イベント検索

Global Thermodynamics for Heat Conduction Systems

2024年12月2日(月) 14:00 - 15:30

中川 尚子 (茨城大学 理工学研究科 教授)

Non-equilibrium phenomena are typically addressed through continuum descriptions based on local equilibrium and linear response theory, such as hydrodynamics. While effective, these approaches often overlook global characteristics. We propose Global Thermodynamics as a minimal-variable framework to describe weak non-equilibrium systems, focusing on two-phase coexistence under weak heat flux. By introducing a unique global temperature and extending entropy to non-equilibrium systems with a non-additive term, the framework predicts phenomena like metastable state stabilization—beyond the scope of traditional heat conduction equations. This talk will outline the framework, its key predictions, and validation efforts through numerical simulations and experiments. (This is a joint seminar with Informatin Theory Study Group.)

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

第27回 MACSコロキウム

2024年11月25日(月) 14:45 - 18:00

濱崎 立資 (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)
榎戸 輝揚 (京都大学 大学院理学研究科 物理学・宇宙物理学専攻 物理学第二教室 准教授)

14:45-15:00 ティータイムディスカッション 15:00-16:00濱崎 立資 博士（理化学研究所 開拓研究本部 非平衡量子統計力学理研白眉研究チーム 理研白眉チームリーダー）「量子力学による統計力学の基礎づけ」 16:15-17:15 榎戸 輝揚 博士（京都大学理学研究科 物理学・宇宙物理学専攻 物理学第２教室 准教授）「学際融合で進める宇宙時代のシスルナ科学へ」 17:15-18:00 継続討論会

会場: 京都大学 北部総合教育研究棟 1階 益川ホール

イベント公式言語: 日本語

Emergence of wormholes from quantum chaos

2024年11月12日(火) 16:30 - 18:00

ガブリエル・ディウバルド (理化学研究所 数理創造プログラム (iTHEMS) 特別研究員)

I will give a broad introduction to some aspects of quantum gravity and the so-called black hole information problem. I will introduce wormholes as novel contributions to the gravitational path integral and how they provide a solution to the black hole information problem. Wormholes, however, are rather mysterious and we don’t have a good microscopic understanding of them and why we should include them in the our theory. In particular, wormholes seem to imply that gravity is not a proper quantum system but rather an average over a statistical ensemble of quantum systems. I will then transition into my own work which addresses these questions in the context of holography. I will show how wormholes in 3D quantum gravity can emerge from quantum chaos in the dual 2D Conformal Field Theory, without averaging. Wormholes capture coarse-grained properties of the CFT and conversely an individual chaotic CFT can effectively behave as an averaged system. Furthermore we will be able to explicitly factorize wormholes to extract microscopic information on black hole microstates. To achieve this I will (briefly) introduce and use tools such as Random Matrix Theory, the Gutzwiller Trace formula and Berry’s diagonal approximation, and the theory of SL(2,Z) non-holomorphic modular forms.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Quantum signature kernels

2024年10月30日(水) 14:00 - 15:00

Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)

Arising from rough path theory, the signature transform captures features of time-series data by constructing a so-called path signature. This feature has proven valuable for various machine learning tasks. However, computing the associated signature kernel classically remains computationally intensive. In this talk, I will present recent developments in generalising the signature kernel to randomised Lie group path developments. I will discuss a quantum approach via matrix models with an associated unitary quantum signature kernel to propose a quantum algorithm for its computation.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

RIKEN Quantum Workshop on “Quantum-Like Modeling” in Cognitive & Social Sciences

2024年10月11日(金) 14:00 - 19:00

Recently, there has been a growing trend to consider cognitive, and social phenomena as Open Quantum Systems, and to mathematically define the fundamental principles behind them through so-called “Quantum-Like Modeling”. It has been extremely difficult to systematically explain complexities of such phenomena within humans’ cognitive traits based on classical “rational” reasoning. Quantum-Like Modeling suggests that using quantum probability calculus and its applications could be useful to rationalize such phenomena and expand previous understandings, obtained through simple linear algebra, by applying quantum formalizations. Just as physicists explored a new branch of mathematics, the theory of operators in complex Hilbert space, to describe the quantum phenomena in an effective way, considerations here will be built on the methodology and mathematical apparatus of quantum theory and directed to applications outside of physics, namely to, cognition, psychology, decision-making, economics, finances, as well as the social and political sciences. Programme 14:00~14:10 Atsushi Iriki: Introduction. Potential of quantum computing for humanities 14:10~15:10 Andrei Khrennikov: Tutorial. Ubiquitous Quantum: from genetics and biological evolution to cognition, psychology, decision making, and social science 15:10~15:40 Masanao Ozawa: Quantum Instrument -- Measurement to cognition with QC-simulation Break 16:00~16:30 Haruki Emori: Applications of quantum computers to cognitive sciences based on Quantum Instrument 16:30~17:00 Miho Fuyama: Subjective Experiences and Superposition State in Narrative Reading 17:00~17:30 General Discussion 18:00~19:00 Networking Mixer (RIKEN canteen #1) Registration Deadline September 26 (Thur), 2024 (for those attending both the workshop and networking mixer (banquet, free of charge)) October 4 (Fri), 2024 (for those attending only the workshop)

会場: セミナー室 (359号室)

イベント公式言語: 英語

Understanding Diffusion Models by Feynman's Path Integral

2024年10月9日(水) 15:00 - 16:30

広野 雄士 (大阪大学 大学院理学研究科 物理学専攻 助教)

Diffusion models have emerged as powerful tools in generative modeling, especially in image generation tasks. In this talk, we introduce a novel perspective by formulating diffusion models using the path integral method introduced by Feynman for describing quantum mechanics. We find this formulation providing comprehensive descriptions of score-based diffusion generative models, such as the derivation of backward stochastic differential equations and loss functions for optimization. The formulation accommodates an interpolating parameter connecting stochastic and deterministic sampling schemes, and this parameter can be identified as a counterpart of Planck's constant in quantum physics. This analogy enables us to apply the Wentzel-Kramers-Brillouin (WKB) expansion, a well-established technique in quantum physics, for evaluating the negative log-likelihood to assess the performance disparity between stochastic and deterministic sampling schemes.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Dynamics of Phase Transitions: Between First and Second Order

2024年10月8日(火) 16:00 - 17:30

鈴木 史花 (CNLS Postdoctoral Research Associate, T4 / Center for Nonlinear Studies, Los Alamos National Laboratory, USA)

Phase transitions are typically classified as either first-order or second-order. The formation of topological defects in second-order phase transitions is well described by the Kibble-Zurek mechanism, while nucleation theory addresses first-order phase transitions. However, certain systems, such as superconductors and liquid crystals, can exhibit “weakly first-order” phase transitions that do not fit into these established frameworks. In this presentation, I introduce a new theoretical approach that combines the Kibble-Zurek mechanism with nucleation theory to explain topological defect formation in weakly first-order phase transitions. Additionally, I will discuss nonlinear quantum phase transitions that exhibit behaviors similar to weakly first-order transitions, which can be related to experiments with ultra-cold Rydberg atoms.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催 (メイン会場) / via Zoom

イベント公式言語: 英語

RIKEN - LBNL Workshop on Quantum Information Science

2024年9月3日(火) - 6日(金)

This international workshop will bring together researchers worldwide to discuss and collaborate on the latest developments in quantum technologies and quantum computing. Other focus areas will be algorithms, hybrid classical - quantum computing, error mitigation, and applications in physics and chemistry. With an emphasis to galvanize the participants into future collaborations, in addition to presentations on recent trends, the workshop will dedicate time in the afternoons for facilitated brainstorming and planning sessions.

会場: Lawrence Berkeley National Laboratory (Berkeley, California)

イベント公式言語: 英語

NCTS-iTHEMS Joint Workshop on Matters to Spacetime: Symmetries and Geometry

2024年8月26日(月) - 29日(木)

The National Center for Theoretical Sciences (NCTS) and the Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) at RIKEN have long maintained a collaborative relationship, even before the Memorandum of Understanding was signed in December, 2022. This partnership has successfully facilitated joint activities in high energy physics over recent years. As the impact of the COVID-19 pandemic wanes, we are excited to announce the inaugural joint workshops focusing on condensed matter physics and (quantum) gravity. These workshops are designed to foster international collaborations and stimulate interdisciplinary research. We are pleased to invite you to the 2024 NCTS-iTHEMS Workshop on Matters to Spacetime: Symmetries and Geometry, to be held from August 26 (Monday) to August 29 (Thursday), at the National Center for Theoretical Sciences, located on the campus of National Taiwan University (NTU) in Taipei, Taiwan. This workshop will feature presentations on the latest research findings, foster discussions to spark new ideas, and provide opportunities for initiating collaborative projects. While we strongly encourage in-person attendance to maximize engagement and interaction, an online platform will also be available to accommodate participants who are unable to attend physically.

会場: NCTS Physics Lecture Hall, 4th Floor, Cosmology Hall, National Taiwan University

イベント公式言語: 英語

RIKEN iTHEMS & AIPmath Special Lecture: Contact geometry in 3-dimensional space and higher

2024年7月29日(月) 15:30 - 16:30

Emmy Murphy (Professor, Princeton University, USA)

In mathematics, contact geometry is a type of geometry describing a variety of dynamical systems. They are the phase spaces of systems arising in geometric optics, semi-classical quantum systems, classical dynamics, and control theory. On the mathematical side, contact geometry relates to a variety of other geometric structures, such as Kahler geometry, smooth topology, and foliation theory. It can be especially interesting to look at contact geometry in 3-dimensional space, because we can explicitly visualize the spaces. Additionally, by connecting contact geometry with our understanding of 3-D topology, mathematicians have the ability to understand the large-scale structure of these spaces like never before. The talk will introduce the basics of contact geometry and its applications. We'll particularly focus on the 3-dimensional case, while also mentioning some of the unique properties of higher-dimensional spaces which are recently being explored. Registration required: Register before Wednesday, July 24, 15:00.

会場: 理化学研究所 東京連絡事務所 (メイン会場) / via Zoom

イベント公式言語: 英語

Lectures on Black Holes, Holography and Quantum Gravity

2024年7月29日(月) - 8月1日(木)

野村 泰紀 (Professor/Director, Berkeley Center for Theoretical Physics, University of California, Berkeley, USA)

The information problem of black holes has evolved modern physics and led to the holographic principle, considered the fundamental principle of quantum gravity. Through a series of four lectures (blackboard style), including naive questions from the audience and lively discussions, I will introduce these fundamental ideas as well as the current state of the art and problems in cutting-edge research. Lecture 1: July 29 (Mon) 13:30~15:00 (Lecture 2: July 30 (Tue) 13:30~15:00 was canceled) Lecture 3: July 31 (Wed) 13:30~15:00 Lecture 4: Aug 1 (Thu) 13:30~15:00 (+ A possible lecture )

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Stringy Nonlocality: Operator Formalism and Implications

2024年7月26日(金) 14:00 - 15:30

ウェイシャン・シャオ (Ph.D. Student, Department of Physics, National Taiwan University, Taiwan)

Nonlocality is a fundamental property of string theory, where point-like particles are replaced by extended strings. This feature is especially evident in string field theories, where field components interact through form factors containing spacetime derivatives of infinite order. The usual approach to canonical quantization is no longer applicable, and thus a non-perturbative treatment of nonlocal effects at the quantum level remains unclear. In this seminar, I will discuss a recent attempt to construct an operator formalism for stringy nonlocal field theories, and explore the potential implications for black hole radiation and primordial fluctuations in the early universe.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Probing Majorana excitations in the Kitaev magnet α-RuCl3 through bulk heat capacity measurements

2024年7月22日(月) 10:30 - 11:45

今村 薫平 (東京大学 大学院工学系研究科 物理工学専攻 博士課程／日本学術振興会 特別研究員 DC)

Recently, the layered honeycomb material α-RuCl3 exhibits several anomalous features that are consistent with expectations of the Kitaev quantum spin liquid (KQSL) under in-plane magnetic field. Most remarkably, finite planar thermal Hall conductivity has been observed, whose magnitude is close to the half-integer quantization value expected for the chiral edge currents of Majorana fermions[1]. However, it has been reported that the thermal Hall conductivity shows strong sample dependence. Also, there are attempts to offer a different explanation by the bosonic edge excitations due to topological magnons or phonon. A key to distinguishing between fermionic and bosonic origins of unusual features in the high-field state of α-RuCl3 is the difference in the field angle dependence of the excitation gap. Therefore, we distinguish these origins from combined low-temperature measurements of high-resolution specific heat and thermal Hall conductivity with rotating magnetic fields within the honeycomb plane. A distinct closure of the low-energy bulk gap is observed for the fields in the Ru-Ru bond direction, and the gap opens rapidly when the field is tilted. Notably, this change occurs concomitantly with the sign reversal of the Hall effect. General discussions of topological bands show that this is the hallmark of an angle rotation–induced topological transition of fermions, providing conclusive evidence for the Majorana-fermion origin of the thermal Hall effect in α-RuCl3[2]. Furthermore, to understand the nature of the high-field state, it is crucial to elucidate the effects of disorder, which inevitably exists in real materials. We artificially introduce point defects by electron irradiation and compare the low-energy excitations in the pristine and irradiated sample by high-resolution specific heat measurements. We observed an additional in-gap T-linear term in C/T, whose coefficient shows distinct field-sensitive behaviors suggestive of Majorana physics in the KSL. This can be interpreted by the weak localization of Majorana fermions, which is induced by the disorder[3]. Moreover, recently, we succeed in synthesizing very high-quality crystals of α-RuCl3[4].

会場: via Zoom / セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Thermal radiation exchange in primordial gravitational waves

2024年7月18日(木) 13:30 - 15:00

太田 敦久 (Postdoctoral Fellow, Institute for Advanced Study, Hong Kong University of Science and Technology, China)

The radiation-dominated universe is a key component of standard Big Bang cosmology. Radiation comprises numerous quantum elementary particles, and its macroscopic behavior is described by taking the quantum thermal average of its constituents. The dynamics of gravitational waves are considered in this smooth fluid. While interactions between individual particles and gravitational waves are often neglected in this context, it raises the question of whether such a hydrodynamical approximation is reasonable. To address this question, we explored the quantum mechanical aspects of gravitational waves in a universe dominated by a massless scalar field, whose averaged energy-momentum tensor serves as background radiation. We computed thermal loop corrections for the gravitational wave power spectrum using the Schwinger-Keldysh formalism. Interestingly, we found that the loop effect enhances the super-horizon primordial gravitational wave spectrum, indicating that the inflationary spectrum is not conserved, contrary to conventional wisdom. These findings have significant implications for our understanding of the early universe. In this talk, I will begin with the basics of cosmology and explain the significance of these results and their relevant observational consequences.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Quantum Simulation in High Energy Nuclear Physics

2024年7月18日(木) 10:00 - 11:30

郭 星雨 (Lecturer, Institute of Quantum Matter, South China Normal University, China)

Quantum simulation is a novel method of simulation physical systems with quantum computers. Compared to conventional methods, quantum algorithms have various advantages in doing non-perturvative calculations and real-time evolutions, which makes it very promising to apply them in high energy nuclear physics. We propose a systematic quantum algorithm, which integrates both the hadronic state preparation and the evaluation of real-time light-front correlators. This algorithm can be applied to the calculation of a wide range of quantities in high energy nuclear physics. As a demonstration, we calculate the parton distribution functions, the light-cone distribution amplitudes and scattering amplitudes in the 1+1 dimensional NJL model. The results are qualitatively consistent with QCD calculations.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Quantum Error Transmutation

2024年7月17日(水) 10:30 - 11:30

Daniel Zhang (Postdoctoral Fellow, University of Oxford, UK)

We introduce a generalisation of quantum error correction, relaxing the requirement that a code should identify and correct a set of physical errors on the Hilbert space of a quantum computer exactly, instead allowing recovery up to a pre-specified admissible set of errors on the code space. We call these quantum error transmuting codes. They are of particular interest for the simulation of noisy quantum systems, and for use in algorithms inherently robust to errors of a particular character. Necessary and sufficient algebraic conditions on the set of physical and admissible errors for error transmutation are derived, generalising the Knill-Laflamme quantum error correction conditions. We demonstrate how some existing codes, including fermionic encodings, have error transmuting properties to interesting classes of admissible errors. Additionally, we report on the existence of some new codes, including low-qubit and translation invariant examples.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Dynamics of the very early universe: towards decoding its signature through primordial black hole abundance, dark matter, and gravitational waves.

2024年7月5日(金) 14:00 - 15:15

Riajul Haque (Postdoctoral Researcher, Department of Physics, Indian Institute of Technology, India)

I will start my talk with a brief overview of the standard reheating scenario. Then, I will discuss reheating through the evaporation of primordial black holes (PBHs) if one assumes PBHs are formed during the phase of reheating. Depending on their initial mass, abundance, and inflaton coupling with the radiation, I discuss two physically distinct possibilities of reheating the universe. In one possibility, the thermal bath is solely obtained from the decay of PBHs, while inflaton plays the role of the dominant energy component in the entire process. In the other possibility, PBHs dominate the total energy budget of the universe during evolution, and then their subsequent evaporation leads to a radiation-dominated universe. Furthermore, I will discuss the impact of both monochromatic and extended PBH mass functions and estimate the detailed parameter ranges for which those distinct reheating histories are realized. The evaporation of PBHs is also responsible for the production of DM. I will show its parameters in the background of reheating obtained from two chief systems in the early universe: the inflaton and the primordial black holes (PBHs). Then, I will move my discussion towards stable PBHs and discuss the effects of the parameters describing the epoch of reheating on the abundance of PBHs and the fraction of cold dark matter that can be composed of PBHs. If PBHs are produced due to the enhancement of the primordial scalar power spectrum on small scales, such primordial spectra also inevitably lead to strong amplification of the scalar-induced secondary gravitational waves (GWs) at higher frequencies. I will show how the recent detection of the stochastic gravitational wave background (SGWB) by the pulsar timing arrays (PTAs) has opened up the possibility of directly probing the very early universe through the scalar-induced secondary gravitational waves. Finally, I will conclude my talk by elaborating on the effect of quantum correction on the Hawking radiation for ultra-light PBHs and its observational signature through dark matter and gravitational waves.

会場: via Zoom

イベント公式言語: 英語

Worldline Path Integrals for the Graviton and 1-Loop Divergences in Quantum Gravity

2024年6月28日(金) 16:00 - 17:20

Fiorenzo Bastianelli (Professor, University of Bologna, Italy)

In this talk, I will discuss perturbative quantum gravity at the 1-loop level by reviewing and systematizing old results on UV divergences and presenting new findings along with new methods for their calculation. The traditional approach to this problem employs the Schwinger-DeWitt heat kernel method. We extend this approach by incorporating worldline path integrals to compute the perturbative expansion at small proper time. In addition, we explore a more principled approach that utilizes the BRST path integral quantization of the N=4 spinning particle, which describes the graviton in first quantization. Using these methods, we calculate the one-loop divergences in quantum gravity with a cosmological constant in arbitrary dimensions. When evaluated on-shell, these calculations yield a set of gauge-invariant coefficients that characterize pure quantum gravity with a cosmological constant. These coefficients may serve as benchmarks for comparing various approaches to quantum gravity.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Quantum Computation Study Group Seminars

2024年6月18日(火) 13:30 - 15:00

菊池 勇太 (クオンティニュアム株式会社 Quantum Algorithms and Machine Learning Research Scientist)
エルマル・ルラーバイ (Computer Systems Engineer, National Energy Research Scientific Computing Center (NERSC), Lawrence Berkeley National Laboratory (LBNL), USA)

Speaker: Yuta Kikuchi Title: Simulating Floquet scrambling circuits on trapped-ion quantum computers Abstract: Complex quantum many-body dynamics spread initially localized quantum information across the entire system. Information scrambling refers to such a process, whose simulation is one of the promising applications of quantum computing. We demonstrate the Hayden-Preskill recovery protocol and the interferometric protocol for calculating out-of-time-ordered correlators to study the scrambling property of a one-dimensional kicked-Ising model on 20-qubit trapped-ion quantum processors. The simulated quantum circuits have a geometrically local structure that exhibits the ballistic growth of entanglement, resulting in the circuit depth being linear in the number of qubits for the entire state to be scrambled. We experimentally confirm the growth of signals in the Hayden-Preskill recovery protocol and the decay of out-of-time-ordered correlators at late times. As an application of the created scrambling circuits, we also experimentally demonstrate the calculation of the microcanonical expectation values of local operators adopting the idea of thermal pure quantum states. Speaker: Ermal Rrapaj Title: Exact block encoding of imaginary time evolution with universal quantum neural networks Abstract: Quantum computers have been widely speculated to offer significant advantages in obtaining the ground state of difficult Hamiltonian in chemistry and physics. The imaginary-time evolution method is a well-known approach used for obtaining the ground state in quantum many-body problems on a classical computer. In this work we develop a practical method for such purpose. We develop a constructive approach to generate quantum neural networks capable of representing the exact thermal states of all many-body qubit Hamiltonians. The Trotter expansion of the imaginary-time propagator is implemented through an exact block encoding by means of a unitary, restricted Boltzmann machine architecture. Marginalization over the hidden-layer neurons (auxiliary qubits) creates the non-unitary action on the visible layer. Then, we introduce a unitary deep Boltzmann machine architecture, in which the hidden-layer qubits are allowed to couple laterally to other hidden qubits. We prove that this wave function ansatz is closed under the action of the imaginary-time propagator and, more generally, can represent the action of a universal set of quantum gate operations. We provide analytic expressions for the coefficients for both architectures, thus enabling exact network representations of thermal states without stochastic optimization of the network parameters. In the limit of large imaginary time, the ansatz yields the ground state of the system. The number of qubits grows linearly with the system size and total imaginary time for a fixed interaction order. Both networks can be readily implemented on quantum hardware via mid-circuit measurements of auxiliary qubits. If only one auxiliary qubit is measured and reset, the circuit depth scales linearly with imaginary time and system size, while the width is constant. Alternatively, one can employ a number of auxiliary qubits linearly proportional to the system size, and circuit depth grows linearly with imaginary time only.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語