Shiling Liang 梁师翎

Shiling Liang 梁师翎

ELBE Postdoctoral Fellow @ CSBD | MPI-PKS | MPI-CBG

Statistical Physics Youth Communications Seminar Series (Online)

An online seminar series in statistical physics, organized by the Statistical Physics Youth Communications (统计物理青年通讯) - a Chinese community of early-career researchers in statistical and biological physics.

15. Response kinetic uncertainty relations for classical and quantum Markovian processes

Speaker: Kangqiao Liu, Xihua University

Host: Shiling Liang, CSBD

Abstract: The thermodynamics and kinetics of a nonequilibrium classical system fundamentally constrain the precision of an observable regarding the celebrated thermodynamic uncertainty relation (TUR) and the kinetic uncertainty relation (KUR). They have also been extended to open quantum systems obeying the Lindblad master equation where unique quantum effects are identified. Recently, a new set of principles that further incorporate the response of a classical system to an external perturbation has been discovered, named the response TUR [1]. In this talk, we present two response KURs (R-KUR). In the first part, we introduce a fundamental trade-off between the precision of response for generic observables and dynamical activity in classical Markovian systems [2]. The practical applicability and tightness of the derived bound are demonstrated through illustrative examples. Our results apply to a broad spectrum of Markov jump processes, ranging from currents to non-current variables, from steady states to time-dependent driving, from continuous to discrete time, and including Maxwell’s demon or absolute irreversibility. In the second part, we generalize the derived classical R-KUR to the steady state of the Lindblad master equation for open quantum systems [3]. The precision and the sensitivity of a measured observable are bounded from above by the conventional quantum dynamical activity and a perturbation-induced inter-subspace transition term. We provide sufficient conditions such that either of the two contributions vanishes, implying their equal importance. We verify our result and illustrate the conditions in an exactly solvable two-level atom.

[1] Krzysztof Ptaszyński, Timur Aslyamov and Massimiliano Esposito, Dissipation Bounds Precision of Current Response to Kinetic Perturbations, Physical Review Letters 133, 227101 (2024).

[2] Kangqiao Liu and Jie Gu, Dynamical activity universally bounds precision of response in Markovian nonequilibrium systems, Communications Physics 8, 62 (2025).

[3] Kangqiao Liu and Jie Gu, Response Kinetic Uncertainty Relation for Markovian Open Quantum System, arXiv:2501.04895.

Time: February 22, 2025 (Saturday) 8:00 PM Beijing Time (1:00 PM Central European Time, 9:00 PM Japan Time, 7:00 AM Eastern Time)

Location: Tencent Meeting: 634-759-251 https://meeting.tencent.com/dm/PnJSQ0kzZmMB

14. Particle exchange statistics beyond fermions and bosons

Speaker: Zhiyuan Wang, Max-Planck Institute for quantum optics

Host: Xiao Wang, Shanghai Jiaotong University

Abstract: It is commonly believed that there are only two types of’particle exchange statistics in quantum mechanics, fermionand bosons, with the exception of anyons in two dimension [1-3]. In principle, a second exception known aparastatistics, which extends outside of two dimensions, has been considered [4 but was believed to be physicallequivalent to fermions and bosons [5,6]. In this talk I present a recent work of mine [7] which shows that nontriviaparastatistics ineguivalent to either fermions or bosons can exist in physical systemms. I first formulate a secondauantization theory of paraparticles that is significantly diferent fromm previous theories. which turns out to be thkey to get new physics. I then present a family of exactly solvable guantum spin models in one and two dimensionwhere free paraparticles emerge as quasiparticle of parastatistics by proposing a challenge gamme [8] that can only be succeeded using physical systems (in 2D or 3Dhosting paraparticles, as passing the challenge requires the two participating players to secretly commmunicateinformation by exploiting the nontrivial exchange statistics of the emergent paraparticles. Finally, I describe thuniversal properties of emergent paraparticles in gapped topological phases in the framework of tensor categortheory, and show that in 2D and 3D, parastatisties correspond to an exotic type of symmetric fusion categories. Thiswork demonstrates the possibility of a new type of guasiparticle in condensed matter systems, and, morespeculatively, the potential for previously unconsidered types of elementary particles

[1]J. M. Leinaas and J. Myrheim, Nuovo Cim.B 37,1(1977).

[2]F Wilczek, Phys. Rev. Lett. 48,1144 (1982); Phys. Rev. Lett. 49,957(1982).

[3] C. Nayak, S. H. Simon, A. Stern, M. Freedman, and S. Das Sarma, Rev. Mod. Phys. 80,1083 (2008)

[4]H.S. Green, Phys. Rev. 90,270(1953).

[5] S. Doplicher, R. Haag, andJ.E. Roberts, Commun. Math. Phys. 23, 199 (1971);35, 49 (1974)

[6]S. Doplicher and I.E. Roberts, Commun. Math. Phys. 28,331(1972).

[7]Z. Wang and K.R.A. Hazzard, Nature 637,314 (2025).

[8]Z. Wang, arXiv:2412.13360 (2024).

Time: January 21, 2024 (Tuesday) 9:00 PM Beijing Time (2:00 PM Central European Time, 10:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 253-804-361 https://meeting.tencent.com/dm/y7zSZQhHFk1N

13. Law of Balance, Stationary Distribution and Noise Equilibrium of Stochastic Gradient Descent (SGD)

Speaker: Hongchao Li, University of Tokyo

Host: Ruicheng Bao, University of Tokyo

Abstract: How the stochastic gradient descent (SGD) navigates the loss landscape of a neural network remains poorly understood. In this seminar, I am going to introduce our recent work towards understanding the stationary solution and noise equilibrium in the dynamics of SGD. We directly show that the minibatch noise of SGD regularizes the solution towards a noise-balanced solution whenever the loss function contains a rescaling symmetry. We prove that when the rescaling symmetry exists, the SGD dynamics is limited to only a low-dimensional subspace and prefers a special set of solutions in an infinitely large degenerate manifold, which offers a partial explanation of the effectiveness of SGD in training neural networks. We then apply this result to derive the stationary distribution of stochastic gradient flow for a diagonal linear network with arbitrary depth and width, which is the first analytical expression of the stationary distribution of SGD in a high-dimensional non-quadratic potential. The stationary distribution exhibits complicated nonlinear phenomena such as phase transitions, loss of ergodicity, memory effects, and fluctuation inversion. For a general exponential symmetry, we show the existence and uniqueness of the fixed point in the SGD and apply the result to directly calculate the noise equilibrium of a fully-connected deep neural network.

Time: November 30, 2024 (Saturday) 8:00 PM Beijing Time (1:00 PM Central European Time, 9:00 PM Japan Time, 7:00 AM Eastern Time)

Location: Tencent Meeting: 253-804-361 https://meeting.tencent.com/dm/y7zSZQhHFk1N

12. A fluctuation-sensitivity-timescale trade-off in feedback-controlled dynamics

Speaker: Ka Kit Kong, Peking University

Host: Shiling Liang, MPI-PKS

Abstract: Signal transduction is ubiquitous in biological systems and vital for most biological functions, which is, however, inevitably impeded by noise due to the stochastic nature of biochemical reactions. While noise attenuation mechanisms, such as feedback control, have been studied for decades, noise is not the sole factor determining the performance of signal transduction. Effective signal transduction generally necessitates small noise, high response sensitivity, and short response timescale, along with other factors. However, how noise attenuation mechanisms affect these factors simultaneously remains unclear.

Feedback control is a renowned mechanism for buffering intrinsic fluctuation in regulatory networks. Here, we study a general feedback-controlled network in which the feedback is achieved by a complex interactive module, and analytically derive a fundamental trade-off between fluctuation, sensitivity, and timescale altered by the feedback. We show that feedback control cannot infinitely suppress fluctuation without the cost of reducing sensitivity or response speed. Furthermore, the lower bound for this trade-off can be reduced up to half in non-gradient dynamical systems compared to gradient systems. We validate this trade-off as a tight bound for high-dimensional systems in nonlinear regime through numerical simulations. These results elucidate the fundamental limitation of feedback control in enhancing the information transmission capacity of regulatory networks.

References:

[1] Ka Kit Kong, and Feng Liu. “A fluctuation-sensitivity-timescale trade-off in feedback-controlled dynamics.” arXiv preprint arXiv:2410.00559 (2024).

[2] Ka Kit Kong, Chunxiong Luo, and Feng Liu. “A phase diagram structure determines the optimal sensitivity-precision trade-off in signaling systems.” Communications Physics 7.1 (2024): 80.

Time: November 9, 2024 (Saturday) 8:00 PM Beijing Time (1:00 PM Central European Time, 9:00 PM Japan Time, 7:00 AM Eastern Time)

Location: Tencent Meeting: 360-132-773 https://meeting.tencent.com/dm/sCsJjGWqQZiu

11. Robust Edge Flows in Swarming Bacteria Colonies

Speaker: He Li, IGBMC

Host: Shiling Liang, MPI-PKS

Abstract: Understanding if and how the chirality of biomolecules is transferred across scales into larger components and active processes remains elusive. For instance, flagellated bacteria swim in helical trajectories but chirality seems absent from the active turbulence dynamics they display in dense suspensions. We address this question by examining multi-scale dynamics in Paenibacillus vortex colonies. We find active turbulence without manifest chirality in the bulk, but wide, clockwise (viewed from the air side) circulation all along the tortuous centimeter-scale external boundary, while similar but counter-clockwise flows follow internal boundaries. We trace back the origin of these robust edge flows to an unexpected asymmetry at the individual level that is amplified by local interactions. We rationalize our findings with a model of noisy self-propelled particles immersed in a Stokes fluid that accounts faithfully for our observations. Our modeling and experimental efforts reveal that local nematic alignment and hydrodynamic interactions amplify the weak chiral bias in individual motion, promoting the formation of strong edge flows. The likely topological protection of these flows provides robust transport mechanism over large scales. Such robust boundary phenomena in weakly chiral active fluids may inspire new control strategies for active and biological matter.

References:

[1] He Li, Hugues Chaté, Masaki Sano, Xia-qing Shi, and H. P. Zhang, Robust edge flows in swarming bacterial colonies, Physical Review X (accepted) (2024)

[2] C. J. Ingham and E. Jacob, Swarming and complex pattern formation in Paenibacillus vortex studied by imaging and tracking cells, BMC Microbiology 8, 36 (2008).

[3] K. Dasbiswas, K. K. Mandadapu, and S. Vaikun- tanathan, Topological localization in out-of-equilibrium dissipative systems, Proceedings of the National Academy of Sciences 115, E9031 (2018).

[4] V. Soni, E. S. Bililign, S. Magkiriadou, S. Sacanna, D. Bartolo, M. J. Shelley, and W. T. M. Irvine, The odd free surface flows of a colloidal chiral fluid, Nature Physics 15, 1188 (2019).

[5] E. Lauga, W. R. DiLuzio, G. M. Whitesides, and H. A. Stone, Swimming in circles: Motion of bacteria near solid boundaries, Biophysical Journal 90, 400 (2006).

Time: October 3, 2024 (Thursday) 8:00 PM Beijing Time (2:00 PM Central European Time, 9:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 547-397-560 https://meeting.tencent.com/dm/pNfQgboP5i9X

10. Designing self-adaptive network with thermodynamics

Speaker: Mingyang Bai, Beihang University

Host: Shiling Liang, EPFL

Abstract: To realize survival goals in unknown environments, animals and plants learn the environment property and adjust their behavior accordingly. Such adaptability is widely believed to be the essence of general intelligence. Compared to fixed strategies, adaptive strategy seems more reasonable for designing complex systems in uncertain environments. However, many adaptive control methods are challenged by numerous degrees of freedom and limited information for complex systems. Inspired by thermodynamics, we propose a self-adaptation strategy enabling complex systems to adaptively realize the desired landscape in unknown environments with only macroscopic information.

We choose the macroscopic landscape as our target, which corresponds to free energy landscape in thermodynamics. In our strategy, when environmental disturbance drives system from one microstate to another, systems only use macroscopic information to decide whether to accept or reject. We derive the suitable acceptance probability from target landscape and environment entropy under detailed balance condition. To estimate environment entropy in unknown environments, we propose a simple method enabling system to update estimation on environment entropy by extending the Wang-Landau method. Thus system could adaptively realize desired target landscape in unknown environments. Then we employ our self-adaptation strategy to design a self-adaptive network programmed with desired target landscape represented by topological measures, which realizes target under several scenarios. In addition, the adaptation process is described by unique power law distinguishing our adaptive systems from non-adaptive systems. Our self-adaptive strategy can be applied to designing future intelligent complex systems and help understand the principle behind complex system adaptability and system intelligence.

References:

[1] Bai, Mingyang, and Daqing Li. “Designing self-adaptive network with thermodynamics.” arXiv preprint arXiv:2407.04930 (2024).

Time: September 14, 2024 (Saturday) 8:00 PM Beijing Time (2:00 PM Central European Time, 9:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 575-980-657 https://meeting.tencent.com/dm/fPMcOHIFggf0

9. Geometry of optimal control in chemical reaction networks

Speaker: Yikuan Zhang, Peking University

Host: Shiling Liang, EPFL

Abstract: Although optimal control (OC) has been studied in stochastic thermodynamics for systems with continuous state variables, less is known in systems with discrete state variables, such as Chemical Reaction Networks (CRNs). Here, we develop a general theoretical framework to study OC of CRNs for changing the system from an initial distribution of states to a final distribution with minimum dissipation. We derive a “Kirchhoff’s law” for the probability current in the adiabatic limit, from which the optimal kinetic rates are determined analytically for any given probability trajectory. By using the optimal rates, we show that the total dissipation is determined by a L2-distance measure in the probability space and derive an analytical expression for the metric tensor that depends on the probability distribution, network topology, and capacity of each link. Minimizing the total dissipation leads to the geodesic trajectory in the probability space and the corresponding OC protocol is determined by the Kirchhoff’s law. To demonstrate our general approach, we use it to find a lower bound for the minimum dissipation that is tighter than existing bounds obtained with only global constraints. We also apply it to simple networks, e.g., fully connected 3-state CRNs with different local constraints and show that indirect pathway and non-functional transient state can play a crucial role in switching between different probability distributions efficiently. Future directions in studying OC in CRNs by using our general framework are discussed.

References:

[1] Zhang, Y., Ouyang, Q. and Tu, Y., 2024. Geometry of optimal control in chemical reaction networks. arXiv preprint arXiv:2407.05620.

Time: August 21, 2024 (Wednesday) 8:00 PM Beijing Time (2:00 PM Central European Time, 9:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 931-530-560 https://meeting.tencent.com/dm/AujTAtguVnNM

8. Emergence of Memory in Equilibrium versus Nonequilibrium Systems

Speaker: Xizhu Zhao, Max Planck Institute for Multidisciplinary Sciences

Host: Shiling Liang, EPFL

Abstract: Experiments often probe observables that correspond to low-dimensional projections of high-dimensional dynamics. In such situations distinct microscopic configurations become lumped into the same observable state. It is well known that correlations between the observable and the hidden degrees of freedom give rise to memory effects. However, how and under which conditions these correlations emerge remain poorly understood. Here we shed light on two fundamentally different scenarios of the emergence of memory in minimal stationary systems, where observed and hidden degrees of freedom either evolve cooperatively or are coupled by a hidden nonequilibrium current. In the reversible setting the strongest memory manifests when the timescales of hidden and observed dynamics overlap, whereas, strikingly, in the driven setting maximal memory emerges under a clear timescale separation. Our results hint at the possibility of fundamental differences in the way memory emerges in equilibrium versus driven systems that may be utilized as a “diagnostic” of the underlying hidden transport mechanism.

References:

[1] Zhao, X., Hartich, D., & Godec, A. (2024). Emergence of Memory in Equilibrium versus Nonequilibrium Systems. Physical Review Letters, 132(14), 147101.

Time: June 29, 2024 (Saturday) 8:00 PM Beijing Time (2:00 PM Central European Time, 9:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 590-602-403 https://meeting.tencent.com/dm/nO1tJyz6V79w

7. Universal Fluctuation-Response Relations of Nonequilibrium Dynamics: A Trajectory Information Geometry Framework

Speaker: Jiming Zheng, UNC Chapel Hill

Host: Shiling Liang, EPFL

Abstract: Unraveling the universal principles governing the response of complex systems to environmental changes is crucial for predicting and controlling their behavior. While fluctuation-dissipation relations have been established for systems near equilibrium, a general framework for understanding the responsiveness of systems far from steady states remains elusive. Here, we introduce a novel approach based on the information geometry of stochastic trajectories to derive a set of universal thermodynamic bounds on the response of any Markov system, regardless of its proximity to steady states. This theory establishes a new paradigm in non-equilibrium statistical mechanics, providing a unified perspective on the behavior of non-stationary systems, from biological processes to engineered devices, and paving the way for designing complex responsiveness in far-from-equilibrium systems.

References: [1] Zheng, Jiming, and Zhiyue Lu. “Information Geometry and Universal Bounds on Non-stationary Responsiveness of Markov Dynamics.” arXiv preprint arXiv:2403.10952 (2024).

Time: June 1, 2024 (Saturday) 8:00 PM Beijing Time (2:00 PM Central European Time, 9:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 802-687-365 https://meeting.tencent.com/dm/J6uQE1nxmjso

6. Restart Expedites Quantum Walk Hitting Times

Speaker: Ruoyu Yin, Bar-Ilan University

Host: Shiling Liang, EPFL

Abstract: Classical first-passage times under restart are used in a wide variety of models, yet the quantum version of the problem still misses key concepts. We study the quantum hitting time with restart using a monitored quantum walk. The restart strategy eliminates the problem of dark states, i.e., cases where the particle evades detection, while maintaining the ballistic propagation which is important for a fast search. We find profound effects of quantum oscillations on the restart problem, namely, a type of instability of the mean detection time, and optimal restart times that form staircases, with sudden drops as the rate of sampling is modified. In the absence of restart and in the Zeno limit, the detection of the walker is not possible, and we examine how restart overcomes this well-known problem, showing that the optimal restart time becomes insensitive to the sampling period.

References:

[1] Yin, R. and Barkai, E., 2023. Restart expedites quantum walk hitting times. Physical Review Letters, 130(5), p.050802. [2] Yin, R. and Barkai, E., 2023. Instability in the quantum restart problem. arXiv preprint arXiv:2301.06100.

Time: December 23, 2023 (Saturday) 3:00 PM Beijing Time (8:00 AM Central European Time, 4:00 PM Japan Time, 11:00 PM Pacific Time)

Location: Tencent Meeting: 297-722-647 https://meeting.tencent.com/dm/Bi7r0uKGtsQG

5. Quantum Reliability

Speaker: Lianxiang Cui, Beijing Computational Science Research Center

Host: Shiling Liang, EPFL

Abstract: In this talk, we are going to establish a bridge between quantum mechanics and reliability in system engineering, introducing a novel framework for reliability analysis specifically designed for quantum devices with quantum coherence, known as Quantum Reliability. For engineering, the reliability characterizes equipment’s ability to function flawlessly. The concept of reliability gained its precise meaning during the twenties of the last century, coinciding with the birth of quantum mechanics. Today, with the fast advancement of quantum technology, the promotion of quantum devices enhanced by quantum coherence has become a subject of intense fascination. The preservation of a quantum device’s long-term functionality has emerged as a great concern, inevitably leading to the convergence of quantum physics and reliability engineering. The quantum reliability is proposed in a general framework, that the significant influence of quantum coherence on device structure and degradation is clearly characterized. In the future applications to quantum engineering, quantum reliability will serve as a vital measure, enabling the evaluation and optimization of quantum devices’ design. As this captivating journey unfolds, the alliance between quantum reliability and cutting-edge quantum technologies will shape a future of unparalleled reliability and innovation.

References:

[1] L. X. Cui, Y-M. Du and C. P. Sun, Phys.Rev.Lett.131.160203(2023)

Time: November 4, 2023 (Saturday) 8:00 PM Beijing Time (1:00 PM Central European Time, 9:00 PM Japan Time, 6:00 AM Eastern Time)

Location: Tencent Meeting: 882-576-393 https://meeting.tencent.com/dm/Kfaryki9ySjf

4. Cas9 Target Search and Recognition from a Physical Perspective

Speaker: Qiao Lu, OIST

Host: Shiling Liang, EPFL

Abstract: Originating from the immune system of prokaryotes, Cas9 protein can recognize any target on DNA under the guidance of RNA. We first use a physical model to analyze and reconcile seemingly contradictory experimental results, confirming that Cas9 can perform facilitated diffusion, and draw an analogy to Anderson localization in condensed matter theory, which can be extended to other protein-DNA interactions. Then we theoretically study the search efficiency of Cas9, finding an “overkill” effect and calculating its optimal solution, which is unique to Cas9 but similar to the “stability-speed paradox” in previously studied protein-DNA interactions.

References:

Q. Lu, D. Bhat, D. Stepanenko, S. Pigolotti, “Search and localization dynamics of the CRISPR/Cas9 system”, Phys. Rev. Lett. 127, 208102, arXiv/2103.10667, recommended by APS online journal Physics, (2021)

Time: October 14, 2023 (Saturday) 9:00 PM Beijing Time (3:00 PM Central European Time, 10:00 PM Japan Time, 9:00 AM Eastern Time)

Location: Tencent Meeting: 990-982-267 https://meeting.tencent.com/dm/ENloNxuEXkiz

3. Surface Tensions in Active Fluids

Speaker: Yongfeng Zhao, Schoow University

Host: Shiling Liang, EPFL

Abstract: Surface tensions are state variables that control various interfacial phenomena in equilibrium systems, including Laplace pressure jump, wetting, and interface fluctuations. Phase boundaries are also commonly found in active materials, due to the wealth of phase transitions they display, such as the motility-induced phase separation. However, in the absence of free-energy-abiding dynamics, what controls the properties of interfaces in active media remains elusive. The situation is particularly confusing for active particles interacting with purely repulsive forces, for which a liquid-vapor surface tension has been predicted to be negative [1]. This questions whether a proper surface tension can actually be defined and the properties it may control.

In this talk, we consider fluid-solid and fluid-fluid interfaces. In both cases, we show that tangential forces can be defined and measured, which allows us to provide a mechanical definition of surface tension [2]. The situation is shown to be much richer than for equilibrium systems due to the emergence of non-equilibrium currents and drags, which alter the mechanical balance at interfaces. This is shown to play an important role in wetting phenomena, where we show how the Young-Dupré’s law, which controls the contact angle of a droplet partially wetting a solid surface, has to be generalized for active fluids.

References:

[1] Julian Bialké, Jonathan T. Siebert, Hartmut Löwen, and Thomas Speck, Phys. Rev. Lett. 115, 098301 (2015)

[2] R. Zakine, Y. Zhao, M. Knežević, A. Daerr, Y. Kafri, J. Tailleur, and F. van Wijland, Phys. Rev. Lett. 124, 248003 (2020)

Time: September 10, 2023 (Sunday) 8:00 PM Beijing Time (2:00 PM Central European Time, 9:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 443-178-011 https://meeting.tencent.com/dm/z7Lk9ZNISGM2

2. Expanding Sensory Horizons: Multiplexing and Temporal Pattern Recognition in Stochastic Sensors

Speaker: Zhiyue Lu, University of North Carolina at Chapel Hill

Host: Shiling Liang, EPFL

Abstract: Macromolecular sensory receptors, despite their microscopic scale, serve as essential information transduction units in biological cells. Contrary to the prevailing assumption that thermal noise impedes information transduction, we find that it can facilitate multiplexing, enabling a single sensor to scramble and convey multiple information channels. We demonstrate that even a simple binary-state ligand-receptor sensor can simultaneously encode multiple independent environmental variables. We also propose a general theory of stochastic sensory multiplexing, suggesting two theoretical upper bounds on a sensor’s sensory ability. Building on this foundation, we focus on the sensor’s state dynamics and explore its capacity for discerning temporal patterns within a limited sensing period. We present a theoretical upper bound for a sensor’s ability to distinguish temporal patterns of different ligand concentration protocols. This upper bound is expressed as a weighted expectation of the cumulative number of binding events within the observation time. This insight illuminates the path for designing stochastic sensors, opening the door to developing more efficient artificial sensors and enhancing our understanding of sensory processes in biology.

Time: June 25, 2023 (Sunday) 8:00 PM Beijing Time (2:00 PM Central European Time, 9:00 PM Japan Time, 8:00 AM Eastern Time)

Location: Tencent Meeting: 270-811-198 https://meeting.tencent.com/dm/JORutG9nmaal

1. The nonequilibrium thermodynamics of flocking of active spins

Speaker: Qiwei Yu, Princeton University

Host: Shiling Liang, EPFL

Abstract: The collective coherent motion known as flocking is a nonequilibrium phenomenon and is sustained by a continuous input of free energy. By studying the energy dissipation of the active Ising model (AIM), we show that the energy cost can be decomposed into two parts, namely the cost for self-propelled motion and an additional energy dissipation required to align spins in order to maintain the flocking order. We find that this additional alignment dissipation reaches its maximum at the flocking transition point in the form of a cusp with a discontinuous first derivative with respect to the interaction strength. To understand this singular behavior, we analytically solve the two-site and three-site AIM models and obtain the exact dependence of the alignment dissipation on the flocking order parameter and control parameter, which explains the cusped dissipation maximum at the flocking transition. Our results reveal a trade-off between the energy cost of the system and its performance measured by the flocking speed and sensitivity to external perturbations. This trade-off relationship provides a new perspective for understanding the dynamics of natural flocks and designing optimal artificial flocking systems.

References:

[1] Yu, Q. and Tu, Y., 2022. Energy Cost for Flocking of Active Spins: The Cusped Dissipation Maximum at the Flocking Transition. Physical Review Letters, 129(27), p.278001.

Time: May 13, 2023 (Saturday) 9:00 PM Beijing Time (3:00 PM Central European Time, 10:00 PM Japan Time, 9:00 AM Eastern Time)

Location: Tencent Meeting: 829-938-730 https://meeting.tencent.com/dm/Kru1K7lDPEro