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

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

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

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

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"