RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences

RIKEN NEWS: The Appeal of the ECL Program in Nurturing Early-Career Researchers

An interview with Leo Speidel (RIKEN ECL Research Unit Leader, Mathematical Genomics RIKEN ECL Research Unit) has been featured in the Topics section, as part of the Close-up RIKEN 2025 series on RIKEN’s research introduction page. A video interview is also available alongside the article. The RIKEN Early Career Leaders (ECL) Program was launched in 2023 to provide more substantial support for early-career researchers. Building on and expanding the previous RIKEN Hakubi Program, the ECL Program enables researchers to pursue agile and flexible research. In addition to appointing Team Leaders (equivalent to department heads or young professors at universities), the program has introduced the position of Unit Leader (equivalent to section heads or associate professors/lecturers at universities) to support outstanding young researchers with limited experience. These Unit Leaders are provided with a highly mobile and independent research environment at their host research centers. We spoke with Dr. Leo Speidel, the RIKEN ECL Research Unit Leader of the Mathematical Genomics RIKEN ECL Research Unit, Mathematical Science Core Division, at the Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS), who is part of the program's first cohort. He is working to uncover human evolution and history through the study of DNA mutations, and he shared with us the appeal of the ECL Program. For more information, please see the related links below.

2025-07-08

Using viral load tests to help predict mpox severity when skin lesions first appear

A research group led by Shingo Iwami (Visiting Scientist, iTHEMS) has revealed through an international collaborative study that there is significant individual variation in the progression of skin lesions among patients infected with mpox (Clade Ia). The study also suggests that the blood viral load at the time of onset may serve as a useful indicator for predicting the progression of these symptoms. For more details, please refer to the related links.

2025-07-03

A New Intelligence Deciphering the Universe: Discovery of Anomalous Energy Emission Phenomena through Quantum × AI

A research group, including Shigehiro Nagataki (Chief Scientist, Astrophysical Big Bang Laboratory, RIKEN PRI / Deputy Director, iTHEMS) and Shunji Matsuura (Senior Research Scientist, iTHEMS), has successfully detected 113 anomalous energy (X-ray) emission events. This was achieved by constructing and applying a quantum machine learning model that integrates quantum computing with machine learning to a large-scale dataset of X-ray variability in space accumulated over approximately 24 years by the X-ray astronomical satellite XMM-Newton, operated by the European Space Agency (ESA). For more information, please refer to the related links below.

2025-07-03

Theoretical Discovery of Angular Momentum Reversal in Magnetic Vortical Matter

A collaborative research group, including Kazuya Mameda (Visiting Scientist, iTHEMS) has theoretically discovered that in quantum systems where strong magnetic fields and rotation coexist, the polarization of angular momentum becomes dominated by orbital angular momentum—originating from the particles’ orbital motion—rather than spin. This leads to a reversed direction of polarization compared to conventional expectations. For more information, please refer to the related links below.

2025-07-03

AI-Driven High-Resolution Galaxy Simulations: Accelerating Galaxy Evolution Modeling from 8 Months to 2

An international collaborative research group, including Keiya Hirashima (Special Postdoctoral Researcher, iTHEMS), has developed a surrogate model using deep learning, a form of artificial intelligence (AI), to predict the complex physical processes of supernova explosions. This model has been integrated into a galaxy simulation code for the first time. This achievement marks the first instance of accelerating high-resolution "star-by-star" galaxy simulations by performing deep learning inference in real time during the simulation—something that was previously difficult to realize. The new method is expected to contribute to detailed analysis of supernova feedback in the formation and evolution of our own Milky Way galaxy. For more information, please refer to the related links below.

2025-07-03

Bulk-Edge Correspondence of Measurement-Induced Topological Phases

A research group including Ryusuke Hamazaki (Senior Research Scientist, iTHEMS) has proposed a method to investigate the effective energy level structures and bulk topological invariants in quantum systems under measurement. Utilizing this approach, the team conducted a theoretical analysis of topological phase transitions induced by quantum measurements. Their findings revealed that zero-energy edge states originating from so-called "Majorana particles" can emerge in topological phases under continuous measurement. Furthermore, the study demonstrated that the bulk-edge correspondence, a universal principle typically known to hold in isolated quantum systems, also manifests in measurement-driven quantum systems. This work establishes a robust theoretical foundation for measurement-induced topological phase transitions. The method developed is broadly applicable to a wide class of topological phases, offering a versatile tool that may lead to a systematic and unified understanding of quantum phases induced by measurement. For more details, please refer to the related links.

2025-06-23

Success in Quantum Chemistry Calculations through Quantum–Supercomputer Collaboration

An international research team, including Senior Research Scientist Tomonori Shirakawa, has demonstrated the practical potential of quantum computing by performing calculations that combine IBM's quantum computer with RIKEN's supercomputer "Fugaku" to address quantum chemistry problems that have been difficult to analyze using conventional classical computers. In this study, by processing output data obtained from a real quantum computer with a supercomputer, the team successfully obtained scientifically meaningful results for a large-scale quantum chemical system exceeding 50 qubits for the first time. This achievement demonstrates that quantum computing is effective even for quantum chemistry problems that surpass the limitations of classical computation, marking a significant step forward toward the practical application of quantum computing. For more details, please refer to the related links.

2025-06-23

RIKEN NEWS: A New World Unlocked by a Data Geek

An interview with Catherine Beauchemin (Deputy Director, iTHEMS) has been featured in the RIKEN People section, as part of the Close-up RIKEN 2025 series on RIKEN’s research introduction page. With her quick wit, rapid-fire speech, and warm smile, she embodies the charm and potential of what it means to be human. Dr. Beauchemin is pioneering a new research field known as “virus physics.” By applying the tools of physics, she investigates viruses, unseen entities that can pose serious threats to our lives. To read the full story, please see the related link below.

2025-06-23

Developing a framework for inferring spatial biodiversity: quantifying the "beta-diversity" patterns

An international research team led by Ryosuke Iritani, Senior Research Scientist at RIKEN iTHEMS, has developed a theoretical framework to estimate the probability distribution of spatial biodiversity. This interdisciplinary work uses fuzzy set theory to formulate species presence-absence in a community, armed with analytical techniques and concepts from mathematics and theoretical physics. This work enables a quantitative assessment of differences and variations in species richness across regions, contributing to the prediction of how environmental changes in the biosphere influence biodiversity. For more details, please refer to the related link.

2025-06-12

Understanding dynamics and quantum chaos through Krylov space

In everyday life, we often associate chaos with randomness, disorder, or unpredictability—phenomena that appear to lack any discernible pattern. However, from a physics standpoint, understanding chaos requires a more rigorous and precise mathematical framework. In classical physics, chaos is often perceived through its sensitive dependence on initial conditions. Small perturbations in an initial state of a system can lead to vastly different outcomes over time, a behavior commonly known as “butterfly effect”, and typically analyzed within the framework of phase space trajectories, and its detailed topological properties. In contrast, chaos in the quantum realm presents unique challenges. The notion of sharp trajectories in phase space clashes with Heisenberg’s uncertainty principle in quantum mechanics, and initial perturbations cannot be treated in a way that mirrors classical intuition. As a result, quantum chaos requires distinct formulations, relying on diagnostic tools like spectral statistics, out-of-time-order correlators, and entanglement measures. However, the relationships between these different probes are not always clear, and a unified understanding remains an open area of research. In recent years, significant progress has been made in understanding quantum chaos through the lens of operator growth, where localized quantum information encoded in simple operators spreads across a system—a process known as information scrambling. Such phenomena is crucial in understanding the thermalization of a system. Krylov space, a subspace of the operator Hilbert space, provides an elegant framework to describe such operator growth. By decomposing operator dynamics using an orthonormal basis, it traces how simple operators evolve into increasingly complex ones—quantified by a complexity measure in Krylov space. A parallel formulation exists for the evolution of quantum states, offering a complementary perspective. Importantly, to make these ideas applicable to realistic physical scenarios, one must consider open quantum systems—systems that interact with their environment. In such contexts, the dynamics become richer, requiring more generic theoretical and computational techniques. Furthermore, efficient quantum control protocols often leverage the structured Hilbert space, with Krylov subspace methods providing computationally efficient frameworks. These methods facilitate guiding systems along desired adiabatic trajectories, reducing runtime and mitigating decoherence effects, as often required for quantum technologies. These developments form the core focus of this review article.

2025-06-04

Interview with Mathematician Taketo Sano [PART I]

A Century of Quantum Mechanics

Interview with Mathematician Takashi Tsuboi [Part Ⅱ]

Interview with Physicist Yasunori Nomura - Part Ⅳ

Interview with Physicist Yasunori Nomura - Part Ⅲ

Interview with Mathematician Takashi Tsuboi [Part Ⅰ]

Interview with Mathematician Yuto Moriwaki [Part2]

Interview with Mathematician Yuto Moriwaki [Part 1]

Interview with Mathematician Eiji Inoue [Part 2] (in Japanese)

Interview with Physicist Yasunori Nomura - Part Ⅱ

The Connection Between Mathematics and Microbial Research: From Fisheries Science to the Path of Mathematics

Contributed to the 'One Poster per Household' Project – Like the Ones You See in Science Classrooms

Interview with Dr. Misako Tatsuma, a Planetary Formation Theorist

Interview with Mathematician Eiji Inoue [Part 1]

Interview with Physicist Yasunori Nomura - Part I

Interview with Physicist Ryo Namba [Part 2]

Interview with Physicist Ryo Namba [Part 1]

Interview with Ryosuke Iritani, Mathematical Biologist [Part 1]

Theoretical Physicist Tetsuo Hatsuda Interview Vol.2: About Research and Mathematics

Theoretical Physicist Tetsuo Hatsuda Interview Vol.1: About RIKEN iTHEMS

What about climate change in actuality?

Describing Quantum Phenomena with Classical Gravity

Statistical Signatures of Quantum Chaos in Non-Hermitian Systems

Computers as a Playground for Mathematics

The Free Will Theorem in Quantum Mechanics

Renormalization revisited

Renormalization: Awareness of Ignorance

Recipe for soup of quarks and gluons

A subjective view on what is a quantum effect

Mathematical aspects of the entropic uncertainty relation

Forming black holes from stars

Singularity Theorems

Resurgence: making sense out of non-convergent series

How can we use a quantum computer to study the ground state of the hydrogen molecule?

Applications and Extensions of the Nielsen-Ninomiya Theorem in Condensed Matter Physics

COVID-19: then, now, and into the future

Exploring Quantum Spacetime

Classical simulations of quantum computers

When a Cretan says all Cretans are liars

Physical and local observables in gravitational theory

Can you hear the shape of a drum?

Quantum many-body physics with cold atoms

complexity in non-unitary dynamics of photons

Physics Through the Looking Glass

A new B.O.A.T. in astrophysics

Evolution and our daily rhythms

Area law of entanglement entropy in quantum many body systems and its implication in tensor network calculation

Comparison between conventional computers and quantum computers

A glimpse of enumerative geometry

Message-passing algorithms for graphical models

Canonical form of tensor networks in one and two dimensions

The basics of topological band theory

Building something from nothing: a mathematical framework for aperiodic/amorphous sets

Planetary lightning: Current State-of-the-art and outstanding questions

Collective Power of Science ~ from the High-Energy Atmospheric Physics to our New Exploration of the Universe ~

Morse theory and Floer theory

Knot theory and topological semimetals

On Dark Matter

Odd couples of interdisciplinary research

Khovanov homology theory - an introduction to categorification by Dr. Taketo Sano on May 13, 2022

Fundamentals Fest, mini Pre-event on Science "Exploring and Bridging: The Potential of Basic Science"

In Search of Pc pentaquark - Simulate Hadron Interactions with FUGAKU

AAS Journal Author Series: Hirotaka Ito on 2021ApJ…918...59I

Will Useless Knowledge Change the Future? - What is the Black Hole Recorder?

RIKEN 2019 (in Japanese)