[No. 169] Yukiko Shimizu

Thank you very much for this opportunity to contribute to the Keio University Alumni Relay Column.

For me, the greatest asset from my time at Keio University is the people I met: my mentors, senior colleagues, friends, and my research. And I live my daily life keeping in mind the motto of my mother, who is also a researcher: "Continuity is power."

Both of my parents were physics teachers at a university, so I think it was a natural progression for me to pursue a path in physics. When I was little, they would sometimes explain things I found mysterious or interesting through simple experiments. I believe I was also greatly influenced by the thrill of being able to explain familiar natural phenomena with physics, even at a young age.

After entering the Faculty of Science and Technology at Keio University, I chose to major in the Department of Physics. For my master's program, I was accepted into the laboratory of Professor Hiroyuki Sasada, who specialized in laser spectroscopy. There, I first worked on research related to the generation of donut-shaped Laguerre-Gaussian (LG) beams, which have orbital angular momentum. In Professor Sasada's lab, the mainstream research theme was molecular spectroscopy, but I believe he gave me a topic that was more novel and interesting than something squarely in the middle of that field.

My memory of my first physics conference is very vivid. I was presenting in the same quantum electronics field as the students from my father's and mother's labs. The venue was filled with familiar faces, perhaps curious about what kind of presentation the professor's daughter would give. I remember when I took the stage, I saw the worried faces of my professor and parents, alongside a row of curious faces, and I felt an immense pressure to succeed. I must have been so nervous that my memory stops there; I don't remember what I presented or what questions I was asked at all. I was able to make my conference debut with my close female friends from the Department of Physics, and I clearly remember that we enjoyed sightseeing in Kobe without a care in the world after the presentation.

Furthermore, when I was in my second year of the master's program, Professor Sasada gave me the opportunity to participate in a joint research project with the laboratory of Professor Takahiro Kuga at the University of Tokyo's Komaba Campus. Professor Kuga was researching the optical trapping of atoms using laser cooling in the fields of quantum optics and quantum electronics. The challenge was to optically trap atoms within an LG beam. Since this was a precious opportunity given to me by Professor Sasada, I wanted to continue this experiment for my doctoral studies, so I decided to transfer to Professor Kuga's lab for my Doctoral Programs.

My research theme for the Doctoral Programs was the control of the quantum state of an atom-light coupled system using a microcavity. We created a state with about 10 atoms inside a microcavity and propagated a light pulse with a specific frequency through it. In the region where the refractive index of the atom-light coupled system changes significantly with frequency, the propagation speed (group velocity) of the light pulse can become extremely slow, slower than the speed of light, or conversely, appear to exceed the speed of light, compared to when there are no atoms in the cavity. This observation was a culmination of all the techniques developed up to that point, and the difficulty level for me was quite high. I went through a tough period with no results, but I will never forget the moment I finally succeeded.

Now, during the course of these experiments, I looked at the number of digits displayed on the wavelength system and suddenly wondered, "Is this value correct to the last digit? Who decides this, and how?" It was then that I learned that this value is traceable to the national "standard," and that the institution responsible for this standard is the National Institute of Advanced Industrial Science and Technology (AIST). Having struggled daily with experiments under extreme conditions, it was at this moment that I deeply felt the importance of the institution that determines these values.

Greatly interested in creating national standards and ensuring their reliability, I applied to the Metrology Standard Research Division at AIST and was hired as a researcher. Here, we conduct research and development to create metrology standards that serve as the basis for measuring physical quantities such as temperature, mass, and length, and we supply them to academia and industry. The fact that the metrology standards I develop become the "national standard" and can directly contribute to society is, while a great responsibility, the greatest appeal of this job.

After joining AIST, I worked on developing temperature standard technology for calibrating radiation thermometers and thermography systems, which can measure temperature with light. The task was to establish a standard in a temperature range that had not yet been established in Japan. I had to verify whether this sole national standard was correct using every means possible myself. The moment I sent the standard out into the world with confidence, shouldering that entire responsibility, was the moment all my efforts were rewarded. In parallel, I also conducted research and development on high-speed radiation thermometry technology based on this standard technology. I presented at an international conference in the United States and was able to meet Dr. John Hall of the JILA research institute, who won the Nobel Prize in Physics that year.

Currently, I have moved beyond my previous group and belong to the Frequency Measurement Research Group. Utilizing dual-comb spectroscopy, which employs an ultrashort pulse laser called an optical frequency comb—used for ultra-precise frequency and length measurements due to the accuracy of its frequency intervals—I have developed a new technology with my group members to measure the temperature of a gas by measuring the absorption spectrum of its molecules. Amazingly, my former mentor, Professor Sasada, is currently conducting research in this group as a guest researcher. Once again, I am reminded that the greatest asset from my time at Keio University is the people I met.

On a personal note, I wake up at 5 a.m. every morning to make a bento lunch for my eldest daughter, who started junior high school in April. Lately, I've found enjoyment in seeing how quickly I can prepare ten different items, and it has now become a hobby. My eldest son is a third-grader and a table tennis enthusiast. He travels to various tournaments in places like Kobe and Aichi, which is a double bonus for our travel-loving family.