# Seminar Report

## Information Theory SG Seminar by Dr. Qibin Zhao on July 28, 2021

2021-08-02

In the Information Theory SG seminar on July 28th, Dr. Qibin Zhao gave us an exciting talk about the basics and applications of tensor networks (TNs) in machine learning. His talk was divided into three parts, (i) tensor methods for data representation, (ii) TNs in deep learning modeling, and (iii) frontiers and future trends. In the first part, he started with a graphical introduction of tensors and dimension reduction methods. He then presented the important question of how the imperfect data represented by tensors can be completed using the low-rank approximation, and introduced several possible approaches with impressive examples. Here he explained the TNs and decomposition methods in detail using diagrammatic notations, which can concisely express the tensor operations such as the contraction. In the second part, he talked about the useful application of TNs to model compression in machine learning. He illustrated the ways to represent the neural network model by tensors and to learn the weights through the contraction. Interestingly, the density matrix renormalization group (DMRG), which was originally proposed in the quantum physics field, may be used as a learning algorithm. In the last part, he showed an overview of recent topics on TNs and machine learning such as TNs for probabilistic modeling and supervised learning with projected entangled pair states (PEPS). Intriguingly, the topological structure of TNs can be optimized for a given image, and the learned topology significantly depends on the input data and is more complex than conventional simple structures such as lines, trees, or cycles. The clearly structured talk took us from the basics to the cutting-edge subjects, and there were many questions and discussions during the talk. We are deeply grateful to Dr. Qibin Zhao for his excellent talk on the fast-growing interdisciplinary field.

Reported by Kyosuke Adachi

Overview of Tensor Networks in Machine Learning

July 28 at 13:30 - 14:50, 2021

# Seminar Report

## iTHEMS Biology Seminar by Prof. Mayumi Seto on July 29, 2021

2021-07-30

On July 29th, Mayumi Seto (Nara Women's University) gave a talk on the application of thermodynamics to microbial modeling. She first introduced some important concepts of adenosine tri-phosphate (ATP), its synthesis in biology, and chmotrophic interactions between microorganisms. She then moved on to mathematical models explicitly incorporating energy flows in the microbial interactions. She finally gave implications from her work for future and ongoing studies, and after the talk we casually discussed her exciting projects.

For me, she was the person whom I met on the very first visitation at Kyushu University in 2009 when I was, as an undergrad student at another university, yet unsure to start my Ph.D. at Kyushu University or not, and I'm sure her kind and encouraging guidance was one of the decisive factors for me being here as a researcher. Thanks again for the fantastic talk, Mayumi!

Reported by Ryosuke Iritani

Application of bioenergetics to microbial modeling

July 29 at 10:00 - 11:00, 2021

# Upcoming Events

## Seminar

### From Yang-Mills theory to enumerative geometry on Calabi-Yau 4-folds

August 6 at 16:00 - 18:10, 2021

Dr. Yalong Cao (Research Scientist, iTHEMS)

Yang-Mills theory was studied from mathematical perspectives in the 1970s by Atiyah and his collaborators (notably Drinfeld, Hitchin, Singer). Subsequent breakthroughs were made on dimensions 3 and 4 by Floer and Donaldson (based on deep analytic results obtained by Uhlenbeck and Taubes) in the 1980s. In 1996, Donaldson and Thomas proposed to study Yang-Mills theories on dimensions bigger than 4. In higher dimensions, the analytic method is limited and algebro-geometric method is heavily used instead. This powerful tool usually enables us to compute partition functions and lead to amazing links to other invariants in enumerative geometry, e.g. Gromov-Witten and Gopakumar-Vafa invariants. In this talk, I will review some of these inspiring stories and discuss how my works on Calabi-Yau 4-folds fit into them.

Venue: via Zoom

Event Official Language: English

## Seminar

### Application of AdS/CFT to non-equilibrium phenomena in external electric fields

August 16 at 13:00 - 15:00, 2021

Dr. Shunichiro Kinoshita (Collaborative Researcher, Faculty of Science and Engineering, Chuo University)

The AdS/CFT correspondence is a useful tool for studying strongly-coupled gauge theories.

According to this correspondence, the D3/D7 brane system in string theory is one of the simplest toy model dual to supersymmetric QCD-like gauge theory.

In the dual field theory, the mesons, i.e., the quark-antiquark bound states are stable in vacuum when the quark is massive, while the dielectric breakdown occurs by pair production of quark-antiquark under strong electric fields.

In this talk, I will review a series of our works of D3/D7 systems and show time-dependent, non-equilibrium phenomena driven by external electric fields such as suddenly increasing or rotating electric fields.

Venue: via Zoom

Event Official Language: English

## Workshop

### RIKEN-Vancouver Joint Workshop on Quantum Computing

August 24 - 25, 2021

The main aim of this workshop is that the quantum people in RIKEN (iTHEMS and RQC) and Vancouver (Quantum BC) get together online to discuss scientific activities and explore future collaborations.

Program:

August 24, 2021 (8:30am - 1:00pm) Tokyo

August 23, 2021 (4:30pm - 9:00pm) Vancouver

Tetsuo Hatsuda (iTHEMS): Welcome + iTHEMS overview

Yasunobu Nakamura (RQC): RQC overview

Lukas Chrostowski (UBC): Quantum BC overview

Shunji Matsuura (1QBit): Accurate state preparation on noisy quantum devices

Olivia Di Matteo (UBC): Operational, gauge-free quantum tomography

Yasunobu Nakamura (RQC): Towards superconducting quantum computing

Jason Chang (iTHEMS): Improving Schroedinger equation implementations with gray code for adiabatic quantum computers

Robert Raussendorf (UBC): Computationally universal phase of quantum matter

Akira Furusawa (RQC): Large-scale quantum computing with quantum teleportation

August 25, 2021 (8:30am - 1:30pm) Tokyo

August 24, 2021 (4:30pm - 9:30am) Vancouver

Etsuko Itou (iTHEMS): Digital quantum simulation for screening and confinement in gauge theory with a topological term

Joe Salfi (UBC): Engineering long coherence times of spin-orbit qubits in silicon

Seiji Yunoki (RQC): Quantum simulations for quantum many-body systems: Variational quantum algorithms and beyond

Takumi Doi (iTHEMS): Hybrid quantum annealing via molecular dynamics

Drew Potter (UBC): Simulating highly-entangled matter with quantum tensor networks

Seigo Tarucha (RQC): High-fidelity quantum gates in silicon quantum computing

Organizing Institutes:

iTHEMS: RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program

RQC: RIKEN Center for Quantum Computing

Quantum BC

Organizers:

Tetsuo Hatsuda (iTHEMS)

Yasunobu Nakamura (RQC)

Shunji Matsuura (1QBit)

Joseph Salfi (UBC)

Erika Kawakami (RQC / RIKEN CPR)

Neill Lambert (RIKEN CPR)

Venue: via Zoom

Event Official Language: English

## Colloquium

### Finding Gravitational Waves from the Early Universe

September 27 at 16:00 - 17:30, 2021

Prof. Eiichiro Komatsu (Director, Max Planck Institute for Astrophysics, Germany)

The Cosmic Microwave Background (CMB) gives a photographic image of the Universe when it was still an “infant”. We have been using it to test our ideas about the origin of the Universe. The CMB research told us a remarkable story: the structure we see in our Universe such as galaxies, stars, planets, and eventually ourselves originated from tiny quantum fluctuations in the period of the early Universe called cosmic inflation. While we have accumulated strong evidence for this picture, the extraordinary claim requires extraordinary evidence. The last prediction of inflation that is yet to be confirmed is the existence of primordial gravitational waves whose wavelength can be as big as billions of light years. To this end we have proposed to JAXA a new satellite mission called LiteBIRD, whose primary scientific goal is to find signatures of gravitational waves in the polarisation of the CMB. In this presentation we describe physics of gravitational waves from inflation, and the LiteBIRD proposal.

Venue: via Zoom

Event Official Language: English

# Person of the Week

## Self-introduction: Congcong Le

2021-08-05

My name is Congcong Le from China, and I join iTHEMS on August 1st 2021 as a Postdoctoral Researcher. After graduation, I came to the Institute of Physics, Chinese Academy of Sciences to study theoretical physics, and obtained my PhD in July 2017. My research focuses on the theoretical study in condensed matter systems, including unconventional superconductivity, strongly correlated system, and novel topological system (topological insulators, Dirac semimetal, Weyl semimetal), and I start to be interested in twisted bilayers and topological phases in the non-Hermitian systems. I have enjoyed using mathematics to explore condensed matter physics and working with theorists and experimenters. In my spare time, I like Chinese chess, badminton, table tennis and climbing.

# Paper of the Week

## Week 2, August 2021

2021-08-05

Title: LMC N132D: A mature supernova remnant with a power-law gamma-ray spectrum extending beyond 8 TeV

Author: H. E. S. S. Collaboration

arXiv: http://arxiv.org/abs/2108.02015v1

Title: Relativistic spin hydrodynamics with torsion and linear response theory for spin relaxation

Author: Masaru Hongo, Xu-Guang Huang, Matthias Kaminski, Mikhail Stephanov, Ho-Ung Yee

arXiv: http://arxiv.org/abs/2107.14231v1

Title: Convergence of a finite difference scheme for the Kuramoto--Sivashinsky equation defined on an expanding circle

Author: Shunsuke Kobayashi, Shigetoshi Yazaki

arXiv: http://arxiv.org/abs/2108.00593v1

Title: Locally equivalent quasifree states and index theory

Author: Chris Bourne

arXiv: http://arxiv.org/abs/2108.01230v1

Title: Toward ab initio determination of charge symmetry breaking strength of Skyrme functionals

Author: Tomoya Naito, Gianluca Colò, Haozhao Liang, Xavier Roca-Maza, Hiroyuki Sagawa

arXiv: http://arxiv.org/abs/2107.14436v1

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