拓扑相变与拓扑量子物态 || 本周物理学术讲座

报告人：张广铭，清华大学

时间： 5月11日（周四）10:00

单位：清华大学物理系

地点：理科楼C302报告厅

以经典二维Ising自旋模型系统为例，将全面系统地回顾有关热力学物态及其相变的基本概念和重要结论，即凝聚态物理学奠基石之一的朗道连续相变理论。随后在经典二维XY自旋模型研究中，Kostrlitz-Thouless发现自旋涡旋激发的存在，从而建立了首个超越朗道范式的拓扑相变。受此影响，D. F. M. Haldane研究了一维量子海森堡自旋链模型系统，首次提出自旋整数链为有能隙的拓扑量子态，而自旋半整数链为自旋液体态。随着整数量子Hall效应的发现，Thou less及其合作者研究表明，二维固体系统中的电子在磁场下可以形成量子Hall态，并证明Hall电导即为拓扑不变量--Chern数。Haldane自旋拓扑态、量子Hall态及其变种（如：量子自旋Hall态、量子反常Hall态），以及分数量子Hall态等形成了大量的新奇拓扑量子物态，研究这些拓扑量子物态及其之间的拓扑量子相变形成了凝聚态物理学的新篇章，具有极大的挑战性和重大的物理意义。

报告人：丁阳，北京高压科学研究中心

时间： 5月10日（周三）10:00

单位：中科院物理所

地点：M楼238会议室

高压科学和现代同步辐射源的结合极大推进了多个学科领域的进步和发展，其中也包含了对凝聚态物理中强关联电子体系的研究。一方面，压力作为一种干净的，理论上相对简单的调制手段,可以有效地调节改变强关联电子体系中的各种竞争作用，而产生新的物质态；另一方面，同步辐射和高压环境的结合，使得高压下呈现的各种新现象可以被观测和研究。 据此本讲座将简单地介绍近几年来，我组在利用先进的高压同步辐射技术研究过渡金属化物的磁性，绝缘体-金属相变的一些工作，并着重介绍我组对高温超导体Bi2212的最新研究成果。

报告人：胡雪元，山东大学

时间：5月9日（周二）14:30

单位：北京大学物理学院

地点：物理楼中楼215教室

若可执行的操作受限，某些难以制备的物理性质则显得尤为珍贵，这些物理性质可被用于提高特定任务的效率，因而被称为资源。资源理论，是为分析在计算、通信、能量提取等任务中所需的物理资源而建立的普适理论，被称为“理论的理论”。量子资源理论主要致力于刻画和度量包含在在量子态中纠缠、相干性等具体资源，包括如下三要素：自由态、自由操作和单位资源态。我们提出资源消除映射(Resource Destroying Map)的概念，并由此给出量子操作的分类和一种数学形式简单的普适的资源度量。上述理论可应用于量子相干性等资源理论，并有助于量子关联的资源理论建立。此外，我们关注量子相干性这一具体资源理论，探讨相关性和量子关联之间的内在联系，并讨论各类相干性度量在非相干产生信道下的单调性。

报告人：翟荟，清华大学

时间：5月9日（周二）15:00

单位：中科院高能物理研究所

地点：Theoretical Physics Division，319

In this talk, the speaker will discuss several examples of interesting universal dynamics with quantum simulation. In the first example, he will discuss an expansion dynamics of scale invariant quantum gases in a time-dependent harmonic trap, that displays a discrete temporal scaling symmetry, and we term it as “the Efimovian expansion”. This dynamics reveals the scaling symmetry and the emergent conformal symmetry of strongly interacting quantum system. In the second example, he will discuss quench dynamics from a topological trivial Chern insulator to a topological nontrivial one, and we show how to extract a quantized value from the quench dynamics, that exactly equals to the topological Chern number of the final Hamiltonian after the quench. In the third example, he will prove a theorem that relates the entropy growth after a quench to the out-of-time-ordered correlation that recently discussed in the content of quantum chaos and holographic duality. This three examples reveal the interplay between quantum dynamics with symmetry, topology and entropy, respectively.

报告人：Jiajun Liao，University of Hawaii

时间：5月9日（周二）15:30

单位：中科院理论物理研究所

地点：新楼6620报告厅

Neutrino physics is entering the precision era, and the current and future neutrino oscillation experiments will be sensitive to new physics beyond the standard model (SM). A model-independent way of studying new physics in neutrino oscillation experiments is provided by the framework of nonstandard interactions (NSI). In this talk, I will first show a hint of NSI may have been seen in the current NOvA and T2K data, and then I will discuss sensitivities to SM and NSI parameters at future long-baseline neutrino experiments like DUNE, T2HK and T2HKK. Detection of NSI in solar neutrino oscillations with Hyper-Kamiokande and JUNO will also be shown and discussed.

报告人：Rajesh Gopakumar，ICTS-TIFR

时间： 5月10日（周三）15:30

单位：中科院理论物理研究所

地点：Conference Hall 322

We describe a new approach towards analytically solving for the dynamical content of Conformal Field Theories (CFTs) using the bootstrap philosophy. This combines the original bootstrap idea of Polyakov with the modern technology of the Mellin representation of CFT amplitudes. We illustrate the power of this method in the epsilon expansion of the Wilson-Fisher fixed point by reproducing anomalous dimensions and obtaining OPE coefficients to higher orders in epsilon than currently available using other analytic techniques (including Feynman diagram calculations). Our results enable us to get a somewhat better agreement of certain observables in the 3d Ising model, with the precise numerical values that have been recently obtained.

报告人：Long Zhang, ICQM, PKU

时间： 5月11日（周四）11:00

单位：中科院物理所

地点：中国科学院大学中关村校区教学楼S401

In this journal club presentation, I will introduce the notion of "Floquet time crystals", i.e., periodically driven systems that spontaneously break the discrete time translation symmetry.

报告人：Junfeng Wang，XMU

时间： 5月11日（周四）14:00

单位：清华大学物理系

地点：蒙民伟科技南楼S727

The circumnuclear region in nearby active galaxies allows a more detailed view of the AGN-host galaxy interaction than their high redshift siblings. However, it is ubiquitously highly complex with presence of ionized gas, collimated radio outflow, and star formation activities, besides the active nucleus. I will present the CHandra Extended Emission Line Region Survey (CHEERS), an X-ray imaging spectroscopic study of the circumnuclear regions of nearby archetypal Seyfert galaxies, designed to take full advantage of Chandra's unique angular resolution by spatially resolving feedback signatures, jet-cloud interactions and merger activities. Supplemented with observations in other wavelength, the line ratios and kinematics provide keys to diagnose if the line emission is excited through photoionization by the active nucleus or through high-velocity shocks generated at the interface between an outflow and the ISM.

报告人：Joachim Ankerhold， Ulm University

时间： 5月11日（周四）10:30

单位：北京师范大学物理学系

地点：物理楼106

Activities to combine these two previously almost distinct fields, quantum optics and quantum electronics, have appeared only very recently with the advent of Josephson photonics. This opens a new playground to study a wealth of phenomena far from equilibrium including non-classical light sources, ultra-strong charge-light interactions, nonlinear quantum oscillators, and quantum phase transitions in steady state. In this talk I will discuss experimental developments in line with the theoretical background.

报告人：仇旻，浙江大学

时间： 5月11日（周四）14:30

单位：北京师范大学物理学系

地点：物理楼106

表面等离激元纳米结构由于其能提供亚波长光场约束与光场调控，能大大提高局域光场强度，提升光电器件性能，在光电集成、通讯、传感、显示等等方面具有着重要的应用意义。然而通常的表面等离激元纳米结构由金属构成，具有几乎不可避免的材料损耗（吸收），造成器件性能低下。我们最近几年则另辟蹊径，专注于研究如何利用表面等离激元纳米结构来增强光吸收并实现高效光热转换。在本报告中，我们将回顾我们实验室在表面等离激元纳米结构宽带、窄带吸收器，吸收增强的分子-谐振强耦合，光热转换，光热调控，纳米焊接，光热力，热辐射等等方面的工作，并探讨其实际的应用。

报告人：Yury Bliokh and Valentin Freilikher，Technion-Israel Institute of Technology (YB) and Bar-Ilan University (VF)

时间： 5月11日（周四）15:00

单位：中科院理论物理研究所

地点：新楼6620报告厅

In this talk, the physical and mathematical aspects of Anderson localization are discussed, and a review of the recent theoretical and experimental studies of this phenomenon is presented. It is shown that the unique spectral and transport properties of random structures can be utilized for developing "disordered photonics" as an alternative for periodic optical systems.

报告人：赵俊，复旦大学