冷原子动量晶格、费米液体、量子材料、银河系中心黑洞 | 本周物理讲座

报告 人 ：Jinwu Ye，Great Bay University

时间： 4月16日（周二）14:00

报告 人 ：陈叶鸿，福州大学物信学院

时间： 4月16日（周二）14:30

报告 人：Prof. Luca Delacretaz, University of Chicago

时间： 4月17日（周三）10:00

I will show how to formulate Fermi liquid theory as an effective field theory of bosonic degrees of freedom, using the formalism of coadjoint orbits. While at the linear level, this theory reduces to multidimensional bosonization, it necessarily features nonlinear corrections that are fixed by the geometry of the Fermi surface. These are crucial to reproduce nonlinear response, which is not captured by previous bosonization approaches. The effective field theory framework furthermore systematically parametrizes power law corrections to Fermi liquid behavior, and provides a computationally advantageous approach for non-Fermi liquids -- strongly interacting fixed points obtained by deforming Fermi liquids with relevant interactions.

Ferromagnetic ground states have often been overlooked in comparison to seemingly more interesting antiferromagnetic ground states. However, both the physical and mathematical structure of ferromagnetic ground states are particularly rich. The highly degenerate and highly entangled ground states of the ferromagnetic spin-1 biquadratic model are scale invariant, originating from spontaneous symmetry breaking from SU(3) to U(1)×U(1) with two type-B Goldstone modes. The ground state degeneracies are characterized as the Fibonacci-Lucas sequences. Similarly rich physics occurs in other models, such as SO(4) spin-orbit model.

Professor Ian McCulloch received his PhD from the Australian National University, before moving to Europe for postdoctoral positions at the Instituut-Lorentz in The Netherlands, and RWTH-Aachen University in Germany. In 2007, he returned to Australia, to the University of Queensland, in Brisbane. Since August 2023, he is a Visiting Professor at National Tsing Hua University, Taiwan. His research interests are computational methods for quantum many-body systems using tensor network methods and DMRG. He was a pioneer of several key technical developments including non-Abelian symmetries, and the iDMRG method for translational invariant infinite systems. He has worked on applications in a variety of areas of condensed matter physics including atomic gases and topologically ordered states.

动量晶格使用原子外态作为等效维度，实现了晶格体系的单格点独立调控，非常适合开展拓扑，无序等实验研究工作。近来，我们发展了拉曼动量晶格新技术，实现原子内外态结合的晶格构型，极大地拓展了系统的模拟能力。利用此技术，我们开展了一系列拓扑量子模拟的研究工作，包括实现非厄米SSH模型，AB cage模型，SU(2)等效规范场等。相信此技术将为冷原子研究注入新的活力。此外，报告也将简要介绍我们在激光冷却极性分子研究的进展，包括BaF分子精密光谱测量，BaF分子的激光偏转，BaF分子的多普勒冷却，以及它在精密测量领域的展望。

时间： 4月 17 日（周 三 ）1 5 :00

While enchanting non-flermitian properties umattainable in Hermitian systems are widely revealed, genuine quantum non-Hermitian phenomenology remains largely uncharted teritory, Here, we show how engineered non-Hermiticitb gives rise to novel phenomena with a genuine quantum nature. We investigate a system of atoms (or artificial atoms)embedded in a particular type of bath, which in turn interacts with an outer bath and dissipates. By engineering the interaction with the bath and the bath itself, the atomic properties can be influenced in an unprecedented manner. ln particular, we find the atomic emission can be suppressed by dissipation in an unusual way; the algebraic scaling with the relevant parameters acquires firactional power - the fractional Quantum Zeno effect, Ths interestig behavior cannot occur if the results in exotic long-range interactions of atoms. We futher find FOZ-induced strong single-photon nonlinearity. Remarkably, we identify that the sub-Poissonian quantum statistics of photons，which has no classical  analogues，stems here from the key role of non-Hemmiticity. Our setup is experimentally feasible with the techiquesused to design lattice models with dissipative couplings. This work opens a path to exploring non-Hermitian guantum optics as wel as quantum many-body non-Hemmitian physics.

报告 人：史志文，上海交通大学

时间： 4月 18 日（周 四 ）1 0 : 00

石墨烯虽具有优异电输运性质，但由于没有能隙而无法用于构建晶体管器件。理论上，准一维的石墨烯纳米带因量子限域效应而打开能隙，且能隙大小可通过纳米带宽度和边缘结构来调控，是构建高性能电子器件与芯片的理想材料。尽管目前已经发展了多种制备石墨烯纳米带的方法，但是可用于半导体器件的高质量石墨烯纳米带的制备问题一直没有解决。在本报告中，我将介绍一种在绝缘基底上直接生长高质量石墨烯纳米带的全新技术方法。基于该方法，我们实现了石墨烯纳米带在氮化硼层间的嵌入式生长，形成“原位封装”的石墨烯纳米带结构。所制备的石墨烯纳米带宽度小于5nm，长度可达250μm，边缘结构整齐，手性一致。基于该“原位封装”纳米带的场效应晶体管具有优异的性能：载流子迁移率达4,600cm2V–1s–1，开关比可达106。这些出色的性能表明六方氮化硼“原位封装”的石墨烯纳米带有望应用于未来高性能碳基纳米电子器件与芯片。

自从银河系中心致密射电源人马座A*于1974年被首次探测到，在过去的近半个世纪里，揭开这一距离我们最近的超大质量黑洞候选者的真面目便成为全球天文学家的共同追求。2020年5月12日晚上9点，上海天文台与全球多地同时召开新闻发布会，展示了位于银河系中心的超大质量黑洞人马座A*的首张照片，这一期待太久的肖像提供了银河系中心真实存在超大质量黑洞的最为直接的视觉证据。这是继2019年4月10日发布的位于更遥远星系M87中央黑洞照片之后的又一重大突破。来自我们银河系中心和来自M87的两个超大质量黑洞质量相差了3个数量级，但它们环状阴影的图像是惊人的相似。本报告将从一个观测者的视角给大家介绍我们是如何一步步靠近黑洞并最终揭开银河系中心黑洞的神秘面纱，以及未来的拍摄黑洞“电影”计划。

This new channel of DCBH formation through super-competitive accretion introduces a novel paradigm for the formation of seed black holes, relaxing the constraints imposed by metallicity and increasing the abundance of seed black holes. The talk concludes by assessing whether seed black holes formed in this manner could explain the population of current supermassive black holes.