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Quantum Simulation of Non-Abelian Gauge Theories: Correcting Common Misconceptions (2/3)

March 31 (Tue) 18:00 - 19:00, 2026

Masanori Hanada (Reader, School of Mathematical Sciences, Queen Mary University of London, UK)

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: Japanese

QFT as a set of ODEs

March 27 (Fri) 13:30 - 15:30, 2026

Qiao Jiaxin (Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)

Correlation functions of local operators in Quantum Field Theory (QFT) on hyperbolic space can be fully characterized by the set of QFT data. These are the scaling dimensions of boundary operators, the boundary Operator Product Expansion (OPE) coefficients and the Boundary Operator Expansion (BOE) coefficients that characterize how each bulk operator can be expanded in terms of boundary operators. For simplicity, we focus on two dimensional QFTs and derive a universal set of first order Ordinary Differential Equations (ODEs) that encode the variation of the QFT data under an infinitesimal change of a bulk relevant coupling. In principle, our ODEs can be used to follow a renormalization group flow starting from a solvable QFT into a strongly coupled phase and to the flat space limit.

Venue: via Zoom (Main Venue) / Seminar Room #359

Event Official Language: English

Quantum Simulation of Non-Abelian Gauge Theories: Correcting Common Misconceptions (1/3)

March 24 (Tue) 18:00 - 19:00, 2026

Masanori Hanada (Reader, School of Mathematical Sciences, Queen Mary University of London, UK)

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: Japanese

Quantum States Over Time: From Foundations To Applications

March 24 (Tue) 15:30 - 17:00, 2026

Minjeong Song (Research Fellow, Centre for Quantum Technologies, National University of Singapore, Singapore)

In this talk, I will introduce quantum states over time (QSOT), a formalism for describing quantum systems over space-time. I will begin by reviewing how QSOT has emerged in the literature. While conventional density operator formalism has been effective across many areas of quantum information theory, QSOT was developed to meet more specialized research needs— most notably, as a key ingredient to develop a quantum version of Bayes’ theorem. I will end the first part of my talk by comparing various QSOT that have been proposed. In the second part, I will discuss the causal compatibility problem as an application of QSOT. I will focus on the temporal compatibility problem, which asks the following: from correlations in measurement outcomes alone, can two otherwise isolated parties establish whether such correlations are atemporal (i.e., temporally incompatible)? That is, can they rule out that they have been given the same system at two different times? I will first explain how characterizing measurement statistics in a causal agnostic scenario is equivalent to characterizing a specific type of QSOT, known as pseudo-density operators. I will then present our recent findings obtained by analyzing pseudo-density operators; In particular, we demonstrate that atemporality is distinct from entanglement, though they appear to be equivalent at first glance. Specifically, we show atemporality implies entanglement, but not vice versa, thus revealing that atemporality is a strictly stronger form of quantum correlations than entanglement. Nevertheless, we also find that sufficiently strong entanglement does imply atemporality.

Venue: #359, Seminar Room #359

Event Official Language: English

Useless Science & Art: The Value of “Useless” Science and Art

March 21 (Sat) 14:00 - 15:30, 2026

Satoshi Iso (Director, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Tetsuo Hatsuda (Executive Director of Science, RIKEN)
Yoshihiro Kozuka (Creative Director, ADK Marketing Solutions Inc.)
Haruka Kodama (Experience Designer, ADK Marketing Solutions Inc.)

A talk event exploring the relationship between science and art will be held, inspired by the artwork “Black Hole Recorder,” which draws on ideas from quantum black hole theory. Using this work as an entry point, scientists and creators will engage in dialogue on topics ranging from the 100-year history since the birth of quantum mechanics, to cutting-edge research in quantum cosmology, and even the question: “What should we leave for the future 1,500 years from now?” Research and artistic expression that may at first seem impractical have, over long periods of time, often led to transformative innovations for the future. How do scientists’ curiosity about the unknown and artists’ imagination intersect to generate new ideas? The event will introduce the concept and creative background of “Black Hole Recorder,” as well as recent developments in quantum black hole research. Through perspectives from both science and art, participants will discuss possibilities for the future. There will also be a special session where visitors can experience audio recordings made with the Black Hole Recorder itself. We warmly invite you to join this unique dialogue where science and art meet.

Venue: Museum of Contemporary Art Tokyo

Perspectives and applications of Koopman Operator Theory

March 19 (Thu) 9:00 - 18:00, 2026

Yoshihiko Susuki (Professor, Graduate School of Engineering, Kyoto University)
Hiroya Nakao (Professor, Department of Systems and Control Engineering, Institute of Science Tokyo)
Alexandre Mauroy (Associate Professor, Mathematics, University of Namur, Belgium)
Yuzuru Kato (Associate Professor, Department of Complex and Intelligent Systems, School of Systems Information Science, Future University-Hakodate)

PROGRAM: 9h45 - 10h15 Registration & Coffee 10h15 - 10h20 Opening Remarks - Satoshi Iso (RIKEN), Director of iTHEMS 10h20 - 11h20 SESSION 1 - Chair: Tetsuo Hatsuda (RIKEN) Yoshihiko Susuki (Kyoto University): Koopman resolvents in dynamical systems and control 11h20 -11h40 Free Discussions 11h40 - 13h00 Lunch Break & Discussions 13h00-14h00 SESSION 2 - Chair: Narumi Fujii (Institute of Science Tokyo) Alexandre Mauroy (University of Namur, Belgium): Analytic EDMD method for spectral analysis of fixed point dynamics 14h00 - 14h30 Coffee Break & Discussions 14h30 - 15h30 SESSION 3 - Chair: Tetsuo Hatsuda (RIKEN) Hiroya Nakao (Institute of Science Tokyo): Koopman operator analysis of coupled oscillator systems 15h30 - 16h00 Coffee Break & Discussions 16h00 - 17h00 SESSION 4 - Chair: Riccardo Muolo (RIKEN) Yuzuru Kato (Future University Hakodate): Analysis of quantum nonlinear oscillators on the basis of Koopman operator theory 17h00 - 17h05 Closing Remarks - Tetsuo Hatsuda, Chair of the Workshop 17h05 - 18h00 Free Discussions

Venue: Room 535-537, 5F, Main Research Building

Event Official Language: English

Testing the quantum nature of gravity "ab absurdo"

March 18 (Wed) 14:00 - 16:00, 2026

Emanuele Panella (Postdoctoral Researcher, Tor Vergata University of Rome, Italy)

The quest for a quantum description of gravity has been long, diverse, and productive. Yet, despite decades of theoretical progress, there is still no direct experimental evidence for the quantum nature of spacetime. In this talk, I explore an alternative, indirect route to probing quantum gravity by assuming the fundamental classicality of the gravitational field and examining the resulting observational conflicts. In particular, I will discuss a key consistency condition—known as the decoherence–diffusion trade-off—that any theory of fundamentally classical gravity coupled to quantum matter must satisfy. By analysing a toy model of a linearised classical–quantum (CQ) gravity–matter system, I will explicitly show how this trade-off implies unavoidable, measurable effects, such as a fundamental stochastic gravitational-wave background, which cannot be eliminated by fine-tuning the model parameters.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Quantum modular form and quantum invariants

March 13 (Fri) 14:00 - 16:00, 2026

Yuya Murakami (Research Scientist, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Quantum invariants are invariants of knots and 3-manifolds which relate deeply to mathematical physics and representation theory. In recent years, it has become increasingly clear that it is also deeply related to number theory, that is, quantum modularity for quantum invariants. This topic is interesting from a topological viewpoint since this is a refinement of establishing asymptotic expansions of quantum invariants, which is an important problem in quantum topology, and is interesting from a number-theores[tic viewpoint since this gives examples of quantum modular forms, which are mysterious objects in number theory. I obtained two linked results on topology and number theory: Establishing explicit asymptotic expansions of quantum invariants for negative definite plumbed 3-manifolds and establishing quantum modularity of false theta functions in full generality. In this talk, I will outline previous progress on quantum modularity for quantum invariants and my results.

Venue: via Zoom / Seminar Room #359, Seminar Room #359

Event Official Language: English

KEK-iTHEMS Workshop “Concepts of Quantum and Spacetime”

March 9 (Mon) - 12 (Thu) 2026

The two fundamental questions—“What is quantum?” and “What is spacetime?”—are deeply intertwined. On one hand, the formulation and interpretation of quantum theory depend both implicitly and explicitly on our conceptions of time and space. On the other hand, we believe that fully taking into account the quantum character of nature will force us to revise our understanding of spacetime. These two conceptual problems lie at the heart of the unsolved challenge of how to quantize classical spacetime, and conversely, how (semi-) classical descriptions of spacetime emerge from quantum theory. Furthermore, if the entire matter-spacetime system is a kind of quantum many-body system, thermodynamics—which governs its statistical behaviors—should play a key role in elucidating these problems. This workshop will discuss the question “How can quantum theory and spacetime be understood in a consistent manner?” from a fundamental and broad perspective. To tackle this challenge, we gather researchers in foundations of quantum theory, quantum gravity, and related fields from around the world, providing a "space and time" to share various ideas with open minds and engage in lively discussions. By exploring new concepts and principles, we hope to uncover directions to guide quantum theory over the next 100 years. This workshop covers… Foundations of quantum theory Quantum gravity and emergence of spacetime Formulation of semi-classical gravity Experimental aspects of fundamental properties in nature and quantum gravity Foundations of quantum many-body systems and thermodynamics Other related topics are welcome. We welcome short talk presentations and poster presentations. This event is a workshop jointly organized by KEK Theory Center and RIKEN iTHEMS.

Venue: Seminar Hall, Building 3, KEK

Event Official Language: English

Causality Constraints on Black Hole Thermodynamics in Nonlinear Electrodynamics

March 6 (Fri) 15:30 - 17:00, 2026

Kaho Yoshimura (Ph.D. Student, Graduate School of Arts and Sciences, The University of Tokyo)

Black holes exhibit thermodynamic properties and provide an important window into the quantum aspects of gravity. In this context, nonlinear electrodynamics (NLED) offers a useful framework for constructing and analyzing charged black-hole solutions beyond Maxwell theory. Requiring causality - namely, excluding superluminal signal propagation - imposes nontrivial constraints on the allowed form of the NLED Lagrangian. In this talk, we focus on two quantities: the charge-to-mass ratio and the entropy density (entropy-to-mass squared ratio). The charge-to-mass ratio is expected to obey a monotonic behavior consistent with the Weak Gravity Conjecture, while the entropy density is also anticipated to be monotonic, reflecting the expectation that higher-energy effective theories contain more degrees of freedom. We show that these monotonic behaviors follow directly from the causality constraints on the NLED sector.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Non-perturbative geodesic length in JT gravity and universal time evolution of holographic complexity

March 2 (Mon) 16:00 - 17:00, 2026

Shono Shibuya (Ph.D. Student, Nagoya University)

The interplay between black hole interior dynamics and quantum chaos provides a crucial framework for probing quantum effects in quantum gravity. According to the holographic "Complexity=Volume" proposal, we investigated non-perturbative generating function of geodesic length in Jackiw-Teitelboim (JT) gravity to uncover universal signatures of quantum chaos and quantum complexity. We observed that the generating function interpolates between two major probes of quantum chaos - spectral form factor and complexity - highlighting its utility as a probe of chaotic spectrum in quantum gravity. Generalizing the result to general chaotic systems, we demonstrated that time evolution of the complexity is universally governed by a certain pole structure of observables, suggesting a validity of wide class of observables as a probe of quantum chaos in quantum gravity.

Venue: via Zoom / Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

RIKEN-Nara Women's University Joint Diversity Promotion Workshop 2026

March 2 (Mon) - 3 (Tue) 2026

The RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) and the Faculty of Science at Nara Women's University are promoting a project to foster female researchers under the auspices of the RIKEN Diversity Promotion Office. As part of the program, 21 undergraduate and graduate students from Nara Women's University will visit several laboratories on the RIKEN Wako campus to ask questions about their research and hold workshops with iTHEMS researchers. Organizers: RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) Faculty of Science, Nara Women's University March 2 (Mon) 13:15-14:15 Center for Brain Science (CBS) (C56 Ikenohata Building) Laboratory for Multi-scale Biological Psychiatry (Team Director: Akiko Hayashi-Takagi) 14:30-15:45 Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) (C01 Main Research Building, 4th Floor Rooms 435-437) Introduction to iTHEMS: Tetsuo Hatsuda (iTHEMS Division Director of Applied Mathematical Science) Lecture and Q&A: Megumi Oya (iTHEMS Medical Science Data-driven Mathematics Team Postdoctoral Researcher) 16:00-17:30 Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) (C01 Main Research Building, 4th Floor Rooms 435-437) Lecture and Q&A: Leo Spiedel (iTHEMS ECL Research Unit Leader) 18:00-20:30 Networking Session (C01, Research Main Building 3F East Side (Okochi Hall Side)) March 3 (Tue) 9:00-10:30 RIBF Facility, RIKEN Nishina Center (RNC) 11:15-12:00 Center for Quantum Computing (RQC) Optical Quantum Control Research Team (Team Director: Hidehiro Yonezawa)

Venue: RIKEN Wako Campus

Event Official Language: Japanese

RIKEN iTHEMS-Kyoto University joint workshop on Asymptotics in Astrophysics and Cosmology

March 2 (Mon) - 4 (Wed) 2026

This joint workshop will bring together physicists and mathematicians who work with asymptotics and perturbation theory techniques. This includes theorists in cosmology, high energy physics, quantum gravity, solar physics, astrophysics. Workshop overview Over three days, there will be approximately 15 invited (1 hour slot) or contributed (20-30 min slot) talks about: Fundamental asymptotics and perturbation theory techniques used in theoretical physics. Various applications of asymptotics and perturbation theory techniques in (wave transport or oscillation related) astrophysics and cosmology eigenvalue problems. The workshop will also feature hands-on Mathematica and Python tutorials introducing: Practical use of WKB methods in applied mathematics for any “Schrodinger-like” wave equations, Resummation methods in high energy theory, Deriving normal modes in stars, and their application to tidal evolution in binary star or planet systems, Eigenvalue problems in core collapse supernova theory.

Venue: 8F, Integrated Innovation Building (IIB)

Event Official Language: English

Testing the quantum nature of gravity with optomechanical systems

February 26 (Thu) 10:00 - 12:00, 2026

Yuta Michimura (Assistant Professor, Department of Physics, Graduate School of Science, The University of Tokyo)

Quantum gravity remains one of the major challenges in modern physics. Even at the most fundamental level, there is no experimental confirmation of whether a mass placed in a spatial superposition generates a corresponding superposition of gravitational fields. In recent years, experiments aiming to create gravity-induced quantum entanglement have attracted significant attention as a way to probe the quantum nature of non-relativistic gravity. In particular, optomechanical systems, which exploit the interaction between light and mechanical oscillators, provide a promising platform for such studies. We are pursuing experiments at the milligram scale, which lies between the smallest mass scale at which classical gravity has been tested and the largest mass scale at which quantum states of mechanical oscillators have been realized [1]. In this seminar, I will discuss experimental approaches to testing the quantum nature of gravity using suspended and levitated mirrors. I will also discuss our recent proposal to use inverted oscillators to enhance gravity-induced entanglement exponentially [2].

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Noninvertible symmetry protected topological phases on lattice

February 25 (Wed) 10:30 - 11:30, 2026

Weiguang Cao (PD, Centre for Quantum Mathematics, University of Southern Denmark, Denmark)

The recent discovery of noninvertible symmetries—a radical extension of conventional symmetry—has challenged long-standing paradigms in condensed matter physics and quantum information and opened new territory in both theory and technology. Unlike ordinary symmetries, which can be inverted, these symmetries behave like projections (one-way operations) yet still strongly constrain quantum dynamics and enable new classes of phases and phase transitions. However, their role in organizing and stabilizing novel quantum phases remains poorly understood. One important example is a symmetry protected topological (SPT) phase, characterized by nontrivial edge modes and potential applications in quantum information. In this talk, I will discuss the classification of noninvertible symmetry-protected topological (NISPT) phases in both closed and open quantum systems using a duality-based method, and present concrete lattice realizations. These lattice models provide controlled playgrounds in which the physics of noninvertible symmetry can be explored numerically and, potentially, experimentally.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Spectral Codes : A Geometric Formalism for QEC

February 19 (Thu) 15:00 - 16:30, 2026

Satoshi Kanno (Researcher, Research Institute of Advanced Technology, SoftBank Corp.)

In this talk, I will introduce a novel geometric framework for quantum error correction based on spectral triples in noncommutative geometry. In this formulation, quantum error-correcting codes are described as spectral projections onto the low-energy eigenspaces of Dirac-type operators, where the separation between logical information and local errors is captured geometrically. This approach provides a unified spectral and geometric understanding of key properties such as code distance and error thresholds. Moreover, it accommodates various existing codes, including classical linear codes, stabilizer codes, GKP codes, and topological codes. This geometric perspective also suggests intriguing connections to deformation quantization and holographic quantum error correction, offering promising directions for future research.

Venue: #359, Seminar Room #359

Event Official Language: English

Brainstorming session on data assimilation with quantum computing

February 18 (Wed) 14:00 - 16:00, 2026

Takemasa Miyoshi (Team Principal, Data Assimilation Research Team, RIKEN Center for Computational Science (R-CCS))

We will discuss the potential of quantum computing for applications in data assimilation.

Venue: #359, Seminar Room #359

Event Official Language: English

Taming the Butterfly: A New "Duality Principle" Turns Chaos into Control

February 18 (Wed) 13:00 - 14:00, 2026

Takemasa Miyoshi (Team Principal, Data Assimilation Research Team, RIKEN Center for Computational Science (R-CCS))

Data Assimilation (DA) is the backbone of modern weather forecasting. It integrates observational data into computer simulations to synchronize the model with nature. The Duality Principle posits that chaos control is mathematically the "twin" (dual) of DA. Data Assimilation: Uses observations to synchronize the Model to Nature. Chaos Control: Uses interventions to synchronize Nature to a desired Model ("target trajectory"). "The butterfly effect has long been a symbol of unpredictability," says Dr. Miyoshi. "But I asked a simple question: If a butterfly's wings can change the future, does that not imply that with the right, tiny push, we could choose a better future?" Instead of suppressing the chaotic system with massive force, this method acts like mathematical judo—leveraging the system's inherent instability. By applying minute, calculated "interventions" (analogous to the butterfly's flap), the system can be guided toward a "target trajectory"—for instance, shifting real-world conditions just enough to align with a model-simulated scenario where a typhoon causes no damage. Once synchronized, control becomes much easier to maintain. This study establishes the theoretical foundation for "Control Simulation Experiments" (CSE), a framework previously proposed by Miyoshi’s team. It provides a roadmap for future disaster prevention research, moving beyond passive prediction to active mitigation. Beyond meteorology, this general framework is expected to serve as a universal tool for studying interventions in various chaotic systems, from ecosystems to economics. Following the seminar, we will hold an informal discussion (brainstorming) on data assimilation with quantum computing in the same room from 2-4 pm.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Recent progress in the resource theory of asymmetry and its applications

February 12 (Thu) 13:30 - 15:00, 2026

Hiroyasu Tajima (Associate Professor, Department of Informatics, Faculty of Information Science and Electrical Engineering, Kyushu University)

If you are not affiliated with RIKEN, please register using the registration form. Registration deadline: 12nd Feb. (Thu), 2026 Symmetry and symmetry breaking are among the central themes in physics and have attracted the interest of many physicists. Recently, the resource theory of asymmetry (RTA) [1-4], which approaches these issues from the perspective of resource theories, has been actively studied. In the past few years, several foundational advances have been made in this framework. In particular, the iid-complete monotone that plays a role analogous to entanglement entropy has been identified for arbitrary compact Lie groups [2] as well as for arbitrary finite groups [3]. The resolution for compact Lie groups includes, as a corollary, a solution to the Marvian–Spekkens conjecture [4]. Building on this theoretical foundation, several developments related to the Wigner–Araki–Yanase (WAY) theorem [5-7] have also been obtained. These include extensions of the WAY theorem to the implementation of arbitrary unitary gates [8], and a unification of the WAY-type theorems, i.e. the WAY theorem, the Eastin–Knill theorem (a fundamental limitation on error correction under symmetry) [9], and the above unitary-gate results. The unification is formulated a universal trade-off inequality relating symmetry, irreversibility, and quantumness for arbitrary quantum dynamics [10]. Using this tradeoff relation, the WAY-type limitations can now be applied, for example, to quantum thermodynamics[11] and black hole evaporation [10] etc. If time permits, I will also briefly touch upon some other recent developments, such as extensions of the above tradeoff and the WAY theorem to general resource theory beyond symmetry [12].

Venue: #359, Seminar Room #359

Event Official Language: English