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
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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
Unitary CFT description of DQCP is denied from quantum entanglememt entropy
The research team developed a new and more efficient quantum algorithm of the Monte Carlo techniques adopted by scientists to measure the Renyi entanglement entropy of objects. With this new tool, they measured the Rényi entanglement entropy at the DQCP and found the scaling behaviour of the entropy, i.e. how the entropy changes with the system sizes, is in sharp contrast with the description of conventional LGW types of phase transitions. Continue reading
from Quantum Materials to the Origin of Black Holes
In the time of quantum technology and big data, scientists start to integrate Artificial Intelligence (AI) and computational approaches into the fundament research about our mother Nature and Universe. This series of two lectures will help us to unfold such interesting discovery processes. Dr Zi Yang MENG, Associate Professor at HKU Department of Physics, will explain the important role played by AI and computation in the modern quantum material research in the first lecture. Find more
A bona fide topological Mott insulator discovered in twisted bilayer graphene model
Imagestacking two sheets of graphene – the 2D form of graphite, or the pencil at your hand – in which the carbon atoms form a hexagonal lattice and twist the top sheet out of alignment with the sheet below, yielding a periodic arrangement of atoms named moiré pattern. Do you know that at a twisted angle of about 1o – people now call it the ‘magic’ angle – the system could exhibit very exotic behaviours such as becoming an insulator, a metal or even a superconductor? Can you imagine the same carbon atom in your pencil (graphite) becoming a superconductor when twisted to the magic angle? It indeed did as people discovered it in 2018, but why? Continue reading
库伦作用无尽期，动量蒙卡寄相思
白石道人姜夔，南宋词人，一生布衣游食四方，存词只有80余首，不算高产（虽然他21岁写下的《扬州慢·淮左名都》入选中学语文课本，诸君可以想想自己21岁时在做什么）。但在他43岁那年的正月里，情感不知为何受到了大的扰动，爆发似的一口气写下一组五首《鹧鸪天》（准确地说是从正月初一到正月十六，从第一首《鹧鸪天 • 丁巳元日》到第五首 《鹧鸪天 • 十六夜出》），曲折地追怀自己生命中一段年轻的爱情，五首皆为精品。 Continue reading
Higgs mode via dimensional crossover in quantum magnets
The Higgs mode or the Anderson-Higgs mechanism (named after another Nobel Laureate Philip W ANDERSON), has widespread influence in our current understanding of the physical law for mass ranging from particle physics - the elusive “God particle” Higgs boson discovered in 2012 to the more familiar and important phenomena of superconductors and magnets in condensed matter physics and quantum material research. Continue reading
瞧！这些发明算法的人
发明量子多体问题算法的人，多与普通人不同。他们身上有一种得道高僧、终南隐士的先知之气，往往想要扬弃和重新评价流俗所看重的种种价值观念，率性而为以至于不被社会所理解，甚至被视为狂士和疯子。这其中的原因，恐怕还是来自于在量子多体问题中发明算法本身的难度。Continue reading
Correlation-Induced Insulating Topological Phases at Charge Neutrality in Twisted Bilayer Graphene
Twisted bilayer graphene (TBG) consists of two stacked layers of graphene rotated relative to one another. With a twist angle of about 1.10° the so-called “magic” angle, many unconventional electronic behaviors emerge, including superconductivity and correlated insulators, a type of insulating phase that arises from interactions between electrons. Elucidating the mechanism responsible for these electronic states in magic-angle TBG is a problem at the frontier of quantum materials research. To help solve this problem, we employ an unbiased quantum many-body numerical method (quantum Monte Carlo simulations) to investigate the possible insulating phases of TBG. Continue reading "Correlation-Induced Insulating Topological Phases at Charge Neutrality in Twisted Bilayer Graphene"