I was deeply saddened to read of the death of my former colleague, Dr Akira Tonomura. For two delightful periods in the late 1980’s, I was the first Western professor invited to the Hitachi Advanced Research Laboratory (ARL) to provide theoretical guidance to the electron microscopy group in matters of quantum physics and the planning of new experiments. During that time, Dr Tonomura and I developed a close working relationship and a friendship that lasted for years after my return to the US.

I still have—some 27 years later—a vivid recollection of our first encounter in Japan. I was traveling with my wife, 4-year old son, and 1-year old daughter, and wondering whether it was sheer madness to take my family to live in an environment where not only could we not speak the language, but were illiterate as well. (By the second long visit, three years later, we had studied Japanese and were better able to read and communicate.) Dr Tonomura, whom I had met only briefly once before at a conference, arranged for a Hitachi limousine to pick us up at the airport and take us to a hotel in Tokyo. We had just concluded a multi-stage trip of more than 24 hours and were exhausted, when I learned that Dr Tonomura was waiting for me to join him (at about 1:00 in the morning!) at a nearby sushi bar. My wife and children went to bed, but I, running on adrenaline, was avid to meet my host. At the sushi bar Dr Tonomura had carefully planned the succession of raw Japanese delicacies for me to try. It was, I believe, a physics experiment to gauge how culturally adaptable his new guest from the West was going to be. He had little to fear. I was then, as I am now, an enthusiast of Japanese food. To his surprise and amusement, I tried and enjoyed everything—with but one exception. I found sea cucumber (which is not a plant, but an echinoderm) to be unpalatable, an opinion that he afterward told me he shared. Apparently, I passed the test, and we both left the sushi bar with good feelings about our future scientific and cultural interaction.

Our interaction began very productively. At the time of my first visit, Dr Tonomura’s group had just completed a difficult experimental demonstration of the Bohm-Aharonov effect, i.e. the influence of a magnetic flux on the self-interference pattern of a split beam of electrons excluded from the region where the magnetic field is nonzero. The Hitachi experiment was designed to address criticisms as to whether the BA effect was really just a subtle manifestation of the Lorentz magnetic force. Dr Tonomura was preparing to present his group’s experimental results at the first ISQM (International Symposium on Quantum Mechanics in the Light of New Technology) sponsored by Hitachi. He was also wondering in what direction his group might go beyond the BA effect. One of my research interests prior to coming to Japan was in extending the idea of intensity interferometry, first demonstrated optically by Hanbury Brown and Twiss, to fermions. Early in my visit, I realized that under conditions comparable to those of the BA effect, a sequestered magnetic flux could influence fermionic fluctuations (e.g. electron antibunching).[1] So excited was he at this potentially new avenue of research, that Dr Tonomura arranged for me to present the work at the ISQM, although the deadline for submission of contributions had passed.[2]

Our time together generally followed a certain established routine. In the morning, Dr Tonomura, who was Chief Researcher of the electron microscopy group, worked with his staff while I, whose official Hitachi designation was “Visiting Chief Researcher” of a theoretical quantum group of 1 person, worked alone on theoretical matters and experimental design. Sharply at noon, work stopped and he, I, and on various occasions a third colleague, Dr Hiroshi Motoda of the information technology unit, went to lunch at one of the numerous local restaurants in Kokubunji where the ARL was then located. (It has since been relocated to Hatoyama.)

It was at one of our lunches that I proposed to Dr Tonomura the experiment, to be performed with the attenuated beam of an electron microscope, that has since come to represent the signature feature of quantum mechanics: the build-up of an electron interference pattern one electron at a time. The idea and details interested him greatly, but he would have to obtain permission from management to undertake such an experiment. Some time later, when we met again for lunch, he looked crestfallen. The management did not approve the project, he explained, because it was not the mission of the ARL, a high-tech industrial research lab, to make “classroom films”. I pointed out that performing such an experimental test, even though the outcome was not in doubt, would attract a lot of attention among educators and science news reporters, and could well have a promotional advantage to Hitachi: recorded on videotape and shown in high school and university physics classrooms throughout Japan, the video could beneficially influence sales and recruitment at Hitachi. I did not hear about the matter again for a long time, but evidently Dr Tonomura must have persuaded Hitachi management because the experiment was eventually performed and the original recording (monochrome and silent) was made. My name is not on the paper, but in recognition of his appreciation, Dr Tonomura gave me a copy of the video, which in subsequent years I have often shown to my classes. Hitachi ultimately replaced the original recording with a full-colour, narrated film one can download from the internet. Conceivably, the original Hitachi recording I have of “the most beautiful experiment in physics” may be the only one left.

During my two long visits, I learned much from Dr Tonomura about the Japanese way of doing things, and reciprocally he learned from me about how things were done in the US. For example, the ARL sought my advice for how best to promote Hitachi research programs internationally. I suggested they adopt an approach then being employed by the Ford Motor Company—namely, to take out, in widely circulated journals like Scientific American, a full page advertisement devoted to the work of a particular scientist or engineer, with a photograph of the individual prominently displayed to give a human face to the project. “Oh no,” I was told, “We could never do that because in Japan emphasis is always on the group, not the individual.” Like the matter of classroom films, the Hitachi management must have reconsidered because in due time there appeared full-page notices of the “Tonomura Electron Wavefront” project with a photograph of Dr Tonomura.

I last saw Dr Tonomura in 2010 at a quantum conference[3] that I co-organized with Herman Batelaan at the Harvard-Smithsonian Center for Astrophysics in Cambridge MA. This was but one stop in a tight schedule he had of other meetings, and I expressed hope, before he left after his talk, that next time we could get together under more relaxing circumstances. I never suspected there would be no next time.

Although most of my daily interactions with Dr Tonomura centered on physics, the strongest memories of my visits at Hitachi are of the many kindnesses that he and Mrs Tonomura bestowed on my family and me in helping us navigate through the difficulties of an unfamiliar culture.