畴壁运动的量子效应

本文用规范交换和热力学平均的办法，讨论畴壁运动的能量变化，发现低温下畴壁运动是由零点振动所决定的，并且这个量子效应与畴壁参数有关，特别与阻尼有关．     

K-场畴壁解

通过考虑五维平直时空中非正则的标量场K-场,得到了解析的单扭结和双扭结K-场畴壁解.然后采用Yukawa耦合机制研究五维费米子在单扭结和双扭结K-场畴壁上的局域化,发现四维零质量的手征费米子可以局域化在K-场畴壁上.最后通过对比费米子在两种扭结畴壁上的有效势,发现双扭结畴壁情况的有效势具有双阱的特征,表明双扭结畴壁具有更加丰富的内部结构.     

科学家首次绘制出3D磁畴图像

磁畴理论是用量子理论从微观上说明铁磁质的磁化机理。所谓磁畴,是指磁性材料内部的一个个小区域,每个区域内部包含大量原子,各个磁畴之间的交界面称为磁畴壁。同一磁畴内的原子磁矩都相同,但是不同磁畴的磁矩却各异,因此,磁畴磁场的方向就在磁畴壁这里发生了改变。科学界对磁畴理论的研究一直都停留在二维图像和材料表层的层面上,只能针对磁畴的横截面进行研究。     

聚丁二炔(Polydiacetylene)单晶中量子成核和热成核相变过程

本文研究聚丁二炔(Polydiacetylene)中的量子成核和热成核相变过程。在从PDB相向PDA相的相变过程中。会出现一个畴壁;相反,在从PDA相向PDB相的相变过程中,会出现一个反畴壁。我们认为,畴壁的形成是一种涨落的结果;利用统计物理的方法,对两种成核过程进行了详细的讨论,发现在ETCD-PD中,主要是热成核相变;而在ETDU-PD中,主要是量子成核相变,与实验事实符合。图5,参13     

金属铁磁小粒子系统矫顽力温度依赖特性的研究

本文首先将经典的铁磁体畴壁运动方程量子化,然后从量子的畴壁运动方程和Egami的激活机制出发,给出了一些金属铁磁小粒子系统低温下矫顽力的温度依赖性,发现在极低温度区域,矫顽力是常数。这一结果至少定性地与实验相符合。     

金属铁磁小粒子系统矫顽力温度依赖特性的研究

本文首先将经典的铁磁体畴壁运动方程量子化，然后从量子的畴壁运动方程和Ｅｇａｍｉ的激活机制出发，给出了一些金属铁磁小粒子系统低温下矫顽力的温度依赖性，发现在极低温度区域，矫顽力是常数。这一结果至少定性地与实验相符合．     

KNbO_3 180°畴的第一性原理计算

利用第一性原理计算方法,考察铁电材料KNbO3的180°畴结构,并计算以K和Nb原子为对称中心的畴壁厚度、畴壁能及两种畴壁间移动的势垒高度.结果表明:该材料的畴壁厚度为1~2个晶胞常数;以K原子为对称中心的畴壁更稳定,其畴壁能为7.58 mJ/m2;以Nb为对称中心的畴壁不稳定,会逐渐变为以K为对称中心的畴壁,其畴壁能为15.16mJ/m2;畴壁移至最近邻晶格位置的势垒值为7.58mJ/m2.     

微观磁化理論(綜合評述)

引言在研究磁化理论时,人们可以从三个不同观点出发: 第一种是宏观的观点,即以B,H等概念为基础,研究磁化—磁滞曲线,磁导率等等。第二种观点是磁畴理论的观点,即从自发磁化Is,磁畴,畴壁与畴壁能,可逆与不可逆的畴壁位移和畴转等概念来研究问题。Landau-Liftshitz的磁畴理论采用了畴壁这一模型。在畴壁内Is随位置而连续地转变其方向。这种观点深入到畴壁内部,但     

在磁泡材料中作用在BL线和BL串上的动力学反作用力

本文讨论了含有BL线和BL串的磁泡畴壁的动力学.应用磁畴壁运动的基本方程推导出作用在单个BL线和正常磁泡畴壁的动力学反作用力并由含有BL串的畴磁壁运动的耦合方程给出这些力的合成形式.     

晶体畴反转过程中畴壁运动与极化电流特性研究

为了解晶体畴反转的动力学过程,利用马赫-曾德干涉实验系统,研究了外电场极化下掺镁铌酸锂和纯净铌酸锂晶体在畴反转过程中的畴壁运动和极化电流特性。实时记录了掺镁7 mol%、掺镁5 mol%铌酸锂和纯净铌酸锂晶体在畴反转过程中的畴壁特征和极化电流变化情况,发现离散的畴壁速度脉冲伴随着离散的极化电流脉冲,连续的畴壁速度脉冲对应着连续的极化电流脉冲。掺镁铌酸锂晶体正向反转和纯净铌酸锂反向反转的畴壁速度变化和极化电流变化比较尖锐,而掺镁铌酸锂晶体反向反转和纯净铌酸锂正向反转的畴壁速度变化和极化电流变化比较缓和。最后对实验现象进行了解释。     

Tunable quantum tunnelling of magnetic domain walls

Perhaps the most anticipated, yet experimentally elusive, macroscopic quantum phenomenon is spin tunnelling in a ferromagnet, which may be formulated in terms of domain wall tunnelling. One approach to identifying such a process is to focus on mesoscopic systems where the number of domain walls is finite and the motion of a single wall has measurable consequences. Research of this type includes magnetotransport measurements on thin ferromagnetic wires, and magnetization experiments on single particles, nanomagnet ensembles and rare-earth multilayers. A second method is to investigate macroscopic disordered ferromagnets, whose dynamics are dominated by domain wall motion, and search the associated relaxation-time distribution functions for the signature of quantum effects. But whereas the classical, thermal processes that operate in these experiments are easily regulated via temperature, the quantum processes have so far not been tunable, making difficult a definitive interpretation of the results in terms of tunnelling. Here we describe a disordered magnetic system for which it is possible to adjust the quantum tunnelling probabilities. For this material, we can model both the classical, thermally activated response at high temperatures and the athermal, tunnelling behaviour at low temperatures within a unified framework, where the domain wall is described as a particle with a fixed mass. We show that it is possible to tune the quantum tunnelling processes by adjusting the 'mass' of this particle with an external magnetic field.     

基于量子辐射场的大数据安全存储寻址算法

大数据存储过程面临着与日俱增的各种威胁,而传统数据存储算法难以有效应对这些新型威胁。以量子力学和量子遗传的关系为基础,构建量子辐射与量子遗传迭代的、双向可逆过程的数学函数和计算机程序,为流数据的大规模量子安全存储构建软件基础环境。在量子力学和量子遗传的映射关系下,将量子染色体的定义和交互作用通过量子比特和量子旋转门的计算实现,将量子染色体的交互通过量子引力作用和量子斥力作用的交互实现,将量子染色体动态过程的主要衡量指标通过引力和斥力的叠加态来计算产生。用量子引力和斥力来引导流数据的动态存储寻址、出入栈过程与路径,进而将大数据存储过程双向映射为量子辐射场和量子空间域问题,得到安全存储路径与存储地址。     

Generation of nonclassical photon pairs for scalable quantum communication with atomic ensembles

Quantum information science attempts to exploit capabilities from the quantum realm to accomplish tasks that are otherwise impossible in the classical domain. Although sufficient conditions have been formulated for the physical resources required to achieve quantum computation and communication, there is a growing understanding of the power of quantum measurement combined with the conditional evolution of quantum states for accomplishing diverse tasks in quantum information science. For example, a protocol has recently been developed for the realization of scalable long-distance quantum communication and the distribution of entanglement over quantum networks. Here we report the first enabling step in the realization of this protocol, namely the observation of quantum correlations for photon pairs generated in the collective emission from an atomic ensemble. The nonclassical character of the fields is demonstrated by the violation of an inequality involving their normalized correlation functions. Compared to previous investigations of non-classical correlations for photon pairs produced in atomic cascades and in parametric down-conversion, our experiment is distinct in that the correlated photons are separated by a programmable time interval (of about 400 nanoseconds in our initial experiments).     

Existence of global attractor for the one-dimensional bipolar quantum drift-diffusion model

In this paper, we investigate a one-dimensional bipolar quantum drift-diffusion model from semiconductor devices. We mainly show the long-time behavior of solutions to the one-dimensional bipolar quantum drift-diffusion model in a bounded domain. That is, we prove the existence of the global attractor for the solution.     

介观电路中的量子效应及其研究路径分析

作者从介观物理的视角介绍了介观电路中量子效应及其研究路径,并从两个方面分析了其研究进展和发展趋势,指出现有理论方法和实验手段方面的成功与不足,并对这一领域的进一步发展提出了可行的研究思路。     

An error-free protocol for quantum entanglement distribution in long-distance quantum communication

Quantum entanglement distribution is an essential part of quantum communication and computation protocols. Here, linear optic elements are employed for the distribution of quantum entanglement over a long distance. Polarization beam splitters and wave plates are used to realize an error-free protocol for broadcasting quantum entanglement in optical quantum communication. This protocol can determine the maximum distance of quantum communication without decoherence. Error detection and error correc-tion are performed in the proposed scheme. In other words, if there is a bit flip along the quantum channel, the end stations (Alice and Bob) can detect this state change and obtain the correct state (entangled photon) at another port. Existing general error detec-tion protocols are based on the quantum controlled-NOT (CNOT) or similar quantum logic operations, which are very difficult to implement experimentally. Here we present a feasible scheme for the implementation of entanglement distribution based on a linear optics element that does not need a quantum CNOT gate.     

两种典型的量子通信技术

量子通信是量子信息中的一个重要分支．而其中最典型的量子通信技术是量子隐形传态和量子密码通信．文章介绍了量子通信中量子叠加和量子纠缠的概念．并介绍两种量子通信技术的理论框架,同时也涉及了这个领域的实验研究进展．     

基于量子演化理论的行人检测改进算法

对视频中移动摄像头下的行人检测问题进行了研究,在AdaBoost行人分类算法、支持向量机(SVM)理论和多目标优化原理的基础之上,并结合三者的特点,提出了一种基于量子演化算法的行人检测优化算法。首先,使用传统的AdaBoost算法对行人进行粗粒度的分类,然后使用支持向量机(SVM)设计精度更高的行人检测器。针对SVM的分类器参数多、关系复杂,而且无好的调节准则,根据核函数的构建条件,将实值量子演化算法引入到SVM参数的寻优问题中,对于分类性能采用多目标优化的方法,取得了较好的效果;同时从理论上分析了算法的复杂度。经过实例测试,算法与经典多目标优化算法NSGA-II的相比,改进效果明显。最后的实验说明了算法检测的准确性。     

The quantum internet

Quantum networks provide opportunities and challenges across a range of intellectual and technical frontiers, including quantum computation, communication and metrology. The realization of quantum networks composed of many nodes and channels requires new scientific capabilities for generating and characterizing quantum coherence and entanglement. Fundamental to this endeavour are quantum interconnects, which convert quantum states from one physical system to those of another in a reversible manner. Such quantum connectivity in networks can be achieved by the optical interactions of single photons and atoms, allowing the distribution of entanglement across the network and the teleportation of quantum states between nodes.