YMSC-BIMSA Quantum Information Seminar

Quantum computers hold the promise of solving problems beyond the reach of classical machines, such as prime factorization. However, to fully realize their potential, we must address the challenges posed by noise during computation. Quantum error correction (QEC) tackles this issue by encoding quantum information with redundant resources, extracting error syndromes during execution, and correcting predicted errors. In this talk, we will discuss how to implement fault-tolerant quantum computation using the 2D planar surface code. We will explore both the progress and the experimental challenges of realizing surface code computation on superconducting quantum computers. Finally, we will introduce the TQEC project, which focuses on building tools for representing, constructing, and compiling fault-tolerant quantum computations based on surface code and lattice surgery.

Bio:

Yiming Zhang is a PhD student in Professor Xiaobo Zhu’s group at the University of Science and Technology of China. He has actively contributed to several high-profile experiments, including demonstrations of quantum advantage using random circuit sampling and surface code logical memory. He is also one of the core maintainers of the TQEC project, which develops design automation tools for surface code computation. His research interests include QEC-aware logical circuit compilation and optimization, as well as quantum resource estimation.

We investigate long-range magic (LRM), defined as nonstabilizerness that cannot be (approximately) erased by shallow local unitary circuits. In doing so, we prove a robust generalization of the Bravyi-König theorem. By establishing connections to the theory of fault-tolerant logical gates on quantum error-correcting codes, we show that certain families of topological stabilizer code states exhibit LRM. Then, we show that all ground states of topological orders that cannot be realized by topological stabilizer codes, such as Fibonacci topological order, exhibit LRM, which yields a “no lowest-energy trivial magic” result. Building on our considerations of LRM, we discuss the classicality of short-range magic from e.g. preparation and learning perspectives, and put forward a “no low-energy trivial magic” (NLTM) conjecture that has key motivation in the quantum PCP context. Our study leverages and sheds new light on the interplay between quantum resources, error correction and fault tolerance, complexity theory, and many-body physics.

Speaker Intro:

Fuchuan Wei is a fourth-year Ph.D. candidate in the Department of Mathematical Sciences at Tsinghua University, supervised by Prof. Zhengwei Liu. His research interests include quantum error correction, the effects of quantum noise, and quantum algorithms.

The branching algorithm is a fundamental technique for designing fast exponential-timealgorithms to solve combinatorial optimization problems exactly. it divides the entire solution spaceinto independent search branches using predetermined branching rules, and ignores the search onsuboptimal branches to reduce the time complexity. The complexity of a branching algorithm isprimarily determined by the branching rules it employs, which are often designed by humanexperts.In this paper, we show how to automate this process with a focus on the maximumindependent set problem. The main contribution is an algorithm that efficiently generate optimalbranching rules for a given sub-graph with tens of vertices. lts efficiency enables us to generate thebranching rules on-the-fly, which is provably optimal and significantly reduces the number ofbranches compared to existing methods that rely on expert-designed branching rules. Numericaexperiment on 3-regular graphs shows an average complexity of 0(1.0441^n) can be achievedbetter than any previous methods

Speaker Intro

Dr. Jinguo Liu is an assistant professor at Hong Kong University of Science and Technology(Guangzhou).He acquired his Ph.D. training in Prof. Qiang-Hua Wang’s group at NanjingUniversity on condensed matter physics. After that, he has been a postdoc in Prof. Lei Wang’sgroup at the Institute of Physics (CAS) for two years, a full-time consultant in QuEra computing folhalf a year, and a postdoc in Prof. Mikhail Lukin’s group at Harvard University for two years. Hisresearch direction is diverse, while all his studies are about developing new and better algorithmsfor solving existing or new problems. He is a passionate open source scientific software developeland he has the superpower of speeding up code in his lab by two orders.

Quantum computers have the potential to solve classically intractable problems. However, realizing a universal quantum computer is challenging with current technology. Before having a fully-fledged quantum computer, a more realistic question is what we can do with current and near-term quantum hardware. In this talk, I will first review the quantum algorithms that are designed for near-term and fault-tolerant quantum computers. Then, I will introduce our recent works about classical simulation of quantum processes. Finally, we discuss the possibility of achieving quantum advantages in the early-fault tolerant era.

Speaker Intro:

Dr. Xiao Yuan received his Bachelor in theoretical physics from Peking University in 2012 and got his PhD in physics from Tsinghua University in 2016. Then he worked as a postdoc at University of Science and Technology China in 2017, at Oxford University from 2017 to 2019, and at Stanford University from 2019 to 2020. He is now an assistant professor at Center on Frontiers of Computing Studies, Peking University. Dr. Xiao Yuan’s current research interests focus on near-term and universal quantum computing, and their applications.

2022 年中国学者提出的量经融合大数分解算法，在近期量子硬件即可尝试破译RSA，引起广泛关注，产生重大影响。量子通信是 “盾”，为信息安全提供新的保护方法。在量子密钥分发快速发展的同时，量子安全直接通信（QSDC）技术也取得快速发展，建立了高噪声下安全通信理论，实现了光纤和空间实验演示，完成了城域、城际和网络三个里程碑系统，并在银行和 5G 专网试用。本报告将介绍近期的进展。

龙桂鲁，清华大学教授，北京量子信息科学研究院副院长。杰出青年基金获得者，英国物理学会和美国物理学会会士，中国通信学会量子通信委员会主任，中国密码学会理事和量子密码专委会副主任，IUPAP量子科技组委员，中央X委某部XX组副组长。长期从事量子计算和通信研究，发表 论文400 余篇，谷歌学术引用 29000 余次，荣获国家自然科学奖二等奖、IBM 全球杰出学者奖、中国电子学会科技奖一等奖等多项殊荣。

Gui-Lu Long is a professor at Tsinghua University & Deputy-President of Beijing Academy of Quantum Information Sciences. He is fellow of IoP and APS. Notably among his contributions, he proposed the quantum secure direct communication that transmits information directly; constructed the Grover-Long algorithm for exact search and the full quantum eigensolver; and established the widely used linear combination unitaries method for quantum algorithm designs. He proposed the WISE interpretation of quantum mechanics. He published 300+ papers with 20000+ citations. He was President of AAPPS and vice-chair of C13 of IUPAP.

In this talk, I will elaborate on our recent experimental advancements in probing many-body correlations through non-equilibrium dynamics. By making use of a loss channel, we observe a universal dissipative dynamic in one-dimensional strongly-correlated quantum gases. This universal dynamic furnishes us with information regarding the anomalous dimension of the system, which is arduous to measure by conventional means. Through non-adiabatic ramping, we can probe the critical regions that lack a well-defined quasi-particle description. Based on non-adiabatic ramping, we have developed an integrable formula to depict the measured observables, and the results go beyond the conventional account of the Kibble-Zurek mechanism. These methods significantly enrich the approaches to measuring a quantum system and can be further extended to diverse systems for extracting different types of many-body correlations.

Speaker Intro:

博士毕业于麻省理工学院，现清华物理系副教授，主要从事于基于超冷原子的量子计算实验工作，发表过2篇Science、1篇Nature、3篇Nature Physics等。