Vol.09　Shigeki TAKEUCHI

After graduating from high school, he entered the Faculty of Science, Kyoto University where his happy campus life began again while surrounded by classmates with whom he had a lot to talk about.
 
“At Kyoto University, there are activities called ‘student-led seminars’ where students themselves choose a textbook that interests them and decide on a leader who gets other students to read it together with them. In one student-led seminar, we decided to read a famous textbook on general relativity theory called ‘The Classical Theory of Fields,’ which is nearly 500 pages long. It’s a very famous book, but it was a bit of a reckless challenge for us to read through it since we were only first-year students.....”
 
Well, it was in fact really reckless but he did read through it anyway.
 
“I was in a university club that dealt with student-led seminars on a variety of topics from philosophy to natural science. A senior fourth-year student in the same club served as our peer tutor (a person who gives guidance and advice), and we all painstakingly read each line of sentences and equations saying this and that. After struggling with ‘The Classical Theory of Fields,’ we all enjoyed playing card games together. I have nothing but happy memories of those days,” says Professor Takeuchi with a laugh.
 
“In my second year of university, I attended a lecture of Professor Shigeru Machida who taught us quantum mechanics using the book ‘Modern Quantum Mechanics’ written by J.J. Sakurai which had just been published at that time. It was a fantastic lecture. I remember that after the last lecture for that semester was finished, we invited Professor Machida to go out for drinks together with us (laughs).”
 
Professor Takeuchi had been interested in quantum theory since he was a high school student, so you can imagine how excited he was to be able to study this field in depth at the university. It’s easy to see how both a teacher and students can hit it off since both are fascinated by the mysterious world of quantum theory.
Professor Takeuchi’s story continues.
 
“Around the same time, I had a profound encounter with the concept of ‘quantum entanglement.’ This came in the form of a book entitled ‘The Quantum Mechanics Controversies’ (written by Franco Cerrelli and translated by Yoshio Sakurayama; Kyoritsu Shuppan) that had just been published. This book summarized the ‘EPR paradox,’ ‘Bell’s inequality,’ and other topics that were truly the royal road to quantum entanglement.”
 
The first experiments to verify the mysterious nature of quantum entanglement were attempted in the 1970s. Following this, further experiments were conducted and discussions at the cutting edge of this new field started to heat up.
 
“The Quantum Mechanics Controversies” book contained the foremost knowledge of quantum theory available at the time. By reading it in a student-led seminar with classmates, Professor Takeuchi became even more deeply involved with the world of quantum.

After a happy undergraduate life, he went on to a master’s degree. You might naturally think he would have gone ahead with research related to quantum theory, but...
“I was interested in physics in general, but had been interested in the theory of relativity since entering the university, so at first I wanted to join a cosmology laboratory. At that time, the mainstream paths in physics were particle theory and relativity theory.”
 
However, when he saw students who were far more talented than him applying to the cosmology laboratory, he gave up gracefully saying “I can’t do this,” and decided to instead apply for the high-temperature superconductivity laboratory at the graduate school which was also a hot topic at that time.
 
After entering the laboratory he chose, he was given a study theme: “What happens when ultrasound is applied to a very thin organic thin film with several layers of molecules?” that was in fact an area actually slightly different from high-temperature superconductivity.
The contents of the study are as follows:
 
When a drop of soap is dropped on clean water, the soap molecules quickly spread over the water, forming a single-layer film of soap molecules. The film is about 1/100,000th the diameter of a human hair or 1/100th the diameter of a coronavirus. When this film is transferred neatly onto glass, a film with only one layer of molecules forms on the glass. Repeating this process creates a layered film made up of various molecules.
 
The study question was: What would happen if ultrasonic waves were incident on the molecular layers of the film created this way?
 
“Seeing such a thin layer of molecules with sound waves is impossible if using sound waves emitted from an ordinary speaker. The wavelength of sound emitted from a speaker is at least a few centimeters long which is not short enough to use. To emit ultrasonic waves with a wavelength as short as the molecular layer thickness, we needed to use a very special ultrasonic generator, a superconducting tunnel junction.”
 
The development of this ultrasonic generator was actually research on quantum devices.
 
After giving up on cosmology research, he instead entered the high-temperature superconductivity laboratory, where he was given ultrasonic waves as his theme, but pursuing this theme required doing research on quantum devices. So, due to the push from a variety of circumstances, he eventually entered the world of quantum research that he had been fascinated with for a long time.
 
Near the end of his master’s degree course, he began looking for a job where he could work for a company that would allow him to conduct research on quantum devices. After visiting several companies, he was fortunate enough to get a job at Mitsubishi Electric Corporation.

At Mitsubishi Electric, where Takeuchi joined with a desire to work on quantum devices, he was assigned to a department called the “Embryonic Science and Technology Department.” There, three or four research groups were already working on their own themes.
However....
 
“The head of the research department was an interesting person and was always thinking deeply about basic research for the company. He probably knew that I wanted to work on quantum devices, so I was assigned to report directly to him without belonging to any particular research group.”
 
Takeuchi was a new employee and assigned to report directly to the department head. In a way, this was special treatment and he felt quite confused about it. He was then given two research themes as a newly employed researcher. One theme was: “Find and propose your own research theme on the quantum.” The other theme for some reason was: “Do research on rice during one year of your training period.” He was told that there were no restrictions on the content of the rice research and that he could do anything and in any way he wanted as long as it was related to rice.
 
Professor Takeuchi always seems to have an interest with no limits in just about everything. Though still wondering “why am I doing rice research?”, he felt immensely curious and began doing “rice” research that seemed to be a subject far removed from the quantum.
 
“I searched for a research theme that would benefit both the company and society. Cooking rice in a rice cooker usually takes about 30 minutes, right? But a grain of rice is less than 1 centimeter long and only a few millimeters wide. Why does it take 30 minutes to cook or gelatinize it? Don’t you think that is strange?” says Professor Takeuchi.
 
 
Curious about this, he started reviewing the available literature.
 
“I worked pretty hard checking various studies in related literature. Some past studies reported results of how the core of rice remained when cooking in a rice cooker was stopped about halfway through the cooking process. But we really didn’t know what was going on between the time that the cooking was stopped and the time that the cooked rice was examined.”
 
“I wondered about such studies since we have no idea of what actually happens to the rice grains,” says Professor Takeuchi.
 
“So, I thought about what I could do in this case and came up with the idea of using NMR (Nuclear Magnetic Resonance)*¹ imaging to nondestructively observe the rice grains internally while the rice is being cooked.”
 
However, NMR imaging was still a new technology at that time and was only just beginning to be used in medicine. Moreover, the object of observation was a grain of rice only a few millimeters in size, so this was quite different from observing the human body.
 
*1: NMR (nuclear magnetic resonance) is a phenomenon in which atomic nuclei in a material in a strong magnetic field interact with electromagnetic waves. Using this interaction allows investigating the molecular structure of matter and the way atoms bond to each other.
 
“After searching for a while, I found that there were only two state-of-the-art NMR imaging systems in Japan at that time that were capable of observing extremely small objects. I contacted the professor at the university who owned one of the NMR systems, and was able to get him interested in this topic, and we entered into a joint research agreement so I was then allowed to use the NMR.”
 
At that time, NMR systems cost several hundred million yen or more. To cook a single grain of rice in such very expensive equipment, we fabricated a special jig.
 
“It was also very difficult to figure out how to cook the rice. After considering various means including lasers, we created a device that cooks a grain of rice in a test tube while feeding air heated by a ceramic heater into the test tube. We placed this device inside the NMR system and also worked along with the professor at the university to create a dedicated pulse sequence that irradiates a special magnetic field to analyze how the rice was being cooked.”
 
The rice research was initially planned to be just one year of the training period, but as research began to gain speed, it lasted a total of three years in parallel with research on quantum computers. However, here, too, an unexpected connection with quantum research emerged.
 
“The principles of NMR pulse sequencing and imaging are exactly the same as those used in the control and measurement of quantum computers. So, when I looked back on my rice research, I found out that it also turned out to be research on quantum computers,” laughs Professor Takeuchi.

When Takeuchi was newly hired and assigned to report directly to the department head, he was given another theme in addition to his rice research. It was: “Find your own next research theme regarding quantum. It should contribute to the company, be cutting-edge, and should definitely not be currently conducted by any other company.”
 
While working on rice research, Takeuchi began to search for his new research theme.
 
“Right around that time, I was fortunate to come across a theoretical research paper that discussed for the first time the possibility of achieving faster computation with a quantum computer. When I first read the paper, I didn’t find it particularly interesting. I understood that the results were obtained as described in the paper by applying quantum mechanics equations, but I felt that these would be the natural results. Also, the problems set there were so particular that I wondered how they would prove useful.”
 
After a while, a senior colleague at work told Takeuchi that there was going to be a lecture on quantum computers in Tokyo. At the lecture, he was able to learn the latest information about the potential of quantum computers to solve problems that even today’s supercomputers could not solve. It turned out that the quantum computer, which he at first found not very interesting, suddenly became the object of his intense interest.
 
In fact, when Takeuchi read the paper on the quantum computer, he already had an idea in his mind as to how he could demonstrate it experimentally. He says, “I’m an experimentalist and I found it difficult to fully understand mathematical formulas written in theory unless replacing them with an actual experimental setup.”
 
The lecture pushed him to start thinking that “It would be interesting to actually experiment with a quantum computer which at that time had not even been developed yet,” and his desire to work on it gradually grew to a fever pitch.
 
Takeuchi is the type of person who can’t hold himself back once he wants to do something. He proposed to the department head to let him conduct an experiment on quantum computers as a theme that would “contribute to the company, be cutting-edge, and was not currently being researched by any other company.” However, the experiment would require a tremendous amount of funding for a basic research project undertaken by a new employee.
 
The quantum computer experiment was thought to be difficult to conduct within the company. But the department head showed him one possible way. That way was to be selected for a “PRESTO” research program of the Japan Research and Development Corporation (now JST, Japan Science and Technology Agency). However, the competition was extremely high, and the acceptance rate was very small.
 
Here, good future fell upon Takeuchi once again. He was selected even though it was just his first try, through help and advice from a senior colleague at the company who had previously been selected for PRESTO research.

So far, we have looked at Professor Takeuchi’s childhood, his student days and also the time he spent working as a company employee. Now, let’s change topics and ask Professor Takeuchi about his views on historical episodes surrounding quantum theory. The topic we will take up now is Einstein and quantum theory.
 
When examining documents on quantum theory, we are always bound to come across descriptions of a mysterious phenomenon called “quantum entanglement.” This “quantum entanglement” is said to be a phenomenon in which particles form a strong bond with each other, and once a quantum entanglement relationship is established between two particles, they continue that relation to each other even if physically apart from each other.

Mysterious phenomena such as quantum theory and quantum entanglement are actually all around us. An exhibition that allows visitors to actually experience this fact will open at the 2025 Expo Osaka, Kansai, Japan. The exhibition is titled “Entangle Moment” which is the moment of quantum entanglement.
 
“When people first hear about quantum entangled light, I suppose many people have the wrong idea about it, misunderstanding that it is some scary type of light, or can only be transmitted inside a vacuum pipe, or can only be generated using a powerful accelerator. In this exhibition, I would like to clearly show that this is not the case,” says Professor Takeuchi.
 
“I think there are only a few people who have actually seen quantum entangled light, even among quantum technology researchers. That is unfortunate, so my motivation for holding this exhibition is to let everyone see it.”
 
The exhibition will not be a video or computer graphics, but will instead use actual experimental equipment to generate quantum entangled light in a realistic way. Not only that, it will also demonstrate the mysterious phenomena that occur when photons “collide” with each other through a semi-transparent mirror.
 
“In quantum mechanics, when photons collide with each other, interference occurs between the physical processes. This is quite different from the ordinary interference of light waves. We often hear about ‘parallel universes’ and ‘space-time interference’ in science fiction, but these actually happen in quantum mechanics.”
What happens in the world of science fiction is actually happening in this universe, so what does all this mean? Professor Takeuchi continues explaining.
 
“For example, when you go from Kyoto to Hamamatsu, you can take the Shinkansen bullet train, or you can also take the Kintetsu line, then the Meitetsu line, and then change trains at or near Toyohashi. You can choose one of these travel plans or physical processes. Normally, these two processes are considered different from each other. In quantum mechanics, however, these two processes interfere with each other, canceling out or enhancing each other.”
As a result of the two physical processes canceling or enhancing each other, you might sometimes arrive at the destination, Hamamatsu, or sometimes might not arrive. Sometimes you might even arrive at the destination twice as fast. This is a world that is far beyond our imagination or common sense.
 
“Even so, it is happening in the world of quantum mechanics. That’s why I’m going to demonstrate it at the Expo,” says Professor Takeuchi with a happy smile on his face.