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RIKEN–Berkeley Workshop on Quantum Gravity 2025

2025年10月23日(木) - 24日(金)

This workshop will serve as the first meeting of the collaboration between the Leinweber Institute for Theoretical Physics (LITP) at the University of California Berkeley and the RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS). Participation is open and researchers from other institutions are welcome to attend. The workshop will feature talks on recent developments in the field of Quantum Gravity and other relevant topics.

会場: via Zoom / 研究本館 3階 359号室 (23日午前) & 4階 435-437号室 (23日午後・24日)

イベント公式言語: 英語

Neural network wavefunctions for SU(2) lattice gauge theory in the Hamiltonian formulation

2025年10月22日(水) 15:00 - 16:30

Tom Spriggs (PostDoc, Kavli Institute of Nanoscience and QuTech, Delft University of Technology, Netherlands)

In this talk I will cover our recent preprint arXiv:2509.12323 where we propose a neural network approach to finding the ground state wavefunction of SU(2) lattice gauge theory. Specifically, we demonstrate that the use of bespoke SU(2)-gauge-equivariant neural network layers increases the extent to which our variational ansatz can represent the ground state of this system. During this talk I will contrast the Hamiltonian and Euclidean formalisms of lattice gauge theories, highlighting the promises that the former offers but also the difficulties: noting briefly the issues of parameterising the continuous Hilbert space that plague tensor network and quantum simulation approaches and how our approach alleviates this. I will try and present our method pedagogically as we are very interested in learning its uses but also the limits of its validity, before closing with some remarks on scaling to larger systems and different gauge groups.

会場: via Zoom

イベント公式言語: 英語

Simulating nonequilibirum quantum dynamics on Reimei

2025年10月21日(火) 10:00 - 12:00

早田 智也 (慶応義塾大学 医学部 准教授)

This is the third quantum computing gathering hold by quantum computing study group.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

Topological Field Theory Coupled to Parameter Spaces

2025年10月15日(水) 13:30 - 15:00

安藤 貴政 (京都大学 基礎物理学研究所 博士課程)

Topological quantum field theories (TQFTs) describe the IR fixed points of wide classes of gapped theories and are useful for studying many-body quantum phases of matter. In this talk, I will talk about TQFTs coupled to parameter spaces. I first explain the motivation for studying such TQFTs with parameter spaces from two perspectives: generalizing the description of the partition function with background gauge fields, and generalizing to invariants of many-body gapped phases over parameter spaces, known as the Berry phase. Then I will explain how these two are related by showing two physically motivated maps that connect them. The construction of these maps provides physical evidence for the Cobordism Hypothesis. I also discuss other related topics, such as the bulk-boundary correspondence. The talk is based on my ongoing work with Ryan Thorngren (UCLA).

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

Algebraic structures in QFT in the presence of a quantum reference frame

2025年10月9日(木) 14:00 - 15:00

Kasia Rejzner (Professor, Department of Mathematics, University of York, UK)

In this talk I will show how operational description of measurement with the use of quantum reference frames (QRF) affects the algebraic structure of quantum field theory (QFT). I will focus on the example of a quantum clock coupled to a QFT on de Sitter spacetime, previously discussed by Chandrasekaran, Longo, Pennington and Witten. This talk is based on my recent work with Chris Fewster, Daan Janssen, Leon Loveridge and James Waldron.

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

Lectures on General Probabilistic Theories: From Introduction to Research Participation

2025年10月6日(月) - 9日(木)

荒井 駿 (東京大学 大学院総合文化研究科 JSPS特別研究員)

(The deadline of the registration is on Sep 30.) 100 years have passed since quantum mechanics was born. The mathematical model has been describing the physical world remarkably well. However, the foundations of this model still remain unclear. A comprehensive understanding of quantum theory, including its foundations, is becoming even more important in an era where the demands of realizing quantum information technologies pose significant theoretical and experimental challenges. The framework of General Probabilistic Theories (GPTs) is a modern approach to the foundations of quantum theory. It deals with mathematical generalizations of both classical and quantum theories and has attracted increasing attention in recent years. Roughly speaking, research on GPTs has three major objectives: characterizing the models of classical and quantum theories, investigating the fundamental limits of physical and information-theoretic properties arising from operational requirements, and deepening our understanding of the mathematical structures underlying classical and quantum theories. The studies of GPTs have provided many new perspectives on these topics. However, at the same time, there remain many important open problems in the field. For this reason, more researchers are encouraged to enter and contribute to research on GPTs. This intensive three-day lecture series is designed to provide researchers and graduate students with the essential knowledge necessary for research on GPTs, starting from an introduction to the subject. The lectures will cover the mathematical foundations, physical and information-theoretic concepts, and both the established results and future directions of GPT research. The 1st day will present the necessary mathematical structures, including convex geometry, positive cones, and the operational formulation of probabilistic models. The 2nd day will explore composite systems, information-theoretic quantities, symmetries, and Euclidean Jordan algebras. The 3rd day will survey key results on discrimination and communication tasks, the characterization of classical and quantum theories, and open problems that connect GPTs to quantum information science and beyond. Note: The content of each lecture may extend into the next slot or be covered earlier, depending on the pace of discussion and participant questions. The 1st day (6th Oct.): Mathematical Introduction to GPTs Venue: Large Meeting Room, 2F, Wako Welfare & Conference Building 10:30-12:00 Lecture 1 (Introduction and Mathematics on Positive Cones) 12:00-13:30 Lunch time 13:30-15:00 Lecture 2 (Mathematics on Positive Cones) 15:00-15:30 Coffee break 15:30-17:00 Lecture 3 (Introduction to General Models and Relation between Operational Probability Theories) The 2nd day (7th Oct.): Physical and Information Theoretical Concepts in GPTs Venue: Large Meeting Room, 2F, Wako Welfare & Conference Building 10:30-12:00 Lecture 4 (Composite Systems in GPTs) 12:00-13:30 Lunch time 13:30-15:00 Lecture 5 (Information Quantities) 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 (Dynamics, Symmetry, and Euclidean Jordan Algebras) The 3rd day (8th Oct): Previous and Future Studies in GPTs Venue: Meeting Room 435-437, 4F, Wako Main Research Building 10:30-12:00 Lecture 7 (Discrimination and Communication Tasks) 12:00-13:30 Lunch time 13:30-15:00 Lecture 8 (Characterization of Classical and Quantum Theories) 15:00-15:30 Coffee break 15:30-17:00 Lecture 9 (Other Topics, Open Problems, and Future Directions) 18:00- Dinner The day of no lecture (9th Oct): Open Discussion and Q&A Research discussions will take place between the lecturer and participants in areas such as the hallways on the 3rd and 4th floors of the Main Research Bldg, RIKEN Wako Campus.

会場: 理化学研究所 和光キャンパス 統合支援施設2階会議室 / 研究本館 435-437号室

イベント公式言語: 英語

Quantum tunneling in the curved spacetime

2025年10月2日(木) 13:30 - 15:00

山口 昌英 (Director, Center for Theoretical Physics of the Universe, Institute for Basic Science, Republic of Korea)

False vacuum decay is theorized to have occurred frequently throughout the history of the universe, particularly during first-order phase transitions associated with spontaneous symmetry breaking. The decay rate of such a vacuum is governed by Euclidean bounce solutions, which can exhibit a wide range of configurations, even under fixed boundary conditions. In the absence of gravitational effects, it was established over four decades ago—under reasonable assumptions—that the most symmetric bounce solution, namely the O(4)-symmetric one, minimizes the Euclidean action. This renders it the dominant tunneling path in flat spacetime. However, when gravitational effects are taken into account—as is essential in cosmological settings—all prior studies have assumed, without rigorous proof, that the O(4)-symmetric bounce continues to minimize the action. This has remained a longstanding unresolved problem for more than forty years. In this work, we address this issue by employing the anti-de Sitter/conformal field theory (AdS/CFT) correspondence to determine the configuration with the lowest Euclidean action in a metastable AdS false vacuum. Within the Euclidean formalism of Callan and Coleman, we identify the most probable decay channel of the AdS vacuum. The AdS/CFT duality enables us to sidestep the technical challenges intrinsic to metastable gravitational systems. We demonstrate that the Fubini bounce in conformal field theory—which is dual to the Coleman–de Luccia (CdL) bounce in AdS—indeed minimizes the Euclidean action among all finite bounce solutions in a conformal scalar field theory. Consequently, under certain conditions, we establish that the CdL bounce yields the lowest action among all relevant configurations, including both large and thin-wall limits. Time permitting, we also discuss the prefactor of the decay rate, as obtained from one-loop quantum corrections.

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

Spontaneous quasiparticle creation in an analogue preheating experiment

2025年9月30日(火) 10:00 - 12:00

アモリ・ミケリ (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 特別研究員)

Abstract: First, I will briefly outline the motivations and concepts that underpin the analogue gravity program. Next, I will provide a detailed description of a specific experiment designed to simulate various features of the cosmological reheating era. Finally, I will present our recent experimental results from this setup, where we demonstrated the parametric creation of quasiparticle pairs from the quantum vacuum, drawing an analogy with the preheating phase of reheating.

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

8th QGG Intensive Lecture: Quantum reference frames and their applications in high-energy physics

2025年9月24日(水) - 26日(金)

Philipp Höhn (沖縄科学技術大学院大学 (OIST) 量子ビットと時空ユニット 助教)

Quantum reference frames (QRFs) are a universal tool for dealing with symmetries in quantum systems. Roughly speaking, they are internal subsystems that transform in some non-trivial way under the symmetry group of interest and constitute the means for describing quantum systems from the inside in purely relational terms. QRFs are thus crucial for describing and extracting physics whenever no external reference frame for the symmetry group is available. This is in particular the case when the symmetries are gauge, as in gauge theory and gravity, where QRFs arise whenever building physical observables. The choice of internal QRF is typically non-unique, giving rise to a novel quantum form of covariance of physical properties under QRF transformations. This lecture series will explore this novel perspective in detail with a specific emphasis on applications in high-energy physics and gravity. I will begin by introducing QRFs in mechanical setups and explain how they give rise to quantum structures of covariance that mimic those underlying special relativity. I will explain how this leads to subsystem relativity, the insight that different QRF decompose the total system in different ways into gauge-invariant subsystems, and how this leads to the QRF dependence of correlations, entropies, and thermal properties. We will then explore how relational dynamics in Hamiltonian constrained systems and the infamous "problem of time" can be addressed with clocks identified as temporal QRFs. In transitioning to the field theory setting, we will first consider hybrid scenarios, where QRFs are quantum mechanical, but the remaining degrees of freedom are quantum fields including gravitons. I will explain how this encompasses the recent discussion of "observers", generalized entropies, and gravitational von Neumann algebras by Witten et al. and how subsystem relativity leads to the conclusion that gravitational entanglement entropies are observer dependent. We will then discuss the classical analog of QRFs in gauge theory and gravity and how they can be used to build gauge-invariant relational observables and to describe local subsystems. This will connect with discussions on edge and soft modes in the literature, the former of which turn out to be QRFs as well. This has bearing on entanglement entropies in gauge theories, which I will describe on the lattice, providing a novel relational construction that overcomes the challenges faced by previous constructions, which yielded non-distillable contributions to the entropy and can be recovered as the intersection of "all QRF perspectives". Finally, I will describe how the classical discussion of dynamical reference frames can be used to build a manifestly gauge-invariant path integral formulation that opens up novel relational perspectives on effective actions and the renormalization group in gravitational contexts, which is typically plagued by a lack of manifest diffeomorphism-invariance. I will conclude with open questions and challenges in the field. Program: September 24 10:15 - 10:30 Registration and reception with coffee 10:30 - 12:00 Lecture 1 12:00 - 13:30 Lunch 13:30 - 15:00 Lecture 2 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 3 17:10 - 18:10 Short talk session 18:20 - 21.00 Banquet September 25 10:15 - 10:30 Morning discussion with coffee 10:30 - 12:00 Lecture 4 12:00 - 13:30 Lunch 13:30 - 15:00 Lecture 5 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 6 17:10 - 18:10 Short talk session September 26 10:15 - 10:30 Morning discussion with coffee 10:30 - 12:00 Lecture 7 12:00 - 13:30 Lunch 13:30 - 15:00 Lecture 8 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 9 & Closing

会場: 研究本館 4階 435-437号室

イベント公式言語: 英語

Japan-UK Workshop on Quantum Gravity

2025年9月22日(月) - 26日(金)

The universe at extremely early times is expected to be described by some theory of quantum gravity, although we still do not know precisely what quantum gravity actually is. In modern approaches to quantum gravity, the path integral point of view provides a fundamental framework towards answering this pressing question. However, an evaluation or even just a precise definition of the path-integral for a full-fledged quantum gravity is one of the most important open problems in modern theoretical physics.

会場: 融合連携イノベーション推進棟（IIB） 8階

イベント公式言語: 英語

Multi-strangeness matter from ab initio calculations

2025年9月16日(火) 13:30 - 15:00

童 辉 (Post-doctoral Fellow, Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, Germany)

Hypernuclei and hypernuclear matter connect nuclear structure in the strangeness sector with the astrophysics of neutron stars, where hyperons are expected to emerge at high densities and affect key astrophysical observables. We present the first ab initio calculations that simultaneously describe single- and double- hypernuclei from the light to medium-mass range, the equation of state for -stable hypernuclear matter, and neutron star properties. Despite the formidable complexity of quantum Monte Carlo (QMC) simulations with multiple baryonic degrees of freedom, by combining nuclear lattice effective field theory with a newly developed auxiliary-field QMC algorithm we achieve the first sign-problem free ab initio QMC simulations of hypernuclear systems containing arbitrary number of neutrons, protons, and hyperons, including all relevant two- and three-body interactions. This eliminates reliance on the symmetry-energy approximation, long used to interpolate between symmetric nuclear matter and pure neutron matter. Our unified calculations reproduce hyperon separation energies, yield a neutron star maximum mass consistent with observations, predict tidal deformabilities compatible with gravitational-wave measurements, and give a trace anomaly in line with Bayesian constraints. By bridging the physics of finite hypernuclei and infinite hypernuclear matter within a single ab initio framework, this work establishes a direct microscopic link between hypernuclear structure, dense matter composition, and the astrophysical properties of neutron stars.

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

Foundations of Relational Quantum Field Theory — scalars

2025年9月9日(火) 16:30 - 17:30

Samuel Fedida (PhD, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK)

We develop foundations for a relational approach to quantum field theory (RQFT) based on the operational quantum reference frames (QRFs) framework considered in a relativistic setting. We focus on scalar fields in Minkowski spacetime and discuss the emergence of relational local observables and pointwise fields from the consideration of Poincaré-covariant frame observables defined over the space of inertial reference frames. We recover a relational notion of Poincaré covariance, with transformations on the system directly linked to the state preparations of the QRF. We introduce various causality conditions which mirror standard Einstein causality and microcausality, now seen in a relational context. The theory makes direct contact with established foundational approaches to QFT: the vacuum expectation values derived within our framework reproduce many of the essential properties of Wightman functions, and we compare the proposed formalism with Wightman QFT with the frame smearing functions describing the QRF's localisation uncertainty playing the role of the Wightmanian test functions. We show how the algebras generated by relational local observables satisfy all of the core axioms of Algebraic QFT. This work is an early step in revisiting the mathematical foundations of QFT from a relational and operational perspective.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

A Fresh Look at Late-Time Hawking Radiation

2025年9月2日(火) 14:00 - 15:30

ウェイシャン・シャオ (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 基礎科学特別研究員)

There is now a common belief that non-perturbative quantum gravity effects are relevant for resolving the black hole information puzzle. But could such effects also largely alter Hawking radiation itself, the main culprit that led to the puzzle in the first place? There are two main lessons that I would like to convey from this presentation: 1. For large black holes formed by dynamical collapse, the usual description of Hawking radiation in the low-energy effective theory breaks down at an early stage, signaling the need for a UV theory to describe the origin of late-time radiation. 2. In UV models of the radiation field that incorporate a form of nonlocality motivated by string theory, Hawking radiation becomes a transient phenomenon that occurs only for a brief period of time. This behavior suggests a major deviation from the conventional picture of black hole evaporation based on local quantum field theory.

会場: via Zoom / 理化学研究所 和光キャンパス 3階 359号室

イベント公式言語: 英語

A Discussion on Quantum Machine Learning for Medical Data

2025年8月26日(火) 14:00 - 15:00

杉本 聡 (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 医科学データ駆動数理チーム 上級研究員)

Our team is investigating the applicability of machine learning using quantum computers to medical data. In this talk, we will provide a brief overview of supervised machine learning for medical data as a topic for discussion.

会場: via Zoom

イベント公式言語: 英語

iTHEMS-NCTS Workshop

2025年8月18日(月) - 21日(木)

This workshop aims to strengthen collaboration between researchers at RIKEN iTHEMS and the National Center for Theoretical Sciences in Taiwan. It will be a four-day event, with the first two days dedicated to interdisciplinary topics. The last two days will focus on specialized areas, with one day devoted to condensed matter physics and the other to high-energy physics, including quantum gravity.

会場: via Zoom / 理化学研究所 和光キャンパス

イベント公式言語: 英語

Targeting SARS-CoV-2 RNA: Insights for RNA-Directed Drug Discovery

2025年7月31日(木) 13:00 - 14:30

マリア・イヴォニナ (九州大学 エネルギー研究教育機構 学術研究員)

Traditional pharmacology fights virus infections by targeting proteins including enzymes, receptors, and structural proteins to break up the viral machinery. Nucleic acid-targeting therapies, on the other hand, can act directly on the genetic code of viruses, blocking their replication or translation in host cells. Coronaviruses and HIV are examples of RNA viruses that use a process called -1 programmed ribosomal frameshifting (-1 PRF) to produce their viral proteins. In this process, the translating ribosome is forced to shift into the alternative reading frame, replicating mRNA in the wrong order. Using small-molecule compounds to block this mechanism could be a promising way to neutralize such viruses. It is difficult to experimentally study the interactions between RNA and a drug candidate to understand where the drug binds and how it changes the shape of the viral RNA. I will discuss how Molecular Dynamics simulations are used to explore the conformational dynamics of mRNA structural elements and to investigate what happens when an antiviral agent binds to it. Additionally, I will show how the quantum-chemical orbital interaction analysis we developed, called Through-Space/Through-Bond Energy Decomposition Analysis (TS/TB-EDA), reveals which RNA nucleotides, at the atomic level, are critical for binding. This molecular modelling approach reveals strategies for targeting structured RNA elements — a crucial step toward expanding the arsenal of RNA-targeting therapeutics for future pandemics.

会場: 研究本館 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

iTHEMS NOW & NEXT 2025

2025年7月24日(木) - 25日(金)

We will hold this fiscal year’s annual in-house gathering, “iTHEMS NOW & NEXT,” as follows. This event is a rare opportunity for all iTHEMS members, including visiting researchers, to gain a comprehensive overview of iTHEMS’s current activities and future directions. Program July 24th 9:30-9:45 Opening by Director Iso 9:45-10:10 Keynote lecture Sonia Mahmoudi 10:10-10:35 Keynote lecture Masazumi Honda 10:35 20-min break 10:55 Fundamental Quantum Science Program (FQSP) introduction Working Group introduction 5-min each 11:30 Lunch break 13:30 Teams introduction part 1 RIKEN-Berkeley Center RIKENｰBerkeley Center (Shigehiro Nagataki) Mathematical Application Research Team (Motoko Kotani / Tsukasa Tada) 13:50 11 SG Presentation 5 min each 14:45 break 15:00 Flash talks & Poster session 18:00 Reception July 25th 9:30 Keynote lecture Yuto Yamamoto 9:55 Keynote lecture Kyosuke Adachi 10:20 break 10:40　Teams introduction part 2 Prediction Science Research Team (Takemasa Miyoshi) Medical Science Deep Learning Team (Jun Seita) Medical Science Data-driven Mathematics Team (Eiryo Kawakami) Quantum Mathematical Science Team (Tetsuo Hatsuda) Mathematical Social Science Team (Yohsuke Murase) 11:30 Lunch 13:30 Flash Talk & Poster presentation 16:30 Concluding remark

会場: 理化学研究所和光キャンパス 本部棟2階大会議室 (メイン会場) / via Zoom

イベント公式言語: 英語

Bridging applied math and quantum many-body physics and beyond via tensor methods

2025年7月23日(水) 16:00 - 17:00

品岡 寛 (埼玉大学)

In modern physics, high-dimensional functions and operators naturally arise in a wide range of contexts, including turbulence simulations, parameter-dependent partial differential equations (PDEs), and quantum field theory. Efficient representations and computations with such high-dimensional objects pose major challenges across disciplines. Dimensionality reduction techniques such as the Quantics Tensor Train (QTT) [1] and Tensor Cross Interpolation (TCI) [2] were originally developed in applied mathematics. In our work, we have extended these methods to quantum many-body problems, demonstrating their effectiveness in handling complex high-dimensional structures in theoretical physics [3–10]. Given their generality, QTT and TCI are expected to find applications beyond quantum theory itself, in fields such as statistical field theory, model reduction, and control of complex systems, where similar high-dimensional structures emerge. This presentation will first review the computational bottlenecks that arise in quantum many-body simulations and other high-dimensional problems. Then, we will introduce QTT and TCI from a broader, method-oriented perspective, aiming to bridge applied mathematics and quantum theoretical physics.

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

Mesoscopic transport via one-dimensional chain with Localized two-body loss

2025年7月23日(水) 10:00 - 11:30

柿元 健佑 (早稲田大学 理工学術院 基幹理工学部 博士課程)

Mesoscopic transport has long served as a powerful probe into the quantum behavior of matter; however, the role of dissipation in such systems remains unresolved. In recent years, quantum simulations of mesoscopic systems with ultracold atomic gases have made significant progress, particularly through the use of optical tweezers to induce local dissipation via atom loss. In this talk, we discuss a two-terminal mesoscopic system in which two-body loss occurs locally at the center of a one-dimensional chain, modeling a dissipative quantum point contact. To analyze this setup, we employ the Keldysh Green’s function formalism in combination with a noise-field representation of Lindblad dynamics. Our analysis reveals that the dissipation strength depends on the occupation number of the central dissipative site, leading to a weaker suppression of particle current in the weakly dissipative regime compared to the case of one-body loss.

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

A free probability approach to quantum chaos in random matrix ensembles

2025年7月22日(火) 16:00 - 17:00

プラティック・ナンディ (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 特別研究員)

In free probability theory, quantum chaos is marked by “free independence” between observables at early and late times, causing certain statistical measures (cumulants) to vanish. Motivated by this, we study the statistics of a time-evolved operator in the Rosenzweig-Porter (RP) random matrix ensembles. Analyzing operator statistics for different spin operators across these regimes reveals close alignment with free probability predictions in the ergodic phase, contrasted by persistent deviations in the fractal and localized phases even at late times. Using the distance measures and statistical methods, we define and characterize the onset of the free time in the ergodic phase. The talk is based on arXiv: 2506.04520.

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