多体量子态、散射振幅机器学习、几何阻挫竞争序、概率与频率 | 本周物理讲座

1

报告人：Li Yan，Fudan University

时间：4月22日（周二）10:30

单位：北京大学物理学院

地点：物理学院西楼B105

摘要：

There must be electromagnetic fields created during high-energy heavy-ion collisions. However, as the quark-gluon plasma (QGP) starts to evolve hydrodynamically (around 1fm/c), these fields become very likely weak comparing to the energy scales of the strong interaction. In this talk, I will introduce the weak magnetic effect in the standard hydrodynamic formulation, which emerges in QGP close to local thermal equilibrium as the dissipative correction to the quark phase space distribution function. Although it is a small correction, we found that the weak magnetic field can be crucial to the anisotropic emission of direct photons (the direct photon puzzle), the polarization of thermal dilepton from QGP, and the sign change of local Lambda hyperon polarization.

报告人简介：

Li Yan is currently an Assistant Professor at the Institute of Modern Physics, Fudan University. He obtained his PhD in 2013 from Stony Brook University. Afterward, he joined the Institut de Physique Théorique (IPhT) at Saclay, France, in 2013, and later the Department of Physics at McGill University in 2016 as a postdoctoral researcher. His research focuses on relativistic hydrodynamics and its application to quark-gluon plasma in high-energy heavy-ion collisions, the electromagnetic properties of quark-gluon plasma, and non-equilibrium systems.

2

报告人：孙志远，清华大学

时间：4月22日（周二）12:00

单位：江苏省物理学会

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摘要：

The ponderomotive force is an effective static force that a particle feels in an oscillating field. We generalize this notion to the static force felt by the collective degrees of freedom in periodically driven quantum many-body systems, and propose it as a tool to engineer their non-equilibrium steady states beyond the single particle level. Applied to materials driven by light, the ponderomotive potential is intimately related to the equilibrium optical conductivity, which is enhanced close to resonances. We show that the ponderomotive force from the uniform incident light may be used to induce exciton condensates in semiconductors, to generate attractive interactions leading to superconductivity in certain electron-phonon systems, and to create additional free energy minima in systems with charge/spin/excitonic orders. We also show that the ponderomotive force is a universal tool to tune electronic phases in optically driven cavities. These effects are presented with experimentally relevant parameters.

报告人简介：

Zhiyuan Sun obtained his BS in 2012 from University of Science and Technology of China, and his PhD in 2018 from UC San Diego. He worked as a postdoctoral/associate research scientist at Columbia University during 2018~2021, and as an HQI postdoc Fellow at Harvard University during 2021~2022. Since 2022, he has been an assistant professor at the physics department of Tsinghua University. Zhiyuan works on condensed matter theory, specifically, nonequilibrium phenomena in many-body systems, light-matter interactions, and nano-optics.

3

报告人：李峣，南开大学

时间：4月23日（周三）10:00

单位：中国科学院理论物理研究所

地点：北楼5层CCAST报告厅

摘要：

Topological defects are fundamental concepts in theoretical physics, widely interested by fields from cosmology to condensed matter. To tile the surface by triangular lattice cells alone, topological defects become inevitable due to geometric frustration. The theory is well developed by Casper-Klug inspired by viruses. However, to tile the spherical surface by both types of lattice cells, the answer is wide open. We have discovered surprising novel types of topological defects, including enclave d and counter - enclaved domain defects, which possess unexpected topological intensities. We will also discuss the new global symmetries arising from the newly found topological defects. Our study unlocks new avenues for understanding numerous challenges in physics, materialscience, and related biological physics.

报告人简介：

李峣，2014年于清华大学物理系获得理论物理博士学位，期间2013-2014年在加拿大滑铁卢大学访问研究。随后在AMOLF和代尔夫特理工大学从事博士后研究工作，2021年加入南开大学物理学院任副教授。长期从事软物质统计物理理论和模拟研究工作，研究兴趣包括微分几何下的统计物理：生物膜弹性和动力学、胶体、高分子、蛋白核酸等生物分子的组装和动力学等。

4

报告人：Ching Hua Lee，National University of Singapore

时间：4月23日（周三）15:00

单位：北京大学物理学院

地点：西563会议室

摘要：

Non-Hermitian phenomena such as the non-Hermitian skin effect (NHSE) and exceptional point sensitivity have no Hermitian analogs, and have lately reshaped the way we understand band structures and topology. In this talk, I shall introduce some new ideas that extend the current repertoire of novel non-Hermitian phenomena. such as system-size dependent generalized Brillouin zones (GBZs), as well as GBZs defined in phase space. I shall also highlight how the NHSE can interplay with the geometric defectiveness of exceptional points to lead to novel exceptional bound bands with super volume-law negative entanglement scaling. Finally, I will also review how non-Hermitian processes havebeen recently simulated in unitary quantum simulators.

报告人简介：

Prof Ching Hua Lee obtained a PhD from Stanford University under the tutelage of Prof Xiaoliang Qi. He joined the National University of Singapore in 2020, and is now heading a team focusing on exploring novel non-Hermitian phenomena, as well as their simulation on classical and quantum circuits. Prof Lee publishes regularly in top scientific journals, and has been cited over 10000 times in the recent years.

5

报告人：蔡子，上海交通大学

时间：4月24日（周四）15:00

单位：北京大学物理学院

地点：物理大楼中212报告厅

摘要：

Spontaneous symmetry breaking and elementary excitation are two of the pillars of condensed matter physics that are closely related to each other. The symmetry and its spontaneous breaking not only control the dynamics and spectrum of elementary excitations, but also determine their underlying structures. In this talk, we study the excitation properties of non-equilibrium quantum matters: In the first part, we propose an instanton-like excitation that represents a tunneling between two ``degenerate'' time crystal phases, which spontaneously breaks the discrete temporal translational symmetry. In the second part, we will discuss how the non-equilibrium feature of a driven-dissipative magnet qualitatively changes the dynamical behavior of the quasi-particles and give rise to an emergent confinement between them.

报告人简介：

蔡子，2010年于中国科学院物理研究所凝聚态理论专业取得博士学位。先后在美国加州大学圣迭戈分校，德国慕尼黑大学，奥地利科学院量子光学与量子信息研究所从事博士后工作。现任上海交通大学物理与天文学院教授，博士生导师。主要从事凝聚态物理以及相关领域的数值和理论方面的工作，研究领域涉及强关联电子系统，光晶格中的超冷原子,开放量子多体系统，非平衡统计物理，机器学习方法在物理学中的应用等方向，近年来发表括1篇Science、12篇Phys. Rev. Lett.在内的SCI论文五十余篇。

6

报告人：Mark Thompson，利兹大学

时间：4月24日（周四）15:30

主办：北京大学物理学院

地点：KIAA-auditorium

摘要：

I will describe the SKA precursor telescope MeerKAT and some of its recent results, concentrating on the largest and deepest Galactic Plane survey carried out with MeerKAT, the SARAO MeerKAT 1.3 GHz Galactic Plane Survey (SMGPS). SMGPS is revolutionising the study of Galactic radio populations and has resulted in the discovery of many new Supernova Remnants, planetary nebular, and a novel population of non-thermal radio filaments in the Galactic Plane. I will also look forward to potential upgrades to MeerKAT and the kinds of surveys that will be possible with the Square Kilometre Array.

报告人简介：

Mark started out his studies with a BSc in Astronomy and Astrophysics and an MSc in Electronics at the University of Newcastle-upon-Tyne (UK) from 1990-1994. After working as a software engineer he passed his PhD in Millimetre Wave Astronomy at the University of Kent (UK) in 1999 where he worked as a postdoc for the following 5 years. Mark became a lecturer at the University of Hertfordshire (UK) in 2004, eventually becoming Dean of the School of Physics Astronomy and Mathematics in 2015 and Professor Astrophysics in 2019. In 2021 Mark joined the University of Leeds (UK) as their new Head of the School of Physics and Astronomy, where he is now the Head of the Astrophysics Research Group. Mark’s main research interests are in massive star formation and Galactic Plane surveys. He works mainly in the far-infrared to radio wavelength ranges and has been closely involved in most of the major Galactic Plane surveys, e.g. with Herschel, the JCMT, JVLA and MeerKAT. His most recent survey project is the SARAO MeerKAT 1.3 GHz Galactic Plane survey, the most sensitive radio survey of the Galactic Plane yet carried out.

7

报告人：Nicolò Defenu，ETH Zurich

时间：4月24日（周四）16:00

单位：中国科大统计和计算物理邓友金课题组

链接：

摘要：

This talk explores the unique non-equilibrium phenomena in quantum many-body systems with long-range interactions, driven by recent experimental advancements. We will review the equilibrium properties of long-range interacting quantum spin systems, focusing on the variable-range quantum XY model and its equilibrium phase diagram. The impact of finite-range interactions on the quantum paramagnetic and ferromagnetic phases will be examined. The core of the talk addresses out-of-equilibrium dynamics, including the spreading of quantum correlations, slowdown of entanglement dynamics, suppression of thermalization, and the appearance of long-lived metastable states. The stabilization of non-equilibrium phases by periodic driving, such as discrete time crystals, will also be discussed.

This talk aims to provide a comprehensive overview of recent advances, emphasizing the need for a unifying framework to connect few-body mean-field physics with many-body physics of quasi-local interactions, with implications for future quantum-technological applications.

报告人简介：

Nicolò Defenu is an Italian physicist specializing in theoretical physics, particularly in quantum many-body systems and critical phenomena. He completed his BSc and MSc with honors at Sapienza University of Rome and earned his PhD from the International School for Advanced Studies (SISSA) in Trieste in 2017. After his PhD, Defenu held postdoctoral positions at the Institute for Theoretical Physics in Heidelberg and ETH Zurich. Among several grants and fellowships, he received the ERC Starting Grant on 2022 and, one year later, became an assistant professor at ETH Zurich. His research focuses universality, low-energy physics and quantum technology.

8

报告人：Anupam Chattopadhyay，南洋理工大学

时间：4月24日（周四）22:00

单位：圣母大学、麻省理工学院

链接：

摘要：

量子计算在算法、软件和硬件等所有设计堆栈方面取得的重大进展，已经让我们无法忽视量子计算对我们周围世界的影响。我们将在本讲座中介绍量子计算的两个方面。首先是高效电路设计和自动化挑战，以及我们如何从经典计算中借鉴一些知识。最后，我们将介绍量子计算机实验案例研究。其次，大规模量子计算机最重要的实际威胁是公钥密码学。我们将通过开发和标准化后量子密码学（PQC）基元来应对这一威胁。我们将讨论各种PQC候选方案以及迁移到量子安全环境的危险。

报告人简介：

Anupam Chattopadhyay分别于2000年、2002年和2008年获得印度贾达夫普尔大学电子工程学士学位、RWTH Aachen理学硕士学位和RWTH Aachen博士学位。自2014年9月起，他在新加坡南洋理工大学计算机与数据科学学院担任副教授，任期自2019年8月起。他的研究兴趣包括新兴技术、电子设计自动化、系统设计以及网络安全与人工智能之间的交叉课题。Anupam 是 IEEE 和 ACM 的资深会员。他曾获得 JSPS 访问奖学金，并担任过IEEE EDA理事会杰出讲师。他的研究成果发表在 ACM/IEEE Transactions、Nature Scientific Reports、Physical Review、多部研究专著、Springer Major Reference Works上，并促成了 EDA、物联网和网络安全领域的多项衍生产品/技术转让。

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报告人：蔡恬吉，SLAC National Accelerator Laboratory

时间：4月25日（周五）11:00

单位：北京大学物理学院

地点：物理学院西楼B105

摘要：

AI for fundamental physics is now a burgeoning field, with numerous efforts pushing the boundaries of experimental and theoretical physics, as well as machine learning research itself. In this talk, I will introduce a recent innovative application of Natural Language Processing to the state-of-the-art precision calculations in high energy particle physics. Specifically, we use Transformers to predict symbolic mathematical expressions that represent scattering amplitudes in planar N = 4 Super Yang - Mills theory—a quantum field theory closely related to the real - world QCD at the Large Hadron Collider. Our first results have demonstrated great promises of Transformers for amplitude calculations, while its major challenges are being addressed by ongoing work. This study opens the door for an exciting new scientific paradigm where discoveries and human insights are inspired and aided by an AI agent.

报告人简介：

Tianji Cai (蔡恬吉) is a postdoctoral research associate in the Fundamental Physics Directorate at the SLAC National Accelerator Laboratory, and a research affiliate at the Lawrence Berkeley National Laboratory. She obtained her Ph.D. degree in 2023 at University of California, Santa Barbara, and holds two bachelor's degrees from Duke University and Shanghai Jiao Tong University. Her research interest lies at the intersection of High Energy Theory (HEP) and Artificial Intelligence (AI), with a focus on developing novel machine learning frameworks for collider phenomenology and scattering amplitudes. She’s also interested in using HEP to aid theoretical understanding of AI systems.

10

报告人：吴从军，西湖大学

时间：4月27日（下周一）9:00

主办方：国际纳米热力学读书会、《概率论沉思录》读书会、蔻享学术、科普中国、返朴

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摘要：

E.T.Jaynes 是著名数学物理学家，曾任华盛顿大学和斯坦福大学教授:在统计力学和概率统计推断方面有杰出贡献。因提出了最大原理(1957年)和 Jaynes-Cummings 模型(1963 年) 而闻名于世。Jaynes 大力提倡将概率论解释为逻辑的延伸。《概率论沉思录》(Jaynes,ProbabilityTheory: The Logic of Science)凝聚了他毕生的研究成果和心得,将概率论和统计推断融合在一起，作为整个科学的逻辑基础。该书表明，概率论的应用范围远比传统频率派所设定的要广泛，他用新的观点生动描述了概率论(特别是贝叶斯理论)在数学、物理学、化学、生物学和经济学等领域中的广泛应用,揭开了众多悖论背后的玄机。

本次报告将详细讲解《概率论沉思录》第9 章“重复实验：概率与频率”。

报告人简介：

吴从军教授于2005年获得斯坦福大学Ph.D.学位 (物理学)，并从2005年至2007年期间在加州大学圣芭芭拉分校Kavli理论物理研究所从事博士后研究。他于2007年加入加州大学圣迭戈分校物理系任助理教授，2011年晋升副教授, 2017年正式晋升为正教授。他曾于2008年获Sloan Research Fellowship和海外华人物理协会（现名全球华人物理学会）杰出青年科学家奖。2018年，他当选为美国物理学会会士（APS Fellow）。2021年起，他已全职加入西湖大学，受聘物理学讲席教授。在2022年，他被选为新基石研究员。吴从军教授的研究兴趣是探索新的物质状态及其深层次的组织原理，包括超导、量子磁性、轨道物理、拓扑物态、强关联冷原子系统、数学物理、和量子蒙特卡洛模拟。

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