Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Z01: Chaotic and Driven Systems |
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Sponsoring Units: GSNP Chair: Marija Vucelja, Univ of Virginia Room: Room 124 |
Friday, March 10, 2023 11:30AM - 11:42AM |
Z01.00001: Nonlinear dynamics, chaos and applications in intertropical Africa Paul Woafo The contribution of Africa and specifically that of the intertropical Africa is low. But since some years, it is noticed, some research groups are contributing regularly in the field of nonlinear dynamics and chaos, using both theoretical and experimental methods. This presentation will review the main contributions obtained by those research groups located mainly in the following three countries: Cameroon, Benin and Nigeria. The goal is not only to present scientific results, but also provide information to APS members on the development of physics in intertropical Africa. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z01.00002: A toy computational model of evolution of directed motility Sergio Eraso, Jennifer Rieser, Ilya M Nemenman Nonequilibrium systems dissipate energy and hence break time-reversal symmetry. As a result, a polarization vector in such systems is allowed to couple to the system's velocity vector. Thus, one expects that, generically, a polarized nonequilibrium system would exhibit directed motion along the polarization direction. However, the coupling between polarization and motion may be very weak. Here we conduct a computational experiment with a model of a 1-d gas of active agents (motors) in an enclosure (cell) with polarized mechanical properties to demonstrate that (1) generic values of the parameters of the system, indeed, result in a weak directed motion, and (2) a biological evolution-inspired genetic algorithm can strongly amplify the polarization-velocity coupling in relatively few generations. This toy model suggests that directed motility (e.g., chemotaxis) may be present generically in the context of living cells, and evolution may only need to amplify the taxis speed instead of performing a much harder task of evolving the taxis from scratch. |
Friday, March 10, 2023 11:54AM - 12:06PM |
Z01.00003: Understanding complex wave scattering systems through the Generalized Wigner-Smith operator Jared M Erb, Steven M Anlage We use the Generalized Wigner-Smith (GWS) operator Q?=-iS-1dS/d?, where S is the scattering matrix of a ray-chaotic enclosure and ? is an arbitrary parameter, to understand the dependence of the scattering matrix on various parameters of interest. A particular example of the GWS operator is the Wigner time delay operator where ? is frequency, and we can use the eigenvalues of that operator to determine the locations of the zeros and poles of S and to find conditions for coherent perfect absorption (CPA). By using the GWS operator, we can gather more information about how a complex scattering system interacts with incoming waves, and use this information to create conditions for CPA, create hot or cold spots in specific areas, etc. In our experimental setup, we use a nonlinear variable globally biased varactor metasurface inside a ray chaotic quarter bowtie microwave billiard. In this setup we can explore how the scattering matrix nonlinearity depends on frequency, bias voltage, rf power, etc. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z01.00004: Perturbation-Induced Quantum Scars Joonas Keski-Rahkonen, Eric J Heller, Esa Rasanen The scarring of a single-particle wave function is one of the most striking phenomena in the field of quantum chaos. In consequence of quantum interference, the probability density of a quantum state can be concentrated along short unstable periodic orbits of the corresponding chaotic classical system, and the quantum state bears an imprint of the orbit – a quantum scar. In addition to this conventional scarring, we here consider a new class of quantum scars: some of the high-energy eigenstates of a locally perturbed quantum well are strongly scarred by the periodic orbits of the unperturbed classical counterpart. This perturbation-induced scarring emerges as a combination of near-degenerate states in the unperturbed system and the localized nature of the perturbation. Besides being a striking visualization of quantum-mechanical suppression of classical chaos, the existence, geometry and orientation of the scars are highly controllable. In addition, these kind of scars can be exploited to propagate quantum wave packets in the perturbed system with very high fidelity, thus paving a way towards new experimental schemes to manipulate electronic current in two-dimensional nanostructures. In particular, the generality of the presented scarring mechanism indicates that these new scars may be much more common in disordered quantum systems than previously thought. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z01.00005: Sublinear Sensors with Enhanced Signal-to-Noise Ratio Arunn Suntharalingam, Lucas Fernández-Alcázar, Rodion Kononchuk, Tsampikos Kottos The enhanced wave-matter interactions occurring at the exceptional point degeneracies (EPDs) of the resonant spectrum of non-Hermitian systems has inspired a whole new class of hypersensitive sensors. The main feature of these sensors was their enhanced signal due to a sublinear resonant detuning from the EPD, occurring when a perturbing agent was interacting with the sensor. The initial excitement for these developments has been followed by a skepticism associated with the observation that in some lasing platforms the enhanced measured signal is accompanied by an equally enhanced noise. The excess noise can be of fundamental nature (owing to the eigenbasis collapse) or of technical nature associated with the amplification mechanisms utilized for the realization of EPDs. Here, we proposed another EPD scheme based on the lasing modes of a parity-time symmetric electromechanical system with an additional saturable lossy nonlinearity. We show that in the appropriate parameter range, the system has two stable lasing modes which form a EPD at a critical value of the coupling between the gain and loss resonators of the system. A subsequent noise analysis indicates that nonlinearities suppress the noise leading to an order of magnitude enhancement of the signal-to-noise ration in the proximity of the EPD. The experimental results are nicely supported by a theoretical analysis. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z01.00006: The Metastable State of the FPUT Problem Nachiket Karve, Kristen Bestavros, David K Campbell We study the approach to thermalization in the Fermi-Pasta-Ulam-Tsingou (FPUT) problem of a chain of non-linearly coupled oscillators. It is expected that these non-linear interactions play a role in the exchange of energy between different modes of the chain leading to equipartition. However, it is observed that giving low to intermediate energies to the initial wave packet results in the formation of a far-from-equilibrium ”metastable” state which can persist for a very long time. We investigate the existence of a critical energy below which the system does not reach equilibrium at all and study this threshold’s dependence on the system’s size. We compare and extend previous studies of the metastable state and find consistency. Further, we compare our results to theoretical predictions made with the multi-wave resonant approach [1]. |
Friday, March 10, 2023 12:42PM - 12:54PM Author not Attending |
Z01.00007: The Mpemba effect for phase transitions by Landau theory Roi Holtzman, Oren Raz The Mpemba effect describes the situation in which a hot system cools faster than an identical copy that is initiated at a colder temperature. In many of the experimental observations of the effect, e.g. in water and clathrate hydrates, it is defined by the phase transition timing. However, none of the theoretical investigations so far considered the timing of the phase transition, and most of the abstract models used to explore the Mpemba effect do not have a phase transition. We show how one can define the phase transition time in a non-equilibrium state using the Landau theory for phase transitions. With this definition, we show that a Mpemba effect with respect to phase transitions can exist in such models, namely that the hotter system undergoes the transition before the colder one when quenched to a cold temperature. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z01.00008: Anomalous thermal relaxation in unimolecular chemical reactions and connections to symmetries of the system Saikat Bera, Matt R Walker, Marija Vucelja The Mpemba effect is a prime example of anomalous thermal relaxations. Imagine two identical systems are prepared at different temperatures, and each is separately coupled to an infinite bath with yet another temperature. If the process of relaxing to the environment were quasistatic, the system with a smaller temperature difference would asymptotically equilibrate faster. However, things might not be so for other kinds of relaxation dynamics. The system, which initially has a larger mismatch between its and the environment's temperature, can, in some cases, equilibrate sooner. When this happens, we call it the Mpemba effect. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z01.00009: The Strong Mpemba effect in over-damped Langevin dynamics and connections to Kramer's escape rate Matt R Walker, Marija Vucelja Rapid cooling or heating of a physical system to its environment can lead to unusual thermal relaxation phenomena, which we call anomalous. A prime example of anomalous thermal relaxation is the Mpemba effect. The phenomenon occurs in cooling when a system prepared at a hot temperature overtakes an identical system prepared at a warm temperature and equilibrates faster to the cold environment. A similar effect exists in heating. Comparing two identical physical systems in their relaxation to the environment, we would expect that the system with a smaller mismatch between its own and the environment's temperature will thermalize faster -- yet it is not always the case. The effect was observed in various physical systems, including water, magnetic systems, clathrate hydrates, polymers, and colloidal particle systems. Here study the Mpemba effect in over-damped Langevin dynamics. We build upon our previous results for the case of piecewise-continuous potentials and on the experimental observations of Kumar and Bechhoeffer (Nature, 2020). Our analytical results are within the limit of small diffusion, which is the limit where Kramer's escape rate can be analytically determined. We connect the properties of the potential and Kramer's escape rate with the effect's existence. The continuous case extends and generalizes our previous work. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z01.00010: Thermodynamic constraints on the nonequilibrium response of one-dimensional diffusions Qi Gao, Jordan M Horowitz, Hyun-Myung Chun The utility of the fluctuation-dissipation theorem near equilibrium has led to significant interest in expanding its validity and developing generalizations to nonequilibrium situations. Such generalizations, while immensely informative, tend to be rather formal. In this poster session, I will suggest a new approach to the study of static response of nonequilibrium steady states that can be modeled as one-dimensional diffusions on the circle. I will demonstrate that an arbitrary perturbation can be broken up into a combination of three specific classes of perturbations that can be fruitfully addressed individually. For each class, there is a simple formula that quantitatively characterizes the response in terms of the strength of nonequilibrium driving valid arbitrarily far from equilibrium. As an application, I will discuss how these predictions allow us to bound the violation of the fluctuation-dissipation theorem in nonequilibrium steady states in terms of the degree of nonequilibrium. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z01.00011: Theoretical analysis and experiment on large ions adsorbed in charged small micropores: A highly nonequilibrium system Yu Qiao, Zhaoru Shang, Meng Wang, Rui Kou In this research, we investigate the concept of locally nonchaotic barrier. The barrier can be either an energy barrier or an entropy barrier. The barrier width is much less than the nominal mean free path of the particles, so that the particle-barrier interaction tends to be nonchaotic. Our analyses suggest that under the condition of local nonchaoticity, the steady-state particle distribution cannot reach thermodynamic equilibrium. It has interesting effects: When the system is operated in an isothermal cycle, the produced work may be effectively more than the consumed work; when the barrier forms an asymmetric couple with an equilibrium counterpart, at the steady state, the particle velocity distribution may be anisotropic. The theorical and numerical results were validated by an experiment on large ions adsorbed in small charged micropores. The ion size was slightly less than the micropore diameter, but larger than the micropore radius. The testing data demonstrated a large voltage difference, as the ion concentration was varied. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z01.00012: Temporal and spatial Taylor's law induced by synchronization of periodic and chaotic oscillators Yuzuru Mitsui, Hiroshi Kori Taylor's law, a scaling relationship between the mean and variance, has been confirmed in various fields. However, the following three questions are unclear. 1. Why is it widely observed especially in ecosystems? 2. Why are the exponents around 2 often recorded in ecosystems? 3. Are the mechanisms of temporal and spatial Taylor's law the same? Here, we show that synchronization, a widely observed phenomenon in ecosystems as well as Taylor's law, can induce Taylor's law. In particular, we find numerically and analytically that strong synchronization, in which time series are proportional to each other, induces temporal and spatial Taylor's law with exponent 2. |
Friday, March 10, 2023 1:54PM - 2:06PM |
Z01.00013: Swarmalators with thermal noise Hyunsuk Hong, Kevin P O'Keeffe, Jae Sung Lee, Hyunggyu Park We study of a population of swarmalators, mobile versions of phase oscillators that both sync in time and swarm through space. In particular, we study a XY-type model where the swarmalators run on a 1D ring and are subject to thermal noise. We find four collective states, some of which capture the behavior of real-world swarmalators such as vinegar eels and sperm. Of the four states, the most surprising is the 'mixed state', which blends two of the other states (such mixed states do not occur in Kuramoto model of phase oscillators, for instance). We present the full phase diagram and compute many of the stability boundaries analytically. Being tractable, our model is a natural toy model for studying systems which self-assemble and self-synchronize interdependently. |
Friday, March 10, 2023 2:06PM - 2:18PM |
Z01.00014: Anisotropic Domain Structure in Late-Stage Coarsening Benjamin P Vollmayr-Lee, Jaime Wallace, Ella Carlander We study the asymptotic late stage of phase separation dynamics, where the characteristic domain size grows as a power of time, and the growth exponent and scaled domain structure are universal, behavior suggestive of a dynamical renormalization group (RG) fixed point. We consider in particular the influence of surface tension anistropy on the resulting growth and structure. Since this RG fixed point is not accessible via a controlled perturbation theory, we resort to simulations of the two-dimensional Cahn-Hilliard equation, modified to include an anisotropic surface tension. We find that anisotropy persists in the asymptotic state, modifying the domain structure but not the growth exponent. The Porod tail of the angle-resolved structure factor S(k,t) provides a sensitive diagnostic, which allows us to quantify the degree of anistropy in the scaled domain structure. Evidently the underlying RG fixed point must depend on the full shape of the surface tension anisotropy. |
Friday, March 10, 2023 2:18PM - 2:30PM |
Z01.00015: Dendritic crystal growth: A comparison of ammonium nitrate and ammonium chloride Andrew J Dougherty, Charles Mann Dendritic crystal growth is an important example of nonequilibrium pattern formation that involves both nonlinear dynamics and noise-driven effects. It is commonly observed in the growth of metal alloys, but can also be observed in the solidification of some transparent organic and inorganic compounds. The resulting large-scale structures are sensitively dependent on relatively small effects, such as surface tension, and also on small anisotropies in those quantities. In this work, we present new results for ammonium nitrate dendrites grown from supersaturated aqueous solution, and compare them with previous results for the well-studied ammonium chloride system. This new system has been studied previously by van Driel et al.[1]. Specifically, we present new measurements of the tip radius ρ, growth speed v, and sidebranch spacing λ, along with initial estimates of the stability constant σ*=2d0D/vρ2, where D is the chemical diffusion constant and d0 is the capillary length. Preliminary results at higher temperatures show non-parabolic dendrites, where the tip is approximately a hemispherical cap followed almost immediately be a large set of sidebranches. We will discuss similarities and differences between the two materials. |
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