In组分渐变提高InGaN/GaN多量子阱发光二极管发光性能

利用金属有机物化学气相沉积系统在蓝宝石衬底上通过有源层的变温生长,得到In组分渐变的量子阱结构,从而获得具有三角形能带结构的InGaN/GaN多量子阱发光二极管(LED)(简称三角形量子阱结构LED).变温光致发光谱结果表明,相对于传统具有方形能带结构的量子阱LED(简称方形量子阱结构LED),三角形量子阱结构有效提高了量子阱中电子和空穴波函数的空间交叠,从而增加了LED的内量子效率;电致发光谱结果表明,三角形量子阱结构LED器件与传统结构LED器件相比,明显改善了发光峰值波长随着电流的蓝移现象.通过以上     

具有三角形InGaN/GaN多量子阱的高内量子效率的蓝光LED(英文)

对InGaN量子阱LED的内量子效率进行了优化研究。分别对发光光谱、量子阱中的载流子浓度、能带分布、静电场和内量子效应进行了理论分析。对具有不同量子阱数量的InGaN/GaN LED进行了理论数值比对研究。研究结果表明,对于传统结构的LED而言,2个量子阱的结构相对于5个和7个量子阱具有更好的光学性能。同时还研究了具有三角形量子阱结构的LED,研究结果显示,三角形多量子阱结构具有较高的电致发光强度、更高的内量子效率和更好的发光效率,所有的优点都归因于较高的电子-空穴波函数重叠率和低的Stark效应所产生的较高的载流子输入效率和复合发光效率。     

GaAs量子阱太阳能电池量子效率的研究

将量子阱结构引入到单结GaAs太阳能电池中能够有效扩展吸收光谱.为了研究量子阱结构在GaAs太阳能电池中的作用机理,本文采用实验和理论的方法研究了InGaAs/GaAsP量子阱结构对电池量子效率的影响.实验结果表明,量子阱结构的窄带隙阱层材料将电池的吸收光谱从890 nm扩展到1000 nm.同时,量子阱结构的引入提高了680—890 nm波长范围内的量子效率,降低了波长在680 nm以下的量子效率.通过计算得到的量子阱结构和GaAs材料的光吸收系数,可以用来解释量子阱结构对太阳能电池量子效率的影响.     

量子点量子阱中的三阶非线性光学特性的研究

利用紧致密度矩阵近似方法，研究了一个特殊量子点量子阱中的三阶非线性光学特性(三次谐波产生)，得到了量子点量子阱系统的三次谐波产生系数的解析表达式，而且考虑了量子点量子阱系统中的两种电子束缚态-壳层阱内与阱外两种束缚态。对CdS/HgS构成的典型的量子点量子阱进行了数值计算，得到了10^-15(m／v)^2量级的三次谐波产生系数，并且绘出了三次谐波产生系数作为量子点量子阱的尺寸和泵浦光子能量的函数曲线，最后对曲线的特征及其形成的原因进行了解析。     

有机量子阱电致发光器件

制备了普通的有机量子阱结构,并对结构进行了表征.在此基础上,制备了量子阱结构的白光电致发光器件.在分析了制作工艺对有机量子阱结构特性可能产生的影响之后,为了减少垒、阱界面互扩散效应的影响,提出了有机掺杂量子阱的概念,即垒与阱的母体是相同材料,只是在生长垒层的过程中同时掺入少量发光剂.由于掺杂剂的浓度梯度只有百分之零点几,因此,界面互扩散的影响很小,实际上我们用这种办法制备的有机量子阱器件的亮度、效率均有明显提高.在研究了阱数对器件特性的影响之后,我们发现一般情况下,两个阱是最好的.进一步研究了阱母体材料对有机量子阱器件特性的影响,结果发现,用NPB作母体比Alq作母体更好,这时器件的效率(cd/A)在45～13V工作电压范围内变化不大.     

量子计算与量子模拟中离子阱结构研究进展

离子阱系统是实现量子计算和量子模拟的主要体系之一.世界范围内的各个离子阱研究小组共同推动着离子阱结构的丰富化发展,开发出一系列高性能的三维离子阱、二维离子芯片、以及具有集成器件的离子阱系统.离子阱的结构逐渐向小型化、高通光性和集成化方向发展,并表现出卓越的量子操控能力—对多离子的囚禁能力和精确控制能力越来越高.本综述将总结过去的十几年里离子阱在结构上的演化历程,以及离子阱在量子计算与量子模拟实验研究中的最新进展.通过分析具有代表性的离子阱结构,总结离子阱系统在加工工艺、鲁棒性和多功能性等方面取得的进步,并对基于离子阱系统的可扩展量子计算与模拟作出展望.     

非对称耦合量子阱吸收与色散的理论研究

基于V型三能级模型研究了非对称耦合量子阱（ACQW）线性吸收与色散特性. 理论结果表明：在小偏置区，由沿生长方向的外加电场引起的强量子限域Stark频移导致非共振吸收，线性折射率大幅度降低，表现为色散猝灭特性. 而随负偏压进一步增加, 由于量子限域Stark效应消失，其吸收与色散特性则与单量子阱最低激子态相类似. 这意味着ACQW具有随外加电场变化的可控色散特性. 关键词： 非对称耦合量子阱 量子相干 可控色散     

无限深量子阱量子比特及其声子效应

采用Peaker变分法,研究无限深量子阱中量子比特及其声子效应。量子阱中这样的二能级体系可作为一个量子比特。当阱中电子处于基态和第一激发态的叠加态时,电子的概率密度在空间作周期性震荡,得出了振荡周期随耦合强度的增加而减小,随振动频率的增加而增大。     

非对称ZnO/ZnMgO双量子阱内量子效率的提高

在c-plane面蓝宝石衬底上生长了ZnO/Zn0.85Mg0.15O非对称双量子阱,其内量子效率相对于对称量子阱有了显著的提高。ZnO/Zn0.85Mg0.15O的10周期对称量子阱和5周期非对称双量子阱都是利用等离子体辅助分子束外延技术制备的。ZnO/Zn0.85Mg0.15O非对称双量子阱的内量子效率提高至对称阱的1.56倍。时间分辨光谱和光致发光谱测试结果证实,在ZnO/Zn0.85Mg0.15O非对称双量子阱中存在从窄阱到宽阱的激子隧穿过程,这是内量子效率提高的主要原因。     

无限深量子阱量子比特及其声子效应

采用Peaker变分法,研究具有束缚势的无限深量子阱中量子比特及其声子效应。量子阱中这样的二能级体系可作为一个量子比特。当阱中电子处于基态和第一激发态的叠加态时,电子的概率密度在空间作周期性震荡,得出了振荡周期随耦合强度的增加而减小,随振动频率的增加而增大。     

Weakly Regular Quantum Grammars and Asynchronous Quantum Automata

In this paper, we define weakly regular quantum grammars (WRQG), regular quantum grammars (RQG), asynchronous quantum automata (AQA) and synchronous quantum automata (SQA). Moreover, we investigate the relationships between quantum languages generated by weakly quantum regular grammars and by asynchronous quantum automata. At the mean time, we discuss the relationships between regular quantum grammars and synchronous quantum automata. This work is supported by National Science Foundation of China (Grant No. 10571112) and 973 Program of China (No. 2002CB312200).     

Realization of Quantum Circuits in Fock Space

In this letter, by using the method we offered in our paper [L. Ma and Y.D. Zhang, Commun. Theor. Phys. (Beijing, China) 36 (2001) 119], some extended quantum logic gates, such as quantum counter, quantum adder, are studied and their expressions are given. It may be useful for us to study the more complicated quantum logic circuits deeply.     

Quantum machines

We discuss quantum information processing machines. We start with single purpose machines that either redistribute quantum information or identify quantum states. We then move on to machines that can perform a number of functions, with the function they perform being determined by a program, which is itself a quantum state. Examples of both deterministic and probabilistic programmable machines are given, and we conclude with a discussion of the utility of quantum programs.     

Quantum Ratchet in Disordered Quantum Walk

Symmetrically evolving discrete quantum walk results in dynamic localization with zero mean displacement when the standard evolution operations are replaced by a temporal disorder evolution operation. In this work we show that the quantum ratchet action, that is, a directed transport in standard or disordered discrete‐time quantum walk can be realized by introducing a pawl like effect realized by using a fixed coin operation at marked positions that is, different from the ones used for evolution at other positions. We also show that the combination of standard and disordered evolution operations can be optimized to get the mean displacement of order ∝ t (number of walk steps). This model of quantum ratchet in quantum walk is defined using only a set of entangling unitary operators resulting in the coherent quantum transport.     

Dynamics of Super Quantum Correlations and Quantum Correlations for a System of Three Qubits

The dynamics of quantum discord for two qubits independently interacting with dephasing reservoirs have been studied recently.The authors [Phys.Rev.A 88(2013) 034304] found that for some Bell-diagonal states(BDS)which interact with their environments the calculation of quantum discord could experience a sudden transition in its dynamics,this phenomenon is known as the sudden change.Here in the present paper,we analyze the dynamics of normal quantum discord and super quantum discord for tripartite Bell-diagonal states independently interacting with dephasing reservoirs.Then,we find that basis change does not necessary mean sudden change of quantum correlations.     

量子计算与量子模拟

量子计算和量子模拟在过去的几年里发展迅速,今后涉及多量子比特的量子计算和量子模拟将是一个发展的重点.本文回顾了该领域的主要进展,包括量子多体模拟、量子计算、量子计算模拟器、量子计算云平台、量子软件等内容,其中量子多体模拟又涵盖量子多体动力学、时间晶体及多体局域化、量子统计和量子化学等的模拟.这些研究方向的回顾是基于对现阶段量子计算和量子模拟研究特点的考虑,即量子比特数处于中等规模而量子操控精度还不具有大规模逻辑门实现的能力,研究处于基础科研和实用化的过渡阶段,因此综述的内容主要还是希望管窥今后的发展.     

Quantum metrology

The statistical error is ineluctable in any measurement. Quantum techniques, especially with the development of quantum information, can help us squeeze the statistical error and enhance the precision of measurement. In a quantum system, there are some quantum parameters, such as the quantum state, quantum operator, and quantum dimension, which have no classical counterparts. So quantum metrology deals with not only the traditional parameters, but also the quantum parameters. Quantum metrology includes two important parts： measuring the physical parameters with a precision beating the classical physics limit and measuring the quantum parameters precisely. In this review, we will introduce how quantum characters （e.g., squeezed state and quantum entanglement） yield a higher precision, what the research areas are scientists most interesting in, and what the development status of quantum metrology and its perspectives are.     

Decomposition Properties of Quantum Discord

The quantum discord was introduced by Ollivier,Zurek,Henderson,and Vedral as an indicator of the degree of quantumness of mixed states.In this paper,we provide a decomposition condition for quantum discord.Moreover,we show that under the condition,the quantum correlations between the quantum systems can be captured completely by the entanglement measure.Finally,we present examples of our conclusions.     

Mutual Information and Quantum Discord in Quantum State Discrimination with a Fixed Rate of Inconclusive Outcomes

We studied the mutual information and quantum discord that Alice and Bob share when Bob implements a discrimination with a fixed rate of inconclusive outcomes (FRIO) onto two pure non-orthogonal quantum states, generated with arbitrary a priori probabilities. FRIO discrimination interpolates between minimum error (ME) and unambiguous state discrimination (UD). ME and UD are well known discrimination protocols with several applications in quantum information theory. FRIO discrimination provides a more general framework where the discrimination process together with its applications can be studied. In this setting, we compared the performance of optimum probability of discrimination, mutual information, and quantum discord. We found that the accessible information is obtained when Bob implements the ME strategy. The most (least) efficient discrimination scheme is ME (UD), from the point of view of correlations that are lost in the initial state and remain in the final state, after Bob’s measurement.     

Multiparty Quantum Secret Sharing Using Quantum Fourier Transform

A （n, n）-threshold scheme of multiparty quantum secret sharing of classical or quantum message is proposed based on the discrete quantum Fourier transform. In our proposed scheme, the secret message, which is encoded by using the forward quantum Fourier transform and decoded by using the reverse, is split and shared in such a way that it can be reconstructed among them only if all the participants work in concert. Fhrthermore, we also discuss how this protocol must be carefully designed for correcting errors and checking eavesdropping or a dishonest participant. Security analysis shows that our scheme is secure. Also, this scheme has an advantage that it is completely compatible with quantum computation and easier to realize in the distributed quantum secure computation.