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市民講演会「数学と量子材料のコラボ！」

2020年9月29日(火) 19:00 - 20:30

西森 秀稔 (理化学研究所 数理創造プログラム (iTHEMS) 客員主管研究員 / 東京工業大学 特任教授)
小澤 知己 (理化学研究所 数理創造プログラム (iTHEMS) 客員研究員 / 東北大学 材料科学高等研究所 (AIMR) 准教授)

理化学研究所（理研）と東北大学は、2019年3月20日に連携・協力の推進に関する基本協定を締結し、数理科学、テラヘルツ光科学、放射光科学、人工知能といった、両機関の強みである研究分野・研究課題を軸として連携研究を進めています。なかでも数理科学研究においては、東北大学・片平キャンパスに連携拠点・SUURI-COOL Sendaiを展開するなど、連携研究のネットワークが広がっております。 このたび、高校生以上を対象として、トポロジーや量子コンピュータといった数学・物理学の最先端の話題をわかりやすく紹介する市民講演会「数学と量子材料のコラボ！」を開催します。 理研 数理創造研究プログラム（iTHEMS）の研究者でもある、東北大学 材料科学高等研究所（AIMR）の小澤知己准教授と東京工業大学 科学技術創成研究院の西森秀稔特任教授がそれぞれ講演いたします。 プログラム 19:00-19:45 「物理学とトポロジー：半導体・地球物理から生命現象まで」 小澤知己（東北大学AIMR准教授・ジュニア主任研究者、理化学研究所iTHEMS兼任） 19:45-20:30 「量子力学とそれを使った計算の話」 西森秀稔（東京工業大学特任教授、理化学研究所 iTHEMS・東北大学情報科学研究科兼任） 詳細およびイベントの申し込みは、関連リンクよりご参照ください。

会場: via Online

イベント公式言語: 日本語

東北大＆理研 第２回連携ワークショップ Math meets Quantum Materials

2020年9月29日(火) - 30日(水)

西森 秀稔 (理化学研究所 数理創造プログラム (iTHEMS) 客員主管研究員 / 東京工業大学 特任教授)
小澤 知己 (理化学研究所 数理創造プログラム (iTHEMS) 客員研究員 / 東北大学 材料科学高等研究所 (AIMR) 准教授)
邱 靖凱 (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員)
濱崎 立資 (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員 / 理化学研究所 開拓研究本部 (CPR) 濱崎非平衡量子統計力学理研白眉研究チーム 理研白眉研究チームリーダー)
足立 景亮 (理化学研究所 数理創造プログラム (iTHEMS) 基礎科学特別研究員 / 理化学研究所 生命機能科学研究センター (BDR) 生体非平衡物理学理研白眉研究チーム 基礎科学特別研究員)
クリストファー・ボーン (理化学研究所 数理創造プログラム (iTHEMS) 客員研究員 / 東北大学 材料科学高等研究所 (AIMR) 助教)

The second Tohoku University - RIKEN joint workshop, entitled "Math Meets Quantum Materials," takes place from September 29 - 30. Tohoku University and RIKEN have been holding a series of joint workshops based on the agreement on collaboration and cooperation signed in 2019. The second workshop focuses on collaboration in the fields of mathematical sciences and quantum materials; two fields that have significantly merged in recent years. Like topological materials, which are discovered using the mathematical concept of topology, materials science is currently evolving from the conventional way of finding materials. Instead of developing materials with good properties through numerous experiments, materials science is increasingly finding materials using mathematical predictions. This workshop will discuss these latests developments and related topics. Although some lectures will take place in Japanese, the majority of talks will be in English. The deadline for registration is Monday, September 28. For more information, please click on the relevant link.

会場: via Online

イベント公式言語: 英語

Potential Toolkit to Attack Nonperturbative Aspects of QFT －Resurgence and related topics－

2020年9月7日(月) - 25日(金)

Aleksey Cherman (University of Minnesota, USA)
Gerald Dunne (University of Connecticut, USA)
Mithat Unsal (North Carolina State University, USA)
藤森 俊明 (慶應義塾大学)
初田 泰之 (立教大学 理学部 物理学科 助教)
本多 正純 (京都大学 基礎物理学研究所 助教)
森川 億人 (九州大学 博士課程)
居石 直久 (名古屋大学)
山崎 雅人 (東京大学 カブリ数物連携宇宙研究機構 (Kavli IPMU) 准教授)

Recently, there have been significant developments in theoretical techniques/frameworks to tackle non-perturbative aspects of quantum field theory (QFT) such as the resurgence theory, the Lefschetz thimble method, ’t Hooft anomaly matching, and novel lattice setups. Such developments are still growing very rapidly and making fruitful connections not only among physicists involved in fields with broad energy scales but also with mathematicians. These developments would enable us to unveil rich and exciting physics of QFT in the non-perturbative regime. It is of primary importance to hold a workshop for researchers in various fields related to the topics to get together and overview/share the recent progresses, to discuss future directions, and to seek for possible new collaborations bridging various fields of physics/mathematics. For more information, please see on the related link.

会場: YITP (Kyoto University), Zoom, and Mozilla hubs

イベント公式言語: 英語

Lefschetz-thimble inspired analysis of the Dykhne–Davis–Pechukas method and an application for the Schwinger Mechanism

2020年8月21日(金) 13:00 - 14:30

島崎 拓哉 (東京大学 ハドロン理論グループ 研究生)

Dykhne–Davis–Pechukas (DDP) method is a common approximation scheme for the transition probability in two-level quantum systems, as realized in the Landau–Zener effect, leading to an exponentially damping form comparable to the Schwinger pair production rate. We analyze the foundation of the DDP method using a modern complex technique inspired by the Lefschetz-thimble method. We derive an alternative and more adaptive formula that is useful even when the DDP method is inapplicable. As a benchmark, we study the modified Landau–Zener model and compare results from the DDP and our methods. We then revisit a derivation of the Schwinger Mechanism of particle production under electric fields using the DDP and our methods. We find that the DDP method gets worse for the Sauter type of short-lived electric pulse, while our method is still a reasonable approximation. We also study the Dynamically Assisted Schwinger Mechanism in two methods.

会場: via Zoom

イベント公式言語: 英語

Complex Langevin study of an attractively interacting two-component Fermi gas in 1D with population imbalance

2020年7月10日(金) 13:30 - 14:30

筒井 翔一朗 (理化学研究所 仁科加速器科学研究センター (RNC) 量子ハドロン物理学研究室 基礎科学特別研究員)

We investigate an attractively interacting two-component Fermi gas in 1D described by the Gaudin-Yang model with population imbalance. While the Gaudin-Yang model is known as a solvable model based on the thermodynamic Bethe ansatz, the binding energy and mass of poralon at finite temperature and moderate impurity density are still unknown. Moreover, in such a system, quantum Monte Carlo simulation suffers from the sign problem because the population imbalance makes the fermion determinant non-positive definite. In this study, we apply complex Langevin method, a holomorphic extension of the stochastic quantization to overcome the sign problem. We first confirm our numerical results satisfy a criteria for correct convergence [1], and present how the polaron energy depends on temperature and density of impurity. We also compare our results with a recent study based on a diagrammatic approach [2].

会場: via Zoom

イベント公式言語: 英語

Universal Error Bound for Constrained Quantum Dynamics

2020年6月24日(水) 16:00 - 18:10

濱崎 立資 (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員 / 理化学研究所 開拓研究本部 (CPR) 濱崎非平衡量子統計力学理研白眉研究チーム 理研白眉研究チームリーダー)

In quantum mechanics, the existence of large energy gaps allows us to trace out the degrees of freedom of irrelevant energy scale. Consequently, we can treat a system within a constrained subspace obtained by the projection of the total Hilbert space. While this statement has widely been used to approximate quantum dynamics in various contexts, a general and quantitative justification stays lacking. In this talk, we show a universal and rigorous error bound for such a constrained-dynamics approximation in generic gapped quantum systems [1,2]. This universal bound is a linear function of time that only involves the energy gap and coupling strength, provided that the latter is much smaller than the former. If time allows, I will briefly talk about generalizations of our result to e.g., quantum many-body systems and open quantum systems.

会場: via Zoom

イベント公式言語: 英語

Information geometry of operator scaling

2020年6月17日(水) 16:00 - 18:10

相馬 輔 (東京大学 大学院情報理工学系研究科 助教)

Matrix scaling is a classical problem with a wide range of applications. It is known that the Sinkhorn algorithm for matrix scaling is interpreted as alternating e-projections from the viewpoint of classical information geometry. Recently, a generalization of matrix scaling to completely positive maps called operator scaling has been found to appear in various fields of mathematics and computer science, and the Sinkhorn algorithm has been extended to operator scaling. In this study, the operator Sinkhorn algorithm is studied from the viewpoint of quantum information geometry through the Choi representation of completely positive maps. The operator Sinkhorn algorithm is shown to coincide with alternating e-projections with respect to the symmetric logarithmic derivative metric, which is a Riemannian metric on the space of quantum states relevant to quantum estimation theory. This talk is based on joint work with Takeru Matsuda.

会場: via Zoom

イベント公式言語: 英語

Field theoretical approach to relativistic hydrodynamics

2020年6月12日(金) 13:00 - 14:30

本郷 優 (理化学研究所 数理創造プログラム (iTHEMS) 客員研究員 / Postdoctoral Research Associate, Physics Department, The University of Illinois at Chicago (UIC), USA)

Hydrodynamics is a low-energy effective theory of a conserved charge density, which describes a long-distance and long-time behavior of many-body systems. It is applicable not only to a non-relativistic weakly-interacting dilute gas but also a relativistic strongly-interacting dense liquid like a quark-gluon plasma. The main purpose of this seminar is to explain how we can derive the hydrodynamic equation from the underlying field-theoretical description of systems [1-3]. Our derivation is based on the recent development of non-equilibrium statistical mechanics, and we show that the procedure to derive hydrodynamic equations is similar to the so-called renormalized/optimized perturbation theory. Also, to describe transport phenomena in local thermal equilibrium, we give a path-integral formula for a thermodynamic functional, which results in the emergence of thermally induced curved spacetime [2]. These results enable us to derive hydrodynamic equation based on quantum field theories.

イベント公式言語: 英語

Localization and universality in non-Hermitian many-body systems

2020年5月29日(金) 15:00 - 16:30

濱崎 立資 (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員 / 理化学研究所 開拓研究本部 (CPR) 濱崎非平衡量子統計力学理研白眉研究チーム 理研白眉研究チームリーダー)

Recent study on isolated quantum many-body systems have revealed two different phases distinguished by their dynamics and spectral statistics. One is an ergodic phase whose spectral statistics exhibit universality of random matrices, and the other is a many-body localized phase where dynamics is constrained due to strong disorder. In this talk, we show that novel and rich physics concerning such localization and universality appears in non-Hermitian many-body systems, which have been utilized in diverse scientific disciplines from open quantum systems to biology. As a first topic, we analyze non-Hermitian quantum many-body systems in the presence of interaction and disorder [1]. We demonstrate that a novel real-complex transition occurs upon many-body localization of non-Hermitian interacting systems with asymmetric hopping that respect time-reversal symmetry. As a second topic, we show that “Dyson’s threefold way,” a threefold symmetry classification of universal spectral statistics of random matrices, is nontrivially extended to non-Hermitian random matrices [2]. We report our discovery of two distinct universality classes characterized by transposition symmetry, which is distinct from time-reversal symmetry due to non-Hermiticity. We show that the newly found universality classes indeed manifest themselves in dissipative quantum many-body ergodic systems described by Lindblad equations.

会場: via Zoom

イベント公式言語: 英語

How many electrons can atoms bind?

2020年5月13日(水) 16:00 - 18:10

後藤 ゆきみ (理化学研究所 数理創造プログラム (iTHEMS) 基礎科学特別研究員)

In this talk, I will introduce the mathematical studies on the ionization problem. Some experimental & numerical evidences say that any doubly charged atomic ion X^{2-} is not stable. This 'fact' is called the ionization conjecture in mathematical physics literatures. My hope is to illustrates the interplay between mathematical and physical ideas. The talk is directed towards researchers on various aspects of quantum mechanics. In the first part, we will discuss the many-body aspects of quantum mechanics and introduce some basic notions. The second part will deal with the mathematical results in some approximation theories.

会場: via Zoom

イベント公式言語: 英語

Interaction Models in Quantum Optics, Representation Theory and Number Theory

2020年4月10日(金) 15:30 - 17:00

若山 正人 (理化学研究所 数理創造プログラム (iTHEMS) 特別顧問 / 東京理科大学 副学長)

Recently, interaction models originated in quantum optics, with the quantum Rabi model (QRM) as a distinguished representative, are appearing ubiquitously in various quantum systems including cavity and circuit quantum electrodynamics, quantum dots and artificial atoms, with potential applications to quantum information technologies such as quantum computing. Together with the integrability of QRM, demonstrated by Daniel Braak in 2011, this has led to wide discussion and development of various aspect of the QRM and its generalizations from the point of view of theoretical physics and mathematics. In this talk, firstly, we characterize the structure of the spectra of QRM and its asymmetric version via sℓ2-representations. Secondly, we introduce the non-commutative harmonic oscillator, which may be considered to be a “cover” of the QRM in the Heun ODE picture, and describe certain number theoretical aspects arising from its spectral zeta function. Further, we discuss the heat kernel and partition function of the QRM toward the number theoretical investigation of the model. In addition, a number of related open problems will be presented.

会場: via Zoom

イベント公式言語: 英語

Holography from field theories: a realization of AdS/CFT correspondence and beyond

2020年3月18日(水) 13:30 - 14:30

青木 愼也

*Seminar room changed from 160 to 433. We argue that the Anti-de-Sitter (AdS) geometry in $d+1$ dimensions naturally emerges from an arbitrary conformal field theory in $d$ dimensions using the free flow equation. We first show that an induced metric defined from the flowed field generally corresponds to the quantum information metric, called the Bures or Helstrom metric, if the flowed field is normalized appropriately. We next verify that the induced metric computed explicitly with the free flow equation always becomes the AdS metric when the theory is conformal. We also show that the conformal symmetry in $d$ dimensions converts to the AdS isometry in $d+1$ dimensions after $d$ dimensional quantum averaging. This guarantees the emergence of AdS geometry without explicit calculation. We next apply this method to non-relativistic systems with anisotropic scaling symmetries, such as Lifshitz field theories and Schr\”odinger invariant theories. In consequence we obtain a new hybrid geometry of Lifshitz and Schr\”odinger spacetimes as a general holographic geometry. We also show that the bulk hybrid geometry is realized by an Einstein-Maxwell-Higgs system plus a gauge fixing term for diffeomorphism, which may be interpreted as a holographic dual of a general non-relativistic system at the boundary.

会場: 研究本館 433号室

イベント公式言語: 日本語

Nucleon Structure from Quantum Chromodynamics

2020年1月30日(木) 11:00 - 12:00

張 家丞 (理化学研究所 数理創造プログラム (iTHEMS) 研究員 / LBNL/UCB, USA)

Talk of this seminar is a colloquium style, so that non-expert can enjoy. Please feel free to join. The origin of matter is one of the longest standing mysteries that have captured the human imagination. The modern description of particle and nuclear physics hypothesizes that our matter filled universe must have resulted in the underlying physical processes favoring the preservation of matter over antimatter during the initial formation of our universe. This mechanism is attributed to the fundamental breaking of particle and antiparticle symmetry in physics beyond the Standard Model. One source of asymmetry is hypothesized to reside in the neutrino sector, and intense international efforts are being pursued to observe this phenomena in neutrino scattering experiments. Precise interpretation of experimental observations benefits from a Standard Model prediction of how nuclear matter interacts with neutrinos. The modern theory governing matter and their properties is the theory of the strong interaction, quantum chromodynamics (QCD). In this talk I will discuss a QCD calculation of the nucleon form factor at zero momentum transfer, which is related to how a neutrino at rest interacts with a single proton or neutron, followed by current progress on the calculation of the proton radius which is related to the slope of the form factor. Together the calculations paves a novel way forward towards a precise determination of the nucleon form factor up to momentum transfer relevant for neutrino scattering. I will end the talk by discussing future milestones and challenges as we work towards calculations for nuclear physics starting from QCD.

会場: 研究本館 433号室

イベント公式言語: 英語

量子コンピュータ研究開発の現在とこれから-量子ビットからソフトウェア・アプリケーションまで-

2020年1月29日(水) 10:00 - 18:00

会場: 鈴木梅太郎記念ホール

イベント公式言語: 日本語

Semiclassical methods in mathematical quantum mechanics

2020年1月23日(木) 16:00 - 18:10

中村 周 (学習院大学 教授)

Plan of the seminar: we separate each talk into two. In the first 60 minutes the speaker gives an introductory talk for non-mathematicians. After a short break, the second 60 minutes is spent for a bit more detailed talk for mathematicians (working in other areas). We welcome you joining both parts of the seminar or only the first/second half. Talk 1: Semiclassical analysis, microlocal analysis and scattering theory. I plan to talk about overview on the semiclassical analysis and related topics, especially its intrinsic relationship with microlocal analysis and (microlocal) scattering theory. Roughly speaking, the microlocal analysis is an application of semiclassical idea to the analysis of singularities, and its analogue in momentum space is the microlocal scattering theory. We discuss basic notions of these, and mention several recent results. Talk 2: Microlocal structure of the scattering matrix with long-range perturbations. As an example of topics discussed in Talk 1, we discuss recent results on the scattering matrix with long-range perturbations. In particular, we show that the scattering matrix is expressed as a Fourier integral operator, and in some cases we can decide its spectral properties. Our approach is fairly geometric and abstract, and thus applies not only to usual Schrödinger operators but also to higher order operators and discrete Schrödinger operators.

会場: 研究本館 435-437号室

イベント公式言語: 英語

Variational methods in quantum annealing

2019年11月15日(金) 13:30 - 15:00

松浦 俊司 (Fundamental Researcher, Quantum Simulation Division, 1QBit, Canada)

The rapid progress in the manufacturing of quantum computing hardware has opened up the possibility of exploring its application in solving computationally challenging problems. In this work, we present variational methods in quantum annealing for solving problems more efficiently than the standard adiabatic methods. Important limitations common to all near-term quantum devices include the absence of error correction and the short coherence time, which restrict the computational power of these systems. Therefore, shortening the time taken to perform an individual run of a quantum algorithm and making the annealing process noise resilient is essential for successfully obtaining accurate results. The efficiency of the methods is demonstrated in the ground-state energy estimation of simple molecular systems. Compared with the standard annealing method, the variational algorithms show significant improvements in the annealing time required to achieve a high accuracy.

会場: 研究本館 433号室

イベント公式言語: 英語

Introduction to 1QBit Open Software QEMIST "Quantum-Enabled Molecular ab Initio Simulation Toolkit"

2019年10月17日(木) 13:30 - 15:00

松浦 俊司 (Fundamental Researcher, Quantum Simulation Division, 1QBit, Canada)

会場: 研究本館 433号室

イベント公式言語: 英語

Topological phases of matter and operator algebras

2019年10月4日(金) 15:30 - 17:00

河東 泰之 (理化学研究所 数理創造プログラム (iTHEMS) 客員主管研究員 / 東京大学 大学院数理科学研究科 教授)

Topological phases of matter are hot topics in recent physics and related to a wide range of mathematical fields. I will talk about their aspects related to operator algebras. Our emphasis will be on theory of tensor categories which describe interactions of anyons. This theory plays an important role in topological quantum computations. In theory of operator algebras, Jones initiated theory of subfactors and discovered the Jones polynomial, a new topological invariant for knots as an application. We apply this theory to mathematical studies of anyons.

会場: 大河内記念ホール

配信:計算科学研究棟 R511 / SUURI-COOL (Kyoto) / SUURI-COOL (Sendai)

イベント公式言語: 英語

量子多体系入門－格子模型を中心に－

2019年9月5日(木) - 6日(金)

桂 法称 (東京大学 大学院理学系研究科 物理学専攻 准教授)

2019.09.05 @ 理研 研究本館 535-537号室 10:00-11:30 (1)イントロダクション -連続系から格子系へ- 13:00-14:30 (2)自由フェルミオン系と二次形式 15:00-16:30 (3)自由ボゾン系と二次形式 2019.09.06 @ 理研 研究本館 435-437号室 10:00-11:30 (4)古典・量子Ising模型 13:00-14:30 (5)量子スピン系の話題 15:00-16:30 (6)まとめと展望

会場: 研究本館 535-537号室 / 研究本館 435-437号室

イベント公式言語: 日本語

量子コンピュータの産業応用への展望

2019年9月4日(水) 15:30 - 18:00

中川 裕也 (株式会社 QunaSys チーフエンジニア)

会場: 大河内記念ホール

配信:計算科学研究棟 R311 / SUURI-COOL (Kyoto) / SUURI-COOL (Sendai)

イベント公式言語: 日本語