RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences

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

Information entropy untangles vortices and flows in turbulent plasmas: A turbulence analysis inspired by quantum information theory

A research team including Motoki Nakata (Visiting Scientist, iTHEMS) has proposed a novel method that interprets structural transitions and nonlinear interactions in turbulent fields from the perspective of “information,” inspired from information entropy and its mathematical formalism used in quantum mechanics theory. This approach has enabled the discovery of new turbulent states in plasma—states that had been overlooked by conventional energy-based analysis methods—and the extraction of key interactions among vortices and flows in various scales. The team also proposes an application of this method to experimental measurements that observe turbulence and fluctuations. Looking ahead, this technique is expected to be applied beyond turbulent plasmas to a wide range of research domains involving “complex flows” and “mutually correlated fluctuations,” appearing in atmospheric, oceanic, and social systems. For more details, please refer to the press release available through the related links.

2025-06-03

International and Interdisciplinary Collaboration at the RIKEN-Berkeley Center - Yuuka Kanakubo

"I’m leaving for the U.S. tomorrow," says Yuuka Kanakubo, who joined iTHEMS in October 2024 as a Postdoctoral Researcher and RIKEN-Berkeley Fellow. Her specialty is elementary particle and nuclear theory. She will be conducting research during a long-term stay at the RIKEN-Berkeley Center, iTHEMS' satellite office. "This position is perfect for me," Kanakubo says. We asked her about her journey so far and what makes this opportunity ideal. Please see the full article via the related link.

2025-05-22

Yoshimasa Hidaka received the 25th Soryushi Medal for his unified description of the Nambu-Goldstone theorem

Yoshimasa Hidaka, our Deputy Director, is awarded 25th SORYUSHI MEDAL (Paricle Physics Medal) from Japanese Particle Theory Community. The title of the achievement is “Unified Description of the Nambu-Goldstone Theorem”. The award will be presented at the 80th Annual Meeting of the Physical Society of Japan, to be held at Hiroshima University from September 16 to 19, 2025. Congratulations!!

2025-05-22

Haruki Emori received the “Second Prize”

Our colleague Haruki Emori (Junior Research Associate, iTHEMS) has received the “Second Prize’” in the Poster Session for the Quantinuum 2025 May Training Session. The outstanding presentation poster is entitled “Quantum algorithm for implementing arbitrary quantum instruments based on parameterized quantum circuits”. Congratulations, Haruki!

2025-05-22

Looking for “Overlap” to Connect - Akihisa Yamamoto

"I have always walked along the boundaries between different fields," says Research Scientist Akihisa Yamamoto. Currently, he is focusing on the interdisciplinary field between medicine and mathematics, seeking to identify patterns in doctors' experiential knowledge, translating them into mathematical models, and applying them to deepen our understanding of biological phenomena while contributing to clinical practice. We spoke with him about the encounters that led him to this path, as well as the unique challenges and excitement of working at the intersection of disciplines. Please see the full article via the related link.

2025-05-20

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?

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)