報告人：朱詩亮，南京大學物理學院
時間：12月27日（周四）16:00
單位：清華大學
地點：理科樓鄭裕彤講堂
相位因子被稱為二十世紀理論物理學研究三大主旋律之一。幾何相因子(幾何相位)的提出是量子力學研究的開創性成果。相位因子是量子力學最核心的概念之一，對它的認識伴隨著整個量子力學和量子場論的發展。薛丁格方程的提出，虛數i首次出現在物理學運動方程中，表明複數的引進不僅是數學工具的方便，更是量子力學描述世界的必須，相位開始成為物理學的核心概念。稍後，狄拉克引入波函數相位因子，並用它證明，如果世界上有一個磁單極，那麼電荷必須是量子化的，這一優美的理論把相位和拓撲聯繫在一起。1954年，楊振寧-米爾斯非阿貝爾規範場理論的提出，把U(1)相位推廣到SU(2)相位，構築了粒子之間相互作用的基石。1959年，Aharonov 和Bohm 發現了AB相位，認識到要描述電磁場，場強不夠，矢勢更為基本。從1974年開始，楊振寧等用系列文章證明，要描述規範場，場強不足夠，矢勢有冗餘，而相位因子恰好能描述規範勢。
1984年，Berry發表了提出幾何相位的論文。證明相因子只能分成動力學相位和幾何相位。幾何相位及其相關的Berry聯絡（Berry曲率）因深刻地反映了Hilbert空間的基本結構而在物理學的各個領域都有重要應用，這些領域包括較早的量子霍爾效應，及最近物理學的一些重要研究領域，如拓撲絕緣體和拓撲超導、量子計算、量子模擬等。在本報告中，我將主要介紹：(1) 相位和幾何相位的簡史；（2）幾何相位在容錯量子計算中的重要應用；（3）幾何相位在超冷原子模擬人工規範勢中的應用。量子計算和超冷原子量子模擬都是當代物理學研究的重要前沿課題。
報告人：Zhou Chen
時間：12月26日（周三）10:30
單位：清華大學
地點：物理系理科樓C302
Observation of Higgs boson production in association with a top quark pair (ttH) is presented, based on the analysis of up to 79.8 fb 1 of proton-proton collision data produced at 13 TeV center-of-mass energy by the Large Hadron Collider and recorded with the ATLAS detector. The results for Higgs boson decay channels of bb, diphoton, WW, ditau, and ZZ are combined. The observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the ttH searches using a dataset corresponding to integrated luminosities of 4.5 and 20.3 fb 1 at 7 and 8 TeV, respectively, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total ttH production cross section at 13 TeV is measured to be 670 ± 90 (stat.) +110/-100 (syst.) fb, while the Standard Model prediction is 507+35 50 fb. CERN issued a press release for both the ATLAS and CMS ttH results on June 4th 2018. Moreover, this talk will give detailed description of the new ttH (H→gamma gamma) analysis. Applying advanced machine learning package XGBoost BDT, exceptional performance is achieved by using object level kinematic variables from jets, leptons, and photons to separate the ttH signal from the background.
報告人：Helen Poon，Hiroshima University
單位：清華大學
時間：12月26日（周三）10:30
地點：蒙民偉科技南樓S727
Since LIGO detected GW150914, there has been a revolution in the field of astronomy. Japan has been making a lot of contribution to the understanding of gravitational waves. In the end of 2017, a nation-wide project called "Gravitational wave physics and astronomy: Genesis" has been set up which combines the effort of theories, observations and experiments. As an important collaboration institute, Hiroshima University contributes a lot in the field of high energy and optical observations. In this talk, I will introduce the gravitational wave activities in our group, including a CubeSat with good localization under development - CAMELOT, a UV-optical telescope in Tibet - Hinotori and the 1.5m optical-NIR telescope KANATA in East Hiroshima.
報告人：郭春付
時間：12月26日（周三）13:30
單位：北京師範大學
地點：物理樓106
報告人：李向平，暨南大學
時間：12月26日（周三）15:10
單位：北京大學
地點：物理樓 中212
Surface plasmons (SPs) propagating along the interface between metals and dielectrics are capable of tailoring light matter interaction at the nanoscale, which emerges as a research frontier in nanophotonics. In this talk, we introduce the recent progress of multi-dimensional high capacity optical information storage and multi-functional metasurfaces by nanoplasmonics. As a consequence of resonant excitation of plasmonic nanoparticles, strong photothermal effect leads to permanent shape transitions, which unfolds a new platform for multiplexed information storage. Through the investigation of polarization-sensitive and orbital angular momentum sensitive plasmonic resonance in plasmonic nanostructures, information can be multiplexed in the multiple physical divisions of light for orders of magnitude increased information capacity. Moreover, metasurfaces composed of arrays of subwavelength artificial meta-atoms offer unprecedented capability of wavefront manipulation for a variety of applications. By structuring and patterning plasmonic nanostructures in a diatomic arrangement we demonstrate wide-angle and full-polarization controlled vectorial holography. Further, precise structuring the plasmonic nanostructures leads to vivid color generations. Color images can be encrypted in the angular anisotropy by utilizing the laser splashed 3D structures.
報告人：李聯合，英國利茲大學
時間：12月27日（周四）10:30
單位：清華大學
地點：物理系理科樓B406
半導體太赫茲(THz)量子級聯雷射器(QCL)是迄今為止唯一能夠在THz波段實現連續工作的高功率、緊湊型固態相干輻射源。自2002年研製成功以來，就引起了人們的廣泛關注和興趣，並迅速成為THz研究領域的熱點。經過不斷的器件設計改進和性能提高，其工作頻率已經可以覆蓋1.2到5.6 THz，脈衝輸出峰值功率達2.4 W。然而，由於基本物理機制的限制，目前THz QCL還需在低溫200 K以下工作。儘管如此，採用斯特令製冷器的「turn-key」 THz QCL系統卻已出現在商用市場上。THz QCL的材料生長製備是一項極具挑戰性的工作，僅有為數不多的研究所和大學有能力製備高性能器件。利茲大學是這一研究領域的先行者。經過十幾年的不懈努力和探索，已經實現了器件的可控性生長，能夠可重複性地製作實現各種頻率的高性能THz QCL並成功將其應用在了商用THz系統中。這一報告將討論這些高性能器件的生長製備、最新研究進展和部分應用。.
報告人：Weiwei Xu，National Astronomical Observatories, Chinese Academy of Sciences
時間：12月27日（周四）12:00
單位：北京大學
地點：first floor meeting room, KIAA
Some indications for tension have long been identified between cosmological constraints obtained from galaxy clusters and primary cosmic microwave background (CMB) measurements. Typically, assuming the matter density and fluctuations, as parameterized with Omega_m and sigma_8, estimated from CMB measurements, many more clusters are expected than those actually observed. This has been reinforced recently by the Planck collaboration. One possible explanation could be that certain types of galaxy groups or clusters were missed in samples constructed in previous surveys, resulting in a higher incompleteness than estimated. In this work, we aim to determine if a hypothetical class of very extended, low-surface-brightness galaxy groups or clusters have been missed in previous X-ray cluster surveys based on the ROSAT All-Sky Survey (RASS).We applied a dedicated source-detection algorithm sensitive also to more unusual group or cluster surface-brightness distributions. We found many known groups but also a number of new group candidates, which are not included in any previous X-ray or SZ cluster catalogs. In this talk, I will present a pilot sample of 13 very extended groups discovered in the RASS at positions where no X-ray source has been detected previously and with clear optical counterparts. The X-ray fluxes of at least 5 of these are above the nominal flux-limits of previous RASS cluster catalogs (> 3x10^{-12} erg s^{-1} cm^{-2} in the 0.1-2.4 keV energy band). They have low mass (10^{13} Msun We demonstrate that galaxy groups were missed in previous RASS surveys, possibly due to the flat surface-brightness distributions of this potential new population. Analysis of the full sample will show if this might have a significant effect on previous cosmological parameter constraints based on RASS cluster surveys.
報告人：Hui Li，MIT
時間：12月27日（周四）14:00
單位：清華大學
地點：蒙民偉科技南樓S727
Over the past decades, the discovery of a large number of young massive clusters (YMCs) in the local Universe and giant clumps in high-z galaxies suggests that clustered star formation is the dominant star formation mode. Mass and energy feedback from these enormous clusters is inevitably responsible for shaping the properties of their host galaxies. To model star formation in a more realistic way, I implemented a novel prescription in cosmological hydrodynamic simulations by treating star clusters as a unit of star formation. I tested this algorithm by running a suite of cosmological simulations with unprecedented parsec-scale spatial resolution. I found that various observed properties of host galaxies and star clusters are reproduced. Interestingly, we find some of these properties can be used to calibrate the subgrid models in the simulations. We follow the orbits of all simulated star clusters, estimate the cluster mass loss due to tidal disruption, and for the first time, investigate the connection between YMCs formed at high-z and the globular clusters observed at present. In parallel, to study how giant molecular clouds (GMCs) collapse to form star clusters and how they are eventually disrupted by stellar feedback from massive stars, I performed a suite of high-resolution hydrodynamic simulations of individual GMCs with self-consistent star formation and momentum feedback. I find that the final star cluster mass depends strongly on the surface density of the cloud due to the force balancing between gravity and momentum feedback.
報告人：Guoxing Xia，the University of Manchester and the Cockroft Institute
時間：12月28日（周五）09:30
單位：中科院高能物理所
地點：B326 main building
Proton-driven plasma wakefield acceleration (AWAKE), current status and future plans Plasma-based accelerators have achieved tremendous progress in the last three decades, thanks to the availability of ultrashort and high power lasers and relativistic electron beams. Nowadays, laser wakefield acceleration (LWFA) has routinely achieved GeV beam energy in centimeter long plasma channel. Electron beam driven plasma wakefield acceleration (PWFA) has achieved the energy doubling of a 42 GeV SLC electron beam at SLAC and proved the high efficiency acceleration for electrons and positrons, respectively. The new plasma-based acceleration experiment, so-called AWAKE at CERN has very recently demonstrated the successful acceleration of electrons to up to 2 GeV in a proton driven plasma wakefield. In this talk, I will introduce the basic principles and the development of proton-driven plasma wakefield acceleration scheme. The latest experimental results and its future plans.
報告人：Hui Li，MIT
時間：12月28日（周五）12:00
單位：北京大學
地點：KIAA, 1st meeting room
Over the past decades, the discovery of a large number of young massive clusters (YMCs) in the local Universe and giant clumps in high-z galaxies suggests that clustered star formation is the dominant star formation mode. Mass and energy feedback from these enormous clusters is inevitably responsible for shaping the properties of their host galaxies. To model star formation in a more realistic way, I implemented a novel prescription in cosmological hydrodynamic simulations by treating star clusters as a unit of star formation. I tested this algorithm by running a suite of cosmological simulations with unprecedented parsec-scale spatial resolution. I found that various observed properties of host galaxies and star clusters are reproduced. Interestingly, we find some of these properties can be used to calibrate the subgrid models in the simulations. We follow the orbits of all simulated star clusters, estimate the cluster mass loss due to tidal disruption, and for the first time, investigate the connection between YMCs formed at high-z and the globular clusters observed at present. In parallel, to study how giant molecular clouds (GMCs) collapse to form star clusters and how they are eventually disrupted by stellar feedback from massive stars, I performed a suite of high-resolution hydrodynamic simulations of individual GMCs with self-consistent star formation and momentum feedback. I find that the final star cluster mass depends strongly on the surface density of the cloud due to the force balancing between gravity and momentum feedback.
報告人：劉雄軍，Peking University
時間：12月28日（周五）15:00
單位：中科院物理研究所
地點：M樓236會議室
Topological phase of matter is a main stream of research in condensed matter physics. In this talk I introduce how to characterize topological phases by non-equilibrium quantum dynamics, and show its application to detecting topological physics with high precision. The framework of the theory consists of basic findings. First, we show that classifying a generic d-dimensional (dD) gapped topological phase with integer invariants can reduce to a (d-1)D invariant defined on so-called band inversion surfaces (BISs), rendering a bulk-surface duality. Further, we show in quenching across phase boundary the (pseudo)spin dynamics to exhibit emergent topological patterns on BISs, which are attributed to the post-quench bulk topology and manifest a dynamical bulk-surface correspondence. The topological phase is then classified by a dynamical topological invariant measured from the emergent dynamical field on the BISs. Applications to quenching experiments on feasible models are proposed and studied. The dynamical detection with high precision of the topological quantum physics has been achieved in experiments. We generalize this theory to correlated topological phase by quenching the spin-1/2 topological Haldane-Hubbard model. Novel correlation effects are shown in the non-equilibrium quantum dynamics for real spin and pseudospin spaces, with which both the topological phase and conventional magnetic order can be detected. These results may facilitate the experimental investigation of correlated topological physics.
報告人：汪的華，武漢大學
時間：12月29日（周六）10:00
單位：中科院高能物理所
地點：C305會議室
本報告在介紹 CO2 電化學和熔鹽CO2捕集與電化學轉化(MSCC-ET)技術的基礎上，主要報告本課題組在熔鹽CO2捕集吸收、電化學還原的過程機理、還原產物的表徵和應用、電解體系關鍵材料以及技術放大方面的若干研究進展。
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