[No. 197] Suguru Endo

I am currently conducting research on quantum computers at NTT Computer & Data Science Laboratories. Quantum computers are a new type of computer that can perform high-speed calculations by leveraging the properties of quantum mechanics, the physical laws that describe the microscopic world of atoms and electrons. They are expected to have various applications, including in chemical calculations and machine learning. Within this field, I am engaged in the theoretical research and development of quantum algorithms and methods for suppressing computational errors for what are known as Noisy Intermediate-Scale Quantum (NISQ) computers—the small-scale and still imperfect quantum computers of the present and near future, which are prone to significant computational errors. Quantum computers have not yet reached the stage of practical application where they have made the world more convenient in some tangible way, but it is a rapidly growing field where research institutions around the world are competing fiercely. I conduct my research daily, believing that the algorithms and error-suppression methods I create will become essential technologies in the future and accelerate the practical application of quantum computers. In this article, I would like to look back on how I became a theorist in quantum computer research, including my experiences as a student.

A crucial step in my journey to researching quantum computers was my laboratory assignment in my fourth year of undergraduate studies. Although I was interested in physics, I had no particular field I wanted to pursue. For the simple reason that it seemed difficult and cool, I requested to join the Hayase Laboratory, which experimentally studied the interaction between matter and light, and I ended up researching quantum memory for storing quantum information. I actually wanted to do theoretical work, but my grades were only average, so I wasn't confident in my abilities as a theorist and deliberately chose to do experiments. As a result, I realized that I was too clumsy and not suited for experimental work.

During my undergraduate years, I conducted experiments using laser light, and I lost count of how many lenses and mirrors I broke. Despite this, Professor Junko Hayase and my senior lab members guided me with great warmth. They took the time to discuss things with me thoroughly and patiently mentored me until I, a slow learner, understood. Physics textbooks and papers are naturally often written based on mathematical formulas, but Professor Hayase often told me to "be able to explain phenomena physically," not just rely on equations. This is something I still value today. When writing my graduation thesis, I still wanted to conduct theoretical research, so I attempted to build a theory to explain my experimental results and discovered a "strange relationship between experiment and theory." In the end, I couldn't resolve it in my thesis, but Professor Hayase and a senior lab member introduced me to Dr. Yuichiro Matsuzaki (now at the National Institute of Advanced Industrial Science and Technology), a theorist at NTT Basic Research Laboratories, and I had the opportunity to discuss it with him. Meeting Dr. Matsuzaki would significantly change the course of my life.

I also made a major decision upon graduation. It was to transfer to a theoretical research laboratory in the Department of Physics upon entering the master's program and switch to theoretical research. I had no background in theory and was behind my peers, but my academic advisor, Professor Tatsuhiko Furuike, kindly guided me. The members of my group also frequently engaged in discussions with me and held independent study sessions together. At first, I had no foundational knowledge for conducting research, but I remember gaining a great deal of confidence when Professor Furuike told me something to the effect of, "It's a very good thing that you have a sense cultivated from experiments." Gradually, I acquired the fundamentals for conducting theoretical research. I still remember the intense pleasure I felt back then as the theory, based on physics and mathematical formulas, clicked firmly into place.

Now, in April, right after entering the master's program, I went to NTT Basic Research Laboratories to have a discussion with Dr. Matsuzaki. Dr. Matsuzaki and his fellow researchers generously spent time discussing with me, and the "strange relationship between experiment and theory" from my graduation thesis was resolved (Professor Furuike and Professor Hayase also participated in the discussions). This result was directly connected to the famous "wave-particle duality" of quantum mechanics, and I became even more engrossed in my research. Afterward, Dr. Matsuzaki encouraged me to do an internship at NTT, where I was mentored by him and began theoretical research on superconducting quantum bits, one of the promising physical systems for realizing quantum computers. I also wrote my first submitted paper during this internship. Dr. Matsuzaki often said, "If you want to conduct cutting-edge theoretical research on quantum computers, you should study abroad," and I naturally began to aspire to do so.

Dr. Matsuzaki also had the experience of studying abroad in the Doctoral Programs at the University of Oxford in the UK, and he used that experience to give me advice on studying abroad. As a result, after completing my master's degree and working as a researcher at RIKEN, I also went on to the University of Oxford and studied my current research field under Professor Simon Benjamin. Professor Simon Benjamin was also a wonderful mentor, and I can proudly say that I was able to conduct world-leading research.

Having been supported by NTT after graduation, I wanted to give back, so I joined the company, which brings me to the present.

Thinking back, I am deeply aware that I am who I am today because of the immense support I have received from so many people. To all the junior students who will embark on various career paths, I sincerely hope that you will cherish the encounters you have with people, reflect on their meaning for yourselves, and lead wonderful lives.