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The National Center for Theoretical Sciences Physics Division
Chong-Sun Chu
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The National Center for Theoretical
Sciences Physics Division

CHONG-SUN CHU
NATIONAL TSING-HUA UNIVERSITY, TAIWAN

HISTORY

The National Center for Theoretical Sciences (NCTS) was established in August 1997, by the Ministry of Science and Technology (MoST) of Taiwan. The center has a Department of Mathematics and a Department of Physics. For the first 18 years, the center was located on the campus of National Tsing Hua University (Figure 1) and was administered jointly by National Tsing Hua University and the adjacent National Chiao Tung University.

In response to the needs of the community, sub-projects at the National Taiwan University (NTU) and National Cheng Kung University (NCKU) were added to the center's operations from 2002-2014. This arrangement of NCTS, together with the implementation of the Focus Group Program, greatly broadened and strengthened the interaction and collaboration among domestically based scientists, which were the medium-term goals set up for that period of time.

In 2013, an international review on NCTS was conducted. A restructuring of the center, including the discontinuation of the operation of sub-projects, together with a significant increase in funding, was recommended. A national call for competition was made in the beginning of 2014. As a result, the Department of Physics of NCTS remained with National Tsing Hua University, and the Department of Mathematics is now hosted by National Taiwan University. The two divisions operate separately to serve their separate communities and cooperate on some of their national programs.

The division of physics is committed to contributing to the advancement of frontier research in physics. It has the goals to act as an effective platform to stimulate and to enhance interaction and collaboration among researchers; to empower talented students and postdoctoral researchers to make significant contributions in the frontier of research subjects; to serve as an efficacious channel to network researchers with other scholars and preeminent institutions abroad so as to explore new frontiers in physics research and innovation; and to enhance the extent and breadth of interdisciplinary research, and to promote collaboration with scientists in the experimental fields.

 



Fig. 1: NCTS is located near Kum Ming Lake on NTHU's campus.

SCIENTIFIC ACTIVITIES

High Energy Particle Physics

It is clear that the Standard Model of particle physics is an effective theory; however, despite its great success, there remains a great amount of new physics waiting to be explained and discovered. One of the most important questions is the origin of mass, which may be explained by electroweak symmetry breaking (EWSB) in particle physics. Nevertheless, the internal mechanism of EWSB is largely unknown. It is therefore important to further investigate all the basic properties of the observed Higgs boson in order to better understand the true nature of the electroweak symmetry breaking. This includes: precise measurements of EWSB couplings to gauge bosons and fermions; the search for nonstandard decay modes of the Higgs boson, in particular the invisible mode, decays into other light Higgs bosons, etc.; Higgs boson pair production, which is the most direct probe of the self-coupling of the Higgs boson; and the search for heavier Higgs bosons and scattering of the longitudinal vector bosons. Another urgent problem in particle physics is to understand the nature of dark matter. Although the existence of dark matter is favored by gravitational evidence, its particle identity is still unknown. All we know is that a significant portion of 22% of the total energy budget of the Universe is composed of dark matter. Does it purely involve gravitational interaction? Is it a weakly interacting massive particle (WIMP)? One should study both the particle and non-particle physics aspects of dark matter without any prejudices. There is also a theoretical problem – the gauge hierarchy problem – which is related to the naturalness of the Higgs boson, which motivates a large number of models beyond the standard model. NCTS researchers attack these problems from different and related frontiers.

String Theory, Quantum Field Theory and Gravity

One of the most important questions in theoretical physics since Einstein's discoveries is the fundamental origin of spacetime. In fact, simple analysis involving quantum mechanics and general relativity already indicates the non-trivial nature of spacetime at the quantum level. The breakdown of the classical concept of spacetime is also seen in, for example, singularity of blackholes and the Big Bang singularity of the Universe. Recently, there has been much activity and progress in this direction, most notably in the studies of AdS/CFT, where the bulk of spacetime is not fundamental but emerged as properties of holographic field theory. The studies of AdS/CFT have stimulated many activities in the study of the properties of supersymmetric Yang-Mills (SYM) gauge theory, with the important discovery/conjecture of integrability in certain sectors or limits of the theory. More recently, people have turned their attention to the studies of the scattering amplitudes in supersymmetric Yang-Mills, and more generally in quantum field theories and string theory. This has risen to prominence due to its far reaching implications for high energy physics, ranging from the more phenomenological aspects of precision predictions in the Standard Model, necessary for searches of new physics in collider physics, to the more formal aspects of short-distance behavior of gravity scattering amplitudes, which hold key insights to properties of quantum gravity. It has also been conjectured that some of the very simple and elegant properties of amplitudes may lead to a completely new conceptual reformulation of quantum field theory, where spacetime and locality would emerge, rather than be assumed in advance as in usual Lagrangian field theory. Researchers at NCTS are actively pursuing a number of theme research ideas.

Condensed Matter Physics

Spintronics, Topological and Strongly Correlated Physics

Spintronics generally aim at both achieving a more refined control of the (electron) spin and also at engineering interesting quantum states of matter. One such topic is the use of strain, multilayer structures, and/or chemical functionalization to tailor, at the atomic level, the electronic and magnetic properties of two-dimensional materials like graphene and the semi-conducting transition metal dichalcogenides (TMDCs). On this topic, we have only started to 'scratch the surface' of the possibilities offered by these new materials for the creation of topological insulators. The latter are the most interesting and possible systems for the applications. Thus, a major current challenge is to find new and cleaner materials exhibiting robust quantum spin-Hall and anomalous Hall effects at higher and higher temperatures. NCTS researchers have been collaborating with experimentalists closely, and have not only predicted materials from first principles or ways to engineering "topological devices" based on conventional insulators like the TMDCs, but have also carefully studied and classified the different sources of (back) scattering at the metallic one-dimensional edge states of such insulating materials.

Novel 2D Materials

In recent years, many low-dimensional materials were found to exhibit a number of intriguing emergent phenomena and thus they have exciting potential for technological applications. For example, when bulk layered -group VIB transition metal dichalcogenides, such as 2H- MoS2, is cleaved down to a single monolayer, the materials become a direct bandgap semiconductor due to the lack of interlayer interaction, leading to potential applications in, e.g., optical and electro-optic devices with efficient light emission. Furthermore, due to its broken spatial inversion symmetry, the MoS2 monolayer also exhibits a number of novel properties, such as the valley Hall effect, piezoelectric properties and second-order nonlinear optical properties, thus promising entirely new paradigms for novel technologies such as valleytronics. Another prominent example is the metallic interface between two insulating oxides such as SrTiO3 and LaAlO3. Both bulk SrTiO3 and LaAlO3 are non-ferroelectric insulators. However, their interface becomes conductive and this fuels the modern quest for electronics based on correlated electrons in oxides, and collective characteristics of superconductivity and ferromagnetism. In order to exploit these novel phenomena, researchers at NCTS have strived to understand the mechanisms that control the physical properties of the emergent materials by performing powerful ab initio quantum mechanical calculations to investigate the microscopic mechanisms of these fascinating phenomena.

AMO and QIS

Quantum gas (or ultracold atoms/molecules) is a fascinating new field, as it is the interplay between condensed matter theory, quantum information, and atomic-molecular-optical experimentation. The large degrees of freedom to manipulate atoms and the laser field (through quantum statistics, spin, spatial dimensions, interaction and temperature, etc.) make it possible to investigate novel many-body physics as well as quantum information technology. Recent technological advances have created the possibility to build very small electronic and photonic devices at the atomic scale. Therefore, precisely controlling realistic open quantum systems is one of the most important and timely issues in the field of QIP. Furthermore, in the development of quantum information sciences, quantum entanglement has played a key role in many different problems. With the advances of ultra-fast-optical probing technology, experiments on photosynthetic 'Light Harvesting Complexes' (LHC) and their constituents have indicated that quantum coherence may play an important role in one of the most fundamental and important of biological processes.

 



Fig. 2: A group photo from the celebration of the 20th anniversary of NCTS.

Soft Matter, Biophysics and Interdisciplinary Subjects

Active matters are made of particles that are driven by chemical energy of (for example) ATP hydrolysis. Motor proteins, specially designed colloids, bacteria, cells in biological tissues, even birds and fish are examples of such "particles". The emergent behavior of these systems give us cell cytoskeletal dynamics, pattern-forming active colloidal suspensions, swarming bacteria, tissue physiology, and dynamics of bird flocks and fish schools. The study of active matter can be viewed as the study of complex physical systems. At NCTS, a number of key questions are probed, including bifurcation, or non-equilibrium phase transitions; self-organized patterns and self-organized movements; and the roles of fluctuations in these systems.

SCIENTIFIC PROGRAMS

Topic Programs at NCTS

The purpose of the Topic Program at NCTS is to promote the development of research, to encourage collaboration, and to foster the generation of innovative new ideas and initiatives. A week-long workshop focused on a few advanced topics, or a well-developed program spanning a few weeks and covering a number of central and related topics of the subject, are some examples of supported programs.

 



Fig. 3: A group photo from the East Asia Joint Workshop on Fields and Strings.

Workshops

We organize about 30 international workshops every year, which are selected from applications by our scientists and group coordinators. We also organize about five international joint meetings each year. Over 300 seminars on various subjects take place each year. These activities at NCTS have helped in maintaining a vibrant program of research for the scientific community in Taiwan and abroad.

We also organize a number of rapid response workshops, where the goal is to respond actively and quickly to any sudden development in a field, and where the development has significant potential for impact. Examples of rapid response workshops include the Rapid Response Workshop on 750 GeV Diphoton Resonance (2016), and the Rapid Response Round Table Discussion Meeting on Excess of Electron-Positron Cosmic Rays from DAMPE (2017).

Visitor Programs

The Visiting Professors / Visiting Scholars Program is designed for distinguished scholars from abroad to make regular visits to NCTS in order to conduct collaborative projects with NCTS scientists and research staff members. In the previous five years, the center has had an average of 200 short term visitors spending, on average, about 7 days per visit; and about 14 long term visitors per year, spending, on average, about 50 days per visit.

 



Fig. 4: Photo of Prof. Duncan Haldane giving lectures.

The Affiliated Scientists Program at NCTS is used for domestic researchers to visit the center in order to interact with the resident scientists. Long term stays, such as spending one's sabbatical leave, are also highly welcome.

 

Year

Lecturer

Lecture Title

2010

Don Zagier

Modular Forms, Mock Theta Functions, and Black Holes

2011

Gerhard Huisken

Mean Curvature Flow in Geometry and Physics

2012

Fanghua Lin

Theory and Application of Homogenization

2013

Jean-Pierre Serre

Modular Forms Mod 2 and Galois Representation

2014

Manjul Bhargava

The Average Rank of Elliptic Curves

2015

Eric Cornell

Particle Paleontology: Looking for Fossils of the Early Universe inside Electrons

2016

Bei-Lok Hu

Quantum Information in the Face of Gravity - Decoherence and Entanglement

Horosi Ooguri

Entanglement and Geometry

2017

Takaaki Kajita

Gravitational Wave

Shing-Tung Yau

Geometry and Gravity

2018

Misao Sasaki

Gravitational Wave Cosmology

Carlo Beenaaker

Majorana Edge Modes in Topological Superconductors

2019

F.Duncan Haldane

Topological Quantum Matter, Entanglement and Revolution the Second Quantum

 

Distinguished Lecturers

NCTS invites distinguished scholars to give a lecture or a lecture series on a specific topic of research or a topic of general interest. A list of recent distinguished lectures is given below:

 



Fig. 5: The 2016 NCTS Distinguished Lecture Series. From left: Hirosi Ooguri, Takeo lnami, Chong-Sun Chu, and Bei-Lok Hu.

Thematic Research Groups

Focused research groups at NCTS are formed by a team of active home researchers with complementary areas of expertise, sharing the primary goal of solving some of the outstanding problems of their particular subject. Typical group activities consist of regular group meetings, seminars, workshops and conferences, hosting visitors, etc. A list of current thematic research groups can be found in Table 1, below.

Interdisciplinary Research Groups & Experimental Collaboration Groups

The center operates the Experimental Collaboration Program (ECP) and the Interdisciplinary Research Program (IDP) to enhance collaboration between theorists and experimentalists, and to promote intellectual exchange and cooperation between researchers in traditionally different disciplines. In these programs, NCTS acts as an effective platform to bring together researchers with complementary scientific approaches and backgrounds, in order to foster closer cooperation and collaboration of researchers. A list of the current groups at ECP and IDP can be found, respectively, in Table 2 and Table 3, below.

 

Table 1: Thematic Research Groups at NCTS.

TG

Program Title

TG1

Particle Physics

TG2

Dark Physics of the Universe

TG3

Strings

TG4

Topology & Entanglement in Quantum Many-Body Systems

TG5

Complex Systems

TG6

Quantum Information Science and Quantum Control

TG7

Quantum Gases

TG8

Topology & Strong Correlations in Quantum Many-Body Systems

TG9

New Quantum Materials and Transport

Table 2: The Experimental Collaboration Program: Groups at NCTS.

ECP

Program Title

E1

Quantum Optics and Quantum Manipulation of Ultra cold Atoms

E2

Light Dark Matter

E3

LHC Experimental/Theoretical Exploration

E4

Gravitational Wave and Numerical Gravity

Table 3: The Interdisciplinary Research Program: Groups at NCTS.

IDP

Program Title

I1

Multiscale studies for complex materials, catalysts, and biological systems - theoretical and computational approaches, and experimental stimulus

I2

Geometry, Topology and String Theory

I3

Complex Systems and Mathematical Biology

 

Chong-Sun Chu is the director of the physics division of the National Center of Theoretical Science (NCTS) and a professor of physics at National Tsing-Hua University (NTHU), Taiwan. He received his BSc in physics from the Chinese University of Hong Kong in 1991, and his PhD in physics from the University of California, Berkeley in 1996. He joined the faculty of the Department of Mathematical Sciences of Durham University, UK in 2000 and moved to NTHU in 2012. His research area is in string theory and quantum field theory.

 
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