Physics and Society · Cross-listed from cs.IT
The Informational Cost of Structure: Representational Complexity in Networked Dynamical Systems
Cyril Rommens, Pietro Traversa, Guilherme Ferraz de Arruda et al. (+1 more)
How much information is required to represent a dynamical system in terms of an interaction structure and an
evolution rule? We address this question using algorithmic information theory. We introduce Representational Complexity, the excess description length of a structure-plus-rule model relative to the shortest possible description of the dynamics itself. This intrinsic description defines a universal lower bound: no exact structural representation can be more concise. If arbitrary rules are allowed, graphs, hypergraphs, and other formalisms can all reach this bound by shifting information between structure and dynamics, so expressiveness alone cannot distinguish them. Meaningful differences arise only when scientific modeling restricts the admissible structures and rules. Within this setting, we identify conditions under which graph and hypergraph descriptions are informationally equivalent, and show how graph-preferred, hypergraph-preferred, and mixed regimes can emerge when those conditions are relaxed. Because Kolmogorov complexity is not computable, we complement the formal results with explicit description-length estimates. Our framework reframes the choice of network representation as a question of informational cost and mechanistic transparency rather than universal expressive power.
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All authors Cyril Rommens, Pietro Traversa, Guilherme Ferraz de Arruda, Yamir Moreno
Fluid Dynamics
Transferable inference of turbulence models for urban flows with the Parameter-Regularised Ensemble Kalman Filter
Emanuele Bombardi, Andrea Nóvoa, Luca Magri et al. (+1 more)
The accurate simulation of urban flow is key to designing building ventilation, understanding cities' micrometeorology, and predicting pollutant dispersion. Reynolds-Averaged Navier-Stokes (RANS) simulations are a common modelling approach for simulating urban flow, but their accuracy depends on the closure model and its parameters. These parameters are inferred from
benchmark cases, but they are not necessarily suitable for realistic urban environments, which involve different physical mechanisms. This is referred to as the transferability problem of RANS urban modelling. The objective of this work is to propose a robust
Bayesian method to {sequentially} infer RANS parameters for urban flow modelling. Key to the approach is the mathematical derivation of the parameter-regularised ensemble Kalman filter (PR-EnKF), which is the analytical solution of the data assimilation problem for the sequential parameter estimation. The cost functional is regularised using the prior knowledge on the
turbulence parameters, thereby ensuring that the
Bayesian updates remain within physical ranges. The parameters are first inferred on an isolated building, and then transferred to three cases of increasing complexity: (i) a high-rise building, (ii) a multi-building array, and (iii) the Shinjuku district urban environment. Results show that the PR-EnKF achieves faster convergence, reducing parameter uncertainty by an order of magnitude and reconstruction errors by up to 50%. Because of the regularisation, the PR-EnKF selectively updates the most important parameters. This work enables robust large-scale urban flow simulation whilst reducing the computational overhead of model optimisation for urban planning and air quality assessment.
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All authors Emanuele Bombardi, Andrea Nóvoa, Luca Magri, Alessandro Parente
Optics
Intrinsic Limitations of Single Layer Polychromatic Metalens for Virtual Reality Visors
Myunghoo Lee, Ben Nguyen, Zhihao Zhou et al. (+7 more)
Virtual and augmented reality (VR/AR) visors require compact and lightweight optics. Metalenses have been widely proposed as ultrathin replacements for bulky refractive eyepieces, with performance typically assessed using point spread function (PSF) and modulation transfer function (MTF) measurements. Here, we design, fabricate, and characterize a single-layer silicon nitride metalens optimized for the three emission peaks of an RGB OLED display, and
benchmark it against refractive and Fresnel eyepieces. Under coherent illumination, the metalens exhibits a tightly confined PSF and strong mid-to-high spatial-frequency MTF, suggesting excellent optical performance. However, when evaluated in a realistic system-level VR testbed incorporating incoherent OLED illumination, a dynamic-pupil eye model, and near-eye-relevant focal lengths, the same device exhibits pronounced ghosting and background haze. We show that these artifacts arise from the intrinsic multifocal nature of polychromatic diffractive focusing and demonstrate that common mitigation strategies such as narrowband filtering and long-focal-length relay optics merely mask, rather than resolve, the issue. Our results establish that meta-optics for AR/VR must be evaluated under realistic system-level conditions to reveal their true imaging performance.
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All authors Myunghoo Lee, Ben Nguyen, Zhihao Zhou, Prannav Jayashanker, Shane Colburn, Ethan Tseng, Felix Heide, Praneeth Chakravarthula, Arka Majumdar, Johannes E. Fröch
Optics
Half-wave plasmonic nanolasers near the localization limit
Sangyeon Cho and Seok-Hyun Yun
Miniaturized
lasers with sub-micron dimensions are of broad interest for optical science, on-chip communication, sensing, and biomedical barcoding. Recently, lowest-order half-wave lasing was demonstrated in
semiconductor-on-metal cavities by operating away from the highly dispersive and absorptive surface-plasmon resonance. Here, we demonstrate half-wave-mode lasing near the surface-plasmon resonance at ~630 nm using high-gain indium phosphide (InP) nanoparticles on ultrasmooth gold substrates. The smallest lasing particle, estimated from simulated dispersion curves to have a length of ~115 nm and height of ~100 nm, emitted at 730 nm in air, representing one of the smallest reported active
laser cavities. Linewidth and threshold pump fluence generally decreased as the lasing wavelength shifted farther from the plasmon resonance. In larger particles with lengths of 280~480 nm, we observed lasing attributable to second- and third-order plasmonic modes with progressively narrower linewidths. These results extend half-wave dipolar lasing toward near-infrared and visible wavelengths and further push
laser miniaturization toward the plasmonic localization limit.
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Chemical Physics
Intrinsic Matching Frustration in Fluctuating Finite Systems
Leonid Rubinovich and Micha Polak
We formulate intrinsic matching frustration (IMF), a fluctuation-induced, kinetics-independent reduction in the mean capacity permitted by a prescribed matching rule. For complementary one-to-one matching, the instantaneous capacity is set by the minority population, so fluctuations produce a nonzero mean deficit even when the two populations are balanced on average. At finite size, this deficit depends on the full distribution of the population difference and is determined by its variance alone only in the Gaussian limit. Compartmentalization hides matching capacity by preventing cancellation between local imbalances of opposite sign. Fusion releases this hidden capacity monotonically under coarse graining, producing a measurable recovery of product yield following local reaction to completion.
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Atomic Physics · Cross-listed from quant-ph
The arrival position problem in quantum mechanics
Ali Ayatollah Rafsanjani and Will Cavendish
The problem of making unambiguous probabilistic predictions about experiments involving waiting "always on" detectors remains a challenge for
quantum theory. While most research on this problem studies arrival time, i.e., predicting the distribution of when detection events occur, this paper studies the arrival position problem, which is the complementary challenge of predicting the distribution of where detection events occur. Despite the widespread recognition of the arrival time problem, the inability of standard
quantum theory to address the arrival position problem remains a pervasive theoretical blind spot. In this paper, we compare quantitative arrival position predictions derived from prominent proposed solutions to the screen problem. As we show, these models yield distinguishable predictions even in relatively simple experiments achievable with current technology. Notably, many of these discrepancies persist even in the far-field limit, where standard semiclassical approximations are typically assumed to be valid.
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Chemical Physics
AquaGen: Scaling generative models to molecular dynamics precision on thousands of atoms
Emmanuel Bengio, Sanjeev Raja, Yui Tik Pang et al. (+5 more)
We present AquaGen, the first all-atom, explicit solvent, periodic-boundary-condition-aware generative model that produces molecular configurations from the Boltzmann distribution at a fraction of the cost of molecular dynamics (MD). This is in contrast with existing generative models that remove degrees of freedom by operating on coarse-grained,
vacuum, or implicit solvent systems. Operating at this resolution allows for post-processing through force field energy evaluations and MD simulations, and enables the prediction of relevant properties in a gray-box manner (as ensemble averages of potential energy evaluations over generated samples). We demonstrate the utility of this paradigm on absolute hydration free energy (AHFE), producing estimates 4-10x faster and with comparable accuracy to standard GPU-based MD. By generating uncorrelated samples from alchemical Boltzmann distributions, we create more accurate, interpretable, and refinable ensemble predictions with calibrated uncertainty estimates, unlike regression methods which are entirely black-box predictors. Our approach also yields predictable benefits from increasing train- and test-time compute, realized by scaling model size and generating more samples, respectively. We believe that this approach demonstrates the utility of high-resolution ensemble generation for free energy estimation, with future potential to replace MD in tasks such as the prediction of lipophilicity, membrane permeability, or absolute binding free energy (ABFE) – whose grounding and interpretability may be critical for the development of new drugs and materials.
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All authors Emmanuel Bengio, Sanjeev Raja, Yui Tik Pang, Kerstin Klaeser, Cristian Gabellini, Nikhil Shenoy, Francesco Di Giovanni, Prudencio Tossou
Instrumentation and Detectors
A high-sensitivity resistance bridge for nanoscale thermal microscopy
Wilfrid Poirier, Victor Guillemot, Mohammed Mghalfi et al. (+2 more)
Measurements of heat flux between micro-objects, in
vacuum or in air, are challenging because of their small size and the low thermal conductance of the medium between them. One way to address this issue consists in using a scanning thermal microscope (SThM) equipped with a temperature dependent resistance thermometer. However, this requires an instrument able to both injecting a defined heating Joule power and performing highly-sensitive resistance measurements. Here, we present such an instrument based on a Wheatstone bridge equipped with three Kelvin arms. It can perform resistance measurements in the range from 100 $\Omega$ to 1000 $\Omega$ not only in direct current but also in alternating current regimes at frequencies up to a few tenths of kHz. We first show that measurements of resistance standards are accurate to within one part in $10^4$ with a relative experimental standard deviation which can be as low as one part in $10^8$ for one second measurement. The instrument is then tested with a SThM thermometer. With the support of an electro-thermal model considering thermal time constants of the thermometer, we explain the frequency dependence of detected signals and optimize the measurement protocols of temperature and heat flux. By measuring sub-mK temperature variations, this instrument is then used to determine with a few nanowatts uncertainty the near-field radiative heat flux between a heated glass microsphere and a glass substrate, which is caused by the coupling of surface
phonon-polaritons.
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All authors Wilfrid Poirier, Victor Guillemot, Mohammed Mghalfi, Valentina Valentina Krachmalnicoff, Yannick De Wilde
Instrumentation and Detectors
Online Data Reduction with Spiking Neural Networks: A Temporal-Coincidence Encoder and Distributed SNN for the ePIC dRICH Detector
Pierpaolo Perticaroli, Roberto Ammendola, Andrea Biagioni et al. (+10 more)
The dual-radiator Ring Imaging Cherenkov (dRICH) detector of the ePIC experiment at the Electron-Ion
Collider (EIC) will read out $\sim$320,000 silicon photomultiplier (SiPM) channels at a bunch-crossing rate of 100 MHz. The dark count rate (DCR) of the SiPMs is expected to rise up to 300 kHz per channel over the experiment lifetime, saturating the output bandwidth and requiring an online data reduction factor of at least five. Most crossings contain only uncorrelated DCR hits, while genuine Cherenkov hits cluster within $\sim$2 ns of the 10 ns crossing window: an intrinsically temporal discrimination problem. We present a two-stage online data reduction pipeline based on spiking neural networks (SNNs). The first stage is a per-photodetection-unit leaky-integrate-and-fire (LIF) temporal coincidence encoder that converts raw SiPM hits into a sparse spike stream, achieving over 90% data sparsification before any learned classifier is applied. The second stage is a distributed SNN (30 sub-sector networks plus an aggregation network) deployed on FELIX-155 DAM boards and a dedicated Trigger Processor board, classifying each crossing as Noise-Only or Signal+Noise. On simulated ePIC events the system reaches a true positive rate above 94% at a true negative rate of at least 80% across the full DCR range; an optional early-exit strategy reduces the average classification latency to $\sim$2 algorithmic timesteps at the cost of a few percentage points on both metrics. A hardware proof-of-concept on an AMD Versal Premium FPGA, integrating the LIF encoder with the AIGOR multi-core neuromorphic architecture, validates a single sub-sector pipeline at $\sim$1.7 MHz throughput; ongoing work targets 100 MHz through an identified set of optimizations of the inference fabric. The methodology may be relevant to other timing-driven detector applications at high rate.
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All authors Pierpaolo Perticaroli, Roberto Ammendola, Andrea Biagioni, Ottorino Frezza, Francesca Lo Cicero, Michele Martinelli, Pier Stanislao Paolucci, Elena Pastorelli, Luca Pontisso, Cristian Rossi, Francesco Simula, Piero Vicini, Alessandro Lonardo
Applied Physics · Cross-listed from cond-mat.mes-hall
Graphene Electric Double-Layer Transistors for Enhanced-Sensitivity Label-Free Detection of Human Serum Albumin
Arslan Liaquat, Ghassem Baridi, Federico Rapuzzi et al. (+14 more)
Accurate detection of human serum albumin (HSA) is essential for the early diagnosis and monitoring of renal and hepatic disorders. We present a
graphene-based electrolyte-gated field-effect transistor (EGFET) for label-free, real-time quantification of HSA under non-Faradaic operation. Devices exploit the high interfacial capacitance of the electric double layer (EDL) to transduce electrostatic perturbations induced by albumin adsorption into measurable conductance modulation. Negatively charged HSA molecules induce systematic modulation of the
graphene channel, producing a concentration-dependent displacement of the Dirac voltage consistent with p-type doping. To establish a molecular-level interpretation of the sensing response, Brownian Dynamics simulations show that HSA adsorbs onto
graphene through multiple adsorption orientations associated with heterogeneous interfacial charge distributions and variable dipole
alignments relative to the surface. Adsorption is energetically stabilized by van der Waals interactions. Analysis of transfer characteristics across concentrations ranging from 0.01 to 30mgmL-1 reveals a correlation between surface charge density and carrier transport modulation within the electric double layer. Optimized devices exhibit a limit of detection of 0.0087 mg mL-1 and a linear dynamic range extending to 10 mg mL-1. The response remains non-Faradaic under sub-volt operation with reversible and reproducible behavior. The use of an inverse-mobility analytical metric highlights the role of disorder-enhanced carrier scattering in signal amplification, enabling sensitive electrostatic detection while preserving reversible device operation. These results establish
liquid-gated
graphene EGFETs as a promising platform for quantitative
protein sensing and provide insight into disorder-mediated transport mechanisms in
graphene bioelectronic devices.
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All authors Arslan Liaquat, Ghassem Baridi, Federico Rapuzzi, Daniele Goldoni, Vito Clerico, El Hadj Abidi, Yahya Moubarak Meziani, Mario Amado, Enrique Diez, Naveen Kumar, Camilia Coletti, Beatrice Cipriani, Hender Lopez, Giorgia Brancolini, Leonardo Martini, Luigi Rovati, Francesco Rossella
History and Philosophy of Physics
The influence of the Academy of Gondishapur on the formation of the House of Wisdom in Baghdad and the science of the Golden Age of Islam
Rizoi Bakhromzod
The purpose of this study is to determine the role of the Academy of Gondishapur in the formation of the Bayt al-Hikma (House of Wisdom) in Baghdad and the emergence of Islamic science in the 8th-10th centuries. The methodology combines comparative-historical and biographical analysis with a study of institutional continuity based on primary sources and contemporary scholarly literature. The results demonstrate that Gondishapur, the foremost scientific and medical centre of late Sasanian Iran, constituted the primary human, methodological, and institutional source for the Abbasid Bayt al-Hikma. The migration of specialists, especially the Bukhtishu dynasty, Yuhanna ibn Masawayh, and Hunayn ibn Ishaq, transferred Gondishapur's medical traditions, hospital organisation (bimaristans), and translation methodology to Baghdad. Gondishapur's experience also shaped the development of medical education and the compilation of pharmacopoeias within the Bayt al-Hikma. A comparative structural analysis of the two institutions reveals both institutional borrowings and the original features of the Baghdad model. The article concludes that the transmission of Gondishapur's heritage to the Bayt al-Hikma constituted sustained institutional continuity, laying the foundations for the large-scale synthesis of Greek, Persian, and Indian knowledge in the Arabic
language.
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Optics
Non-Diffractive Topological Spin Textures of Relativistic Twisted Fermion Beams
Andrei Afanasev and Carl E. Carlson
In optics and acoustics, in structured beams, non-diffracting polarization measures in clearly diffracting beams, and
spin direction distributions in the core of these waves that have Skyrmionic behavior have been found. We here study the equivalents of these for
fermions and show that in corresponding circumstances the non-diffractive
spin textures persist independently of
spin, statistics, or kinematics (or propagation speed of the structured wave). As a part of the study, we present LG solutions for Dirac particles valid for both relativistic and non-relativistic kinematics.
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Optics
Analytic Theory of Phase Transitions in Optical Metamaterials
Jiahao Yan, Xiaoshui Lin, Junpeng Hou et al. (+2 more)
Optical metamaterials provide a versatile platform for engineering homogeneous electromagnetic media whose distinct phases are characterized by phase diagrams in constitutive-parameter space. However, existing studies of hyperbolicity, topological properties, and exceptional-point formation often rely on highly symmetric models or case-by-case numerical parameter scans, leaving a unified analytic framework that identifies phases and phase transitions directly from the constitutive tensors lacking. Here, we develop a general theory that yields exact analytic criteria for topological transitions, exceptional-point transitions, pinch-off Lifshitz transitions, and optical Lifshitz transitions in homogeneous media. Applying this framework to a tractable example of a gyroelectric medium with anisotropic chirality, we uncover exceptional rings and negative refraction induced by gyroelectric-
chiral coupling. By enabling the exact determination of phase boundaries, our theory provides a predictive framework for discovering previously unexplored electromagnetic phases and offers new principles for the systematic design of optical metamaterials.
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All authors Jiahao Yan, Xiaoshui Lin, Junpeng Hou, Qing Gu, Chuanwei Zhang
Chemical Physics
Photo-thermal 2D spectroscopy: a different type of action
Pavel Malý, Xiaoji G. Xu and Tomáš Mančal
Advances in multidimensional spectroscopy have seen the rise of action detection, where coherent response is encoded into incoherent signals. These are typically proportional to the excited-state population, an example in 2D electronic spectroscopy (2DES) is fluorescence-detected 2DES (F-2DES), and in 2D infrared (2DIR) tag-loss 2DIR (TL-2DIR). Very recently, a new type of photo-thermal action signal has been introduced in 2DIR, detecting the generated heat by atomic force microscopy-based 2DIR (AFM-2DIR). We present a unified theoretical framework for population- and heat-based 2D spectroscopy, highlighting their complementary features. In the infrared, TL-2DIR reflects the system linear response, whereas AFM-2DIR produces spectra resembling conventional 2DIR, with sensitivity to anharmonicity and mode coupling. Our model reproduces key experimental AFM-2DIR features, confirming measurement in a highly nonlinear regime. Extending photothermal detection to electronic spectroscopy, we compare F-2DES with proposed photo-thermal 2DES (PT-2DES). PT-2DES closely resembles conventional 2DES, while enjoying the advantages of action detection.
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Physics Education
Physical Systems as Objects: A Structural Correspondence for Computational Physics Education
Luis E. Sánchez-González
Physical systems and objects in the object-oriented programming (OOP) paradigm share a common organizational structure: identity, state, and governing laws. We argue that making this structural correspondence explicit, rather than leaving it as tacit knowledge embedded in scientific software, provides a natural and general basis for teaching computational physics. The correspondence is independent of both programming
language and mathematical formalism, applying equally to differential equations,
eigenvalue problems, and variational principles. To illustrate this idea, we present Ollin, an open-source Python framework for computational physics education organized around the correspondence principle. Four examples spanning mechanics, celestial mechanics,
quantum mechanics, and variational optics demonstrate that the same representational structure can be preserved across diverse physical domains. In each case, the class definition serves as the physical model, its attributes encode the state and physical parameters of the system, and its methods encode the governing laws, regardless of whether those laws are integrated, diagonalized, or optimized. More broadly, the correspondence principle provides a conceptual framework for relating the organization of physical models to the organization of code.
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Fluid Dynamics
Development and application of a multiphase Lagrangian structure function model in anisotropic turbulence
Andrew P. Grace and David Richter
The energetic response of inertial particles to turbulent flow motions is important for both a fundamental understanding of the multi-phase dynamics at play, and for applications such as reduced-order models of particle dispersion processes, and their two-way coupled effects onto the flow phase. Numerous studies focus on the energetics of ensembles of particles in homogeneous isotropic
turbulence, where the influence of flow anisotropy (such as that provided by boundary conditions, or other external forcing) is not considered a priori. In this work, we investigate the role of flow anisotropy on the Eulerian scale-wise particle phase energetics in a turbulent wall bounded flow for settling inertial Lagrangian particles. By using coupled Eulerian-Lagrangian direct numerical simulations at moderate Reynolds number, we aim to unravel the complex dependency of the scale-wise particle energetics on the
turbulence intensity, particle inertia, and particle settling. In particular, we focus on how the developing anisotropy of the underlying turbulent flow (derived from the presence of the wall) is donated to the particle phase, and how particle inertia and settling preserve this large scale anisotropy into the formally isotropic scale range of the flow. We derive an exact (but unclosed) conservation law for the particle phase energetics at arbitrary scale, and use an asymptotic argument to help elucidate our DNS data. We discuss the relative changes to the quasi-streamwise and vertical components of the fluctuating particle field, and finish by discussing the implications of anisotropic non-local effects for more general flows, and the implications for continuum models of inertial settling Lagrangian particles.
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Physics and Society
The limits of visitation entropy as a summary of mobility patterns
Sílvia de Sojo, Sune Lehmann and Laura Alessandretti
Visitation
entropy, the Shannon
entropy of an individual's distribution of visits across locations, is a widely used metric in the human mobility literature. Yet, its widespread use rests on assumptions that are rarely made explicit:
entropy is defined over a fixed set of states, and estimating it empirically requires abundant, well-sampled observations. The limitations that arise when
entropy is used outside this setting have been documented and explored in fields such as statistical physics, ecology, and cryptography. The implications for mobility studies, however, remain unclear. Here, we leverage synthetic and empirical trajectories to systematically examine the strengths and weaknesses of visitation
entropy as a measure for characterizing human mobility. We show that, for a sequence of locations visited by an individual, the visitation
entropy primarily reflects the number of unique locations visited and sequence length, which together explain 90.7% of its variance in empirical data. We also show that shorter sequences systematically lead to an underestimation of
entropy, showing finite-sample bias to be a key limitation. As a result, comparisons of groups based on visitation
entropy should be treated with caution. We find that apparent
entropy gaps between genders, commuters and non-commuters, and urban and rural residents are reduced, or reversed, once sequence length and the number of unique locations are taken into account. Finally, we show that these issues can be addressed by controlling for sequence length and the number of unique locations, and by complementing
entropy with structural network measures, which provide more nuanced insight into how mobility is organized beyond the aspects that
entropy alone captures.
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Optics
Hz-resolution wide-span photonic integrated terahertz signal analyzer
Aleksei Gaier, Jiawen Liu, Ekaterina Mironova et al. (+2 more)
Wide-span spectral and noise characterization at millimeter-wave and terahertz frequencies is increasingly important for emerging wireless, sensing, and spectroscopy systems, yet remains challenging for conventional electronic instrumentation because of the complexity and calibration burden of extender-, multiplier-, and mixer-chain architectures. Here we show that photonics can provide attractive alternatives to this highly challenging electronic instrumentation through an
antenna-coupled thin-film lithium niobate electro-optic receiver. Our implementation performs fast spectral reconstruction across the widely separated WR 9.0 (80-125 GHz) and WR 2.8 (240-380 GHz) bands with a single component, with carrier-frequency errors below 3 MHz, scan speeds up to 25 THz/s, and a displayed average noise level below -104 dBm/Hz. We then extend to Hz-level resolution and demonstrate phase-noise characterisation capabilities across these ultra-wide bands by using a mode-locked femtosecond-
laser frequency comb as a sampling clock, mapping high-frequency carriers to aliased intermediate-frequency tones. We validate the method by measuring the phase noise of 90.225 GHz and 270.675 GHz carriers using the same chip and system configuration. We further improve the sensitivity of the phase-noise measurement through cross-correlation between two optical probe-pulse channels. Finally, we show that the same technique can be applied synchronously to ten widely spaced frequencies distributed across more than 100 GHz, with the option to quantify their mutual coherence. These results establish TFLN integrated photonics as a scalable route toward compact millimeter-wave/terahertz instrumentation.
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All authors Aleksei Gaier, Jiawen Liu, Ekaterina Mironova, Gabriel Julg, Ileana-Cristina Benea-Chelmus
Optics · Cross-listed from quant-ph
Design of an Electrically Tunable Microtoroid for Frequency Selection of Polarization-Entangled Photons
Yichi Zhang, Enqi Ke and Judith Su
Encoding
quantum information into discrete optical frequencies, or "frequency bins," uses different colors of light as additional information channels, allowing each
photon to carry more information than polarization alone. We present a computational design for an electrically tunable silica microtoroid that selects desired frequency channels after a polarization-entangled
photon pair has been generated without disturbing the
photons' polarization
entanglement. In the proposed architecture, the 750 nm signal
photon passes through the microtoroid, while its entangled 880 nm partner bypasses the resonator and serves as a reference for the selected frequency channel. The principal challenge is resonator birefringence: because horizontally and vertically polarized light resonate at slightly different frequencies, the selected frequency can reveal the
photon's polarization state and weaken the
quantum correlation between the
photon pair. We solve this problem by adding a small lithium-niobate tuning element controlled with a single applied voltage. The voltage shifts the resonator so that it responds almost identically to horizontally and vertically polarized light, reducing the remaining mismatch to only 0.286 optical linewidths across nine frequency channels. The
photons remain strongly entangled after passing through the device, with a concurrence of C = 0.969, a Bell-state fidelity of F = 0.981, and a Bell parameter of S_max = 2.785. If the relative timing between the frequency channels is also controlled, the same device can generate a nine-channel polarization-frequency hyperentangled state with an effective dimension of K = 8.97. This computational design provides a compact, electrically tunable bridge between polarization-entangled
photon sources and future high-capacity
quantum photonic systems.
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Fluid Dynamics
Acoustic Loading Beneath High-Speed Flow Over a Compression Ramp at Different Angles
Ritu Raj Kumar, Nagabhushana Rao Vadlamani and Amareshwara Sainadh Chamarthi
Large-eddy simulations are performed to characterize the pressure fluctuations beneath a hypersonic boundary layer approaching a compression corner. The simulations are carried out at Mach 6.04 and an inlet momentum-thickness Reynolds number of $Re_{\theta}=4340$. The compression-corner angle is varied over $10^\circ$, $20^\circ$, $30^\circ$, and $34^\circ$ spanning attached to strongly separated regimes. The peak root-mean-square wall-pressure fluctuations intensity increases sharply with separation strength, rising by $312\%$ from R20 to R30 and a further $67\%$ from R30 to R34, with the peak located downstream of reattachment. Notably, acoustic loading increases from 140 dB in the approach flow to $\approx177$ dB downstream of reattachment in the $34^\circ$ case. Further analysis reveals that intense intermittent pressure events are concentrated near the shock foot, spatially distinct from the peak acoustic-loading region, where fluctuations are relatively sustained. With increasing interaction strength, spectral energy shifts from
turbulence-dominated high frequencies to broadband low-frequency motion. Band-isolated acoustic loading maps reveal high-frequency fluctuations as the dominant contributor across the interaction zone, with low-frequency fluctuations becoming locally comparable in the R34 case near the separation region. Spatio-temporal maps of bandpass-filtered pressure fluctuations reveal downstream convecting Kelvin-Helmholtz structures and upstream propagating pressure waves near the shock foot.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Dyna-Mat: End-to-end benchmarking of foundation machine learning interatomic potentials in finite-temperature ensembles
Mikołaj J. Gawkowski, Nongnuch Artrith, Silvia Bonfanti et al. (+14 more)
Foundation machine learning interatomic potentials (MLIPs) are increasingly being used as drop-in replacements for first-principles calculations, enabling simulations of materials at length and time scales that were previously inaccessible. However, due to lack of ground truth data, their accuracy on structural and dynamical observables in finite thermodynamic ensembles is yet to be established. Here, we introduce Dyna-Mat-v1.0, a
benchmark dataset of condensed-phase first-principles molecular dynamics trajectories designed to test foundation MLIPs at realistic finite-temperature conditions. Using this
dataset, we evaluate 15 foundation MLIPs across four model tiers by comparing both single-point energy and force errors on first-principles configurations and observables generated from MLIP-driven trajectories. We find that "on average" models with lower single-point force errors also yield lower errors for structural and dynamical observables. However, there are individual systems for which low force errors lead to qualitative failures in the predicted structure. Pressure remains poorly described across most models, pointing to limitations in the density functional theory stress labels available in current large-scale training
datasets. Finally, we construct an accuracy-cost Pareto frontier to identify the best trade-offs for molecular dynamics with foundation MLIPs, finding that the latest generation of cross-trained models is close to Pareto-optimal according to the accuracy metrics considered here. Overall, Dyna-Mat-v1.0 shows that end-to-end finite-temperature validation is essential for quantifying the predictive behaviour of foundation MLIPs, and provides a simple, scalable route for assessing them beyond static and harmonic
benchmarks relevant to materials design.
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All authors Mikołaj J. Gawkowski, Nongnuch Artrith, Silvia Bonfanti, Abhijeet Sadashiv Gangan, Hendrik H. Heenen, Joseph Kioseoglou, Ivor Lončarić, Hemanadhan Myneni, Janosh Riebesell, Mariana Rossi, Matthias Rupp, Jonathan Schmidt, Shubham Sharma, Benjamin X. Shi, Antoni Wadowski, Lukas Hörmann, Venkat Kapil
History and Philosophy of Physics
Becoming, Duration, and the Evolving Block Universe
Nicolò Cangiotti
The two-times problem asks how the directed, oriented time of biological and conscious systems relates to the time of fundamental physics. The Evolving Block Universe, in which spacetime grows through an irreversible
quantum dynamics along physically preferred worldlines, accounts for the direction of physical time and for its emergence across scales up to the time kept by the
brain. It leaves open the relation between this physical time and the experience of passage. We argue that Bergson's durée, the continuous qualitative experience of lived time, names this residue and marks the first-person level at which the physical hierarchy reaches its limit. On this reading the two accounts divide the problem between them: the Evolving Block Universe describes its structural, third-person half, and durée its experiential, first-person half. The remaining gap between the two halves is explanatory. It is an instance of the familiar gap between the physical description of a system and the character of its states as they are lived, and it is compatible with physicalism.
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Fluid Dynamics
Experimental and numerical study of the dynamics of sedimenting pairs of semi-flexible fibers close to attractive `aligned' relative configuration
Harish N. Mirajkar, Chandra Shekhar, Yevgen Melikhov et al. (+2 more)
Dynamics of two short semi-flexible fibers settling under
gravity in a viscous fluid are investigated at Reynolds numbers Re << 1. We focus on fibers initially relatively close to each other, and we check if later they approach an aligned horizontal configuration, previously identified numerically (Bukowicki and Ekiel-Jezewska, Soft Matter 46 (2019) 9379) as attractive for symmetric initial conditions of moderately elastic filaments. In our experiments, two semi-flexible ball chains sediment in a highly viscous silicone oil. They are initially straight and close to a parallel horizontal relative configuration. Their motion and shape deformation are recorded using two synchronized cameras. For most of the trials, ball chains stay together, with damped oscillations around the symmetric aligned configuration. For a few initial conditions, the ball chains move away horizontally or vertically. To study the behavior over a longer time, we perform numerical simulations, modeling moderately elastic filaments as chains of identical beads, with the centers of consecutive beads connected by springs and with the fibers' elastic resistance to bending. Different initial positions and orientations are considered. Their dynamics are determined by the multipole expansion of the Stokes equations, implemented in the precise Hydromultipole numerical code. For short times, we observe the similar dynamics of semi-flexible ball chains and moderately elastic filaments. We provide examples of long-time numerical simulations illustrating that elastic filaments close to each other can move away horizontally or vertically, but after a long time, come back and perform damped oscillations while approaching the aligned configuration with almost touching filament ends. We confirm the attractive nature of the aligned configuration of very close semi-flexible sedimenting fibers, even if they are far away from each other.
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All authors Harish N. Mirajkar, Chandra Shekhar, Yevgen Melikhov, Piotr Zdybel, Maria L. Ekiel-Jezewska
Chemical Physics
Spectroscopic photorelaxation signatures in pyrazine from nonadiabatic dynamics simulations with coupled cluster theory
Sara Angelico, Eirik F. Kjønstad, Yi-Ping Chang et al. (+3 more)
Despite extensive theoretical and experimental efforts, the mechanisms underlying the ultrafast relaxation of pyrazine after photoexcitation remain challenging to disentangle. Recently, theoretical investigations have been converging towards a three-state mechanism, with an ultrafast decay of the bright ${}^{1}B_{2u}$ state followed by beats in the populations of the low-lying ${}^{1}B_{3u}$ and ${}^{1}A_u$ states. However, a clear agreement between the experimental results and the corresponding theoretical predictions remains elusive. Here, we present a high-level simulation of the ultrafast excited states dynamics of pyrazine using coupled cluster theory with single and double excitations and ab initio multiple spawning, together with predictions of the time-resolved photoelectron spectrum and X-ray absorption spectra at the nitrogen and carbon edges. This is made possible by using a newly developed multistate implementation of similarity constrained coupled cluster theory. We find quantitative agreement with the experimental signature of the ${}^{1}B_{2u}$ decay in the photoelectron spectrum, and qualitative agreement with the available experimental X-ray absorption spectra. Moreover, we detail spectroscopic signatures that should be verifiable in experiments with sufficient resolution in the time and frequency domains. Compared to previous theoretical studies, we provide further detailed insight into the interplay of the states involved in the photorelaxation.
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All authors Sara Angelico, Eirik F. Kjønstad, Yi-Ping Chang, O. Jonathan Fajen, Todd J. Martínez, Henrik Koch
Chemical Physics
Improving Jet A-1 Thermal-Oxidative Stability through Selective Removal of Unwanted Trace Species via 3.7 Å Chabazite Filtration
Morteza Roostaeinia, Ehsan Alborzi, Xue Yong et al. (+2 more)
The thermal stability of Jet A-1 fuel is strongly affected by trace heteroatomic species that promote thermal oxidative deposit formation, as well as antioxidant additives such as butylated hydroxytoluene, which preserve fuel stability. 3.7 Å chabazite is a tunable microporous adsorbent, but optimizing its composition requires balancing promoter removal against antioxidant loss. Here, we use density functional theory and ab initio molecular dynamics (AIMD) to evaluate this trade-off using two compositional descriptors: framework acidity (Si/Al $= 35$–$8$) and bimetallic substitution (Co, Mg, Zn) at fixed Al content. Lowering Si/Al strengthens adsorption of all species, including BHT, confirming an intrinsic selectivity penalty for acidity-only tuning. In contrast, bimetallic substitution introduces chemically selective behavior, strengthening uptake of specific promoters while either suppressing or enhancing antioxidant adsorption depending on dopant identity. AIMD simulations at 400 K further show that adsorption energy alone is insufficient to describe calculated trends, because molecular mobility inside chabazite can influence residence time and effective capture during fuel treatment. Analysis of the density of states and the participating wavefunctions reveals signatures that are consistent with dopant-dependent adsorption shifts. These results establish a unified adsorption–transport–electronic screening framework for selecting chabazite compositions that remove deposit promoters while preserving antioxidant functionality in Jet A-1 treatment.
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All authors Morteza Roostaeinia, Ehsan Alborzi, Xue Yong, Kyungwha Park, Vsevolod Ivanov
Biological Physics · Cross-listed from cond-mat.soft
Stability and equilibria of a compressible elastic membrane in Stokes flow
Sho Kawakami, Han Zhou, Po-Chun Kuo et al. (+2 more)
We formulate a continuum model for a compressible lipid-
bilayer membrane immersed in Stokes flow, replacing exact local area inextensibility by conservation of an areal phospholipid density. The membrane free energy combines Helfrich bending, spontaneous
curvature, and a finite area-compression penalty, so that membrane tension becomes a constitutive response to lipid-density variation rather than a Lagrange multiplier enforcing local area conservation. The resulting interfacial stress includes normal elastic forces and tangential Marangoni stresses generated by lipid redistribution; these stresses arise from membrane compressibility and can produce an effective negative tension when the local lipid density exceeds its preferred value. We further derive the linear stability of circular membranes in two dimensions and spherical membranes in three dimensions under full Stokes hydrodynamic coupling. In both cases, bending stabilizes the base shape, while excess lipid density destabilizes it by favoring increased membrane area. The first instability occurs in the lowest nontrivial shape mode, m = 2 in two dimensions and j = 2 in three dimensions. Energy expansions near onset show that the two-dimensional instability is a pitchfork bifurcation, whereas the three-dimensional instability is generically transcritical because prolate and oblate perturbations are geometrically distinct. These results provide a controlled compressible extension of classical vesicle mechanics and directly connect lipid-density variation, membrane tension, hydrodynamic coupling, and shape instability.
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All authors Sho Kawakami, Han Zhou, Po-Chun Kuo, Yoichiro Mori, Yuan-Nan Young
Computational Physics · Cross-listed from cs.LG
CSympNet-ID: conformal-symplectic map learning for linearly damped Hamiltonian systems
Jiale Gong, Pengzhan Jin, Dongyang Kuang et al. (+2 more)
Learning dissipative dynamics from discrete observations is essential for reliable long-horizon prediction and physically meaningful parameter identification. For linearly damped
Hamiltonian systems, the exact flow is generally not
symplectic but conformally
symplectic, contracting the canonical
symplectic form by a scalar factor that reflects the net dissipation. We propose Conformal
Symplectic Networks with damping identification (CSympNet-ID), a discrete-time map-learning framework that learns the one-step flow map directly from snapshot pairs while enforcing exact discrete conformal symplecticity by construction, without penalty terms or projection. The architecture composes an exact
symplectic neural core with explicit diagonal scaling layers whose factors are parameterized exponentially by a scalar damping-rate parameter, thereby guaranteeing positivity and interpretability of the learned dissipation factor. We establish a scaling-conjugacy factorization for conformal
symplectic maps and derive a pointwise-in-step density result for CSympNet-ID. We evaluate an irregular-step damped oscillator, a damped spring-mass chain, a damped nonlinear cubic oscillator, and additional high-dimensional extensions. CSympNet-ID gives the most favorable overall results among the compared models in the reported experiments, particularly in data-scarce regimes, target contraction-law recovery, and high-dimensional tests where unstructured baselines degrade rapidly.
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All authors Jiale Gong, Pengzhan Jin, Dongyang Kuang, Lu Li, Yifa Tang
Optics
Mid-IR single- and dual-electro-optic comb generation with an ultrafast modulator
Gia-Long Ngo, Luca Lucia, Stefano Pirotta et al. (+9 more)
Mid-infrared (mid-IR) frequency combs are powerful tools for molecular sensing, industrial monitoring, and precision spectroscopy, yet their development beyond 5 um remains limited. Electro-optic modulation offers a promising path toward compact, agile comb generation, but extending this approach into the mid-infrared has been hindered by the lack of practical, high-performance modulators. Here we present an approach that leads to efficient generation of mid infrared frequency combs around 9 um, by employing ultrafast, room temperature, free space electro optic intensity modulators. By driving a single modulator with short electrical pulse trains, we realize both single- and dual-comb operation from a continuous-wave
quantum cascade
laser, providing a compact and versatile platform for mid-IR spectroscopy. This scheme produces combs with tunable repetition rates down to the megahertz range with direct observation on an electrical spectrum analyzer without any interferometer. As a proof of concept, we perform single- and dual-comb spectroscopy of a germanium etalon and an ammonia
cell, achieving resolution far beyond that of conventional
Fourier-transform infrared (FTIR) spectrometers and highlighting the potential of this approach for precise measurements in the long-wavelength molecular-fingerprint region. These results establish high-performance mid-IR modulators as a promising route toward practical, energy-efficient frequency-comb systems for sensing and spectroscopy.
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All authors Gia-Long Ngo, Luca Lucia, Stefano Pirotta, Mario Malerba, Lianhe H Li, Stefano Barbieri, Victor Merupo, Edmund H Linfield, Benoit Darquié, Jean-Michel Manceau, Adel Bousseksou, Raffaele Colombelli
Optics · Cross-listed from quant-ph
High Success Probability, Fidelity, and Purity Nonlinear Optical Two-Qubit Gates on Chip
Minghao Shang, Hua-Ying Liu, Ying Wei et al. (+5 more)
Optical two-
qubit gate with high success probability, fault-tolerant fidelity, and high-purity outputs is a fundamental yet unsolved challenge, essential for large-scale optical
quantum computing toward
quantum advantage. Here, we propose a feasible scheme for such gate using thin-film lithium niobate platform, enabling ḩi}(2) nonlinear
photon-
photon interaction with 100% efficiency. By decoupling
photon interaction and
qubit flip operations, fidelity ceiling is removed, and output state purity is recovered by spectral-phase pre-compensation based on a full-spectral
photon interaction model, yielding a CNOT gate with 84% success probability, 93% purity, and unity fidelity.
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All authors Minghao Shang, Hua-Ying Liu, Ying Wei, Xiaoyi Liu, Qianhao Ning, Lijian Zhang, Shi-Ning Zhu, Zhenda Xie
Fluid Dynamics
Mean-flow-based reduced-order models of turbulent channel flow
Ian Addison-Smith, Igor A. Maia, André V. G. Cavalieri et al. (+1 more)
Reduced-order models (ROMs) for turbulent flows based on Galerkin projection can achieve reasonable accuracy using equation-based modal bases derived from the linearized Navier-Stokes equations through the controllability and observability Gramians. The use of the modal bases obtained from linearized equations around a mean state has been seen to enhance the first- and second-order statistics in the ROM, but the use of the mean state was not necessarily extended to the equations of motion, as it implies the treatment of the divergence of the Reynolds stresses in the Galerkin projection. In this work, we present a mean-flow-based framework for ROMs in which the projection of the Reynolds stresses is solved through a modified modal basis and the knowledge of the mean flow. This framework achieves
turbulence statistics comparable to those of a reference direct numerical simulation (DNS) in a minimal channel at $Re_{\tau} \approx 185$. Short-time
forecasting with this framework is assessed, where balanced truncation modal bases outperform controllability modes in ROMs, yielding a reconstruction of the velocity field comparable to the Galerkin projection of proper orthogonal decomposition (POD) modes. This framework can extend analysis based on linearisations around the mean turbulent flow, which became widespread in recent years, to include explicitly non-linear interactions between modes, enabling accurate models at higher Reynolds number.
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All authors Ian Addison-Smith, Igor A. Maia, André V. G. Cavalieri, Benjamin Herrmann