基础物理及宇宙学的疑难问题||本周物理学术讲座

报告人：李惕碚 院士

时间：7月18日（周二）10:00

单位：中国科学院高能物理研究所

地点：化学楼C305

在建立相对论的过程中，由于混淆了时空与位形时空，低估了局域相对论的局限性，爱因斯坦对于物理学时空框架等基本问题说过一些过头话。这些说法，虽然爱因斯坦生前曾经反复地进行过自我质疑，并在与友人的通信中部分地作了改正，却被其后的主流学界奉为教条，视为物理学理论的基础和理论发展的出发点。上世纪90年代以来，微波背景辐射、宇宙膨胀加速及并合黑洞引力波的观测结果挑战了对物理学基本问题（如背景时空、惯性参照系、时空弯曲与能量守恒等）的主流认识。重新审视这些基本问题，有助于更清楚地理解物理理论的基础框架，更合理地构建宇宙学的物理基础，从而对宇宙的构成、起源与归宿问题给出完全另类于标准模型的回答。观测和分析黑洞天体及宇宙真空的演化过程将对涉及物理学及宇宙学基础的争议作出最终判断。

报告人：Chun Ning (Jeanie) Lau

时间：7月18日（周二）10:00

单位：北京大学

地点：Room w563, Physics building, Peking University

Two dimensional materials constitute an exciting and unusually tunable platform for investigation of both fundamental phenomena and electronic applications. Here I will present our results on transport measurements on high mobility few-layer graphene and phosphorene devices. Using quantum Hall effects in graphene as injectors, filters and detectors, we observe robust long distance spin transport through the antiferromagnetic state in graphene. In the second half of the talk, I will present our recent results on quantum Hall effect in air-stable, few-layer phosphorene devices, and the current carrying capacity of carbon nanotubes.

报告人：Qing (Helen) He,Durham University

时间：7月18日（周二）10:00

单位：北京师范大学

地点：物理楼106

Complex phenomena in solids continue to be a major theme of physics in the 21^st century. Competing charge, spin, orbital and lattice degrees of freedom leads to new electronic, magnetic and structural phases in strongly correlated electron systems. They have great potential to fundamentally change our view of the physical world, to significantly impact the technology, and to provide new solutions to our energy problems. The elevated complexity of physics requires sophisticated experimental tools beyond the traditional thermodynamic and transport measurements to be applied in research. As a common theme of the related materials, the rich interplay between orders in the materials calls for the combination of different techniques sensitive to different physical entities to reach a complete understanding of the physical properties. In this talk, I will start stories from the introduction of two advanced techniques: scanning probe microscopy and soft x-ray absorption based techniques (spectroscopy, scattering, microscopy, etc.) and bring you through their special approaches to investigate the electronic, magnetic and structural states in several interesting complex oxide systems.

报告人：梅刚华，中国科学院武汉物理与数学研究所

时间：7月18日（周二）10:00

单位：清华大学

地点：理科楼C302报告厅

原子钟是卫星导航系统的重要组成部分，原子钟精度对系统的定位和授时精度起决定性作用。用于卫星导航的原子钟可分为地面基准原子钟、地面守时原子钟、星载原子钟和应用终端原子钟四大类。报告简述卫星导航系统的工作原理和对各类原子钟的基本要求，分析原子钟精度对卫星导航系统定位和授时精度的影响，综述卫星导航原子钟技术的发展现状，展望卫星导航原子钟技术的发展趋势。报告还将介绍中科院武汉物数所近年来围绕我国北斗卫星导航系统工程建设需求，开展原子钟研究取得的主要进展。

报告人：Jerzy Lewandowski，University of Warsaw

时间： 7月18日（周二）15:30

单位：北京师范大学

地点：物理楼106

The basic structure of the canonical general relativity will be reminded: the vector and hamiltonian constraints, methods of constructing Dirac observables. New results on a reference system related to an observer and geometry will be presented. The tools of canonical Loop Quantum Gravity will be introduced: spin-networks, solutions of vector constraints, quantum scalar constraint operators and their solutions. Capacities of the framework and its applications will be discussed.

报告人：Dr. Raymond Ooi, Faculty of Science Universiti Malaya

时间：7月18日（周二）16:00

单位：中国科学院物理研究所

地点：M830
In this talk I will share my recent research works, mainly theoretical, involving photon-atom interactions that connect the fields of quantum optics, nonlinear optics, nanoplasmonics, nonclassical photon correlations, quantum coherence and entanglement for quantum information and communications, I will focus the topics of the spectra and correlations of mesoscopic particles composed of 4-level quantum particles in double Raman scheme. Quantum Langevin formalism with noise operators is used to describe the field operators of photon pairs (Stokes and anti-Stokes fields) emitted by a mesoscopic spherical particle . The spectra of the fields and photon correlation obtained are sensitive to the dimension of the microsphere and can be controlled by pump and control laser fields. Spectral peaks due to quantum coherence are Stark shifted by the laser fields experiencing autofocusing inside the spherical particle, causing broadening of peaks as the size of the microsphere increases. Next, I will discuss a quantum system (QS) of three-level L scheme near a metallic particle (MP) system. At near field separation, we find giant gain and absorption that are controllable by laser direction, polarization and ellipticity, enhanced by plasmonic effect. I show how the spectra depends on interparticle distance and position/direction of detector. Finally, I will discuss some proposed topics to work on.

报告人：Long-Qing Chen，The Pennsylvania State University

时间： 7月19日（周三）10:00

单位：北京师范大学

地点：物理楼106

Phase decomposition is a well-known process leading to the formation of two-phase mixtures with different compositions. Here we show that a strain imposed on a ferroelastic crystal promotes the formation of mixed phases and domains, i.e., leading to domain and phase de-strain process, with local strains determined by the uniform stress condition that can be graphically represented by a common tangent construction on the free energy versus strain curves. It is demonstrated that a domain structure can be understood using the concepts of domain/phase rule, lever rule, coherent and incoherent de-strain, and strain spinodal within the de-strain model description, in complete analogy to phase decomposition. The proposed de-strain model is tested and validated using phase-field simulations and experimental observations of PbTiO3 and BiFeO3 thin films as examples. The de-strain model provides a simple thermodynamic tool to guide and design domain structures of ferroelastic systems or the microstructures of a crystal separating to a mixture of two phases with different densities or molar volumes.