Decoherence Induced by Spin Chain Environment

We study the decoherence process of an exact solvable model that consists of a central spin-1/2 coupling to the surrounding anisotropy spin-1/2 chain in transverse fields. The Loschrnidt echo is calculated to study the character of decoherence with different degree of anisotropy. Our results show that the degree of anisotropy γ greatly affects the decoherence process of the central spin-system when the spin chain is in weak transverse fields, but it gives weak effect in the strong transverse field. The decoherence process of the central system changed dramatically along the line of the critical points, and this may be explained as the reflection of quantum phase transitions.     

量子纠缠和贝尔不等式及其在量子信息处理中的应用

1964年,爱尔兰数学家约翰·贝尔(John Bell)根据隐变量理论推导出了2个粒子系统的测量结果应该满足的不等式关系和所涉及的测量基本逻辑.法国科学家阿兰·阿斯佩(Alain Aspect)、美国科学家约翰·克劳泽(John Clauser)和奥地利科学家安东·蔡林格(Anton Zeilinger)分别从实验上证伪了该不等式.贝尔不等式的证伪宣告了隐变量理论的终结,展示了量子纠缠的奇特性质.为表彰他们在“纠缠光子实验、验证违反贝尔不等式和开创量子信息科学”方面所做出的贡献,瑞典皇家科学院将2022年诺贝尔物理学奖授予这3位科学家.本文概述了量子纠缠的概念和贝尔不等式的推导,介绍了2022年诺贝尔物理学奖获得者的代表性研究工作,并展示了量子技术的可能应用.     

负U哈伯德模型中η对超导体的热力学性质

本利用平均场近似，研究了负ＵＫ伯德模型中η对超导体的热力性质，给出了临界磁场与温度的关系，式，求出临界温度处的比热跃迁，它们与已知的实验符合行比较好。     

多原子体系与单模腔场相互作用的动力学特性

利用迁移矩阵方法，给出了多体系与单模腔场相互作用的稳态解条件。在大平均光子数极限下，研究了体系的动力学特性。本文讨论了多原子－单模量子化光场的真空效应。     

Mean-Field Dynamics of a Two-Mode Bose-Einstein Condensate Subject to Decoherence

We discuss the dynamics of Bose-Einstein condensates in a double-well potential subject to decoherenee （or particle loss）. Starting from the full many-body dynamics described by the master equation, an effective Gross- Pitaevskii-like equation is derived in the mean-field approximation. By numerically solving the GP equation, we find that macroscopic quantum self-trapping disappears for strong decoherence, while generalized self-trapping occurs under weak decoherence. The fixed points have been calculated, and we find that an abrupt change from elliptic to an attractor and a repeller occurs, reflecting the metastable behavior of the system around these points.     

Discord under the influence of a quantum phase transition

This paper studies the discord of a bipartite two-level system coupling to an XY spin-chain environment in a transverse field and investigates the relationship between the discord property and the environment’s quantum phase transition.The results show that the quantum discord is also able to characterize the quantum phase transitions.We also discuss the difference between discord and entanglement,and show that quantum discord may reveal more general information than quantum entanglement for characterizing the environment’s quantum phase transition.     

Entanglement Distillation for Mixed States Using Particle Statistics

We extend the idea of entanglement concentration protocol for pure states （Phys. Rev. Lett. 88, 187903） to the case of entanglement distillation for mixed states. The scheme works only with particle statistics and local operations, without the need of any other interactions. We show that the maximally entangled state can be distilled out when the initial state is pure, otherwise the entanglement distilled depends on the off-diagonal element of density matrix of the initial state. Because of the requirement for density matrix, the entanglement distilled is always less than one, and this result is the same for both fermionic and bosonic particles. The distillation efficiency is a product of the diagonal elements of the initial state, it takes the maximum 50%, the same as that in the case for pure states.We extend the idea of entanglement concentration protocol for pure states （Phys. Rev. Lett. 88, 187903） to the case of entanglement distillation for mixed states. The scheme works only with particle statistics and local operations, without the need of any other interactions. We show that the maximally entangled state can be distilled out when the initial state is pure, otherwise the entanglement distilled depends on the off-dlagonal element of density matrix of the initial state. Because of the requirement for density matrix, the entanglement distilled is always less than one, and this result is the same for both fermionic and bosonic particles. The distillation effciency is a product of the diagonal elements of the initial state, it takes the maximum 50%, the same as that in the case for pure states.     

非线性一维光学晶格链中的热纠缠

本文对非线性光学晶格链中自旋为1的原子，在两原子以及多原子链中紧邻原子之间的热纠缠问题作了详尽的研究，结果表明非线性耦合和线性耦合系数之间的关系对界定热纠缠是否存在起到关键作用，由于不同的原子这两种耦合对应着不同的关系，这一研究揭示在那些种类的原子中存在热纠缠；这一结果对两粒子以及多粒子体系都是成立的。在多粒子情况下临界温度以及热纠缠仅有少许下降。     

各向异性的费密系统超导转变温度及热力学性质

把超导体作为各向异性的费密系统，考虑到电子拓扑跃变情况下，利用三能带交迭模型计算出超导转变温度Ｔ_ｃ和化学势μ的关系，以及其它的热力学量。计算结果同实验进行了比较。 关键词：     

二能带交迭高温超导理论的Van－Hove奇异性与超导转变温度和反常同位素效应

本文利用二交迭能带理论，计算费米面附近电子态密度的Ｖａｎ－Ｈｏｖｅ奇异性对超导转变温度和同位素指数因子的影响，计算结果表明：费米面附近电子态密度的Ｖａｎ－Ｈｏｖｅ奇异性能同时提高超导转变温度和降低同位素指数因子，这是普通的ＢＣＳ理论不能解释的［３］．