Volume 207

iTHEMS Weekly News Letter

Seminar Report

Quantum Matter Seminar by Dr. Ken Shiozaki on July 12, 2022

2022-07-15

Prof. Ken Shiozaki gave a seminar about adiabatic cycles of quantum spin systems. Topological phases of matter without ground state degeneracy are known as inevitable phases. In the literature, their topological properties have been well-studied in free-fermion and many-body systems. The speaker started with the transverse-field Ising model and the Rice-Mele model to demonstrate the pumping of the 1D chain in an adiabatic cycle. He then generalized the concept to cover broader systems, including general spatial dimensions and generic models with any onsite symmetry, such as time-reversal, Z2 Ising, and U(1). He demonstrated that one can classify adiabatic cycles of a spin model, which can be characterized by a Z2 topological invariant. This talk showed that symmetry-protected topological phases emerge by performing an adiabatic cycle.

Reported by Chen-Hsuan Hsu (YITP, Kyoto University)

Seminar Report

iTHEMS Theoretical Physics Seminar by Prof. Hiroshi Suzuki on July 5, 2022

2022-07-13

The iTHEMS-phys intensive lecture was held on July 5 and 6, 2022. The speaker is Prof. Hiroshi Suzuki at Kyushu University. The title is “Gradient flow exact renormalization group.”
Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has, however, been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Recently, he has proposed a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gauge-covariant diffusion equation. He has explained the basic idea and properties of GFERG. He has also presented a possible application of GFERG to the consideration of the axial anomaly.
The lecture was held via Zoom. There were about 30 participants from iTHEMS and other universities. The participants enjoyed fruitful discussions throughout the lecture.

Reported by Kengo Kikuchi

Upcoming Events

Seminar

iTHEMS Biology Seminar

Bayesian optimization of multivariate genomic prediction models based on secondary traits for improved accuracy gains and phenotyping costs

July 21 (Thu) at 16:00 - 17:00, 2022

Kosuke Hamazaki (Ph.D. Student, Graduate School of Agricultural and Life Sciences, The University of Tokyo)

In recent years, the genomic prediction that predicts phenotypic values from marker genotype data has attracted much more attention in the area of breeding. Especially, genomic selection using prediction values based on genomic prediction models has been contributing to more efficient and rapid breeding. In genomic prediction, it is important to construct the prediction model so that its accuracy becomes higher. Thus, multivariate genomic prediction models with secondary traits, such as data from various omics technologies including high-throughput phenotyping (e.g., unmanned aerial vehicle-based remote sensing), have started to be applied to many datasets because it offers improved accuracy gains compared with genomic prediction based only on marker genotypes. Although there is a trade-off between accuracy gains and phenotyping costs of secondary traits, no attempt has been made to optimize these trade-offs. In this study, we propose a novel approach to optimize multivariate genomic prediction models with secondary traits measurable at early growth stages for improved accuracy gains and phenotyping costs. The proposed approach employs Bayesian optimization for efficient Pareto frontier estimation, representing the maximum accuracy at a given cost. The proposed approach successfully estimated the optimal secondary trait combinations across a range of costs while providing genomic predictions for only about 20% of all possible combinations. The simulation results reflecting the characteristics of each scenario of the simulated target traits showed that the obtained optimal combinations were reasonable. Analysis of real-time target trait data showed that the proposed multivariate genomic prediction model had significantly superior accuracy compared to the univariate genomic prediction model.

Venue: via Zoom

Event Official Language: English

Seminar

NEW WG Seminar

Superconducting-like heat current: Effective cancellation of current-dissipation trade-off by quantum coherence

July 25 (Mon) at 13:30 - 15:00, 2022

Tajima Hiroyasu (Assistant Professor, Graduate School of Informatics and Engineering, The University of Electro-Communications)

Recent developments in statistical mechanics have revealed a tradeoff between heat current and dissipation [1,2]. In various situations, this current-dissipation tradeoff represents a relationship between thermal energy flow and entropy increase, similar to Joule’s law W=RI^2.

On the other hand, the coherence effect on the current-dissipation tradeoff has not been thoroughly analyzed. Here, we systematically analyze how coherence affects the current-dissipation tradeoff [3]. The results can be summarized in the following three rules:

  1. Quantum coherence between different energy levels strengthens the trade-off. In other words, the ratio between the square of the heat current and the entropy production ratio corresponding to electrical resistance R (hereafter referred to as "thermal resistance") is increased by the superposition of different energy levels.
  2. Coherence between degeneracies weakens the trade-off. That is, thermal resistance is weakened by coherence between degeneracies.
  3. With enough coherence between degeneracies, we can cancel the trade-off effectively and make the thermal resistance approximately zero. Then, macroscopic heat flow without entropy increase is realized.

These three results directly reveal the coherence effects on heat engine performance. That is, coherence between different energy levels reduces the performance, while coherence between degeneracies increases it. And when there is a sufficient amount of coherence between degeneracies, the efficiency can asymptotically reach the Carnot efficiency (η=η_{Car}-O(1/N)) while the power is O(N).

References

  1. N. Shiraishi, K. Saito, H. Tasaki, Universal Trade-Off Relation between Power and Efficiency for Heat Engines, Phys. Rev. Lett. 117, 190601 (2016), doi: 10.1103/PhysRevLett.117.190601
  2. A. C. Barato, U. Seifert, Thermodynamic Uncertainty Relation for Biomolecular Processes, Phys. Rev. Lett. 114, 158101 (2015), doi: 10.1103/PhysRevLett.114.158101
  3. H. Tajima, K. Funo, Superconducting-like Heat Current: Effective Cancellation of Current-Dissipation Trade-Off by Quantum Coherence, Phys. Rev. Lett. 127, 190604 (2021), doi: 10.1103/PhysRevLett.127.190604

Venue: via Zoom

Event Official Language: English

Seminar

iTHEMS Math Seminar

Introduction to instanton knot homology

July 25 (Mon) at 16:00 - 18:00, 2022

Hayato Imori (Ph.D. Student, Division of Mathematics and Mathematical Sciences, Graduate School of Science, Kyoto University)

Floer theory is an infinite-dimensional version of Morse theory and has provided powerful invariants in the study of low-dimensional topology. In the context of Yang-Mills gauge theory, some versions of Floer homology groups for knots have been developed. These knot invariants are called instanton knot homology groups and are strongly related to representations of the fundamental group of the knot complement.
In this talk, the speaker introduces basic constructions of instanton knot homology groups and recent developments related to the equivariant version of instanton knot homology theory.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

Colloquium

iTHEMS Colloquium

From the Black Hole Conundrum to the Structure of Quantum Gravity

July 26 (Tue) at 15:30 - 17:00, 2022

Yasunori Nomura (Director, Berkeley Center for Theoretical Physics, University of California, Berkeley, USA)

Having a complete quantum theory of gravity has long been a major goal of theoretical physics. This is because a naive merger of quantum mechanics and general relativity — though it works in certain limited regimes — suffers from major theoretical problems. A particularly acute one arises when one considers the quantum mechanics of black holes: two fundamental principles of modern physics — the conservation of probability in quantum mechanics and the equivalence principle of general relativity — seem to be incompatible with each other. I will explain how recent theoretical progress begins to address this problem and portray the emerging picture of how spacetime and gravity behave at the level of full quantum gravity.

Venue: 2F Large Meeting Room, RIBF Building, RIKEN Wako Campus / via Zoom

Event Official Language: English

Seminar

iTHEMS Theoretical Physics Seminar

Test of the Cosmological principle by observing the primordial gravitational waves

July 27 (Wed) at 13:30 - 15:00, 2022

Yuko Urakawa (Associate Professor, High Energy Accelerator Research Organization (KEK))

In this talk, using the generalized deltaN formalism, which dramatically facilitates a computation of the primordial density perturbation and the primordial GWs (PGWs), we address a violation of the Cosmological principle, namely a violation of the global isotropy in the Universe. It’s turned out that measuring the PGWs provides a powerful tool to explore a violation of the global isotropy. If time permits, I will also discuss some prospects on LiteBIRD.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

Workshop

SUURI-COOL (Kobe) venue photo

iTHEMS Science Outreach Workshop 2022

July 29 (Fri) - 31 (Sun), 2022

This year’s meeting on “Outreach of RIKEN iTHEMS 2022@Kobe&Zoom” will be held from FRI July 29 to SUN July 31, as a face-to-face meeting as much as possible at iTHEMS SUURI-COOL Kobe using ZOOM for the necessary part as well. This is a meeting where members of iTHEMS and science journalists, science writers, etc meet together. iTHEMS researchers explain their research to journalists etc. and science journalists and writers talk about their experiences.

Venue: SUURI-COOL (Kobe), #S704-S705, Integrated Innovation Building (IIB), Kobe Campus, RIKEN / via Zoom

Event Official Language: Japanese

Paper of the Week

Week 3, July 2022

2022-07-14

Title: Spatially resolved study of the SS 433/W50 west region with Chandra: X-ray structure and spectral variation of non-thermal emission
Author: Kazuho Kayama, Takaaki Tanaka, Hiroyuki Uchida, Takeshi Go Tsuru, Takahiro Sudoh, Yoshiyuki Inoue, Dmitry Khangulyan, Naomi Tsuji, Hiroaki Yamamoto
arXiv: http://arxiv.org/abs/2207.05924v1

Title: Constraining primordial curvature perturbations using dark matter substructure
Author: Shin'ichiro Ando, Nagisa Hiroshima, Koji Ishiwata
arXiv: http://arxiv.org/abs/2207.05747v1

Title: QFT approach to dressed particle processes in preheating and non-perturbative mechanism in kinematically-forbidden regime
Author: Hidetoshi Taya, Yusuke Yamada
arXiv: http://arxiv.org/abs/2207.03831v1

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