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Computing n-Time Correlation Functions without Ancilla Qubits

A research team led by Xiaoyang Wang (Postdoctoral Researcher, Quantum Mathematical Science Team, iTHEMS) has proposed a new method for computing n-time correlation functions, which play a central role in understanding the dynamics of quantum many-body systems. The proposed approach requires neither ancilla qubits nor controlled operations, and evaluates correlation functions using only the unitary time evolution of the system of interest. Conventional methods, such as the Hadamard test, rely on ancilla qubits that control the entire system, posing significant challenges for digital quantum processors with limited qubit connectivity and for analog quantum simulators where controlled operations are difficult or impossible to implement. The present work overcomes these limitations and broadens the range of quantum platforms on which multi-time correlation functions can be experimentally accessed. The protocol was demonstrated on IBM quantum hardware with up to 12 qubits, where the team successfully measured the single-particle spectrum of the Schwinger model and the out-of-time-order correlator (OTOC) in the transverse-field Ising model. In addition, an error-mitigation strategy based on signal processing—combining signal filtering and correlation analysis—was introduced, enabling the recovery of ideal noiseless simulation results from noisy experimental data. This work provides a new foundation for experimentally probing complex quantum many-body correlation functions under realistic hardware constraints, thereby strengthening the connection between theoretical predictions and quantum experiments.

2025-12-12
José Said Gutiérrez-Ortega receives the 19th Plant Species Biology Paper Award

José Said Gutiérrez-Ortega (Research Scientist, iTHEMS) has been selected as a recipient of the 19th Plant Species Biology Paper Award. The study analyzes the threats to the biocultural heritage of cycads in the Amami Islands through an international collaboration, including research conducted at RIKEN. The Plant Species Biology Paper Award is presented annually to 1–2 outstanding papers published in Plant Species Biology, selected by vote of the journal’s editorial board. The award was announced on 18 November 2025, and the award ceremony will be held on 20 December 2025 (Sat.) during the meeting of the Society for the Study of Species Biology. Congratulations, José!

2025-12-04
Tomoya Nagai receives the Poster Award at the 29th Interdisciplinary Exchange Evening

Tomoya Nagai (Coordinator, iTHEMS), together with Ayaka Shida (TRIP Promotion Office), Momoko Sato (IMS), and Hiroko Sakuma (Communications Division), has received the Poster Award at the 29th Interdisciplinary Exchange Evening. The Poster Award is presented to several outstanding contributions selected from among 59 poster presentations at this event, which aims to promote communication and collaboration among researchers from diverse fields. Each year, approximately five presentations are selected. The team’s poster investigated researchers’ attitudes and practices regarding the preparation of press releases. Their presentation attracted significant interest from both research and administrative staff within RIKEN. We would like to take this opportunity to express our sincere appreciation to all RIKEN researchers who participated in the survey.

2025-12-04
Seishiro Ono receives the Young Scientist Award of the Physical Society of Japan

Seishiro Ono (Assistant Professor, The University of Tokyo/Visiting Scientist, RIKEN iTHEMS) has received the Young Scientist Award (Division 4) presented by the Physical Society of Japan (JPS). The awarded research is titled “Classification of Topological Superconducting Phases by Symmetry Indicators.” This award recognizes outstanding young researchers under the age of 37 who are expected to contribute to the future of physics. Ono was recognized for his pioneering theoretical work on topological superconductors. Congratulations, Seishiro!

2025-11-13
The 1st Joint General Meeting of RIKEN Quantum and the QII RIKEN User Group on October 24, 2025

On Friday, October 24, the 1st Joint General Meeting of RIKEN Quantum and the QII RIKEN User Group was held at Okochi Hall on the RIKEN Wako campus, bringing together RIKEN researchers who utilize the ibm_kawasaki quantum computer. The meeting featured lively discussions on quantum computing research at RIKEN across a wide range of disciplines, including condensed matter physics, particle, nuclear and astrophysics, biomedical sciences, and the humanities. With over 60 participants, including members from IBM Quantum, the event was a great success. This meeting is expected to further accelerate the development of quantum computing research at RIKEN in the future.

2025-11-12
Miniature satellite NinjaSat discovers an unusually short X-ray burst cycle

An international collaborative research group including Akira Dohi, Special Postdoctoral Researcher, has observed an X-ray binary system known as a “clock burster,” which produces X-ray bursts at regular intervals, using NinjaSat, the CubeSat X-ray satellite led by RIKEN. The team discovered that this object has the shortest burst recurrence time ever recorded, 1.6 hours. For more details, please refer to the related link.

2025-11-06
The tides are changing for white dwarfs

A research team led by Lucy McNeill, a Hakubi Assistant Professor, at the Hakubi Center for Advanced Research, Kyoto University, and a Visiting Scientist at iTHEMS, has revealed that white dwarfs in compact binary systems can become significantly hotter and larger than previously predicted due to strong tidal forces. This “tidal heating” causes white dwarfs to expand to about twice their theoretical size, reaching surface temperatures between 10,000 and 30,000 K. As a result, the onset of mass transfer between the stars may occur at orbital periods up to three times longer than expected. The findings provide new insights into the evolution of white dwarfs and the origins of Type Ia supernovae. For more details, please visit Kyoto University’s press release page via the related link below.

2025-10-22
Tomoki Ozawa received the Frontier Salon Nagase Prize (Special Prize)

Prof. Tomoki Ozawa, Professor at the Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, and Visiting Scientist at iTHEMS, has been awarded the 15th Frontier Salon Nagase Prize (Special Prize) by the Frontier Salon Foundation. This award honors outstanding young researchers who are expected to pioneer the future of science and technology and potentially become future Nobel laureates. Prof. Ozawa is a theoretical physicist working in condensed matter physics. He applies the mathematical concept of topology, which focuses on the “shape” of systems, to discover universal physical principles shared among diverse systems—from metals and gases to light, sound, and even biological structures. His recent work extends these ideas into higher-dimensional topological frameworks, exploring new quantum states of light and matter. These studies are expected to contribute to the development of next-generation quantum and photonic technologies. To commemorate the award, Prof. Ozawa delivered a lecture titled “Horizons of Physics Opened by Topology: Beyond Matter and Dimensions” at the Science Seminar for High School Students held on September 26, 2025, where he introduced the beauty of topological physics and inspired young students with the joy of discovery.

2025-10-21
Paper Accepted at NeurIPS 2025, One of the World’s Premier Conferences in AI

A paper by Tsubasa Masumura and Associate Professor Masato Taki (Visiting Scientist at iTHEMS), both from Rikkyo University, has been accepted for presentation at NeurIPS 2025, an international conference in the field of machine learning. In this study, the authors proposed a new Transformer architecture that incorporates the principles of associative memory, successfully mitigating the issue known as “rank collapse” both theoretically and experimentally. The proposed method improves model performance without introducing additional parameters, offering potential contributions to the further advancement of large language models and generative AI. NeurIPS 2025 will be held in December 2025 in San Diego, USA. For more details, please refer to the Rikkyo University press release via the related link below.

2025-10-20
Students from OTEMAE Senior High School Visited iTHEMS through the “Math Tour” Program

On October 2–3, 2025, students from OTEMAE Senior High School in Osaka visited the RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) as part of the “Math Tour” training program. During their visit, the students attended lectures given by iTHEMS researchers and were inspired by the beauty and diversity of mathematical sciences. The lectures included “Introduction to Machine Learning” by Senior Research Scientist Akinomi Tanaka, “Principles of Biological Growth and Evolutionary Game Theory” by Senior Research Scientist Ryosuke Iritani, and “Spheres and Dimensions” by Research Scientist Taketo Sano. Through these sessions, the students experienced stimulating learning opportunities beyond their regular classroom studies. Many students commented that the visit was “very helpful in thinking about future career paths” and “opened new perspectives on the joy of mathematics.” This program successfully provided a valuable opportunity for the students to deepen their understanding and interest in mathematical sciences.

2025-10-16

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RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) is an international research center at RIKEN. It facilitates close collaborations among researchers from different disciplines in theoretical, mathematical and computational sciences. On April 1, 2025, iTHEMS transitioned from a program to a center. The ultimate goal of iTHEMS is to unravel the mystery of the Universe, matter, and life, as well as to solve key problems in modern society through interdisciplinary approaches.

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