有限温度张量重正化群方法及其在阻挫量子磁性研究中的应用

阻挫量子磁体中的新奇物态与效应是凝聚态物理研究的重要前沿方向,因其与高温超导、拓扑量子计算等的密切联系,近年来吸引了人们浓厚的研究兴趣。实验上,阻挫自旋液体候选材料的 新进展层出不穷,人们系统地研究了若干三角晶格、笼目晶格和六角Kitaev 阻挫磁体等材料,发 现其在一定条件下展现出自旋液体态的特征,但澄清其中的量子物态是充满挑战的量子多体问题。 作者最近的工作指出,可以从有限温度张量重正化群多体计算入手,开展热力学性质的精确计算 与分析,确定阻挫磁体的微观自旋模型,做出进一步理论预言并开展实验验证,从而建立量子磁性 系统的多体计算精确研究方案。有限温度张量重正化群方法是计算大尺寸二维阻挫量子自旋模型 有限温度性质的有力工具,在本文中作者首先介绍新近发展的系列张量重正化群方法,包括线性 和指数张量重正化群等。随后,作者讨论有限温度张量方法在三角晶格量子伊辛磁体TmMgGaO4 和六角晶格Kitaev 磁体α-RuCl3 的微观自旋模型中的具体应用：通过高精度和全面的多体计算, 揭示出其中存在演生U(1) 对称性与拓扑相变,以及高场量子自旋液体态等新颖的结论,这些理 论预言也陆续被实验所证实。通过上述实例,作者展示了有限温度张量重正化群计算方法在自旋 液体候选材料研究中的应用价值,并期待这些方法能在强关联量子物质研究中发挥重要作用。     

Prediction of quantum anomalous Hall effect in CrI3/ScCl2 bilayer heterostructure

Based on first-principles calculations, a two-dimensional (2D) van der Waals (vdW) bilayer heterostructure consisting of two topologically trivial ferromagnetic (FM) monolayers CrI₃ and ScCl₂ is proposed to realize the quantum anomalous Hall effect (QAHE) with a sizable topologically nontrivial band gap of 4.5 meV. Its topological nature is attributed to an interlayer band inversion between the monolayers and critically depends on the symmetry of the stacking configuration. We further demonstrate that the topologically nontrivial band gap can be increased nearly linearly by the application of a perpendicular external pressure and reaches 8.1 meV at 2.7 GPa, and the application of an external out-of-plane electric field can also modulate the band gap and convert the system back to topologically trivial via eliminating the band inversion. An effective model is developed to describe the topological phase evolution in this bilayer heterostructure. This work provides a new candidate system based on 2D vdW materials for realization of potential high-temperature QAHE with considerable controllability.     

压缩真空场与原子非线性作用过程中的纠缠与消纠缠

用Von Neumann熵研究了附加克尔介质的压缩真空场与二能级原子依赖强度耦合相互作用量子体系的量子纠缠特性.讨论了初始压缩真空场的压缩度以及克尔非线性作用的强度对该量子体系纠缠特性的影响.结果表明，克尔介质的非线性作用的强弱可以改变体系量子纠缠的周期性；在初始压缩度较大（r=5）时，克尔介质的非线性作用可导致原子与场持续地处于最大纠缠态，无消纠缠态或持续地处于消纠缠态. 关键词： 压缩真空态 克尔介质 依赖强度耦合J-C模型 Von Neumann熵 量子纠缠     

电声子相互作用对量子点分子中单电子隧穿的影响

研究了双量子点系统中的电子隧穿动力学过程，在考虑电子与声子相互作用的情况下用基于 正则变换的微扰方法解析地得到了电子动态隧穿电流的表达式. 并且详细分析电子与声子耦 合引起的退相干问题，在此基础上指出了可能的退耦机理. 关键词： 电声子相互作用 双量子点 隧穿     

Efficient error estimation in quantum key distribution

In a quantum key distribution(QKD)system,the error rate needs to be estimated for determining the joint probability distribution between legitimate parties,and for improving the performance of key reconciliation.We propose an efficient error estimation scheme for QKD,which is called parity comparison method(PCM).In the proposed method,the parity of a group of sifted keys is practically analysed to estimate the quantum bit error rate instead of using the traditional key sampling.From the simulation results,the proposed method evidently improves the accuracy and decreases revealed information in most realistic application situations.     

The queueing model for quantum key distribution network

This paper develops a QKD (quantum key distribution)-based queueing model to investigate the data delay on QKD link and network, especially that based on trusted relays. It shows the mean packet delay performance of the QKD system. Furthermore, it proposes a key buffering policy which could effectively improve the delay performance in practice. The results will be helpful for quality of service in practical QKD systems.     

Erratum to "Quantum compact model for thin-body double-gate Schottky barrier MOSFETs"

<正>The statement for the third paragraph of the right column of page 3079 (Chinese Physics B, 2008, Vol. 17,No. 8, pp. 3077-3082 )[1]is inappropriate. This paragraph should be restated as follows.     

合肥电子储存环基本参数的测量

 为了给改造后的合肥储存环留下参考数据,同时为了找到储存环存在的物理问题,储存环特性参数首次被系统测量,它们是动量扩张因子、色散函数、自然色品、校正色品和中心频率。     

Dynamical properties of the Haldane chain with bond disorder

By using Lanczos exact diagonalization and quantum Monte Carlo combined with stochastic analytic continuation, we study the dynamical properties of the S = 1 antiferromagnetic Heisenberg chain with different strengths of bond disorder. In the weak disorder region, we find weakly coupled bonds which can induce additional low-energy excitation below the one-magnon mode. As the disorder increases, the average Haldane gap closes at δ_∆ ~ 0.5 with more and more low-energy excitations coming out. After the critical disorder strength δ_c ~ 1, the system reaches a random-singlet phase with prominent sharp peak at ω = 0 and broad continuum at ω > 0 of the dynamic spin structure factor. In addition, we analyze the distribution of random spin domains and numerically find three kinds of domains hosting effective spin-1/2 quanta or spin-1 sites in between. These “spins” can form the weakly coupled longrange singlets due to quantum fluctuation which contribute to the sharp peak at ω = 0.     

Sender-controlled measurement-device-independent multiparty quantum communication

Multiparty quantum communication is an important branch of quantum networks. It enables private information transmission with information-theoretic security among legitimate parties. We propose a sender-controlled measurement-device-independent multiparty quantum communication protocol. The sender Alice divides a private message into several parts and delivers them to different receivers for secret sharing with imperfect measurement devices and untrusted ancillary nodes. Furthermore, Alice acts as an active controller and checks the security of quantum channels and the reliability of each receiver before she encodes her private message for secret sharing, which makes the protocol convenient for multiparity quantum communication.