Program



Program

9/27(Mon)

Chair: Ryo Hanai

    • 14:30 - 16:00 Sergej Flach (PCS-IBS)

      • Title: Thermalization in weakly non-integrable many-body systems

      • Abstract:

Contents:

- Kolmogorov, Arnold, Moser: stay almost like integrable

- Fermi, Pasta, Ulam, Tsingou: or not?

- Classifying thermalization: networks

- Quantifying thermalization: finite-time average distributions

- Lyapunov: spectrum re-classifies and quantifies!

Reads:

PRE 95 060202(R) 2017

PRL 120 184101 2018

PRL 122 054102 2019

PRA 99 023603 2019

PRE 100 032217 2019

PRE 104 014218 2021

arXiv:2107.09385

arXiv:2109.01361

    • 16:30 - 18:00 Bohm-Jung Yang (Seoul National University)

      • Title: Wave function geometry and anomalous Landau levels of flat bands

      • Abstract: Semiclassical quantization of electronic states under magnetic field describes not only the Landau level spectrum but also the geometric responses of metals under a magnetic field. However, it is unclear whether this semiclassical idea is valid in dispersionless flat-band systems, in which an infinite number of degenerate semiclassical orbits are allowed. In this talk, I am going to show that the semiclassical quantization rule breaks down for a class of flat bands including singular flat bands [1-5] and isolated flat bands [6]. The Landau levels of such a flat band develop in the empty region in which no electronic states exist in the absence of a magnetic field. The total energy spread of the Landau levels of flat bands is determined by the quantum geometry of the relevant Bloch states, which is characterized by their Hilbert–Schmidt quantum distance and fidelity tensors. The results indicate that flat band systems are promising platforms for the direct measurement of the quantum geometry of wavefunctions in condensed matter.
        [1] J. W. Rhim and B. -J. Yang, “Classification of flat bands according to the band-crossing singularity of Bloch wave functions”, PRB 99, 045107 (2019)
        [2] J. W. Rhim, K. Kim, B. -J. Yang, “Quantum distance and anomalous Landau levels of flat bands”, Nature 584, 59-63 (2020)
        [3] Y. Hwang, J. Jung, J. W. Rhim, B. -J. Yang, “Wave function geometry of band crossing points in two-dimensions”, PRB 103, L241102 (2021)
        [4] Y. Hwang, J. W. Rhim, B. -J. Yang, “Flat bands with band crossing enforced by symmetry representation”, PRB 104, L081104 (2021); PRB 104, 085144 (2021)
        [5] J. W. Rhim and B. -J. Yang, “Singular flat bands”, Advances in Physics X, 6:1, 1901606 (2021)
        [6] Y. Hwang, J.-W. Rhim, B.-J. Yang, “Geometric characterization of anomalous Landau levels of isolated flat bands”, arXiv.:2012.15132

9/28(Tue)

Chair: Kun Woo Kim

    • 9:00 - 10:30 Yongjoo Baek (Seoul National University)

      • Title: A simple model of symmetry-breaking motility in active fluids

      • Abstract: Living systems maintain their structures and functions by staying far from equilibrium, which they achieve by taking and dissipating energy without any external bias. Active matter, which autonomously converts stored or ambient energy into systematic motion, provides a natural framework for studying the physics of such systems. Unlike the conventional nonequilibrium systems driven by boundary reservoirs or global external fields, active matter is driven out of equilibrium at the level of each particle, which leads to a plethora of novel collective behaviors. In this talk, I will focus on how large-scale motile structures can emerge in a fluid consisting of active matter (“active fluid") only by immersing passive objects in it. While the motion of the latter objects is generally suppressed at equilibrium, in an active fluid, there is a positive feedback mechanism that leads to a sustained motion of the object via spontaneous symmetry breaking, inducing both discontinuous and continuous transitions in the motility of the object. This mechanism can generically be found in a broad range of active fluids, with potential applications to biological transport and colloidal engines.

    • 10:45 - 11:45 Ryo Hanai (APCTP)

      • Title: Non-reciprocal phase transitions

      • Abstract: Phase transitions are ubiquitous in nature. For equilibrium cases, the celebrated Landau theory has provided great success in describing these phenomena on general grounds. Even for nonequilibrium transitions such as optical bistability, flocking transition, and directed percolation, one can often define Landau’s free energy in a phenomenological way to successfully describe the transition at a meanfield level. In such cases, the nonequilibrium effect is present only through the noise-activated spatial-temporal fluctuations that break the fluctuation-dissipation theorem. Here, by generalizing the Ginzburg-Landau theory to be applicable to driven systems, we introduce a novel class of nonequilibrium phase transitions [1-2] and critical phenomena [3] that does not fall into this class. Remarkably, the discovered phase transition is controlled by spectral singularity called the exceptional points that can only occur by breaking the detailed balance and therefore has no equilibrium counterparts. The emergent collective phenomena range from active time (quasi)crystals to exceptional point enforced pattern formation, hysteresis, to anomalous critical phenomena that exhibit anomalously large phase fluctuations (that diverge at d≤4) and enhanced many-body effects (that become relevant at d<8) [3]. The inherent ingredient to these is the non-reciprocal coupling between the collective modes that arise due to the drive and dissipation.

[1] M. Fruchart*, R. Hanai*, P. B. Littlewood, and V. Vitelli, Non-reciprocal phase transitions. Nature 592, 363 (2021).

[2] R. Hanai, A. Edelman, Y. Ohashi, and P. B. Littlewood, Non-Hermitian phase transition from a polariton Bose-Einstein condensate to a photon laser. Phys. Rev. Lett. 122, 185301 (2019).

[3] R. Hanai and P. B. Littlewood, Critical fluctuations at a many-body exceptional point. Phys. Rev. Res. 2, 033018 (2020).

    • 12:00 - 13:00 Changbong Hyeon (KIAS)

      • Title: Generalized iterative annealing model for the action of molecular chaperones

      • Abstract: Molecular chaperones are ATP-consuming molecular machines that have evolved to assist the folding of biomolecules, thus avoiding the deleterious consequences of misfolding. Thus, it is expected that increasing chaperone concentrations should enhance the yield of native states. While this has been observed in GroEL-mediated protein folding, recent experiments on the folding of ribozyme (RNA enzyme) assisted by CYT-19 show the opposite trend. Here, we reconcile these divergent experimental observations by developing a unified model of chaperone-assisted protein and RNA folding. We show that these ATP-fueled machines drive their substrates out of equilibrium, maximizing the nonequilibrium native yield in a given time rather than the absolute yield or folding rate. We also extend our analysis to explore the role of CYT-19 on the RNA metabolism where the dynamics of molecular degradation and self-splicing interfere with the chaperone-mediated dynamics of ribozyme. When chaperones are reactive to the native state, the self-splicing activity of ribozyme depends non-monotonically on the chaperone activity determined by the CYT-19 and ATP concentrations. Our study shows that the self-splicing yield of ribozyme is maximized under cellular concentrations of CYT-19 and ATP.

Chair: Yongjoo Baek

    • 14:30 - 15:30 Alexei Andreanov

      • Title: Ergodicity breaking in flatbands

      • Abstract: Flatbands are disprtsionless single particle bands. The quenched kinetic energy (due to the absence of dispersion), makes them promising hosts for unconventional and exotic phases of matter in presence of perturbations, like disorder or interactions. I am going to discuss how the presence of interactions in flat band models can implement several scenarios of ergodicity breaking: many-body localisation and many-body flatband localisation (with connections to percolation transitions), as well as weak ergodicity breaking.

    • 15:45 - 16:45 Kun Woo Kim (Chung-Ang University)

      • Title: Quantum walks in disorder

      • Abstract: TBA

    • 17:00 - 19:00 Poster session

9/29 (Wed)

Chair: Yuji Hirono

    • 9:00 - 10:30 Jae Kyoung Kim (KAIST/IBS)

      • Title: Mathematics, a 21st Century Microscope for Complex Biological System

      • Abstract: The revolution of molecular biology in the early 1980s has revealed that biological systems consist of non-linear and stochastic biochemical interactions among many molecules. To understand this complex system, mathematical modeling has been an invaluable tool. In this talk, I will introduce the typical process of mathematical modeling including mathematical representation, model fitting to data, analysis, and simulations, and experimental validation with an example of circadian rhythms. Across each step of the modeling process, I will also describe our efforts to develop new mathematical tools and point to the parts of the current toolbox of mathematical biology that need further mathematical development..

    • 10:45 - 11:45 Shodhan Rao (Ghent University Global Campus)

      • Title: Oscillatory behaviour in metapopulation models of ecological competition networks

      • Abstract: In this talk, I will first of all introduce a mean-field model of an ecological competition network consisting of individual species, in which there is a certain dominance relation between any two species of the network. The dynamics of these kinds of models are well studied and conditions for the coexistence of all the species in such networks are well known. In my talk, I shall further introduce balanced metapopulation models which consist of spatially discrete individual habitats called as patches, each being inhabited by the same species with spatial homogeneity and having the same dominance relations between the different pairs of species. Each of these patches can be assumed to be following mean field dynamics and if left to operate by itself, it will have all species coexisting in the long run. If we further assume that each species is able to migrate between the different patches at a rate proportional to its density in the original patch, this results in a model for an ecological situation in which discrete areas of the landscape (ponds, woodlands in agricultural landscapes, and so on) are represented by patches within which demographic processes occur, and the dispersal between them is represented by inter-patch migration. Finally in the talk, I shall discuss about the conditions under which a metapopulation model exhibits oscillatory behaviour in the long run.

    • 12:00 - 13:00 Jinsu Kim (POSTECH)

      • Title: Stability of stochastically modeled biochemical reaction networks

      • Abstract: A reaction network is a graphical configuration that can describe many biochemical systems with interactions between species (molecules). If the abundances of the species involved in a reaction network are small, then the randomness inherent in the molecular interactions is important to the system dynamics, and the abundances are modeled stochastically as a jump-by-jump fashion continuous-time Markov chain. In this talk, we will discuss two approaches for exploring stability of the Markov chains associated with biochemical reaction networks: algebraic and analytic approaches.

Chair: Hye Jin Park

    • 14:30 - 15:30 Yuji Hirono (APCTP)

      • Title: Structural reduction of chemical reaction networks based on topology

      • Abstract: Chemical reactions form a complex network in living cells and they play vital roles for physiological functions. An amusing question is how the structure of a reaction network is linked to its chemical functionalities. I’ll talk about a method of the reduction of chemical reaction networks, which is convenient for extracting important substructures. Mathematical concepts such as homology and cohomology groups are found to be useful for characterizing the shapes of reaction networks and for tracking the changes of them under reductions. For a given chemical reaction network, we identify topological conditions on its subnetwork, reduction of which preserves the original steady state exactly. [Reference: https://arxiv.org/abs/2102.07687 ]

    • 15:45 - 16:45 Sang Hoon Lee (Gyeongsang National University)

      • Title: Mining stochasticity of community detection to refine global and local organization of networks

      • Abstract: The concept of community detection has long been used as a key device for handling the mesoscale structures in networks. Suitably conducted community detection reveals various embedded informative substructures of network topology. A number of algorithms have been developed to determine the most likely community structures in networks. Such a probabilistic or stochastic nature of this problem can naturally involve the ambiguity in resultant community structures. More specifically, stochastic algorithms can result in different community structures for each realization in principle. Throughout the series of work [1,2,3], instead of trying to "solve" this community degeneracy problem, we turn the tables by taking the degeneracy as a chance to quantify how strong companionship each node has with other nodes. In addition, regarding the practical usage of community detection, it has always been a tricky problem to assign a reasonable community resolution for networks of interest. Because of the absence of the unanimously accepted criterion, most of the previous studies utilized rather ad hoc heuristics to decide the community resolution. We harness the concept of consistency in community structures of networks to provide the overall community resolution landscape of networks, which we eventually take to quantify the reliability of detected communities for a given resolution parameter. More precisely, we exploit the ambiguity in the results of stochastic detection algorithms and suggest a method that denotes the relative validity of community structures regarding their stability of global and local inconsistency measures using multiple detection processes. Applying our framework to synthetic and real networks, we confirm that it effectively displays insightful fundamental aspects of community structures. Finally, we discuss the ongoing works on exploration of modularity landscape via separate local contribution to modularity and the possibility of merging the results across different resolution parameters to deduce the most meaningful community structure composed of multi-scale communities. [1] H. Kim, S. H. Lee, and P. Holme, New J. Phys. 17, 113005 (2015). [2] H. Kim and S. H. Lee, Phys. Rev. E 100, 022311 (2019). [3] D. Lee, S. H. Lee, B. J. Kim, and H. Kim, Phys. Rev. E 103, 052306 (2021).

    • 17:00 - 18:00 Seung Ki Baek (Pukyong National University)

      • Title: Friendly-rivalry solution to the iterated n-person public-goods game

      • Abstract: Repeated Interaction promotes cooperation among rational individuals under the shadow of the future, but it is hard to maintain cooperation when a large number of error-prone individuals are involved. One way to construct a cooperative Nash equilibrium is to find a 'friendly-rivalry' strategy, which aims at full cooperation but never allows the co-players to be better off. Recently it has been shown that for the iterated Prisoner's Dilemma in the presence of error, a friendly rival can be designed with the following five rules: Cooperate if everyone did, accept punishment for your own mistake, punish defection, recover cooperation if you find a chance, and defect in all the other circumstances. In this work, we construct such a friendly-rivalry strategy for the iterated n-person public-goods game by generalizing those five rules. The resulting strategy makes a decision by referring to the previous m=2n−1 rounds. A friendly-rivalry strategy for n=2 inherently has evolutionary robustness in the sense that no mutant strategy has higher fixation probability in this population than that of a neutral mutant. Our evolutionary simulation indeed shows excellent performance of the proposed strategy in a broad range of environmental conditions when n=2 and 3.

9/30 (Thu)

Chair: Meesoon Ha

    • 9:00 - 10:30 Deok-Sun Lee (KIAS)

      • Title: Percolation in complex networks

      • Abstract: TBA

    • 10:45 - 11:45 Cheol-Min Ghim (UNIST)

      • Title: Stochastic Gene Expression in Diploid Cells

      • Abstract: Origins and consequences of cell-to-cell variability are essential to the understanding of diverse biological processes underlying the development, aging, immune response, and tumorigenesis, just to name a few. As a micrometer-sized chemical reactor, living cells call for analytical frameworks that respect the stochasticity of biochemical reactions and discrete nature of macromolecules. In the earlier part of the talk, I propose some rationales of genetic noise for tuning the functional stability of a simple synthetic gene switch. The latter part of the talk will focus on the effects of zygosity of diploid cells, which adds another dimension to stochastic gene expression. I will introduce the diploid gene expression systems with homo- and heterozygous combination of alleles in the cis-regulatory sequences and characterize the noise profiles associated with zygosity. An emerging feat of heterozygosity is its counterintuitive capacity for genetic noise control, which offers a novel insight into the rich repertoire of balancing selection enriched in the regulatory sequences of the immune response genes.

    • 12:00 - 13:00 Hye Jin Park (APCTP)

      • Title: How ecological interactions shape communities from the physics perspective

      • Abstract: Natural populations ranging from microbial communities to animal societies consist of many different species. Some species compete to exploit a shared resource, whereas others can help each other. Such interactions affect the death or reproduction of species, thus shaping the composition of populations. As stability and diversity are crucial features of ecological systems, I have studied how the interactions determine extinction behavior and diversity by applied physics tools. By using Wentzel-Kramers-Brillouin (WKB) approximation, I elucidated the most probable extinction trajectory of one species from coexistence [Phys. Rev. E 96 (2017) 042412]. In addition, applying dynamical mean-field theory to the generalized Lotka-Volterra model, I am investigating how heterogeneity of interactions plays a role in maintaining diversity. Our preliminary results show that heterogeneity can induce the catastrophe of species reducing the number of coexisting species.

Chair: Deok-Sun Lee

    • 14:30 - 15:30 Jae Dong Noh (University of Seoul)

      • Title: Phase transitions of diffusing Potts spin systems

      • Abstract: Motility is an important ingredient characterizing the nature of collective phenomena as witnessed in active matter systems. We investigate the role of the motility in order-disorder phase transitions. Specifically, we study the q-state Potts model where Potts spins can diffuse freely in the two-dimensional space of size $L^2$ under the periodic boundary condition. The nature of the order-disorder phase transition will be reported and compared with that of the corresponding lattice model with immobile spins.

    • 15:45 - 16:45 Meesoon Ha (Chosun University)

      • Title: Effect of Disorder on Criticality and Complexity: Universality Perspective of Non-equilibrium Processes

      • Abstract: In my talk, I present how to understand the effect of disorder on nonequilibrium processes in the perspective of the universality class, where I focus on the dynamic scaling analysis and the finite-size scaling ansatz. First, I address the role of a localized defect in one-dimensional driven diffusive systems and argue whether there is a dynamic phase transition or not. Secondly, I show that the sampling method of natural frequencies is relevant to the extended finite-size scaling of synchronization. Thirdly, a comprehensive picture of absorbing phase transitions is provided for the generalized epidemic processes on a variety of underlying structures. Finally, I briefly discuss the interplay of the diffusion and the power-law type temporal feedback on spatio-temporal correlations and extended self-similarity properties in the vicinity of absorbing phase transitions.

    • 17:00 - 18:00 Dong-Hee Kim (GIST)

      • Title: Studying a phase transition with the aid of neural-network quantum states

      • Abstract: We investigate a quantum phase transition in a transverse-field Ising chain with long-range antiferromagnetic interactions using a variational Monte-Carlo method with the aid of the neural-network quantum state (NQS) ansatz. We implement the standard restricted Boltzmann machine for the ansatz of a quantum wave function that we demonstrate has enough expressive power to describe ordered and disordered phases and characterize the phase transition. By measuring the magnetic and fidelity susceptibilities, the connected correlation functions, and the central charge, we argue that the critical behavior emerging at the phase transition does belong to the Ising universality class, regardless of the long-range exponents of the antiferromagnetic interactions that we examine. We also argue the difficulties in analyzing the correlation functions, where it turns out that the algebraic decay due to the long-range nature of the interaction appears together with the conventional behavior expected in the short-range systems.

10/1 (Fri)

Chair: Alexei Andreanov

    • 9:00 - 10:30 Jae Sung Lee (KIAS)

      • Title: Introduction to Stochastic Thermodynamics: from Fluctuation Theorems to Thermodynamic Uncertainty Relations

      • Abstract: Since the late 1990s, thermodynamics has been reformulated in terms of a stochastic trajectory. This has led to a renaissance in thermodynamics, in which the thermodynamic second law is generalized to the fluctuation theorems (FT) by using the definition of stochastic entropy, providing a theoretical framework for general nonequilibrium processes. Moreover, since 2015, there has been a new wave of studies investigating fundamental thermodynamic inequalities beyond the thermodynamic second law, which have set new horizons for our understanding of thermodynamic processes. This inequality is called thermodynamic uncertainty relations (TUR), which is a tradeoff relation between uncertainty and thermodynamic cost provided by a stochastic process. These FT and TUR are two major pillars of stochastic thermodynamics. In the first part of this talk, I will introduce the basic concepts and definitions in stochastic thermodynamics, i.e., heat, work, and entropy in a general non-equilibrium process, and briefly review FT and its applications. In the second part, I will talk about what is TUR, what is its physical implications, and when it is valid. Validity of TUR and its variants have been demonstrated mainly for a system with only even-parity variables under time reversal while its application to a system with odd-parity variables has not been successful in a unified way to date. Here, I will introduce the unified form of TUR for a system with odd-parity variables.

    • 10:45 - 11:45 Juzar Thingna (PCS-IBS)

      • Title: Measuring quantum Otto engines operating far from equilibrium

      • Abstract: Unlike classical systems, measuring a quantum system always alters its state. To know the power output or efficiency of a quantum heat engine, it is vital to measure the engine's energy output. In this talk, I will describe the impact of two different quantum measurement schemes on the performance of a finite-time quantum Otto engine. In one scheme, the diagnoser measures the energy repeatedly after every stroke, and then using the two-point measurement scheme infers the work performed by the engine. In the other scheme, the diagnoser repeatedly brings the engine in contact with an ancilla. The repeated contacts encode the energy information of the engine after each stroke into the ancilla. The diagnoser only measures the ancilla at the very end of the protocol extracting the necessary information to infer the heat and work of the engine. Both schemes allow the diagnoser to evaluate the engine's performance metrics like heat input, work output, efficiency, and reliability. The first scheme (repeated measurements) destroys all coherences generated at the end of each stroke, whereas the second scheme (repeated contacts) preserves coherences throughout the protocol. I will illustrate these two schemes using a two-level system as the engine's working substance. For Otto engines operating at finite times, the repeated contacts scheme consistently outperforms the repeated measurements, mainly due to coherence preservation. The results document the importance of considering the nature of the measurement scheme for monitoring quantum heat engines [1]. [1] J. Son, P. Talkner, and J. Thingna, arXiv:2105.10665 (2021).


List of poster presentations

PDF files of the posters are available from the links.

  • Arindam Mallick (PCS-IBS) [file]

    • Title: Logarithmic expansion of many-body wavepackets in random potentials

  • Jan Olle (IFAE) [file]

    • Title: Operator Delocalization in Quantum Networks

  • Juhee Lee (APCTP) [file]

    • Title: Selection on a microbial group of the desired composition in a simple model

  • Seong-Gyu Yang (APCTP) [file]

    • Title: Buffering structure in Ecological Systems

  • Hyukpyo Hong (KAIST) [file]

    • Title: Derivation of stationary distributions of stochastic chemical reaction networks via network translation

  • Jonghoon Kim (Pukyong National University) [file]

    • Title: Democracy and political polarization in the National Assembly of Republic of Korea

  • JungYun Han (PCS-IBS)

    • Title: Quantum transient heat transport in the hyper-parametric oscillator

  • Kabyashree Sonowal (PCS-IBS)

    • Title: TBA

  • Minjae Kim (Pukyong National University)

    • Title: Social norms in indirect reciprocity with ternary reputation

  • Muhammad Taufiq Murtadho (PCS-IBS)

    • Title: Quantum Synchronization in Degenerate Laser Heat Engines

  • Sanghoon Lee (PCS-IBS)

    • Title: TBA

  • Sanghun Lee (Pukyong National University)

    • Title: Local stability of cooperation in a continuous model of indirect reciprocity

  • Yeongjun Kim (PCS-IBS)

    • Title: Metal-insulator transitions in weakly disordered flatbands: Additional results

  • Yongjae Oh (Seoul National University) [file]

    • Title: Thermodynamics of an active Brownian gyrator driven by chemical fuel

  • Youngjai Park (APCTP) [file]

    • Title: Invasion and interaction determine population composition in an open evolving system

  • Merab Malishava (PCS-IBS)

    • Lyapunov spectrum scaling for many-body dynamics close to integrability

  • Tilen Cadez (PCS-IBS)

    • Metal-Insulator transition in infinitesimally weakly disordered flatbands