物理学从不浅薄、电荷密度波、Chern绝缘体、加速量子多体基态 | 本周物理讲座

1

报告人：曹则贤，中国科学院物理研究所

时间：7月12日（周二）19:00

单位：中国物理学会、北京师范大学科学教育研究院

会议链接：

摘要：

物理学源于对我们周边事物的观察与应用，从可触摸的感知逐渐走进抽象的理论。物理学从不浅薄，任何一个基本概念都有太多意想不到的内容，都有继续深化的可能。以简单的杠杆为例，本报告试图说明一个观念，哪怕是物理的第一课都有很多重要的内容，都深刻地影响了我们的生活，值得我们严肃对待。

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报告人：Prof. Liang Wu，Department of Physics and Astronomy, University of Pennsylvania

时间：7月13日（周三） 10:00

单位：中科院物理所

腾讯会议：517-431-514

Password：0713

摘要：

The kagome lattice provides a fascinating playground to study geometrical frustration, topology and strong correlations. The newly discovered kagome metals AV3Sb5 (A=K, Rb, Cs) exhibit various interesting phenomena including topological band structure, symmetry-breaking charge density waves (CDWs) and superconductivity. Nevertheless, the nature of the symmetry breaking in the CDW phase is not yet clear, despite the fact that it is crucial to understand whether the superconductivity is unconventional. In this work, we perform scanning birefringence microscopy and find that six-fold rotation symmetry is broken at the onset of the CDW transition temperature in all three compounds. Spatial imaging and angle dependence of the birefringence show a universal three nematic domains that are 120？to each other. We propose staggered CDW orders with a relative π phase shift between layers as a possibility to explain the three-state nematicity in AV3Sb5. We also perform magneto-optical Kerr effect and circular dichroism measurements on all three compounds, and the onset of the both signals is at the CDW transition temperature, indicating broken time-reversal symmetry and the existence of the longsought loop currents in the CDW phase. Our work strongly constrains the nature of the CDWs and sheds light on possible unconventional superconductivity in AV3Sb5.

报告人简介：

Liang Wu got his B.S. in Physics from Nanjing University in 2010 and Ph.D in Physics at Johns Hopkins University in 2015. He was a postdoc fellow in Physics at University of California, Berkeley from 2016 to 2018 before joining the department of Physics and Astronomy at the University of Pennsylvania in July 2018 as an assistant professor. He has been using terahertz spectroscopy and ultrafast optics to study topological insulators, Weyl semimetals and quantum magnets. He received the Richard Greene Dissertation Award in Experimental Condensed Matter Physics by the American Physical Society (2017), the McMillan Award for outstanding contribution in condensed matter physics from the University of Illinois (2019), and the Outstanding Young Researcher Award (Macronix Prize) from the International Organization of Chinese Physicists and Astronomer (2020).

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报告人：Shizeng Lin，Theoretical Division，Los Alamos National Laboratory

时间：7月13日（周三） 10:30

单位：中科院物理所

腾讯会议：784-604-337

会议链接：

摘要：

Chern insulator is a special type of insulator with a robust chiral edge model as a consequence of its nontrivial topology. Chern insulators have many important applications ranging from quantum metrology and topological quantum computation. However, experimental realization of the Chern insulator remains a challenge, and only a few materials are known to host the Chern insulating state. In this talk, I will present a new generic routine to achieve the Chern insulators by placing a massive Dirac fermion in a periodic potential. The band folding due to the periodic potential causes hybridization of the Dirac spectrum and stabilizes a Chern band. I will discuss the applications of our theory to two-dimensional transition metal dichalcogenide heterostructures. Finally, I will discuss the realization of the fractional Chern insulating state in the limit of strong Coulomb interaction .

报告人简介：

Dr. Shi-Zeng Lin received his PhD in physics from the University of Tsukuba and National Institute for Materials Science, Japan in 2010. Lin came to Los Alamos National Laboratory as a postdoctoral researcher in 2011 and became a Staff Scientist in 2014. Lin is a condensed matter theorist. His current research interests include magnetic skyrmions, topological and correlated states in two dimensional materials and heavy fermion materials. Lin has published about 100 papers including 17 Phys. Rev. Lett., 1 Phys. Rev. X, 4 Nature Physics / Electronics / Communications and 3 invited review articles.

4

报告人：何天深

时间：7月12日（周二）19:00

单位：Mindspore Quantum Special Interest Group

地点：

摘要：

第一期量子计算论文复现活动因其新颖的活动形式，吸引了众多量子计算兴趣爱好者加入到基于Mindspore Quantum开发算法的行动中来，通过对现有论文的研究，激发创新火花。

在本次活动中，我复现了论文《Accelerated variational algorithms for digital quantum simulation of many-body ground states》（arXiv: 2006.09415v3），该文章受到绝热演化（adiabatic evolution）的启发，巧妙地设计变分量子本征求解器（VQE）的量子线路，加速了一维海森堡模型的基态模拟。

本次分享中，我将首先由物理定律出发，解读文章提出的量子线路背后的物理思维与直觉；随后结合代码，详细展示基于MindQuantum和MindSpore的量子线路搭建和VQE变分优化过程；最后分享在复现过程我的创新思考，以及对于未来可继续研究方向的展望。

5

报告人：严飞，中国科学技术大学

时间：7月13日（周三）10:00

单位：中国科学院国家天文台

会议链接：

摘要：

随着大量的系外行星被发现，行星大气的研究正在成为系外行星领域迅速发展的方向之一。通过对系外行星的大气进行光谱观测，我们可以发现大气的组成成分，并且研究行星大气的温度结构、逃逸速率、全球环流等特性。在本报告中，我将重点介绍超热木星的大气观测。这一类行星具有极高的温度，其大气有丰富的可观测特征。我们在多颗超热木星大气中发现了包括氢、钙、铁、一氧化碳在内的多种大气成分。同时我们对多颗超热木星的热辐射光谱进行了观测，并且发现其大气中普遍存在逆温层。最后我将介绍我加入的三个高分辨率光谱仪项目组的情况，并对GTC-HRS在系外行星大气观测方面的重要作用进行展望。

报告人简介：

严飞，2015年于国家天文台获得博士学位，先后在德国马普天文所和哥廷根大学从事博士后研究。2022年加入中国科学技术大学天文系，入选国家青年人才计划。主要从事系外行星大气的观测与研究，近期在多颗超热木星大气中探测到多种大气成分，并且通过观测大气谱线进一步研究行星属性。目前为CRIRES+/VLT, PEPSI/LBT, CARMENES/CAHA-3.5m等高分辨率光谱仪的仪器项目组成员。共发表学术论文40余篇，总引用1500余次。

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报告人：Prof. Kaoru Sato，University of Tokyo

时间：7月13日（周三）15:00

单位：北京大学空间物理与应用技术研究所

会议链接：

摘要：

It has often been reported that warming at high latitudes in the Southern Hemisphere (SH) summer mesosphere and lower thermosphere (MLT) appears during Arctic sudden stratospheric warming (SSW) events. This phenomenon, which is called ‘‘interhemispheric coupling’’ (IHC), has been thought to occur because of the modulation of Lagrangian mesospheric meridional circulation driven by forcing of gravity waves (GWs) originating from the troposphere. However, quasi-two-day waves (QTDWs) regarded as Rossby-gravity waves (RGWs) develop during SSWs and result in strong wave forcing in the SH mesosphere. In addition, the contribution of secondary GWs generated in the middle atmosphere to the momentum budget has recently been highlighted. Thus, this study revisits IHC following Arctic SSWs from a viewpoint of wave forcing, not only by GWs and Rossby waves (RWs) originating in the troposphere but also by GWs, RWs, and RGWs generated in situ in the middle atmosphere, and elucidates the causes of warm anomalies in the SH MLT region. During SSWs, westward wind anomaly forms because of cold equatorial stratosphere, GW forcing is then modulated, and barotropic/baroclinic and shear instabilities are strengthened in the SH mesosphere. These instabilities generate QTDWs and GWs, respectively, which cause significant anomalous westward wave forcing, forming a warm anomaly in the SH MLT region. The intraseasonal variation in QTDW activity can explain seasonal dependence of the time lag in IHC. Moreover, it is revealed that the cold equatorial stratosphere is formed by middle-atmosphere Hadley circulation, which is strengthened by wave forcing associated with stationary RW breaking leading to SSWs. The IHC mechanism revealed in this study indicates that waves generated in the middle atmosphere contribute significantly to the meridional circulation, especially during SSWs. The key of the IHC mechanism lies in the modulation of the Lagrangian circulation in the middle atmosphere by waves. Thus, this seminar will begin with a review of the dynamics of the meridional circulation in the middle atmosphere in terms of absolute angular momentum conservation.

报告人简介：

Kaoru Sato is a professor at the University of Tokyo, Japan. She has contributed to studies of the dynamics of atmospheric gravity waves in terms of their generation, propagation, and interaction with the mean flow. Her recent research topic is the interhemispheric coupling in the middle atmosphere. She is a leader of the Program of the Antarctic Syowa Mesosphere–Stratosphere–Troposphere/Incoherent-Scatter radar (PANSY). She is the recipient of several awards including the Prize for Science and Technology from the Minister of Education, Culture, Sports, Science and Technology of Japan and the Medal with Purple Ribbon from the Emperor of Japan. She received her B.S. and M.S. degrees from the University of Tokyo and her Ph.D. degree from Kyoto University. Before serving in her present position, she worked as an assistant professor at Kyoto University and as an associate professor at the National Institute of Polar Research. She is currently President of the Meteorological Society of Japan and Section President of Atmospheric and Hydrospheric Sciences of Japan Geoscience Union.

7

报告人：邹卫文，上海交通大学

时间：7月15日（周五）19:00

单位：南京航天航空大学

会议链接：

摘要：

1、电子模数转换面临的挑战

2、光子模数转换的基本原理

3、子模数转换的典型架构与研究进展

4、光子模数转换的应用技术与示范

课程简述：随着5G互联网、人工智能、大数据、云技术的发展，数字化信息技术发展澎湃汹涌，已经浸润到了我们日常生活中的方方面面。模数转换作为数字化的核心环节，在信息化技术变革的浪潮中不断发展和创新。本课堂将简要介绍基于光电融合原理如何实现高速光子模数转换，以及相关研究动态与发展展望。

报告人简介：

邹卫文，上海交通大学教授、博导，智能微波光波融合创新中心主任及中心创始人，现任上海交通大学科研院副院长、科研质量管理处处长，曾任上海交通大学电院副院长（主管科研）。上海交通大学本科（2002年）和硕士（2005年），东京大学博士（2008年）、博士后（2010年）。国家自然科学基金优秀青年基金获得者（2018年）、重点项目首席科学家（2019年）、国家重点研发计划负责人（2020年）、IEEE高级会员（2013年）和OSA高级会员（2017年）、上海市浦江人才（2012年）。长期从事光电融合与集成技术研究。在《Light: Science and Applications》等国际主流期刊发表SCI论文百余篇，论文他引1058次。授权国家发明专利42项、美国专利9项、欧盟专利3项。作为第一完成人获2019年上海市技术发明一等奖。

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