iTHEMS Weekly News Letter

Seminar Report

Information Theory SG Seminar by Prof. Yoshihiko Hasegawa on April 28, 2021


On April 28, Prof. Yoshihiko Hasegawa (Associate Professor, The University of Tokyo) gave us a talk on the thermodynamic uncertainty relation (TUR).
In the first part of his talk, he started from a motivation to consider trade-off relations between energy and cost, showing biological examples. After reviewing general theory of stochastic thermodynamics and TUR for classical Markovian systems, he presented two recent works of him: one is to derive the TUR from information-theoretic method (i.e., the Cramer-Rao bound) and the second is to derive it from the fluctuation theorem.
In the second part, he discussed quantum version of the TUR. After the review of quantum dynamics under measurement, he showed the quantum TUR for general open systems. He applied his theory to continuously measured systems and explained its physical meaning.
There were a lot of interactive discussions during and after the talk. We really thank Prof. Hasegawa for his great talk.

Reported by Ryusuke Hamazaki

Seminar Report

Quantum Matter Seminar by Dr. Se Kwon Kim on April 21, 2021


On April 21st, Dr. Se Kwon Kim from KAIST gave a talk about unconventional spin transport in quantum materials. First, he gave an overview of spintronic physics. The advancements in spintronic techniques can potentially lead to new applications, such as quantum information science.

Then, he showed the realization of magnonic topological insulators, which are Chern insulators with spin current but without electron charge current. Furthermore, he predicted that spin transport induces vortex flow in superconductors. We thank Dr. Kim for giving a wonderful talk.

Reported by Ching-Kai Chiu

Upcoming Events


DMWG Seminar

Emulation for lensing and clustering observables of the cosmological large-scale structure

May 12 at 10:00 - 11:00, 2021

Dr. Takahiro Nishimichi (Yukawa Institute for Theoretical Physics, Kyoto University)

Recent developments in observational technologies open exciting opportunities to map out the detailed structure of the universe. Remarkably, the unique combination of imaging and spectroscopic galaxy surveys is now becoming well established as a standard analysis methodology for precision cosmology. While the former can access directly the underlying clustering of mass dominated by dark matter projected on the sky through the weak gravitational lensing effect, the latter provides us with the three dimensional map of the structure traced by galaxies. One can mitigate the galaxy-bias uncertainty, which has been the major obstacle for cosmology based on galaxy surveys, by jointly analyzing these effects. We still need, however, a robust and versatile theoretical and statistical framework to interpret these datasets. The Dark Quest project, launched in 2015, is a structure formation simulation campaign precisely
for this purpose. We have developed an emulation tool, dubbed as Dark Emulator, based on a large database of simulated dark matter halos in virtual universes with different cosmologies efficiently sampled in six-dimensional parameter space. Dark Emulator employs a simple machine-learning architecture with Gaussian process at its core. It makes predictions of various statistical measures of dark matter halos, both lensing and clustering observables, for a given cosmological parameters in a few seconds on laptop computers without running a new simulation. This AI-aided tool, once supplemented with recipes for the halo-galaxy connection, is therefore applicable to real-data analyses as the theoretical template, which typically requires hundreds of thousands of function calls in the course of parameter inference. I will introduce this project and report the status of its application to Subaru HSC data.
We are looking forward to seeing you online.

Venue: via Zoom

Event Official Language: English


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Quantum Matter Seminar

Aperiodic and amorphous topological phases

May 12 at 17:00 - 18:15, 2021

Prof. Christopher Bourne (Visiting Scientist, iTHEMS / Assistant Professor, Advanced Institute for Materials Research (AIMR), Tohoku University)

Key features of topological insulators and superconductors such as stable edge modes have been found in an increasingly broad class of materials and systems. In this talk, I will introduce a mathematical framework to study Hamiltonians and topological phases on a general class of (aperiodic/random) point atterns. Using techniques from noncommutative geometry, we then show how bulk topological invariants and the bulk-boundary correspondence can be rigorously established in such generic systems.
This is based on joint work with Emil Prodan and Bram Mesland.

*Detailed information about the seminar refer to the email.

Venue: via Zoom

Event Official Language: English

Upcoming Visitor

Dr. Nagisa Hiroshima thumbnail

May 6 - 7, 2021

Dr. Nagisa Hiroshima

Visiting Scientist, iTHEMS / Assistant Professor, Theoretical Physics Group, University of Toyama

Research fields: Dark Matter, High Energy Astrophysics

Visiting Place: RIKEN Wako Campus

Paper of the Week

Week 5 of April, 2021


Title: Hydrodynamic Attractor in a Hubble Expansion
Author: Zhiwei Du, Xu-Guang Huang, Hidetoshi Taya

Title: Deep Learning of the Eddington Tensor in the Core-collapse Supernova Simulation
Author: Akira Harada, Shota Nishikawa, Shoichi Yamada

Title: Positive scalar curvature and homology cobordism invariants
Author: Hokuto Konno, Masaki Taniguchi

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