Strong Field QED | 本周物理学讲座

来源：中国物理学会期刊网

1Strong Field QED

报告人：Sang Pyo Kim，Kunsan National University

时间：8月20日（周二）10:00

单位：中科院理论物理所

地点：新楼6420报告厅

Heisenberg and Euler found the one-loop affective action in a constant electromagnetic field soon after Dirac theory was discovered, and Schwinger introduced the proper-time integral representation of QED action and showed that strong electric fields could spontaneously produce electron-positron pairs, the so-called (Sauter-) Schwinger pair production. With the discovery of neutron stars and/or magnetars, cosmic scale magnetic field and the advent of (ultra-) intense lasers via the chirped pulsed amplification (CPA) technology by Mourou and Strickland, physics in strong electromagnetic fields has been emerging as a new science in the 21st century as much as gravitational waves from strong gravity sources. In the first talk, theoretical aspects of strong field QED will be explained from vacuum polarization to Schwinger pair production to nonlinear Compton scattering.  An electron or charges in a uniform electromagnetic field is described by the dressed propagator, which is equivalent to a free electron interacting with arbitrary number of photons, and which leads to the one-loop effective action. After briefly explaining a few well known methods for finding one-loop effective action, the gamma-function regularization method is introduced, which is based on Schwinger-DeWitt variational principle in the in-out formalism, and Schwinger pair production is discussed in the in-out formalism. Vacuum birefringence, light-light scattering, and nonlinear Compton scattering are discussed in strong electromagnetic fields. Finally, the gamma-function regularization is applied to find the one-loop effective action in a uniform electric and/or magnetic field in (anti-) de Sitter space, and Schwinger pair production is discussed in (anti-) de Sitter space and charged black holes.

2Salient physics of transition metaldichalcogenides

报告人：Shengbai Zhang，Rensselaer Polytechnic Institute

时间：8月20日（周二）10:00

单位：中科院半导体研究所

地点：2号楼303A会议室

3Multifunctional Electronic Devices Based on Transition Metal Oxide

报告人：Yang Chai，The Hong Kong Polytechnic University

时间：8月20日（周二）14:00

单位：中科院物理研究所

地点：M楼253会议室

In this talk, we will first demonstrate multifunctional supercapacitor devices - solar-powered photovoltachromic supercapacitors (PVCSs) by vertically integrating a perovskite solar cell (PSC) with MoO3/Au/MoO3 transparent electrode and electrochromic supercapacitor into>Neuromorphic visual systems have considerable potential to emulate basic functions of the human visual system even beyond the visible light region. However, the complex circuitry of artificial visual systems based on conventional image sensors, memory and processing units presents serious challenges in terms of device integration and power consumption. Here we show simple two-terminal MoO3 optoelectronic resistive random access memory (ORRAM) synaptic devices for an efficient neuromorphic visual system that exhibit non-volatile optical resistive switching and light-tunable synaptic behaviours. The ORRAM arrays enable image sensing and memory functions as well as neuromorphic visual pre-processing with an improved processing efficiency and image recognition rate in the subsequent processing tasks. The proof-of-concept device provides the potential to simplify the circuitry of a neuromorphic visual system and contribute to the development of applications in edge computing and the internet of things.

4Biophysical Characteristics of Revolving Biomotors, Asymmetrical ATPase Hexamers, single pore sensing, and RNA nanotechnology

报告人：郭培宣，美国俄亥俄州立大学

时间：8月20日（周二）14:00

单位：中科院物理研究所

地点：M楼238会议室

5Imaging Electronic and Magnetic States in 2D Quantum Materials

报告人：Yongtao Cui，University of California, Riverside

时间：8月20日（周二）15:30

单位：清华大学

地点：物理系理科楼C302

Two-dimensional materials have served as a rich playground to study emerging phenomena and exotic physics at low dimensions. Since the discovery of graphene, atomically thin materials of many different electronic and magnetic properties have been identified experimentally. The most recent additions are 2D topological insulators and 2D magnets. In this talk, I will present our recent studies on two of these materials, WTe2 and CrI3, with scanning probe microscopy. In the first part, we use microwave impedance microscopy to directly image the edge conduction in monolayer WTe2. The observed behaviors are fully consistent with the expectations for topological edge states, and also reveal many details about the edge conduction that are important for improving transport studies. In the second part, we apply magnetic force microscopy to study thin CrI3 flakes. By probing the magnetic switching process in CrI3, we find that two types of magnetic orders coexist in these flakes, one at surface and the other inside the bulk, corresponding to different layer stacking orders.

6Many-Body Dephasing in a Trapped Ion Quantum Simulator

报告人：Lingzhen Guo，Max Planck Institute for the Science of Light

时间：8月21日（周三）10:00

单位：中科院物理研究所

地点：M253会议室

After a quench in a quantum many-body system, expectation values tend to relax towards long-time averages. However, temporal fluctuations remain in the long-time limit, and it is crucial to study the suppression of these fluctuations with increasing system size. The particularly important case of nonintegrable models has been addressed so far only by numerics and conjectures based on analytical bounds. In this work, we are able to get analytical predictions for the temporal fluctuations in a nonintegrable model. We thus identify a dynamical regime of “many-body dephasing”, where the dephasing is not from thermalization but from the  lift of exponentially large degeneracies of transition energies. We also work together with the trapped-ion experimental group at Maryland University and present a recent (also first) experiment verifying the system size scaling predicted by many-body dephasing.

7Cellular Synthesis of Topological Proteins

报告人：张文彬，北京大学

时间：8月21日（周三）10:30

单位：中科院物理研究所

地点：M楼238会议室

Chemical topology has emerged as a unique dimension for protein engineering. Nature has demonstrated the power of protein topology engineering in a small yet elegant set of proteins with nontrivial topology (such as cyclotides and lasso peptides possessing exceptional bioactivity and stability). However, artificial topological proteins remain scarce. In this talk, I will discuss our recent efforts in the field of protein topology engineering from the development of genetically encoded protein chemical tools to the cellular synthesis of topological/mechano-proteins and further to the their biological significance and potential applications. Through strategies such as the “assembly-reaction” synergy and the active-template method, we have prepared various topological proteins including cyclic proteins, star proteins, protein catenanes, lasso proteins, protein heterocatenanes and polycatenanes. Their unique topologies have been proven by combined techniques such as controlled digestion experiments, NMR spectrometry, and protein crystallography. Among them, proteins with mechanical bonds (“mechanoproteins”) are of particular interest owing to their potential functional benefits such as structure stabilization, quaternary structure control, synergistic multivalency effect and dynamic mechanical sliding/switching properties. Specifically, protein catenanes containing folded structural domains have been found to exhibit enhanced stability toward proteolytic digestion, heat/chemical denaturation, and freeze-thawing treatments, which are highly desired features for enzymes in industry and protein therapeutics. These results suggest that topology is indeed a unique dimension for protein engineering.

8Nucleosynthesis in heavy-ion collisions at the LHC via the Saha equation

报告人：Carsten Greiner，德国法兰克福大学

时间：8月22日（周四）10:00

单位：清华大学

地点：物理系理科楼B315

A major challenge in condensed matter physics, chemistry, and materials is to be able to compute the properties of electrons in real materials. Auxiliary field quantum Monte Carlo is a promising numerical method for these systems. It is proven to be highly accurate and be able to treat large number of electrons in the Simons many-electron collaboration. We apply the state of art auxiliary field quantum Monte Carlo for realistic transition metal systems. The many-body ab initio Hamiltonian is treated directly on transition metal atoms, their ions, and their monoxide molecules. We show ionization energy and dissociation energy on transition metal systems are indistinguishable from experimental results. Then, we studied the low temperature phase diagram of Ca2RuO4 for a range of layered perovskite structures. Our calculations find that the metal-insulator transition in Ca2RuO4 is driven by a structural transition from a long c-axis to a short c-axis perovskite in this material and is accompanied by a ferromagnetic-antiferromagnetic transition. Our many-body simulations capture the phase diagram and explain the origin of the magnetic and metal-insulator transitions in Ca2RuO4.

9Blazar OJ287 and its nano-Hertz GW emitting massive BH binary central engine

报告人：A. Gopakumar，Tata Institute of Fundamental Research

时间：8月22日（周四）12:00

单位：北京大学

地点：1st meeting room, KIAA

Blazars are active galactic nuclei with strong jets. Theytend to exhibit dramatic and unpredictable flux variations, namely outbursts.Certain observed outbursts from an exceptional Blazar OJ287can be explained by invoking a massive black hole binary as its central engine.Detailed General Relativistic modeling allowed us to predict a majoroptical outburst during November 2015. The outburst did occur within the expected time range, peaking on 5/12/2015.A multi-wavelength observational campaign confirmed the  occurrence of certain impact flare and the presence of a major thermal component in the flare, as predicted.These observations and subsequent analysis allowed us to establish the possible presence ofa spinning supermassive black hole binary that spirals in due to the emission ofnano-Hertz gravitational waves in the central engine of OJ287.I will  briefly list our on-going efforts that should be interesting tothe Event Horizon Telescope Consortium and the International Pulsar Timing Array.

10Floquet Higher-Order Topological Insulators: Dynamical Quadrupoles, Singularities, and Detections

报告人：Biao Huang，University of Pittsburgh

时间：8月22日（周四）14:00

单位：中科院物理研究所

地点：M楼830

The theoretical and experimental discovery of topological insulators of higher multipole nature, dubbed “higher order topological insulators”, has triggered heated discussions in recent studies. But so far, researches have chiefly been limited to static systems due to the lack of higher order topological invariants constructed for a genuine dynamical system. Here, we report Floquet-driven models showing the anomalous corner states and a construction of dynamical charge polarization of higher order nature. More generically, we proposed characterizing the topology using higher order dynamical singularities, which coincide with results given by Floquet-Wilson loop constructions. Finally, a cold atom experiment scheme is proposed, which would detect not only the existence of corner states, but also their dynamical origin, which has been absent from previous experiments in all kinds of platforms.

11The mass relations between supermassive Black Holes and their host galaxies at 1<z<2 with HST-WFC3

报告人：Xuheng Ding，UCLA

时间：8月23日（周五）12:00

单位：北京大学

地点：1st meeting room, KIAA

Most galactic nuclei harbor a supermassive black hole (BH), whose mass is well known to correlate with the host properties including luminosity, stellar mass, stellar velocity dispersion. These tight correlations suggest a physical coupling between supermassive BH growth and galaxy evolution. One key to understanding this coupling is tracing this correlation to higher redshift, determining how and when they emerged and evolved over cosmic time. In this talk, I will describe my recent work that overcomes the systematics at higher redshift and establish whether the BH-host relation evolves with cosmic time. I will present the measurements of 32 X-ray selected AGNs (1.2<z<1.7), whose host mass are inferred using HST imaging data and BH masses are estimated using Balmer lines.

更多报告信息：中国物理学会期刊网学术讲座列表

▼

往期精彩回顾

▼

1.基于对称性指标预测拓扑材料（下）

2.人工光学微结构研究进展

3.微纳尺度腔量子电动力学

4.能谷光子晶体与拓扑光传输

5.传染性疾病遇上纳米生物传感器

6.玻恩如何帮助学生——以对杨立铭的关照为例

7.量子十问之九：量子传感刷新测量技术极限 | 郭光灿

8.天行见物理之六：清漏声长

9.如何理解数学？从纠正对数学的偏见开始——得数学者得天下

10.第五届凝聚态物理会议成功举办