转角石墨烯的三昧

三昧是佛教里的话,是说修行的人能够止息杂念,心神平静,进入禅定,一窥事物的真谛。我们这些俗人,又生活在俗世,每天都在吃喝拉撒中辗转,应付尚且不足,禅定更不可及,离三昧境盖益远矣。大先生有篇著名的文章,叫《世故三昧》,很短,很有趣,把在人世间难得三昧的窘境和苦境写得通透,感兴趣的读者可以找来看看,一定强过阅读下面带着公式和图表的物理八股。 Continue reading "转角石墨烯的三昧"

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

我爱纠缠如秋裤

科学研究当然也是揭示规律性的活动,从事这个行业的,也颇有一些愿意思考的人。有趣的是,在笔者熟悉的量子多体系统的研究中,竟也存在一个和秋裤颇为相像的事物,揭示出量子多体系统中无处不在的量子纠缠这样深刻的道理,让科研从业者中愿意思考的人安心,忘却身边的种种不顺遂,进入“此中有真意”的境界而更加起劲地探索其中的奥妙。他们发现通过秋裤的视角可以揭示量子多体系统从朗道—金兹堡对称性自发破缺,到量子相变,再到拓扑序长程纠缠和范畴对称性等等奇异的现象,秋裤之功善莫大焉。 Continue reading "我爱纠缠如秋裤"

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"

Evidence of the topological KT phase of TMGO

Quantum materials are becoming the cornerstone for the continuous prosperity of human society, including the next-generation AI computing chips that go beyond Moore’s law, the high-speed Maglev train, and the topological unit for quantum computers, etc. However, these complicated systems require modern computational techniques and advanced analysis to reveal their microscopic mechanism. Continue reading

蒙蒙卡和张量量

有的童话穿越历史,变成了一个民族心中的文化图腾,如西游记之于中国人,安徒生和格林童话之于欧洲人。有的童话停留的时间稍短,但也是一代人甚至几代人心中共同的启蒙故事,如《星际旅行》、《铁臂阿童木》、《机器猫》甚至《哈利波特》。对中国的孩子来说,尤其是在1980年代至1990年代成长起来的孩子,这样的童话应属皮皮鲁和鲁西西的故事了。Continue reading

The search of non-Fermi liquid

Three passions, simple but overwhelmingly strong, have governed my life: the longing for love, the search of knowledge, and unbearable pity for the suffering of mankind.

—Bertrand Russell

As Russell nicely put it, scientists are often driven by strong passions for the search of knowledge, such search not only benefits the human society, but often times brings the ecstasy to themselves -- the ecstasy for instance of understanding the hearts of men, knowing why the stars shine, and apprehending the Pythagorean power by which number holds sway above the flux -- that is so great that scientists would often have endured the long hours of working and sleepless nights for the pursuit of such joy. Continue reading "The search of non-Fermi liquid"

DQMC Note (行列式蒙卡之我见)

这些笔记是潘高培君学习行列式量子蒙特卡洛方法(Determinantal Quantum Monte Carlo, DQMC)中总结出的心得。基本描述了 DQMC 实现过程。内容主要参考了 Fakher Assaad 等人的综述文章和组里几位学生的笔记,按照笔者自己喜欢的逻辑顺序进行讲述,顺便补充了少数被略过的推导。希望可以作为一个行列式蒙卡学习中的参考资料。欢迎大家批评指正。 Continue reading "DQMC Note (行列式蒙卡之我见)"

非费米液体的追寻

 夫人之相与,俯仰一世,或取诸怀抱,
悟言一室之内;或因寄所托,放浪形骸之外。
虽趣舍万殊,静躁不同,当其欣于所遇,
暂得于己,快然自足,不知老之将至。

——王羲之《兰亭集序》

人的一辈子,乱乱哄哄、热热闹闹,其实很快就过去了。浮名与虚誉、诱惑与利益,很多时候更是在加速这个过程。时间积分之后,烦恼总是大于欢欣的。这样一个悖论,古今中外多少人都看得明白,比如大书法家王羲之,其所言如上所抄录很是通透。Continue reading

神州帽子何其多

在一段悠然慵懒的岁月里,作者一边进行量子蒙特卡洛计算,一边读着二十四史。在量子多体中的呐喊与彷徨中看到了一丝曙光,也在历史的回味与反思中看到当今科研体制下的无奈与坚忍。“学者的贡献在于发扬真理,脱心志于俗谛之桎梏,在于铸造后起的头脑,不在于自己头上有多少帽子。” Continue reading "神州帽子何其多"