19050 cm2·V-1·s-1 has been achieved for an InAs channel of 22.5 nm. The Hall devices with high sensitivity and good temperature stability were fabricated based on the AlSb/InAs QW structures. Their sensitivity is markedly superior to Hall devices of InAs films.     

不同周期数的GaInAs/GaAsP多量子阱太阳能电池

为了研究不同量子阱周期数下GaInAs/GaAsP多量子阱太阳能电池性能的变化规律,利用金属有机化学气相沉积技术(MOCVD)制备了不同周期数的双结多量子阱太阳能电池样品以及无量子阱双结结构的参考样品,利用高分辨率X射线衍射仪(HXRD)和高分辨率透射电镜(TEM)测试了样品的晶体质量,同时在AM0(1×)光谱条件下测试了样品的I-V特性曲线和相应子电池的外量子效率。最终得到了高晶体质量、吸收截止波长在954 nm的Ga_(0.89)In_(0.11)As/GaAs_(0.92)P_(0.08)多量子阱结构,扩展波段的外量子效率最高达到75.18%,电池光电转换效率相对于无量子阱结构提升2.77%。通过对比测试结果发现,随着量子阱结构周期数的增加,太阳能电池在扩展波段(890~954 nm)的外量子效率不断提高,常规波段的短波响应(300~700 nm)会出现下降,长波响应(700~890 nm)会出现上升,短路电流和转换效率相应提升并趋于饱和。     

Circular threshold quantum secret sharing

This paper proposes a circular threshold quantum secret sharing （TQSS） scheme with polarized single photons. A polarized single photon sequence runs circularly among any t or more of n parties and any t or more of n parties can reconstruct the secret key when they collaborate. It shows that entanglement is not necessary for quantum secret sharing. Moreover, the theoretic efficiency is improved to approach 100% as the single photons carrying the secret key are deterministically forwarded among any t or more of n parties, and each photon can carry one bit of information without quantum storage. This protocol is feasible with current technology.