International and Interdisciplinary Collaboration at the RIKEN-Berkeley Center
Yuuka Kanakubo
(Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
"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.
Keywords: Elementary Particle and Nuclear Theory, Relativistic Heavy-Ion Collisions, Quark-Gluon Plasma, RIKEN-Berkeley Center, Lawrence Berkeley National Laboratory (LBNL)
Affiliation and position are as of the interview date: December 2024
Current position: Postdoctoral Researcher, RIKEN-Berkeley Center, Division of Global Collaborations and Research Talent Development, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)
(Written by Shino Suzuki (Photon Create Co., Ltd.) / Photographed by Makoto Oikawa (Photographer))
The Beginning: "Expo 2005 Aichi"
Yuuka Kanakubo shares, "I decided to become a researcher when I was still in elementary school." The turning point came when she was in fourth grade and visited Expo 2005 Aichi, Japan, with her parents. "I saw various exhibits showcasing efforts to solve environmental issues through the latest scientific and technological innovations. I realized the power of science—especially chemistry—to change the world, and it was a life-changing moment. That’s when I knew I wanted to become a researcher and study chemistry," she recalls.
Kanakubo later entered a private integrated junior and senior high school. "The school emphasized English education and boarding school programs overseas—I participated in three boarding school programs. From that time, I developed a strong desire to place myself in international environments," she says.
She went on to study in the Department of Materials and Life Sciences at Sophia University. "Learning chemistry was really enjoyable. But..." she trails off. "When I delved into the 'why' behind certain chemical reactions, I couldn't find satisfactory answers within the framework of chemistry. When I consulted various professors, it was a physics professor who gave me an explanation that truly resonated with me. That was near the end of my second year, and from my third year on, I started taking more physics courses, gradually shifting my interest toward physics."
Discussing a Single Collision Phenomenon with Science as a Common Language
For her graduation research, Kanakubo joined a research group focused on nuclear physics, where she encountered her current research theme: relativistic heavy-ion collisions. "When atomic nuclei are accelerated to nearly the speed of light and made to collide, quarks and gluons are produced in abundance, creating a superhot state reaching temperatures of two trillion degrees. This state is called quark-gluon plasma. It then expands and cools, eventually forming hadrons—the ordinary matter surrounding us today. This process is known as a relativistic heavy-ion collision. It’s believed that the early universe, right after the Big Bang, was filled with quark-gluon plasma," Kanakubo explains.
She continues: "I saw a simulation of a relativistic heavy-ion collision and learned that it involves many phases with complex physical phenomena. In experiments, only the final hadrons are observable. To fully understand the entire collision process, a deep knowledge of various areas of physics is necessary. By combining these different areas, we can extract the information embedded in the hadrons and use it to understand the properties of the quark-gluon plasma and how quarks and gluons interact. I found this incredibly fascinating, and once I started working on it, I was completely drawn in."
Her undergraduate research was highly acclaimed, and during her master’s program, she had the opportunity to attend an international conference. Reflecting on her first experience at an international conference, Kanakubo says, "Seeing researchers from around the world gathering and discussing a single collision phenomenon with science as their common language was deeply inspiring. I strongly wanted to be part of that community. Expo 2005 was also a gathering of people from many countries, discussing solutions to global environmental issues. I realized I love these opportunities where people come together and engage in discussion using science as a shared language."
Learning to Research Across Cultures in Finland
After earning her Ph.D. from Sophia University, Kanakubo chose the University of Jyväskylä in Finland as her next research destination. "People often ask, 'Why Finland?'" she laughs. "Until then, I had been working on simulations of the space-time evolution of the quark-gluon plasma using hydrodynamics. I wanted to venture into new areas of physics, so I decided to focus on the early stages of collisions, which is a research focus at Jyväskylä."
Up until her departure, she was so focused on research that practical concerns—like whether it would be freezing cold or whether language would be a barrier—only hit her at the last moment. Life there turned out to be blessed with natural beauty—forests, lakes—but she did struggle with language barriers and had to adapt to a very different working style.
In Finland, researchers typically arrive at the lab around 9 a.m., take a leisurely lunch together while discussing research and personal topics, and even gather for coffee around 3 p.m. Most people start leaving by 4 p.m., and by 5 p.m., the lab is nearly empty. Initially, Kanakubo tried to match the local working style, but found that she couldn't make enough progress during the day and had to work weekends to catch up.
Eventually, her advisor intervened: "Yuuka, if you keep this up, you’ll burn out. You need to rest properly and keep your mind in a healthy state to do good research." In Finland, winter can bring -30°C temperatures and endless darkness, while in summer, the sun never sets. If you aren't mentally and physically healthy, the extreme environment can take a heavy toll—not just on your research, but on your daily life.
Reflecting on her two years in Finland, Kanakubo says, "I truly learned the meaning of 'When in Rome, do as the Romans do.'" Thanks to her adjustment, she successfully published the research she began in Finland.
The Importance of Casual Conversations
Believing it was time to become more independent in her research, Kanakubo chose iTHEMS as her next step. She had been regularly checking iTHEMS’s website and sensed that the environment valued researchers' independence and active interdisciplinary exchange.
One thing Kanakubo especially values in research is communication. "Meeting people and having casual conversations can lead to research breakthroughs. Talking with researchers from different fields can spark ideas that lead to completely new solutions. I realized the importance of communication many times during my three months at the Wako campus."
In December 2024, she gave a talk at an iTHEMS seminar. "I realized how challenging it is to present to an audience with such diverse backgrounds," she says. "Researchers from fields far removed from mine pointed out aspects I hadn't considered problematic. Some even came to discuss new ideas after the seminar. These interdisciplinary discussions create opportunities to approach a problem from a completely different angle. iTHEMS has truly exceeded my expectations."
Communicating the Excitement of Science as a Social Responsibility
Kanakubo launched her personal website in the summer of 2024. "I enjoy designing things, so creating a website that reflects my personality had long been on my bucket list," she says.
She plans to expand the site to include not only specialized content for researchers but also accessible introductions to her research for the general public. "Researchers are part of society. It's important not only to work in the lab but also to give back to the community. I learned about the excitement of science at the Expo, and that led me to become a researcher. Now, it’s my turn to convey the excitement of science—accurately, clearly, and enjoyably."
Elementary particle and nuclear theory is basic research that doesn't immediately lead to practical applications. Still, Kanakubo emphasizes: "Learning scientific approaches—formulating hypotheses based on logical thinking and objective consideration, testing them, and evaluating whether they're correct—can help solve everyday problems too. I want to convey that science is fundamentally vital for supporting our world."
Building International Collaboration and Engaging in Interdisciplinary Discussions
As a RIKEN-Berkeley Fellow, Kanakubo will be staying long-term at the RIKEN-Berkeley Center at the University of California, Berkeley, to work on research in relativistic heavy-ion collisions. "My office is located at Lawrence Berkeley National Laboratory (LBNL), adjacent to the RIKEN-Berkeley Center. LBNL has researchers specializing in heavy-ion collisions, so it's the perfect environment for me."
Her long-term stay is made possible through the RIKEN-Berkeley Mathematical and Quantum Science Initiative, selected under the Adopting Sustainable Partnerships for an Innovative Research Ecosystem (ASPIRE) program by the Japan Science and Technology Agency (JST). This program fosters the development of young researchers who will become global leaders by promoting long-term dispatches and reciprocal invitations between RIKEN and UC Berkeley.
"I definitely want to live up to the expectations," Kanakubo says with a determined expression. She plans to conduct research while traveling between Japan and the U.S. "First, I want to establish an international collaboration with researchers at LBNL, leading my own research projects. But I also realize that I’ll need to step beyond physics, and reexamine problems from different disciplinary perspectives. I hope to return to Japan occasionally to engage with researchers across various fields at iTHEMS and absorb new ideas and approaches. This is precisely what makes being a RIKEN-Berkeley Fellow at iTHEMS the perfect position for me."