iTHEMS NOW & NEXT 2026

April 13 (Mon) - 14 (Tue) 2026

We will hold an annual in-house gathering, “iTHEMS NOW & NEXT,” for FY 2026. The event provides a great opportunity for all iTHEMS members, including visiting researchers and, in particular, new arrivals, to gain a comprehensive overview of iTHEMS’s current activities and future directions. The detailed program will be announced in due course, but there will be poster sessions for all members, so please be ready to present one.

Venue: 2F Large Conference Room, Administrative Headquarters, RIKEN Wako Campus (Main Venue) / via Zoom

Event Official Language: English

Understanding Biological Clocks Using Methods from Applied Mathematics and Theoretical Physics

April 16 (Thu) 12:30 - 13:30, 2026

Gen Kurosawa (Senior Research Scientist, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Imagine that you are in a room with no information about time. The room is located in a cave, where temperature and light intensity remain constant. In such an environment, would you be able to wake up tomorrow or the day after? In fact, most humans can wake up at roughly similar times on successive days. This is because we possess internal daily rhythms, known as circadian rhythms. Biological experiments have shown that such rhythms are not unique to humans, but are shared by many species on Earth. In this talk, I will introduce some open problems related to these daily rhythms, and discuss approaches based on dynamical systems theory and the renormalization group method, from the perspectives of applied mathematics and theoretical physics.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

RIKEN Seminar: Formulation of Life Phenomena from Quantum Theory

April 16 (Thu) 14:00 - 16:05, 2026

13:45 Opening 14:00-14:05 Introduction Atsushi Iriki (Teikyo University Advanced Comprehensive Research Organization Division of Artificial Intelligence, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)) 14:05-14:35 "Interpretation of Life Phenomena Using Quantum Wave Functions and Field Theory" Kazuhiro Sakurada (Keio University Medical School and RIKEN Center for Integrative Medical Sciences (IMS), Predictive Medicine Special Project (PMSP)) 14:35-14:45 Q&A 14:45-15:30 "Bridging neurophysiology and quantum-like cognition" Andrei Khrennikov (Center for Mathematical Modeling in Physics and Cognitive Sciences Linnaeus University) 15:30-15:45 Q&A 15:45-16:00 "Quantum-Like Measurement" Masanao Ozawa (RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), RIKEN TRIP FQSP, and Nagoya University) 16:00-16:05 Closing Remarks Satoshi Iso (Director, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)) Host Laboratory: Predictive Medicine Special Project, RIKEN Center for Integrative Medical Sciences (IMS) / RIKEN Center for Interdisciplinary Theoretical and Mathematical Science (iTHEMS) *Registration is required by April 14 via the registration form. Contact: Predictive Medicine Special Project (pmsp-web@ml.riken.jp)

Venue: Meeting Room 305, Brain Science Ikenohata Research Bldg. (C56), RIKEN Wako Campus

Event Official Language: English

Searching For Anomalies with Foundation Models

April 16 (Thu) 14:00 - 15:30, 2026

Vinicius Massami Mikuni (Associate Professor, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)

This is a joint seminar with Institute for Physics of Intelligence (iπ), UTokyo Anomaly detection relaxes the assumptions of how new physics should look and extends the reach of what we can discover. However, interpreting the data and estimating backgrounds remains a challenge. In this new work, we investigate anomalous events selected by the OmniLearned Foundation model across different model sizes, performing a full analysis using CMS Open Data. Surprisingly, models of different sizes, trained on the same data with the same loss functions, select entirely different collisions. In particular, the large OmniLearned model (500M parameters) selects events that are not well described by our background model.

Venue: Faculty of Science Bldg.1, School of Science, The University of Tokyo, Hongo Campus (Main Venue) / via Zoom

Event Official Language: English

TJR-iTHEMS Joint Seminar: Golden Age of Neutron Stars

April 17 (Fri) 16:00 - 17:00, 2026

Gordon Baym (Professor Emeritus, University of Illinois, USA)

This is a TJR-iTHEMS Joint Seminar supported by ASPIRE Program ABSTRACT Neutron stars were first posited in the early thirties, and discovered as pulsars in the late sixties; however we are only recently beginning to understand the matter they contain. I will describe the ongoing development of a consistent picture of the liquid interiors of neutron stars, now driven by ever increasing observations as well as theoretical advances. These include observations of heavy neutron stars of about 2.0 solar masses and higher; ongoing inferences of masses and radii by the NICER telescope; and observations of binary neutron star mergers, through gravitational waves as well as across the electromagnetic spectrum. Theoretically an understanding is emerging in QCD of how nuclear matter can turn into deconfined quark matter, which I will illustrate with modern quark-hadron crossover equations of state. BRIEF BIO Gordon Baym is a Professor of Physics at the University of Illinois. Educated at Cornell and Harvard, he spent two years at the Niels Bohr Institute. His interests range from matter under extreme conditions to ultracold atomic physics, astrophysics, and nuclear physics. A pioneer in the study of pulsars and neutron stars, he is a member of the U.S. National Academy of Sciences and received the APS Medal for Exceptional Achievement in Research, the Hans Bethe and Lars Onsager Prizes, and the Eugene Feenberg Memorial Medal.

Venue: H701, The University of Osaka, Toyonaka Campus

Event Official Language: English

iTHEMS x academist Online Event "World of Mathematical Sciences 2026"

April 18 (Sat) 10:00 - 15:30, 2026

Junnosuke Koizumi (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Osamu Fukushima (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Muzi Hong (Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Kenji Okubo (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Venue: via Zoom

Event Official Language: Japanese

Analytical parametrization of the primordial power spectrum in effective Loop Quantum Cosmology

April 20 (Mon) 13:00 - 14:00, 2026

Almudena Sánchez Guillén (Ph.D. Student, Institute of Structure of Matter (IEM-CSIC), Spain)

We investigate the imprints on the angular power spectra of cosmological perturbations of a pre-inflationary bounce phase, as described by the hybrid and dressed metric approaches to loop quantum cosmology. For this purpose, we derive a new parametrization of the primordial power spectrum at the end of the inflationary regime. Apart from slow-roll coefficients and cosmological parameters that are present in the standard cosmological scenario without quantum modifications, this parametrization additionally depends only on pre-inflationary physics. More specifically, we find a dependence on the number of e-folds during the bounce epoch and on a characteristic suppression scale which, given the e-folds accumulated during cosmic evolution, is determined by the energy density at the bounce.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Challenges in virology & neurodegeneration: improving experimental procedures and theoretical insights

April 20 (Mon) 14:00 - 15:00, 2026

Catherine Beauchemin (Deputy Director, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

After repeatedly finding errors in experimental data provided by collaborators, my group developed an online tool (midSIN, https://midsin.roadcake.org/) to improve estimating the concentration of infectious viruses in samples. This led to an unexpected new collaboration with researchers working to measure the concentration of aggregating fibrils in samples from patients suffering from neurodegenerative diseases such as Dementia with Lewy Body and Parkinson's. In the first part of my talk, I will introduce the basics of how infectious virions and aggregating fibril concentrations are measured experimentally, and discuss challenges in tackling these assays' limitations to improve their accuracy and sensitivity. In the second part of my talk, I will discuss the challenges we face in trying to identify the type and minimal number of experimental measurements required to predict the severity and transmission efficacy of diverse influenza viruses collected as part of pandemic surveillance efforts. I hope you will join the talk to learn of these challenges and consider contributing new ideas or approaches to overcome them.

Venue: Hybrid Format (4F #435-437 and Zoom), Main Research Building

Event Official Language: English

Quantum Computing of Molecular Properties for Fundamental Physics

April 21 (Tue) 16:30 - 18:00, 2026

Pradyot Pritam Sahoo (Graduate International Research Student, Graduate School of Science, The University of Tokyo)

This is the self-introduction talk by Pradyot Pritam Sahoo. Pradyot is a Student Trainee in iTHEMS.

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

Event Official Language: English

The math that shows a perfect democracy is impossible

April 23 (Thu) 10:30 - 11:30, 2026

Brian Andrew Mintz (Postdoctoral Researcher, Mathematical Social Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Groups need to make decisions, and there are a wide variety of ways this can be done, each maximizing different notions of fairness. Social Choice Theory provides a mathematical framework to investigate these possibilities rigorously. Infamous for its many impossibility results, this topic reveals some fundamental limits to democracy. Beyond this, we'll discuss potential resolutions to these problems, as well as their real world implications.

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

Event Official Language: English

Mathematical Application Research Team Meeting #14

April 24 (Fri) 14:00 - 15:30, 2026

Shin-ichi Ohta (Professor, School of Science, Osaka University)

Mathematical Application Research Team is honored to invite Prof. Shin-ichi Ohta from the University of Osaka to this meeting. Everyone is welcome to join the meeting to listen to his seminar. Title: Synthetic and comparison Lorentzian geometry Abstract: In this talk we review recent developments of synthetic geometric approaches to Lorentzian geometry, motivated by the theory of less regular spacetimes in general relativity as well as comparison geometry in the Riemannian setting. Among others, optimal transport theory plays a vital role.

Venue: #359, 3F, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

Introduction to quantum resource theories (1)

May 11 (Mon) 13:30 - 17:00, 2026

Ryuji Takagi (Associate Professor, Graduate School of Arts and Sciences, The University of Tokyo)

One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 1st day: May 11 (Mon) 13:30-15:00 Lecture 1 15:00-15:30 Coffee break 15:30-17:00 Lecture 2 This event is in-person only.

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

Introduction to quantum resource theories (2)

May 12 (Tue) 9:00 - 17:00, 2026

Ryuji Takagi (Associate Professor, Graduate School of Arts and Sciences, The University of Tokyo)

One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 2nd day: May 12 (Tue) 9:00–10:30 Lecture 3 10:30–11:00 Coffee break 11:00–12:30 Lecture 4 12:30-13:30 Lunch time 13:30-15:00 Lecture 5 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 This event is in-person only.

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

From Birkhoff's Polytope to Petz Recovery: Unistochastic Matrices, Quantum Channels, and Approximate Markov Chains

May 13 (Wed) 13:30 - 15:00, 2026

Claude Gravel (Assistant Professor, Department of Computer Science, Toronto Metropolitan University, Canada)

A doubly stochastic matrix is unistochastic if its entries correspond to the squared moduli of a unitary matrix. Determining which n × n doubly stochastic matrices admit such a representation remains an open problem at the intersection of convex geometry, combinatorics, and quantum information. For 3 × 3 matrices, elegant triangle inequalities provide a complete characterization: the unistochastic set occupies approximately 75% of the Birkhoff polytope and exhibits deltoid cross-sections. For n ≥ 4, the characterization problem remains unresolved and is influenced in unexpected ways by the prime factorization of n via the defect of the Fourier matrix. This presentation surveys these results and then establishes a connection to a second, seemingly unrelated question: given a tripartite quantum state with small conditional mutual information, to what extent can one subsystem be recovered from the others? The Petz recovery map and its rotated variants offer a universal solution. These two topics are linked through coherification, which concerns when a classical stochastic process can be elevated to coherent quantum dynamics, and through the conditional mutual information as a continuous measure of non-unistochasticity. The talk concludes with open problems at this interface, including the star-shapedness conjecture for n = 4 and the pursuit of tighter recovery bounds.

Venue: #359, Seminar Room #359

Event Official Language: English

Stochastic Schrödinger Diffusion Models for Pure-State Ensemble Generation

May 14 (Thu) 14:30 - 15:00, 2026

Jian Xu (Postdoctoral Researcher, Quantum Mathematical Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

In quantum machine learning (QML), classical data are often encoded as quantum pure states and processed directly as quantum representations, motivating \emph{representation-level generative modeling} that samples new quantum states from an underlying pure-state ensemble rather than re-preparing them from perturbed classical inputs. However, extending \emph{score-based} diffusion models with well-defined reverse-time samplers to quantum pure-state ensembles remains challenging, due to the non-Euclidean geometry of the complex projective space $\mathbb{CP}^{d-1}$ and the intractability of transition densities. We propose \emph{Stochastic Schr\"odinger Diffusion Models} (SSDMs), an intrinsic score-based generative framework on $\mathbb{CP}^{d-1}$ endowed with the Fubini--Study (FS) metric. SSDMs formulate a forward Riemannian diffusion with a stochastic Schr\"odinger equation (SSE) realization, and derive reverse-time dynamics driven by the Riemannian score $\nabla_{\mathrm{FS}} \log p_t$. To enable training without analytic transition densities, we introduce a local-time objective based on a local Euclidean Ornstein--Uhlenbeck approximation in FS normal coordinates, yielding an analytic teacher score mapped back to the manifold. Experiments show that SSDMs faithfully capture target pure-state ensemble statistics, including observable moments, overlap-kernel MMD, and entanglement measures, and that SSDM-generated quantum representations improve downstream QML generalization via representation-level data augmentation.

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

Event Official Language: English

Introduction to quantum resource theories (3)

May 15 (Fri) 9:00 - 17:00, 2026

Ryuji Takagi (Associate Professor, Graduate School of Arts and Sciences, The University of Tokyo)

One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 3rd day: May 15 (Fri) 9:00–10:30 Lecture 7 10:30–11:00 Coffee break 11:00–12:30 Lecture 8 12:30-13:30 Lunch time 13:30-15:00 Free discussion/Summary of the lectures 15:00-15:30 Coffee break 15:30-17:00 Lecture 9/Seminar This event is in-person only.

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

Singularities of differentiable maps and Thom polynomials

May 22 (Fri) 15:00 - 17:30, 2026

Masato Tanabe (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Singularities are locations where something is exceptional. In particular, singularities of differentiable maps are mathematical concepts corresponding to stationary points of functions and apparent contours of surfaces under projection onto the retina. These are unavoidable in general, but important to study the shape of spaces and behavior of maps. The theory for them was initiated by R. Thom in 1950's, and have been deeply studied by many researchers.

Venue: Room 359, RIKEN Wako Campus (Main Venue) / via Zoom

Event Official Language: English