Unlock Tunable Nonlinear Hall Effect in Twisted Bilayer Graphene

A team of international researchers led by HKU (composed of PhD student Xu ZHANG and his advisor Dr Zi Yang MENG) and HKUST has made a significant discovery in the field of quantum materials, uncovering the controllable nonlinear Hall effect in twisted bilayer graphene. The findings, published as an Editors' Suggestion article in the prestigious physics journal Physical Review Letters, discovered that by adjusting the dispersion of the topological flat bands in twisted bilayer graphene, the Berry curvature dipole moments, which play a crucial role in the Hall effect, can be easily controlled and manipulated. Continue reading

Successful PhD defenses for the first-generation HKU PhD graduates

August 18, 2023, is a significant day for Mr. Jiarui Zhao and Mr. Chengkang Zhou, as on this day they have successfully defended their Ph.D. thesis with the title “Disorder Operators, Entanglement Entropies, and Dynamic Spectra in Strongly Correlated Quantum Spin Systems：A Quantum Monte Carlo Study” and “Quantum Monte Carlo simulations of dimension tunability phenomena in the quantum spin system”. They are the first-generation HKU PhD graduates from Zi Yang Meng’s group. Congratulations to Dr. Jiarui Zhao and Dr. Chengkang Zhou! Continue reading

一场游戏一次消遣——量子多体问题的模型设计与计算

本文是为中国物理学会 Chinese Physics B 30周年刊庆邀请撰写的综述文章：A sport and a pastime: Model design and computation in quantum many-body systems 所做的创作谈。从文章发表到今天，不过两个月时间，但这两个月内世界变化之快如同梦境。穿行在分裂的世界中，我们几近不能分辨现实是否只是梦境的替身，抑或是这世上太多人都因为失去了记忆而变得只是随着风向空转。趁着我们还没有失去记忆，在这里记录下综述文章中量子多体问题模型设计与计算求解的物理学内容，和在完成这篇30多页的科学论文时，我们的内心寄托。希望能够在这个没有信用的世界中，留下一些信用的记录。 Continue reading

Advanced computing system ‘Blackbody’ for solving the challenging physics problems

To pursue advances in astronomy, quantum physics, and interdisciplinary science, our research teams worked together to deploy a new supercomputing system, named ‘Blackbody’ supercomputer -- the name stems from their respective research topics of ‘Black hole’ and ‘Quantum many-body‘ physics. The system has been set up in fall 2022 and is currently in full operation. Thank you for the hard work and Congratulations for all the participants! Continue reading

         

好蛋大爷的纠缠谱猜想——路径积分虫洞效应揭示纠缠谱与能谱的迷离关系

一个好的猜想，值得一个漂亮的证明，和一些恰到好处的推广。从路径积分虫洞效应出发，我们的工作提供了理解好蛋大爷的纠缠谱猜想的一个好的思路，也孵出了额外的“好蛋”。... 某天，鄙人在听复旦理论物理报告之时，正好讲到纠缠谱和拓扑物态的关系。受限于目前的数值技术，人们只能研究一维量子系统的纠缠谱。这启发了笔者的一个想法：通过量子蒙卡结合数值解析延拓技术，求解纠缠谱。后面的故事，就这么展开了。 Continue reading

   

Predict the novel entangled states on programmable quantum simulators


Quantum dimer models are known to host topological quantum spin liquid phases, and it has recently become possible to simulate such models with Rydberg atoms trapped in arrays of optical tweezers. By means of large-scale quantum Monte Carlo simulations ... we find distinct odd and even Z2 spin liquids, along with several phases with no topological order: a staggered crystal, a nematic phase, and a trivial symmetric phase with no obvious broken symmetry. We also present dynamic spectra of the phases, and note implications for experiments on Rydberg atoms. Continue reading

   

阿龙探案蒙特卡洛符号问题

量子多体计算领域有几个传统的谜团或者说神话故事，比如量子蒙特卡洛计算一旦遇到符号问题，其重要性抽样就当场失效；比如张量网络计算总能克服万难成功找到指数大的希尔伯特空间中那个甜蜜的小角落；比如第一性原理计算得到的能带可以煞有介事地解释关联电子材料的能谱；……。既然是谜团，就是可以没有标准答案，从业人员信与不信全看当时的心情，或者想也不想，别人怎么说我也怎么说。几十年过去了，谜团或者说神话故事，就这么口口相传下来。但是总有愿意琢磨事儿的人 ...... Continue reading

   

在纠缠中窥见自然的奥秘

身无彩凤双飞翼，心有灵犀一点通

李商隐《无题》

唐代诗人李商隐的这首诗，道尽了人世间痴情男女虽天各一方、但彼此心意相通、似有一条丝线相连的缠绵。

其实，电子的世界亦如此。配对的电子，一旦形成一个纠缠态，无论相距多远，它们都能感受到彼此的“心意” (自旋)。它们一个向上，一个向下，仿佛约好了似的。只要有一方改变状态，那么另一方就会立刻感受到，并且调整成与对方相反的状态。Continue reading

情愿不自由，便是自由了

时令不停流转，经过残酷阴沉荒原般的四月，到了五月，人们总会回过神来想起青年。想起身处初夏阳光中的感觉，看着满山茂盛的树木在微风中摇曳，看着蔚蓝的大海和视线尽头那一片氤氲中满是希望和新鲜的世界，多好，一切都是绿的、蓝的、清澈的、新鲜的、天真的、诚实的和健康的。Continue reading