High Density Regime Research Articles

Orthogonality catastrophe beyond bosonization from post-selection

We show that the dynamics induced by post-selected measurements can serve as a controlled route to access physical processes beyond the boundaries of Luttinger liquid physics. We consider a one-dimensional fermionic wire whose dynamics results from a sequence of weak measurements of the fermionic density at a given site, interspersed with unitary hopping dynamics. This realizes a non-Hermitian variant of the celebrated instance of a local scatterer in a fermionic system and its ensuing orthogonality catastrophe. We observe a distinct crossover in the system's time evolution as a function of the fermion density. In the high-density regime, reminiscent of the Hermitian case, a bosonized version of the model properly describes the dynamics while, as we delve into the low-density regime, the validity of bosonization breaks down, giving rise to irreversible behavior. Notably, this crossover from reversible to irreversible dynamics is nonperturbative in the measurement rate and can manifest itself even with relatively shallow measurement rates, provided that the system's density remains below the crossover threshold. Our results render a conceptually transparent model for exploring nonperturbative effects beyond bosonization, which could be used as a stepping stone to explore novel routes for the control of nonlinear dynamics in low-dimensional quantum systems. Published by the American Physical Society 2024

Lattice study on finite density QC2D towards zero temperature

We investigate the phase structure and the equation of state (EoS) for dense two-color QCD (QC2D) at low temperature (T = 40 MeV, 324 lattice) for the purpose of extending our previous works [1, 2] at T = 80 MeV (164 lattice). Indeed, a rich phase structure below the pseudo-critical temperature Tc as a function of quark chemical potential μ has been revealed, but finite volume effects in a high-density regime sometimes cause a wrong understanding. Therefore, it is important to investigate the temperature dependence down to zero temperature with large-volume simulations. By performing 324 simulations, we obtain essentially similar results to the previous ones, but we are now allowed to get a fine understanding of the phase structure via the temperature dependence. Most importantly, we find that the hadronic-matter phase, which is composed of thermally excited hadrons, shrinks with decreasing temperature and that the diquark condensate scales as ⟨qq⟩ ∝ μ2 in the BCS phase, a property missing at T = 80 MeV. From careful analyses, furthermore, we confirm a tentative conclusion that the topological susceptibility is independent of μ. We also show the temperature dependence of the pressure, internal energy, and sound velocity as a function of μ. The pressure increases around the hadronic-superfluid phase transition more rapidly at the lower temperature, while the temperature dependence of the sound velocity is invisible. Breaking of the conformal bound is also confirmed thanks to the smaller statistical error.

Deep learning for melt pool depth contour prediction from surface thermal images via vision transformers

Anomalous melt pools during metal additive manufacturing (AM) can lead to deteriorated mechanical and fatigue performance. In-situ monitoring of the melt pool subsurface morphology requires specialized equipment that may not be readily accessible or scalable. Therefore, we introduce a machine learning framework to correlate in-situ two-color thermal images observed via high-speed color imaging to the two-dimensional profile of the melt pool cross-section. We employ a hybrid CNN-Transformer architecture to establish a correlation between single bead off-axis thermal image sequences and melt pool cross-section contours measured via optical microscopy. Specifically, a ResNet model embeds the spatial information contained within the thermal images to a latent vector, while a Transformer model correlates the sequence of embedded vectors to extract temporal information. The performance of this model is evaluated through dimensional and geometric comparisons to the corresponding experimental no-powder melt pool observations. Our framework is able to model the curvature of the subsurface melt pool structure, with improved performance in high energy density regimes compared to analytical models. Additionally, the use of ratiometric temperature estimates improves the accuracy of the model predictions compared to monochromatic imaging. This work establishes a framework extensible towards powder-based AM builds.

Which Insights Can Gas Diffusion Electrode Half-Cell Experiments Give into Activity Trends and Transport Phenomena of Membrane Electrode Assemblies?

In order to push the energy turnaround forward, research and development on technologies enabling storage and release of renewable energies, such as water electrolysis and fuel cells is vital in the current decade. For both processes it is essential to collect meaningful data for catalyst activity in terms of transferability to the industrial application already on the lab-scale and at an early stage of material development. Gas diffusion electrode (GDE) half-cell setups were recently presented as a fast and cost-effective tool to characterize oxygen reduction reaction (ORR) catalyst layers at fuel cell relevant potentials and current densities (3 A cm-2) [1]. An Inter-lab comparison demonstrated that GDE testing with various, slightly differing setups can deliver data that is both reliable and comparable if standardized measurement protocols are followed [2]. On the way to widespread application, it is essential to evaluate to which extend GDE half-cell measurements can provide reasonable trends of how catalyst layer properties influence ORR activity in membrane electrode assembly (MEA) applications, despite the major influence of the active metal itself. Elucidating possibilities and limitations of GDE half-cell measurements to study catalyst layer influences is scope of this study.The transferability of trends was studied for i) an ionic liquid modified and unmodified Pt/C catalyst (following our previous work [3]) and ii) employing nitrogen modified carbon support at different ionomer to carbon ratios (following the work of Ott et al. [4]). Regarding the activity increase due to IL modification we will show that rotating disk electrode (RDE) and GDE results at low current densities show the same trend. GDE testing also shows a maximum activity depending on the IL loading at slightly elevated current densities. In the high current density regime, however, MEA testing showed a negative effect of the IL modification, which was also obtained correctly within the GDE testing at the same current densities. For the N-doped Pt/C catalyst a positive effect was observed in MEA characterization with low ionomer content under dry conditions, where proton transport losses are dominant for the unmodified catalyst. However, at higher I/C ratio and under wet conditions, where proton transport is sufficient for both unmodified and N-doped catalyst, worse performance after N modification is observed in the high current density regime. During GDE evaluation only the latter phenomenon could be capture and the unmodified catalyst showed a superior performance over the N-doped material at any I/C ratio in the ohmic and in the mass transport limiting regime.In summary, we showed that GDE half-cell experiments, where the catalyst layer is in direct contact with the liquid electrolyte, can be used to reliably predict trends in catalytic activity for real MEAs at high current densities that are related to differences in oxygen mass transport [5]. However, differences in catalytic activity being related to proton accessibility especially at lower relative humidities cannot be captured completely, as the catalyst layer is always wetted fully. An introduction of an ionomer membrane between catalyst layer and liquid electrolyte might be necessary during GDE evaluation for a reliable description of all transport phenomena in real fuel cells. Nevertheless, our results indicate that GDE measurements without the utilization of an ionomer membrane allow for the study of oxygen mass transport properties independent of other transport phenomena at fuel cell relevant current densities.Literature:[1] Schmitt et al. Electrochemistry Communications 2022, 141, 107362 [2] Ehelebe et al. ACS Energy Lett. 2022, 7, 816-826. [3] Zhang et al. Advanced Functional Materials 31.28 (2021): 2010977 [4] Ott et al. Nature materials 19.1 (2020): 77-85. [5] Schmitt et al. Energy Adv. 2023, 2, 854.

The high dust density regime of dusty plasma: Theory and simulations

It is shown that the dust density regimes in the dusty plasma are characterized by two complementary screening processes: (i) the low dust density regime where the Debye screening is the dominant process and (ii) the high dust density regime where the “Coulomb screening” is the dominant process. The Debye regime is characterized by a state where all dust particles carry an equal and constant charge. The high dust density regime or the “Coulomb plasma” regime is characterized by (a) “Coulomb screening” where the dust charge depends on the spatial location and is screened by other dust particles in the vicinity by charge reduction, (b) “asymptotic freedom” where dust particles, which on an average carry minimal electric charge, are asymptotically free in the high dust density limit, (c) uniform dust charge density and plasma potential, (d) dust charge neutralization by a uniform background of hot ions, and (e) dust is weakly coupled due to strong Coulomb screening. Thus, the dusty plasma is essentially a weakly coupled, one-component plasma with screening in the high dust density limit. Molecular dynamics (MD) simulations verify these properties. The MD simulations are performed, using a recently proposed Hamiltonian formalism to study the dynamics of Yukawa particles carrying variable electric charge. A hydrodynamic model for describing the collective properties of Coulomb plasma and its characteristic acoustic mode called the “Coulomb acoustic mode” arising due to imperfect Coulomb screening is given.

Ground state energy of Bogoliubov energy functional in the high density limit

We consider the Bogoliubov energy functional proposed by Napiórkowski, Reuvers and Solovej and analize it in the high density regime. We derive a two term asymptotic expansion of the ground state energy.

Self-diffusion coefficient as a function of the thermodynamic factor.

Much effort has been put into developing theories for dense fluids; as a result of these efforts many theories work for a certain type of particle or in a certain concentration regime. Rosenfeld proposed a dependence of the self-diffusion coefficient on the excess entropy. Our proposal is similar to Rosenfeld's in that it also attempts to describe diffusion in terms of a thermodynamic function but, instead of the excess entropy, we use the thermodynamic factor or the excess chemical potential. Simulations were taken for hard spheres and our model was fitted with two free parameters. Simulations were then carried out for a Lennard-Jones gas and our model correctly described the new data with the value of the free parameters that we had obtained for hard spheres. This is a feature of our model that we wish to emphasize, since the usual situation is that parameters have to be readjusted for different interaction potentials. An experimental xenon self-diffusion data set was used as an example of where the model can be applied, especially in the high-density regime.

Improved Energy Resolution Measurements of Electron Precipitation Observed During an IPDP‐Type EMIC Event

AbstractHigh energy resolution DEMETER satellite observations from the Instrument for the Detection of Particle (IDP) are analyzed during an electromagnetic ion cyclotron (EMIC)‐induced electron precipitation event. Analysis of an Interval Pulsation with Diminishing Periods (IPDP)‐type EMIC wave event, using combined satellite observations to correct for incident proton contamination, detected an energy precipitation spectrum ranging from ∼150 keV to ∼1.5 MeV. While inconsistent with many theoretical predictions of >1 MeV EMIC‐induced electron precipitation, the finding is consistent with an increasing number of experimentally observed events detected using lower resolution integral channel measurements on the POES, FIREBIRD, and ELFIN satellites. Revised and improved DEMETER differential energy fluxes, after correction for incident proton contamination shows that they agree to within 40% in peak flux magnitude, and 85 keV (within 40%) for the energy at which the peak occurred as calculated from POES integral channel electron precipitation measurements. This work shows that a subset of EMIC waves found close to the plasmapause, that is, IPDP‐type rising tone events, can produce electron precipitation with peak energies substantially below 1 MeV. The rising tone features of IPDP EMIC waves, along with the association with the high cold plasma density regime, and the rapidly varying electron density gradients of the plasmapause may be an important factor in the generation of such low energy precipitation, co‐incident with a high energy tail. Our work highlights the importance of undertaking proton contamination correction when using the high‐resolution DEMETER particle measurements to investigate EMIC‐driven electron precipitation.

Nonrelativistic trace anomaly and equation of state in dense fermionic matter

We investigate theoretically a nonrelativistic trace anomaly and its impact on the low-temperature equation of state in spatially one-dimensional three-component fermionic systems with a three-body interaction, which exhibit a nontrivial three-body crossover from a bound trimer gas to dense fermionic matter with increasing density. By applying the G-matrix approach to the three-body interaction, we obtain the analytical expression for the ground-state equation of state relevant to the high-density degenerate regime and thereby address how the three-body contact or, equivalently, the trace anomaly emerges. The analytical results are compared with the recent quantum Monte Carlo data. Our study of the trace anomaly and the sound speed could have some relevance to the physics of hadron-quark crossover in compact stars. Published by the American Physical Society 2024

A high-density and high-confinement tokamak plasma regime for fusion energy

The tokamak approach, utilizing a toroidal magnetic field configuration to confine a hot plasma, is one of the most promising designs for developing reactors that can exploit nuclear fusion to generate electrical energy1,2. To reach the goal of an economical reactor, most tokamak reactor designs3–10 simultaneously require reaching a plasma line-averaged density above an empirical limit—the so-called Greenwald density11—and attaining an energy confinement quality better than the standard high-confinement mode12,13. However, such an operating regime has never been verified in experiments. In addition, a long-standing challenge in the high-confinement mode has been the compatibility between a high-performance core and avoiding large, transient edge perturbations that can cause very high heat loads on the plasma-facing-components in tokamaks. Here we report the demonstration of stable tokamak plasmas with a line-averaged density approximately 20% above the Greenwald density and an energy confinement quality of approximately 50% better than the standard high-confinement mode, which was realized by taking advantage of the enhanced suppression of turbulent transport granted by high density-gradients in the high-poloidal-beta scenario14,15. Furthermore, our experimental results show an integration of very low edge transient perturbations with the high normalized density and confinement core. The operating regime we report supports some critical requirements in many fusion reactor designs all over the world and opens a potential avenue to an operating point for producing economically attractive fusion energy.

Modeling of high-field-side high-density regime in the Globus-M2 tokamak

Formation of a high-field-side high-density (HFSHD) regime and the role of the high-field-side (HFS) poloidal electric field in the scrape-off layer of the spherical tokamak Globus-M2 are analyzed using SOLPS-ITER edge plasma simulations. The dependence of the HFS poloidal electric field sign and, consequently, radial drift fluxes on the discharge density is discussed. It is demonstrated that the HFS poloidal electric field is the key element in the formation of a HFSHD regime in the Globus-M2 tokamak as in ASDEX Upgrade. It is demonstrated that the physics of HFSHD formation in a small spherical tokamak is similar to that suggested by Kaveeva et al (2009 36th EPS Conf. on Plasma Physics) and is in line with experimental observations and modeling, performed later on ASDEX Upgrade.

Static and Dynamic Properties of SPC/E Water Model

In this work, we have studied static and dynamic properties of bulk water using SPC/E water model. We have considered 1500 water molecules confined to a three dimensional box. LAMMPS software has been used to perform molecular dynamic simulation under canonical ensemble. The partial radial distribution functions, diffusion coefficients, velocity autocorrelation functions, and mean square displacements have been calculated at 300K for different densities ranging from 900 kg/m3 to 1000 kg/m3. The principle peak heights of the partial radial distribution functions are found to decrease with increase in high density regime showing abnormal behaviour in this density regime.

Local Rotational Jamming and Multi-Stage Hyperuniformities in an Active Spinner System

An active system consisting of many self-spinning dimers is simulated, and a distinct local rotational jamming transition is observed as the density increases. In the low density regime, the system stays in an absorbing state, in which each dimer rotates independently subject to the applied torque; while in the high density regime, a fraction of the dimers become rotationally jammed into local clusters, and the system exhibits microphase-separation like two-phase morphologies. For high enough densities, the system becomes completely jammed in both rotational and translational degrees of freedom. Such a simple system is found to exhibit rich and multiscale disordered hyperuniformities among the above phases: the absorbing state shows a critical hyperuniformity of the strongest class and subcritically preserves the vanishing density fluctuation scaling up to some length scale; the locally jammed state shows a two-phase hyperuniformity conversely beyond some length scale with respect to the phase cluster sizes; the totally jammed state appears to be a monomer crystal, but intrinsically loses large-scale hyperuniformity. These results are inspiring for designing novel phase-separation and disordered hyperuniform systems through dynamical organization.

Fermionic physics from abinitio path integral Monte Carlo simulations of fictitious identical particles.

The abinitio path integral Monte Carlo (PIMC) method is one of the most successful methods in statistical physics, quantum chemistry and related fields, but its application to quantum degenerate Fermi systems is severely hampered by an exponential computational bottleneck: the notorious fermion signproblem. Very recently, Xiong and Xiong [J. Chem. Phys. 157, 094112 (2022)] have suggested to partially circumvent the signproblem by carrying out simulations of fictitious systems guided by an interpolating continuous variable ξ ∈ [-1, 1], with the physical Fermi- and Bose-statistics corresponding to ξ = -1 and ξ = 1. It has been proposed that information about the fermionic limit might be obtained by calculations within the bosonic sector ξ > 0 combined with an extrapolation throughout the fermionic sector ξ < 0, essentially bypassing the signproblem. Here, we show how the inclusion of the artificial parameter ξ can be interpreted as an effective penalty on the formation of permutation cycles in the PIMC simulation. We demonstrate that the proposed extrapolation method breaks down for moderate to high quantum degeneracy. Instead, the method constitutes a valuable tool for the description of large Fermi-systems of weak quantum degeneracy. This is demonstrated for electrons in a 2D harmonic trap and for the uniform electron gas (UEG), where we find excellent agreement (∼0.5%) with exact configuration PIMC results in the high-density regime while attaining a speed-up exceeding 11 orders of magnitude. Finally, we extend the idea beyond the energy and analyze the radial density distribution (2D trap), as well as the static structure factor and imaginary-time density-density correlation function (UEG).

Growth Kinetics of Random Sequential Adsorption Packings Built of Two-Dimensional Shapes with Discrete Orientations

We studied random sequential adsorption packings constructed from rectangles, ellipses, and discorectangles, where the orientations of constituent shapes were picked from discrete sets of values with varying spacing. It allowed us to monitor the transition between the two edge cases: the parallel alignment and the arbitrary, continuous orientation of the shapes within the packing. The packings were generated numerically. Apart from determining the kinetics of packing growth in low- and high-density regimes, we analyzed the results in terms of packing density and probed the microstructural properties using the density autocorrelation function.

Polarized room-temperature polariton lasing in elliptical microcavities filled with fluorescent proteins

Organic exciton-polaritons, which arise from the strong light-matter coupling between excitons in organic molecules and cavity photons, have emerged as a versatile platform for the investigation of polariton lasing, Bose-Einstein condensation and many-body phenomena at ambient conditions. Here, we study the condensation of exciton-polaritons in fluorescent protein-filled microcavities with elliptical cross-sections. The structural anisotropy of these cavities yields a distinct optical polarization splitting, which we investigate both experimentally and numerically. In the high-density regime of exciton-polaritons, the pronounced polarization splitting of the fundamental polaritonic resonance enforces selective condensation in one linearly polarized polaritonic mode. Our findings constitute a solid basis for polarization engineering in room-temperature polariton condensates.

Classical models may be a better explanation of the Jiuzhang 1.0 Gaussian Boson Sampler than its targeted squeezed light model

Recently, Zhong et al. [1, 2] performed landmark Gaussian boson sampling experiments with up to 144 modes using threshold detectors. The authors claim to have achieved quantum computational advantage with the implementation of these experiments, named Jiuzhang 1.0 and Jiuzhang 2.0. Their experimental results are validated against several classical hypotheses and adversaries using tests such as the comparison of statistical correlations between modes, Bayesian hypothesis testing and the Heavy Output Generation (HOG) test. In this work we propose an alternative classical hypothesis for the validation of these experiments. We use the probability distribution of mixtures of coherent states sent into a lossy interferometer; these input mixed states, which we term squashed states, have vacuum fluctuations in one quadrature and excess fluctuations in the other. We find that for configurations in the high photon number density regime, the comparison of statistical correlations does not tell apart the ground truth of the experiment (two-mode squeezed states sent into an interferometer) from our alternative hypothesis. On the other hand, the Bayesian test indicates that, for all configurations excepting Jiuzhang 1.0, the ground truth is a more likely explanation of the experimental data than our alternative hypothesis. A similar result is obtained for the HOG test: for all configurations of Jiuzhang 2.0, the test indicates that the experimental samples have higher ground truth probability than the samples obtained from our alternative distribution; for Jiuzhang 1.0 the test is inconclusive. Our results provide a new hypothesis that should be considered in the validation of future GBS experiments, and shed light into the need to identify proper metrics to verify quantum advantage in the context of threshold GBS. Additionally, they indicate that a classical explanation of the Jiuzhang 1.0 experiment, lacking any quantum features, has not been ruled out.

Collective quantum approach to resonant photo-plasmonic effect

In this research, we investigate the resonant photo-plasmonic effect in the framework of the dual length-scale driven damped collective quantum excitations of the spill-out electrons at the metal surface. The bulk plasmon and the spill-out electron excitations are modeled using the Hermitian and the damped non-Hermitian effective Schrödinger–Poisson systems, respectively, matched appropriately at the metal–vacuum boundary. It is shown that, when driven by an external field, the system behaves quite analogous to the driven damped mechanical oscillations in the wavenumber domain, causing the spill-out electron collective excitation resonance. However, in the current model, the resonance takes place due to matching of the wavenumber of the driving pseudoforce with that of the spill-out electron excitations, which can be either due to single-electron or collective oscillations. Hence, the RPP effect considered here leads to both conventional resonant photo-electric and the photo-plasmonic effects due to the dual-tone nature of collective quantum oscillations. The current model may be extended to a similar resonance effect in nanometer-sized metal surfaces with a non-planar geometry. A new equation of state for the electron number density of spill-out electrons is obtained, which limits the plasmonic response in high-density and low-temperature regime due to the small transition probability of electrons to the spill-out energy band.

The effect of magnetized quantum plasma on Jeans instability

Abstract The influence of quantum plasma on Jeans instability is investigated in the presence of magnetic fields, and the dispersion relation obtained in both parallel and perpendicular directions has shown the stabilizing effect on the growth rate of Jeans instability with a moderate temperature high-density regime. The influence of the magnetic field on the Jeans criteria is illustrated through the graphical representation. The inclusion of magnetic fields with quantum effect on the motion of a charged particle involves the essential properties of acceleration and the transport of highly ionized particles is important in connection with a well-known application of the confinement of magnetized plasma. In this paper, we analytically discuss the effect of magnetic field on white dwarfs. The mass-radius relation of highly magnetized white dwarfs is different from their non-magnetic equivalent and leads to a modified super-Chandrashekhar mass limit.

Magnetoresistance in noncentrosymmetric two-dimensional systems

The valley-contrasting geometric features of electronic wave functions manifested in Berry curvature and orbital magnetic moment have profound consequences on magnetotransport properties in both three- and two-dimensional systems. Although the importance of employing beyond-relaxation-time-approximation methods and intervalley scatterings in collision integral has been confirmed in three dimensions, they have been widely overlooked in previous studies on two-dimensional multi-valley systems. Here, we revisit the issue of weak-field magnetoresistance in two-dimensional multi-valley systems with broken inversion symmetry. We provide an exact solution to the Boltzmann equation and demonstrate that the inclusion of in-scattering terms in the collision integral can change the sign of the magnetoresistance in high-density regime. With an initial valley polarization, we also predict an orbital magnetic moment-induced intrinsic contribution to Hall conductivity in the time-reversal-broken situation, which is consistently negative, and in contrast to the anomalous Hall term, it does not depend on the polarization sign. Depending on which valley has the excess charge, our calculations show that a completely various behavior is exhibited in the magnetoresistance which can be considered as a valley-polarization probe in the experiment.