Report of the review committee for
Department of Physics
Research Center for the Early Universe
Universal Biology Institute
Institute for Physics of Intelligence
School of Science
The University of Tokyo

東京大学理学部・大学院理学系研究科

物理学科・物理学専攻
ビッグバン宇宙国際研究センター
生物普遍性研究機構

知の物理学研究センター
に関する外部評価委員会報告書
Committee members 委員会メンバー
Mitiko Go
Masahiko Hayashi
Maki Kawai
Dmitri Kharzeev
Taichi Kugo
Yoshio Kuramoto
Kaichiro Sakuma
Zhi-Xun Shen

郷 通子
林 正彦
川合眞紀
九後太一
倉本義夫 (Chair 委員長)
佐久間 嘉一郎

東京大学理学部物理学科・大学院理学系研究科物理学専攻

2020年2月

February, 2020

Table of Contents

Report of the review committee for
Department of Physics
Research Center for the Early Universe
Universal Biology Institute
Institute for Physics of Intelligence

THE DEPARTMENT AS A WHOLE
1.

Education…1

2.

Research and Hiring Policy…33.

Management…5

INDIVIDUAL RESEARCH FIELDS
1. Elementary Particle Physics
2. Nuclear Physics

…6
…7

3.
4.
5.
6.

…8

Condensed Matter Physics
Astrophysics
Biophysics
General Physics

…11

…13
…14

THE DEPARTMENT AS A WHOLE
The ﬁeld of physics is expanding with tremendous new opportunities, as exempliﬁed bysuch developments as cosmological science featured by the gravitational wave, neutrino
physics going beyond the standard model, condensed matter physics with novel quantum
materials, quantum information and their potential impacts to science and technology,
and the latest frontier at the intersection between physics and biology, just to name afew.
Physics provides exceptional opportunity to train young people for its own ﬁelds and far
beyond, by cultivating commendable quality for future leaders. In addition to providing
rigorous training for investigating fundamental laws of nature, physics encourages criticalthinking. Huge projects as exempliﬁed by LHC, LIGO, super/hyper-Kamiokande, KAGRA, X-ray free electron laser require not only leadership skills but courage of physicists
who are not afraid of thinking diﬀerently. Physicists often have led the world to embark
on risky but rewarding new directions. At the same time, physics research led to technologies that beneﬁt the society at large, as exempliﬁed by Internet, Global Positioning
System (GPS), and Magnetic Resonating Imaging (MRI).
The physics department of the University of Tokyo, hereafter called “the Department”,
is a world class department with outstanding faculty leading in exciting areas of researchand providing eﬀective training for students. It covers very broad topical areas, andexcels in many of them. The committee, while pleased to see the accomplishments of
the Department, will make some suggestions in this report for further development intoa major center of excellence in the international standard. In fact, the committee isconcerned that certain external environment of the Department remains unsatisfactory
for a long time. Especially, its space in Hongo campus is poorer as compared with manyother universities in Japan. The committee strongly urges the university administration
to invest more resources so that the Department can fully realize its potential.

1

Education

Undergraduate Education
The curriculum for undergraduates is mostly consisting of regular lectures, exercises, andexperiments. In addition to this standard form to teach basics of physics, the Department provides compulsory courses with a seminar style which encourages the students tointeract with professors more informally in small groups, each consisting of four students.
The course is in the winter semester of the junior (third grade), and intends to give theﬂavor of research to students. The subjects are chosen from speciﬁc modern topics.
The committee had the opportunity to talk with a few junior students who volunteered.
All students can communicate in English normally, which seems a big change since 2005
when the past report pointed out the opposite. According to the students interviewed,
the level of lectures is optimum for understanding. Most of them are living in area close
to the campus, and do not need a long time to commute even in Tokyo. It appears that
economical situation for students is much above the average in Japan. Another notablefeature is that almost all students go up to the same Department for the graduate course.
The diversity of undergraduate students is low; there are at most a few female students

1per year, and almost no foreign students. The lectures are all delivered in Japanese. The
committee recommends that the Department takes some measure to enhance the diversity.
Graduate Education
The master course students with slightly more than 100 annual enrollment come both frominside and outside with almost equal proportion. The Department provides diﬀerent levelsof course work, and graduate students can also take classes delivered mainly for senior
undergraduate students. If one or more foreign students take the course, the lecture isgiven in English. Otherwise the lectures are delivered in Japanese.
About half of the master course students continue to the doctor (PhD) course. Thosestudents who continue to the PhD course come more from inside. In 2012 the number ofdissertations is about 50, which increased gradually to almost 70 in 2018. These numbers
seem by far the largest among Japanese universities; in other major domestic universities
the typical number is 20 or less.
A notable feature is more than half of them go to industry. Those who continue research
after graduation decreased to less than 30 in 2016, and are still decreasing. This tendency
is understandable in view of the hard situation for Japanese young researchers; most ofthem cannot assume a permanent position, and continue to work in unstable conditions foryears. The tendency also warns the academic sector that many good students may avoid
continuing research. In contrast with most other universities which suﬀer from decreasing
number of enrollment to the PhD course in physics, the unique situation enjoyed by the
Department deserves more systematic analysis. Apparently, the eﬀort of the Department
to ﬁnancially support the students is a major factor for the statistics. The details ofﬁnancial issues are described in the next section.
The committee talked with several students who volunteered and can communicate wellin English. Some of them try to continue the academic career, and others try something
new including entrepreneurship. A student from Europe likes to work in Japan rather
than going back. The language seems the major barrier for such students.
Financial Issues
Students in the PhD course of the graduate school are ﬁnancially supported either by theJapan Society for Promotion of Science (JSPS) or by the University. The Departmentcommits to four graduate course programs and those are the main basis of the support
for students:(1) Advanced Leading Graduate Course for Photon Science (ALPS 2011-2018) went
through Program of Excellence in Photon Science (XPS 2018 – 2019) to Forefront Physics
and Mathematics Program to Drive Transformation (FoPM 2019 – 2026);(2) International Graduate Program for Excellence in Earth-Space Science (IGPEES 2018
– 2026);(3) Materials Education Program for Future Leaders in Research, Industry and Technology (MERIT) to World-leading Innovative Graduate Study Program for Materials
Research Industry and Technology (MERIT-WINGS); and(4) World-leading Innovative Graduate Study for Frontiers of Mathematical Sciences andPhysics (WINGS-FMSP).
On average, 60% of the students are supported either as JSPS fellow or from the gradu-2

ate courses above with the amount close to =Y200,000/month, and 20% are supported as
research assistant from the Department and the School of Science with ca =Y70,000/month.
The Committee is pleased to know the high percentage of students receiving the ﬁnancial support and will encourage the Department to continue or further improve thecondition. One concern we have is the resource of the graduate program described above.
Only one out of four programs is the program certiﬁcated by MEXT and the others are
fully supported by the University as of today. Regarding the freedom for the planning of
the program, we may consider the support from the University is suitable considering thepresent status of the Department. Then the Department should ﬁnd its original ﬁnancial
resource to maintain the stable support for the students.

2

Research and Hiring Policy

Research Fields
The Department at present covers fundamental areas of research in physics, and is making
good eﬀorts to cope with new frontiers and developments in the physical science. For
example, a new biological institute was established in 2016 including professors in Komaba
campus. Another institute dealing with artiﬁcial intelligence was created very recently(2019). In the ﬁeld of astrophysics, the Research Center for the Early Universe (RESCEU)
has a long history since 1999, and is very active in various ﬁelds including experimental
research on the gravitational wave.
In the entrance examination to the graduate course, research groups are classiﬁed
into subcourses basically according to the research ﬁelds. There is a subcourse named“Experimental General Physics”, the meaning of which seems hard to understand forstudents. Actually the subcourse is a mixture of various ﬁelds in condensed matter,and some previous members went out to another subcourse. The committee recognizes
the signiﬁcance of the subcourse if the Department utilizes it to cope ﬂexibly with newly
developing ﬁelds. Nevertheless we recommend the Department to put an intelligible namefor the subcourse in order to make it more attractive to students.
Structure of Research Teams
The Department regards full and associate professors, and lecturers as principal investigators (PI’s). On the other hand, assistant professors, though sometimes included as faculty
members, have a situation rather diﬀerent from that meant by the ordinary sense of theword. The previous name “assistant” for the position is closer to the reality. Namely, eachassistant professor is selected by the relevant PI alone, and the candidate is to be approvedby the faculty meeting. Assistant professors hired without discussion among committee
members have no right to vote in the faculty meeting of the Department, nor to decide on
grading of students. As a matter of fact, such a system used to be common also in otherphysics departments in Japan, but is no longer the case in most physics departments.
This is especially so after the legal change from “Joshu” (assistant) to “Jokyo” (assistantprofessor), which took place in 2007.
Each research unit in the Department consists of a PI and at least one assistant professor. It often happens that one or more postdoctorals join the team. Such research
units may work most eﬃciently in certain experimental research in traditional condensed3

matter, for instance. In particle physics, on the other hand, a larger group consisting ofplural PI’s and assistant professors is more suitable to cooperate in international experimental projects. In theoretical research units, it can happen that the PI actually does
not impose any restriction to activity of the corresponding assistant professor. Then thecurrent system may have a good side to let young assistant professors concentrate mostly
on research. It may also encourage them to be promoted earlier in other universities;
internal promotion is forbidden for assistant professors in the Department. We have to
add that the assistant professorship is permanent in this Department as in other physics
departments.
Since the position is far from the ordinary junior professorship, however, their independent role in driving a new ﬁeld to the international forefront may be discouraged,
especially in experimental research. The selection decided by a single person also makes
it hard for the Department to strengthen certain directions by strategic employment.
The committee recommends the Department to seriously consider the merit and demerit of the current system, and employ a more ﬂexible system for extracting the best
performance of the talented young people in the long run. If the Department selects assistant professors by decision of the relevant committee, it would be natural to treat them as
junior professors instead of assistants. This change will not only give them self-conﬁdence
but also help make the Department more active and attractive for young students andresearchers.
Promotion and Recruitment
Most full professors are promoted internally in this Department. During the period from2013 to 2019, all promotions (ﬁve) were internal. For such a system to work, it is crucial
to judge the quality of candidates by careful comparison with other potential candidates
from outside. To be internationally active, the Department should pay attention to theright proportion of insiders and outsiders. Traditionally in this Department, however, theproportion of insiders, including those who spent some short time outside, is far dominant.
The committee recognizes that the dominance is mostly a result of fair competition, since
this Department has produced competent physicists over many generations. Nonetheless,the Department should care about diversity of professors by hiring more foreigners andfemales in order to enhance the activity, and to gain higher international recognition.
Relation to Industry and Contribution to Society
Advances in science and technology are enriching people’s lives, and at the same time, newsocial problems are emerging. The Japanese government has been advocating the Society
5.0 for sustainable development goals as a growth model for solving these problems andcreating the future. Participation from academic ﬁelds is also highly expected, and inparticular, it is required to contribute to solving social problems by implementing theresults of research on knowledge at universities into the real world through industryacademia collaboration.
Traditionally, industry-academia collaboration has been mainly based on technology.
It will be more important now to start collaboration from the stage of searching forproblems to be solved, and to collaborate at the organizational level by making full use of
the knowledge possessed by both industry and academia. In particular, physics is the most4

important foundation supporting scientiﬁc and technological innovation. In addition, theprogress of digital transformation, including AI, IoT, and quantum computers, has beenremarkable, and it has become possible to solve complex problems that could not be dealt
with before.
In this context, it is timely to have created the Institute for Physics of Intelligence inthe Department. The results of its activities are expected in the near future. It would
also be eﬀective to promote industry-academia collaboration using this institute as a hub.
At present, corporate sponsored research programs have been realized only by the one
from DAIKIN, and it should be further vitalized in the future. In order to achieve this,
it is necessary to make the intellectual foundation of the Department more widely known
to the public. It will be useful to consider upgrading of its website, and opening it to the
public through various means such as the open campus.
In addition, in an era of uncertain future, it is necessary to have human resources capable of tackling unknown issues in all ﬁelds without limitation to research and development.
In universities, the diversity of professors and students is important in this respect. It ishighly expected to bring up mentally tough students with intellectual skills of physicalthinking, who can powerfully lead the next generation.
The Department has an enormous store of intelligence. Utilizing this resource throughindustry-academia-government collaboration, we expect that some of the social problems
facing Japan may be solved ahead of the rest of the world. In this way the Department
may contribute to realization of a sustainable future.

3

Management

Budget and Space
The total amount of annual budget from the government has been reduced by 2% constantly in most public universities in Japan. This situation applies also to the Department.
It is very diﬃcult to maintain the high level of education and research without additional
income from other sources. The professors in the Department are very competitive in getting research funds from both governmental and non-governmental sources. As a result,the external scientiﬁc grants amount to about 150% of the operating budget from theuniversity. However, such external funds have strong restrictions to be used for education
and administration. Furthermore, there is always a ﬂuctuation in the amount of externalfunds, which makes it diﬃcult to build the long-range plan.
The ﬂoor space at present is only 67% of the allocated space according to the regulation
with the current number of faculty members and students. Obviously, the reasonable
space is a necessary condition for researchers. The students also beneﬁt from the space
to interact more spontaneously, have group discussions and brainstorming outside theordinary lectures. If not carefully attended, the leadership position of the Department
may erode, which will be huge loss for science in general, and for Japanese science inparticular. The committee supports the continuous eﬀort of the Department to improve
the situation.

5

Gender Equality and Diversity
The ﬁelds covered by physics are diverging. Correspondingly, more diversity in professors
and students should be necessary for harmonious development. A major indicator of thediversity is the number of female professors and students. The current status for female
professors at the Department is as follows: one full professor, one associate professor, andthree assistant professors. The presence of only one female professor in the Department is
far from enough, even in the current standard in Japan. The number of female students is
ﬁve in the senior (undergraduate) in 2019, which is the maximum in the past seven years.
In the newest enrollment to the graduate course, the number amounts to 11 including
three from abroad who entered in autumn. The Committee urges the Department toconsider seriously how to improve the situation. At the same time, the Committee hopesthat female students recognize the Department as a wonderful place to continue study
and research of physics further.
Another indicator of diversity is the number of international professors and students.
The current status for the number of foreign professors is far from all right; only one full
professor at RESCEU and one assistant professor at Institute for Physics of Intelligence.
We encourage the Department to improve the situation. A good sign is that the numberof foreign students in the graduate course increased during the past ﬁve years, and reached
to a maximum number (19) in 2019. We expect that the number will keep increasing.

INDIVIDUAL RESEARCH FIELDS
1

Elementary Particle Physics

The particle theory group consists of three units at present, two specializing in phenomenology and cosmology led by Prof. Takeo Moroi and Associate Prof. Koichi Hamaguchi, and the other one specializing in formal aspects of string theory and quantum ﬁeld
theory led by Prof. Yutaka Matsuo. They are the same members as those at the previous
external review in 2012, aside from moving out of Associate Prof. Yuji Tachikawa (2016)
and promotion of Matsuo from associate professor.
The phenomenology group is investigating physics beyond the standard model (BSM)
like supersymmetry and grand uniﬁed theory, together with particle cosmology as its
application or the clue for it. Their active work is still well recognized in the world.
While the supersymmetry (SUSY) is excluded in the expected 100 GeV regions in LHC
experiment and only little direct experimental data are available, they are working on
fundamental problems in particle physics using particle cosmology/astrophysics data. The
constraints on long-lived new particle masses and reheating temperature from the big-bang
nucleosynthesis have been being updated since 1995. Other constraints on possible axion
decay constant and on dark matter signal are obtained from the neutron star cooling.
Those limits are cited in Particle Data Book. Two phenomenology groups, each adopting ayoung assistant professor, have mutually a close interaction including direct collaborations
and keep active level of researches.
The formal theory group has been studying the universal symmetry structure in supersymmetric string and gauge theories hidden behind the celebrated Alday-Gaiotto-

6Tachikawa (AGT) relation, found by Tachikawa, which directly connects the partition
functions of four-dimensional (4D) SUSY gauge theory and 2D conformal ﬁeld theory.
Matsuo made a remarkable ﬁnding that the quantum toroidal algebra exists as a more
universal structure containing both Virasoro algebra and duality, which led not only theproof of AGT relation for some set-up but also the quantum version of Seiberg-Witten
curve.
The present form of only one group in the formal theory is too thin-layered to play sucha leading role in the ﬁeld in Japan as this group did so-far. The Committee recommends
to ﬁll one more group up as quickly as possible.
The communication between phenomenology group and formal theory group is stillpoor as the previous (2012) review pointed out. If the fulﬁllment of the theory grouphelps to improve the situation, this particle theory group will become a ﬁrmer central
base to lead the research and education of graduate students in Japan.
The experimental particle physics group consists of Profs. Hiroaki Aihara, Shoji Asaiand Associate Prof. Masashi Yokoyama; they are the same members as at the previous
external review aside from the retirement of Prof. Sachio Komamiya and promotion of
Asai from associate professor.
Asai is a world’s visible physicist and one of the important leaders of the Japaneseparticipation in ATLAS/LHC experiment at CERN. Also after the historical discoveryof the Higgs boson, they measured precisely the Yukawa- and gauge-coupling constants
and searched the SUSY particles excluding already wide low-energy regions which provide
important clues for the BSM physics.
Aihara continues the experiments in Belle and Belle II collaborations. Aside fromupdating B-B̄ asymmetry data further conﬁrming Kobayashi-Maskawa mechanism for
CP-violation, he searched new BSM physics performing precision experiments of rare/new
tau decay processes. He recently extends the horizon into astro-particle physics and plays
a co-PI of HSC dark energy survey at Subaru Observatory, beginning to obtain new data
there.
Yokoyama made important contributions to epoch-making observations in T2K experiments, the electron neutrino appearance and non-vanishing leptonic CP-violating phaseon 2σ conﬁdence level. He is now leading the project in hyper-Kamiokande experiment
as a steering committee member and technical coordinator.
While they all show their existence in each big international experiment, all thesethree groups are also doing small-scale experiments simultaneously; it is very good andessential for educating graduate students as it is one of the most important missions of
the Department. It is, however, a miracle for the present staﬀs, two professors and one
associate professor, to manage this situation. Performing three or four big international
experiments plus even more small-size ones is clearly an overload for them. The Committee thinks it better to reﬁll the professor position and simultaneously to reorganize theexperiment group to focus on fewer big-scale projects.

2

Nuclear Physics

The nuclear physics program at the Department is world class, both in theoretical andexperimental physics. Nuclear theory group is led by Prof. Kenji Fukushima, one of themost prominent nuclear theorists of his generation in the world. The hire of Fukushima

7

assures not only the Department’s leadership in QCD and hadron physics, which wasdesired in the previous review in 2012, but also in the emerging cross-disciplinary ﬁeldof chiral matter where the nuclear theory group successfully collaborates with condensed
matter and AMO colleagues within the Department and elsewhere.
The retirement of Prof. Takaharu Otsuka however left the Department with a gap in theimportant area of low energy nuclear physics and nuclear structure, where the Universityof Tokyo has traditionally been a leader, and where it has a thriving experimental program.
The recent approval by the Department to hire associate professor in the nuclear theory
group is commendable, and can solve the problem created by retirement of Otsuka, if thehire is made in the area of low energy nuclear physics.
Nuclear experiment group is led by Prof. Hiroyoshi Sakurai who is a pioneer in experimental studies of nuclear structure and neutron-rich nuclei. The group’s ground-breaking
research resulted in the discovery of anomalies in magic numbers of the neutron-richnuclei, marked by 2015 Nishina Memorial Prize awarded to Sakurai.
However the group does not currently have an experimentalist working in high orintermediate energy nuclear physics. This creates a disconnect to current large-scale
experimental eﬀorts at high or intermediate energy nuclear facilities both within Japan(J-PARC) and elsewhere, including Electron-Ion Collider at BNL, FAIR at GSI, NICA
at JINR. Therefore a new hire is desirable at the associate professor level in nuclear
experiment with a program at one of the high or intermediate energy nuclear facilities.
This experimental hire will match the theoretical work of Fukushima, and position the
Department as a leader in all important areas of modern nuclear physics.

3

Condensed Matter Physics

TheorySince the topics covered by condensed matter are wide-ranged, there are two contrasting
strategies for the structure of a theory group. For a small university, it is impossible tocover all relevant ﬁelds. Hence trying to form a single peak or two in the speciﬁc area will
be a natural choice. On the contrary, in a large organization such as the University ofTokyo, presence of many people in similar topics is unreasonable. In this sense, the present
structure of professors in condensed matter theory is well balanced. Namely, the important topics in condensed matter are basically covered; strongly correlated electrons (Prof.
Masao Ogata, Associate Prof. H. Katsura), energy band theory (Prof. Shinji Tsuneyuki),
statistical physics (Prof. Masahito Ueda, Prof. Synge Todo), and a newly developed ﬁeldof quantum information (Prof. Miho Murao). In statistical physics, the ﬂavors of Ueda
and Todo are rather diﬀerent; Ueda is particularly interested in fundamental aspect andoptical properties, while the main expertise of Todo is numerical calculation for model
systems. At the time of previous review in 2012, Ueda and Murao belonged to the groupof General Physics, and Katsura was not in the Department.
The wide research activity of Ogata in electronic properties in solids ranges from anumerical study for the Mott transition to topological aspect of Dirac electrons in bismuth.
His high level of research has led him to a leading ﬁgure in the academic community, andalso education of students. On the other hand, Katsura, who is by far the youngest
newcomer, has already made highly visible research in disordered topological systems andmany-body systems.

8

The modern version of band theory has been actively explored by Tsuneyuki, who has
developed a new method complementary to the standard density functional formalism.
He has also long been involved in the community of utilizing large computers such as one
at ISSP and the K computer.
For the study of quantum spins and highly-correlated electrons, numerical simulation
is a major tool, which bridges analytic theory and experiment in real materials. Todo
has developed not only simulation algorithms but provided open-source softwares, whichhave been widely used in the community.
In statistical physics, the most fundamental problem is the condition for the increaseof entropy. Ueda has challenged the long-standing problem of Maxwell’s demon from a
new point of view emphasizing the energy cost of information. He has thus developed a
new ﬁeld known as information thermodynamics.
Recent experimental progress has removed doubt on quantum mechanics at least on
consequences of its paradoxical prediction, which has plagued many physicists including
Einstein. Murao has been investigating the fundamental problems in quantum information
with a scope to connect to quantum computing and quantum cryptography. She has
proposed a protocol to estimate parameters of a quantum state in a precision-guaranteedmanner, which is beyond the scope of classical computations.
As described above, the professors of the theory group are all very active and playleading roles in the world-wide research. It seems, however, that the theory group has
not fully made use of the merit of size and diversity of ﬁelds. In order to bring about akind of fusion and integration, the Committee recommends to consider some device suchas informal report meetings to encourage interaction among members.
Experiment
The experimental condensed matter physics program consists of eight faculty groups,
with a healthy seniority distribution as exempliﬁed by the recent addition of three newgroups (Profs. Masamitsu Hayashi 2016, Kensuke Kobayashi 2019 and Satoru Nakatsuji
2019). The ﬁeld of condensed matter physics is vast – ranging from physics at extremely
low temperature, quantum Hall/topological phases of matter, correlated electron systems/high temperature superconductivity, novel magnetism, 2D/surface physics, device
physics and quantum technology. All major topics over the last ﬁve decades, as indicatedby the nine related Nobel prizes are touched by the groups. Advanced tools that are important hallmarks of successful condensed matter physics program, are also represented,
with terahertz (THz) spectroscopy and low temperature STM being examples.
The Department manages to cover impressive range of topics with a philosophy ofdiversity and presence. This ensures that the students get wide exposures to the fundamentals in their basic education and ample selections in their research topics. The
need to cover a wide range makes it a necessity to collaborate, both internally throughshared facilities (e-beam lithography, PPMS, LT-STM) and joint projects, and externallythrough Collaborative Institute of Trans-scale Quantum Science, joint appointments withother institutions and exchange programs like MPI-UBC-Tokyo exchange.
Fukuyama group covers the fundamental physics at extremely low temperature, suchas quantum liquid and quantum solid. Speciﬁc-heat experiment for 2D He on graphite
surface by the group succeeded to provide solid evidence for the quantum liquid crystal
representing anomalies at 1.4 and 0.9 K for 4 He and 3 He, respectively. This ﬁnding has

9

provided an existence of new phase on the state of 3 He as a two-dimensional matter. In
more recent years, the activity expands to synthesis and STM study of zigzag nano-ribbonsof graphene, with focus on spin-polarized edge states.
Hasegawa group has an active program in surface physics focusing on an exotic electronic and structural properties originating from the symmetry breaking at surfaces. The
group has enormous experience on the study of electronic properties of metallic atomic
layer at Si(111) surfaces. In recent years the group has found Pb and Tl on Si(111) exhibiting the property of the 2D Rashba superconductor where spin-orbit interaction plays
an important role, while the normal BCS type is expected for the case of In on Si(111). Superconductivity for single graphene bilayer with Ca/Li intercalation is conﬁrmed as well.
The group has unique technique of micro-four-point probes, combining with STM/STS
and ARPES to conﬁrm the local property of transport, and the heterogeneous physicalproperty at surfaces.
Okamoto group focuses on the physics of two dimensional systems, such as 2D electron
gases in semiconductor heterostructures and cleaved surfaces. The group explores bothtransport and STM/STS experiments. In addition to the traditional topic of quantum
Hall Eﬀect, the group’s activity expands to 2D Rashba superconductor, and demonstrated
a new type of superconductivity induced by magnetic ﬁeld.
Hayashi group studies spin-conversion eﬀects in spin-orbit materials, including spin HallEﬀect, spin Nernst eﬀect, and anomalous Seebeck eﬀect, chiral magnetism, Dirac materials
and current induced domain wall motion. They have found certain heterostructures thatenable fast motion of domain walls via the Dzyaloshinskii-Moriya interaction. This ﬁnding
is being applied to the domain-wall (or racetrack) memory.
Kobayashi group covers device physics, with focus on the non-trivial behavior of
charge/spin in non-equilibrium when the states are subjected to ﬂow and/or change.
In addition to unique opportunities to study “on-chip” condensed-matter physics, thisactivity is at the heart of electronics, chemical reactions and life. Taking advantage ofrecent progresses in materials science and nano-technology, the group actively studies
spintronics, strongly correlated electron system, and molecular electronics.
Takagi-Kitagawa group has an active program in material physics with focus on searching and studying material platforms to realize novel physics. This includes exotic phasesof correlated d-electrons in novel transition metal compounds with strong Coulomb repulsion and strong spin-orbit interaction. An example is their discovery of the spin-orbital
Mott state in Sr2 IrO4 where the 5d5 of Ir conﬁguration has the eﬀective spin Jeﬀ = 1/2.
The group has a string of important discoveries: spin-orbital entangled quantum liquidwith Jeﬀ = 1/2 on 2D honeycomb lattice H3 LiIr2 O6 ; correlated Dirac semimetals made of
4d and 5d electrons; and excitonic insulator Ta2 NiSe5 .
Nakatsuji group has an active program at the rich interface of superconductivity, topological materials, quantum spin liquid, spintronics and energy harvesting. Its activity
expands from fundamental condensed matter physics to application of these novel phenomena and devices. A notable success is the pioneering contribution on the magnetic
Weyl fermion in antiferromagnet Mn3 Sn, and other important progresses by measurements of anomalous Nernst eﬀect, magneto-optical Kerr, and magnetic spin Hall eﬀect inthis compound.
Shimano group has an active search program using laser and THz spectroscopy tounderstand and light-control/create macroscopic quantum states in matter. This is an
excellent combination of important conceptual issues and novel experimental techniques.

10Notable achievements include discovering Higgs modes in superconductors, realizationof electron-hole BCS-like states in a semiconductor, optical quantum Hall eﬀect in 2D
electron gas and graphene.
Over all, this is a highly successful program, with the groups very productive andglobally recognized. Some issues encountered by this group are common among diﬀerent
ﬁelds – gender, internationalization, but others may require speciﬁc attention – such as
shared facility and theory/experiment balance among the student body.

4

Astrophysics

There are ﬁve professors and four associate professors at the Department and ResearchCenter for the Early Universe (RESCEU). Each of them, as a principal investigator (PI),is responsible for a research unit with assistant professors, graduate and undergraduate
students, and other staﬀ members. Their research covers the entire area of astrophysics,
both theoretical and observational, from the solar neighborhood of the present Universeto the farthest reaches and to the ﬁrst moment of the Universe. The overall activity of
the astrophysics group is of the highest quality competing with the world.
All the professors have demonstrated their expertise for many years, contributing to theadvancement of their respective research ﬁelds, thus achieving renown and receiving highreputation. They play principal roles in their research communities, also enlightening
the public. Associate professors are relatively young, but are all established front-line
researchers with brilliant expectations.
It deserves high praise that the astrophysics group has expanded its research areas to
new ﬁelds such as exoplanets (including their formation sites and astrobiology) and CMB(cosmic microwave background) experiments. Also noted is the increase of researchers
in the gravitational-wave experiments, of which the Department has a long history. The
Committee admires the eﬀorts made by the Department and RESCEU to take such new
research areas in by closely observing the forefront of astrophysics.
The details of each research group (or team) are given below.
Department of Physics
The theoretical astrophysics group consists of Profs. Yasushi Suto and Naoki Yoshida ascore members. Their research areas include observational and computational cosmology,
ﬁrst stars and blackholes, and exoplanets.
Suto’s research is primarily on exoplanets, leading one of the RESCEU projects (seebelow). One of his recent works is the discovery of an exoplanetary system where a planet
has a signiﬁcantly diﬀerent direction of orbital angular momentum with respect to thespin of the central star. He supervised eight PhD students in 2013 - 2019. He has been
inﬂuencing the public by writing articles for major Japanese newspapers.
Yoshida received Japan Academy Award and JSPS Prize in 2017 for his numericalsimulations of structure formation in the early universe. One of his recent interests is theapplication of machine learning to cosmology. His team applied the technique to classify transient objects in Subaru HSC images, automatically identifying many supernova
explosions with diﬀerent types. He supervised eight PhD students in 2015 - 2020.

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The experimental astrophysics group is comprised of Prof. Satoshi Yamamoto and
Associate Profs. Aya Bamba, Masaki Ando, and Akito Kusaka as core members. Theirresearch areas cover a wide range of observational astrophysics: the interstellar matterand formation of stars and planets, X-ray emission from supernova remnants and clustersof galaxies, gravitational-wave, and the cosmic microwave background radiation.
Yamamoto’s interest is in astrochemistry. His recent work includes the discovery ofchemical diversity in star and planet forming regions, showing a new picture of chemical
evolution in the star and planet forming process. He is a leading ﬁgure of radio astronomy
communities in Japan and in the world, essentially contributing to the success of world
frontier large projects like ALMA.
Bamba is an X-ray astrophysicist. She contributed to the Hitomi mission and obtained
high spectral resolution X-ray data of the Perseus cluster, measuring for the ﬁrst time its
Ni/Fe ratio, an important parameter to characterize the nature of the cluster of galaxies
to infer the chemical enrichment history of the Universe. Her team is instrumental in the
XRISM mission to be launched in 2022.
Ando’s research ﬁeld is gravitational-wave. He is an executive member of the KAGRA
collaboration playing a key role for its planning, construction, and commissioning, withhis team contributing to the main interferometer system. The research activity of his teamis diverse, including smaller scale experiments on gravitational-wave detection technique.
He supervised nine PhD students in the last eight years.
Kusaka’s research target is CMB polarization. His latest publications include the ﬁrst
evidence of correlated gravitational lensing between the Polarbear CMB measurement
and Subaru HSC data. His team is a member of the Simons Observatory collaboration,
contributing to the hardware development crucial to its operation and success.
Research Center for the Early Universe (RESCEU)The RESCEU, also called the Big Bang Center, consists of Profs. Jun’ichi Yokoyama andKipp Cannon, and Associate Prof. Toshikazu Shigeyama as core members, with Suto in
the Department as director. In addition, the RESCEU has nine aﬃliated professors andassociate professors belonging to the Department of Astronomy, Institute of Astronomy,
and Department of Earth and Planetary Science.
In 2016, the RESCEU reorganized its research projects into the following three:(1) Evolution of the Universe and cosmic structure;(2) Gravitational-wave astrophysics and experimental gravity; and(3) Formation and characterization of planetary systems.
It hosts frequent international symposia and annual summer schools, facilitating its visibility from foreign and younger generation researchers.
Yokoyama leads the ﬁrst project (1). His main research interest is theoretical studiesof the early Universe (inﬂation) and gravitational wave. He supervised nine PhD students
in 2012-2019, publishing 59 research papers. For many years, he has been contributing
to the Association of the Asia Paciﬁc Physical Societies (AAPPS) as editor and currently
serves as president.
Cannon leads the second project (2), focusing on detection and interpretation of gravitational wave. His team played a major role in the discovery of GW170817, the ﬁrst
observation of a neutron star collision, and contributed to developing the infrastructure

12required to incorporate KAGRA into the international network of gravitational-wave detectors.
Shigeyama, member of the ﬁrst project (1), leads theoretical studies of supernova
explosions, nucleosynthesis, and chemical evolution of galaxies. He suggested that rare
neutron star mergers are the main site of the rapid neutron-capture process (r-process)to create elements in the Universe. He predicted the detection of gravitational wave
from neutron star mergers with current detectors before the neutron star merger event
GW170817 was detected.
The third project (3) was led by Suto (see above).

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Biophysics

Biophysics group used to be a part in the program of General Physics before 2016. The
Committee congratulates the Department on the successful action to establish biophysics
as an independent and important group.
The biophysics group was consolidated through establishment of Universal Biology Institute (UBI) in the Graduate School of Science. By the end of 2016, the UBI was further
extended to Collaborative Research Organization for Universal Biology Institute (Collaborative UBI) by including research groups in Komaba campus. The name “Universal
Biology” comes from intention to regard the life system as a kind of universality class innature. The UBI performs theoretical and experimental researches to resolve the fundamental question of life from the viewpoint of physics. To promote the research further,
the UBI has contracted with Quantitative Biology Center in Riken. As a whole, scientiﬁc
activities in biophysics group are excellent. The cooperation between theoretical physics
and experimental biology is quite successful.
The following is the report of the research by the members of the UBI at the Department. The UBI consists of Profs. Chikara Furusawa and Sosuke Ito as full time members,
and Profs. Hideo Higuchi, Yasuyoshi Okada and Akinao Nose as concurrent members.
Okada belongs, besides the School of Science, to the School of Medicine in the Universityof Tokyo, and also to RIKEN.
Furusawa made an important contribution to evolutionary biology on the basis of theoretical and experimental studies of Escherichia (E.) coli. He has contributed to show
evolutionary robustness causes reduction which restricts possible phenotypic changes in
response to variety of environmental conditions. A reduction in high-dimensional phenotypic states to a few degrees of freedom is essential to understand biological systems.
He found that the evolutionary changes are constrained to the changes along a onedimensional major axis, within a huge-dimensional state space.
Ito has been discussing connections between thermodynamics and information theory
which are applicable to biochemical systems. He and his group applied the generalized
second law to the biochemical signal transduction of E. coli bacterium chemotaxis. In thisapplication, they focused on the information ﬂow from the kinase activity (CheA) andthe methylation level of the receptor in E. coli cell. As a result, they could quantitatively
show that the generalized second law gives the informational bound of the robustness ofthe sensory adaptation.
Higuchi, who is the director of UBI, and his group observed the walking of single motor
molecule for the ﬁrst time, and formulated its mathematical model of the movement13

of protein. Cytoplasmic dynein is a molecular motor moving toward the minus end of
microtubules. The swing of the dynein linker is supposed to be crucial for walking ofdynein. There was no measurement of the displacement generated by the swing. Higuchi
investigated the displacement of microtubule driven by the swing of single molecules ofsingle-headed dynein by optical tweezers. The displacement of swing by dynein is close totubulin spacing in microtubule, indicating that dynein is able to walk only by the swingof dynein lever.
Okada and his group are trying to understand the dynamics of the protein molecules
working in the living cells, especially motor protein undergoing the intracellular transport. They observed dynamic processes of ﬁne structures in the living cells, using their
original device which is called the Spinning-Disk Super Resolution Microscope (SDSRM).
They have identiﬁed that the microtubles, the rail polymer for the transport, can taketwo diﬀerent conformations. It was disclosed that the binding of kinesin-1, the motor
protein for the axonal transport, triggers the cooperative conformational changes in the
microtubule, which serves as the road sign for the following kinesins. Axonal transport isessential logistics in neurons and is related with Alzheimer’s disease.
Nose is interested in mechanisms of how the neural circuits develop and function to
generate speciﬁc behavior, by using the nervous system of the fruitﬂy called Drosophila
as a model. In this organism, the relative simplicity and highly sophisticated genetic
techniques allow one to identify and manipulate speciﬁc neurons. To dissect the circuitlogic, Nose and his group use calcium imaging to record the activity of speciﬁc populationof neurons. By using optgenetics, they manipulate the activity of speciﬁc neurons withlight at high resolution. Connectomics, which makes reconstruction from 3D images ofelectron microscopy, allows determination of neuronal wiring diagrams at the cellular andsynaptic level.

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General Physics

General Physics
Important changes have occurred in “General Physics” since the last review in 2012. Reﬂecting the report of the 2012 review, also following the 2005 review, the Department
has strengthened biophysics as one of their major branches. Simultaneously, topics suchas “ultracold gases and information thermodynamics” and “quantum information” arenow transferred to the program of “Condensed Matter Physics”. Another point to noteis the weakening of the activity in atomic, molecular and optical (AMO) physics, which
was carried out by Profs. Makoto Gonokami, Masahito Ueda, and Hirofumi Sakai. Since
Gonokami is now the president of the University, his commitment to experimental research cannot be the same as before. If the presence of “General Physics” is regarded
as eﬀective in coping with new tidal changes in physics, the Department should consider
next candidates to succeed the tradition and pursue further development.
Atomic, Molecular and Optical (AMO) physics
Sakai has developed novel technique to align and to control the orientation of molecules
at dilute condition. His unique technique to realize molecular orientation under the laserﬁeld-free condition is to combine electrostatic and intense nonresonant shaped laser ﬁelds

14with a slow turnon and a rapid turnoﬀ and wherewith succeeded to maintain molecularorientation in nano-second time scale. As suggested in the 2012 review, the technique
has been applied, for example, to the study of stereodynamics of dissociative ionization of
OCS molecules where the orientation dependence was observed. Considering the future
development of free-electron laser systems, his physics and technology are expected todevelop toward complex molecular systems.
Plasma Physics
Prof. Yuichi Takase is one of the international leaders in fusion plasma physics. The research is carried out using the spherical Tokamak device, TST-2, at Kashiwa campus. It is
important for research and human resource development that his group has its own experimental equipment and can freely conduct experiments by driving it by itself. Utilizing thisadvantage, the group is investigating on issues that complement large-scale experimental devices such as ITER (the International Thermonuclear Experimental Reactor). At
present, plasma current ramp-up using the lower-hybrid wave (LHW) without the central
solenoid (CS) is being investigated, with the aim of realizing a compact Tokamak device
by removal of CS. It is also expected that the group will provide scientiﬁc leadership in theinternational collaboration between Japan and Europe at the JT-60SA. The leadershipwill promote Japan’s fusion strategy in ITER and the subsequent demonstration reactor(DEMO), and contribute to the realization of fusion.
Experimental Statistical Physics
Prof. Kazumasa Takeuchi leads an active research program on statistical physics of noneequilibrium systems by using soft matter (liquid crystal, colloids, granular systems, etc.)
and living matter (mostly bacteria), in search of large-scale and universal phenomena.
This includes topological defect turbulence of liquid crystal, order formation in bacteria
turbulence, statistical physics of dense bacteria suspensions. The program boosts synergetic activities of simulations and experiments. For example, they have a string ofbeautiful experiments that uncovered the Kardar-Parisi-Zhang (KPZ) class of physics,
providing a bridge to KPZ exact solution. For this work, Takeuchi received the MEXT
Young Scientist Prize in 2018.
Laser Physics
Prof. Junji Yumoto serves as a director of the Research Institute for Photon Science andLaser Technology since 2017, providing an important technical platform for the physics
research in the ﬁeld within the University of Tokyo. The research in the lab is undercontinuing advice of President Gonokami and in collaboration with the Institute.

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