Research progress in terahertz quantum cascade lasers

The terahertz(THz)quantum cascade laser(QCL)is a coherent THz source based on intersubband transitions of unipolar carriers.As semiconductor lasers,THz QCLs are solid-state,electrically pumped,tunable,and can be easily integrated.This paper reviews the state of the art for the design,operation temperature,and output power of THz QCLs.Their applications in THz communication and imaging are also discussed.     

Deterministic secure quantum communication without unitary operation based on high-dimensional entanglement swapping

By analysis of the basic properties of entanglement swapping of high-dimensional Bell states,a universal and general deterministic secure quantum communication(DSQC)protocol is proposed,in which unitary operation is not required.By making use of the results of high-dimensional Bell measurement,the sender and the receiver can encode and decode the message respectively by performing the modular addition and subtraction.Two mutually complementary bases are constructed;and according to the property of mutual complement,a method for checking security of the high-dimensional quantum channel is put forward.Some common attack strategies are analyzed,and the corresponding error rates are calculated.Then the upper bound of the threshold of error rate is deduced.     

Group codes on certain algebraic curves with many rational points

We construct a series of algebraic geometric codes using a class of curves which have many rational points. We obtain codes of lengthq ² over _q , whereq = 2q ₀ ² andq ₀ = 2 ⁿ , such that dimension + minimal distance q ² + 1 – q ₀ (q – 1). The codes are ideals in the group algebra _q [S], whereS is a Sylow-2-subgroup of orderq ² of the Suzuki-group of orderq ² (q ² + 1)(q – 1). The curves used for construction have in relation to their genera the maximal number of GF _q -rational points. This maximal number is determined by the explicit formulas of Weil and is effectively smaller than the Hasse—Weil bound.Supported by Deutsche Forschungsgemeinschaft while visiting Essen University     

小波域最小嵌入失真函数设计及其在隐写中的应用

为了提高隐写方案的安全性,提出一种基于最小嵌入失真原理和网格码的图像隐写算法。首先在离散小波域结合人眼视觉特性和整数提升小波变换设计了失真测度函数,主要考虑了亮度、频率和纹理掩蔽因子对载体失真的影响。然后结合网格码设计了隐写算法,将嵌入信息对载体的修改最小化并且集中在人眼不敏感区域。实验结果显示,方案具有良好的视觉不可见性,且能抵抗空域、小波域等隐写分析的攻击,安全容量达到0.4 bits/pixel。     

基于l1范数相干度的量子态区分

为探究区分量子态的最优策略,以相干作为资源,利用附加辅助系统的方法来区分非正交量子态,并给出了l₁范数相干度与区分量子态的成功概率之间的数值关系,同时量化了某些特定情况下不出错的量子态区分(UQSD)的最优协议所需的l₁范数相干均值.本文的研究结果表明,通过调整生成的相干度可以提高区分量子态的成功几率.     

新的基于Huffman编码的追踪方案*

面对DDoS攻击,研究人员提出了各种IP追踪技术寻找攻击包的真实源IP地址,但是目前的追踪方案存在着标记过程中的空间问题、追踪源是否准确及追踪所需包的数量等问题.提出一种新的基于Huffman编码的追踪方案,可以节省大量的存储空间,提高空间效率,而且当遭遇DoS(拒绝服务攻击)和DDoS的攻击时能迅速作出反应,仅仅收到一个攻击包即可重构出攻击路径,找到准确的攻击源, 将攻击带来的危害和损失减小到最低程度.     

不可逆量子斯特林热泵循环性能分析与优化

建立了以一维无限深势阱中极端相对论粒子为工质的不可逆量子斯特林热泵循环模型。考虑高低温热源之间的热漏,导出了循环的性能系数与无量纲泵热率的表达式。分析了循环性能与各性能参数之间的关系。研究发现,热泵的性能系数与无量纲泵热率都随粒子在状态1进处于激收态上的占有几度单调递减,性能系数与无量纲泵热率都是势阱宽度比的凸单调函数。无量纲泵热率关于性能系数的关系曲线为回原点的扭叶型,并确定了该不可逆量子斯特林热泵的最优运行区间。     

Long-lasting photoluminescence quantum yield of cesium lead halide perovskite-type quantum dots

Cesium lead halide perovskite(CsPbX₃,X=Cl,Br,I)quantum dots(QDs)and their partly Mn²⁺-substituted QDs(CsPb1–xMnxX3)attract considerable attention owing to their unique photoluminescence(PL)efficiencies.The two types of QDs,having different PL decay dynamics,needed to be further investigated in a form of aggregates to understand their solid-state-induced exciton dynamics in conjunction with their behaviors upon degradation to achieve practical applications of those promising QDs.However,thus far,these QDs have not been sufficiently investigated to obtain deep insights related to the long-term stability of their PL properties as aggregated solid-states.Therefore,in this study,we comparatively examined CsPbX₃-and CsPb1–xMnxX₃-type QDs stocked for>50 d under dark ambient conditions by using excitation wavelength-dependent PL quantum yield and time-resolved PL spectroscopy.These investigations were performed with powder samples in addition to solutions to determine the influence of the inter-QD interaction of the aged QD aggregates on their radiative decays.It turns out that the Mn²⁺-substituted QDs exhibited long-lasting PL quantum efficiencies,while the unsubstituted CsPbX₃-type QDs exhibited a drastic reduction of their PL efficiencies.And the obtained PL traces were clearly sensitive to the sample status.This is discussed with the possible interaction depending on the size and distance of the QD aggregates.