Statistical Mechanics
A Statistical Analysis of Diffusion Dynamics in Networks
A. Talebi
Network
diffusion is a well-known model for studying how a quantity in a network propagates to reach a steady state, where its value becomes uniformly distributed across all nodes. Previous studies of network
diffusion have mainly focused on the second-smallest
eigenvalue of the network
Laplacian to determine the timescale associated with the slowest decaying mode. However, this study investigates the eigenspectrum of the network
Laplacian in terms of its statistical properties. This method is useful for studying the statistical properties of network
diffusion without calculating all
eigenvalues, which can be useful for large networks. Additionally, this study introduces a condition under which the system is less diffusive and investigates how changes in the network structure influence the overall
diffusion dynamics.
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Cosmology and Nongalactic Astrophysics
To USR or not to USR: An effective description of two-field dynamics
Samuel Sánchez López and Eemeli Tomberg
Single-field models of inflection point inflation experience a phase of ultra-slow roll (USR), leading to amplified
curvature perturbations. Recently, Lorenzoni et al. modified the scenario by adding a light spectator field, showing that it ruins USR by setting a floor for the first slow-roll parameter $\epsilon$. Mixing with isocurvature perturbations still amplifies the
curvature power spectrum. We offer an alternative point of view, arguing that the inflaton still undergoes effective USR. The spectator lifts the potential by a constant amount, and the inflaton perturbations follow single-field dynamics in the lifted inflection point potential, decoupling from the spectator perturbations. Mode mixing only affects the power spectrum dip, making it milder. We demonstrate this effective single-field behavior numerically for example models. Our results offer a simple way to study the models' parameter dependence.
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Fluid Dynamics · Cross-listed from cs.RO
Underwater Navigation in Unsteady Flows Using Measurement Histories from a Single Sensing Unit
Linhao Jin, Qimin Feng, Peter Gunnarson et al. (+1 more)
Spatial flow measurements support
underwater navigation, but distributed sensing is constrained by
robot size and sensor layout. We use a causal observer to estimate current lateral velocities from a finite history of measurements collected by a single sensing unit, supplying the inputs of a fixed
navigation controller. In two-dimensional wake simulations with access to body-frame ambient velocity, this virtual sensing interface reduces simultaneous flow sampling from three points to the
robot center. Trained only in a circular-cylinder wake at Re = 100, the flow-history observer achieves 84.4% and 80.6% success at held-out Re = 205 and 240 without retraining. These rates are 7.4 and 4.6 percentage points below direct spatial sensing and more than 30 points above a matched current-only observer. Past flow remains beneficial when past goal and yaw information is available. Across obstacle geometries, performance remains close to direct sensing in square-prism wakes but declines in triangular-prism wakes. Component replacement identifies the lateral velocity difference as control-relevant, while controlled perturbations reveal sensitivity to error persistence. The results demonstrate the closed-loop utility of single-point flow histories under the assumed observation model.
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All authors Linhao Jin, Qimin Feng, Peter Gunnarson, Qiang Zhong
Quantum Physics
Quantum Broadcast Channels with Mutually Confidential Messages
Paula Belzig, Sukanya Ghosal, Farzin Salek et al. (+1 more)
We study the transmission of two independent confidential classical messages over a
quantum broadcast channel, one for each receiver. Each message must remain secret from the other receiver, including when that receiver knows its own message. For classical inputs and
quantum outputs, we establish the classical Marton-type inner bound under average reliability and conditional strong secrecy. The encoder selects pairs of codewords from independently generated codebooks using normalized likelihood weights. We prove reliability through a change-of-distribution argument. Our main technical result is a bipartite classical-
quantum resolvability
theorem that accounts for the dependence created by pair selection and establishes secrecy for the same encoder. We also obtain a multi-letter capacity characterization and extend it to arbitrary
quantum inputs under secrecy against the other receiver, together with the Stinespring environment. We recover confidential capacity regions for deterministic classical and degraded classical-
quantum channels, with an explicit evaluation for the classical Blackwell channel. For coherent isometric extensions of injective deterministic classical broadcast channels, we show that the confidential classical capacity region equals that of the corresponding classical channel. We then compare confidential classical communication with
quantum transmission. For the coherent isometric extension of the Blackwell channel, we determine the unassisted
quantum-capacity region and show that some achievable confidential classical rate pairs lie outside it. The Platypus channel provides another example of this separation.
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All authors Paula Belzig, Sukanya Ghosal, Farzin Salek, Graeme Smith
Quantum Physics
Explicit channels with unbounded gains in classical communication using entangled inputs
Hao-Chung Cheng, Benjamin Lovitz and Peixue Wu
A seminal result of Hastings showed that entangled inputs can increase the rate of classical communication through independent uses of a
quantum channel. While Hastings' result proved the existence of this phenomenon, it has remained a major open problem to find an explicit channel with this property. In this work, we resolve this question by constructing an explicit family of finite-dimensional
quantum channels for which entangling inputs between pairs of channel uses yields an unbounded separation from the achievable communication rate using unentangled inputs. We describe a
circuit implementation of our channel that uses only deterministic qudit Clifford
unitaries and a single binary measurement with classical feedforward. The key ingredient is a careful design of the measurement and feedforward process that yields the required one-copy and two-copy output
entropy bounds from moment estimates alone, without requiring strong convergence of the underlying
unitary family.
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Plasma Physics
Analytic toroidal 3D MHD equilibria and steady Euler flows with invariant surfaces
Matt Landreman
Families of explicit analytic solutions of the magnetohydrodynamic
equilibrium equations are presented, equivalent to steady incompressible Euler flow. The solutions are non-axisymmetric and possess exact nested toroidal flux surfaces. No expansion is made in inverse aspect ratio or in the deviation from axisymmetry. The
magnetic field and flux surfaces are given explicitly in Cartesian coordinates using elementary functions. The field, current density, and scalar pressure are smooth over the toroidal domain. The pressure gradient vanishes only on the
magnetic axis. One family of solutions has uniform rotational transform $\iota=2$, while another family has a sheared $\iota$ profile. These counterexamples to Grad's
conjecture are valuable for understanding the existence and regularity of 3D
equilibria and for testing numerical codes.
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Nuclear Theory
Longitudinal $\Lambda$ polarization as a competition between freeze-out geometry and elliptic flow in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.36\,\mathrm{TeV}$
Yilong Xie, Simin Wu and Laszlo P. Csernai
The second sine harmonic $\Pz$ of longitudinal $\Lambda$ polarization is sensitive to the balance between the kinematic-vorticity contribution $\Pz^\omega$ and the kinematic-shear contribution $\Pz^\Xi$ at decoupling. We quantify this competition in a scan of 48 Pb-Pb initial states evolved with the (3+1)-dimensional Particle-In-
Cell Relativistic (PICR) ideal-hydrodynamic code. With the isothermal local-
equilibrium (ILE) prescription, the total harmonic follows $\Pz\simeq a\,\efo-b\,v_2$, with $a\simeq0.010$ and $b\simeq0.014$, where $\efo$ is the freeze-out eccentricity and $v_2$ the
elliptic flow of $\Lambda$ hyperons. With coefficients fixed on these 48 states, the relation describes 86% of the variation of $\Pz$ in 12 states outside the fit. To identify the origin of the two terms, we decompose the ILE integrand exactly into an emission-gradient term and a curl term. On the PICR decoupling surfaces, the tangential emission gradient is positive on average, correlates most strongly with $\efo$, and admits a surface-
curvature representation, whereas the normal emission gradient and the curl term are negative on average and correlate most strongly with $v_2$. A blast-wave calculation with the same integrand gives coefficients of comparable magnitude and shows how the cancellation point $\efo/v_2=b/a$ changes with the flow and the surface geometry; both PICR and blast-wave calculations predict that $b/a$ rises with
hadron mass from the
proton to the $\Omega$ when the decoupling surface is held fixed. Although the geometry inferred from ALICE data depends on the background, the measured polarization constrains the displacement of $\efo$ from the cancellation boundary $\efo=(b/a)v_2$. For the central ALICE measurement values at $5.36\,\mathrm{TeV}$, the backgrounds examined give $\efo\simeq0.2$–$0.4$ in 30–50% Pb-Pb collisions.
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Quantum Physics
A Syndrome-Extraction Framework for Distributed Lattice Surgery on Arbitrary Rotated Surface-Code Layouts
Pritesh Thakur, Daniel Dilley and Zain Saleem
Modular
quantum computing is a leading candidate for scalable fault tolerant
quantum computation. Performing
lattice surgery using surface code patches in different modules requires the use of inter-module gates that are noisier than the local gates. Furthermore, the merged layouts during
lattice surgery expose multiple directions in which hook errors can propagate to reduce the fault distance. Existing hook-avoiding schedules either increase the syndrome extraction
circuit depth, or let link faults propagate into the bulk. We introduce a seam construction that allows splitting arbitrary merged rotated surface code layout into smaller patches with uniform boundaries that could keep their own hook-avoiding N/Z shaped schedule. At the seam we split weight-4 stabilizers into pairs of weight-2 stabilizers that are mediated through a Bell pair and measured within a CNOT depth of 4. We also employ the use of three-
qubit $\texttt{CXX}$ gates for parity measurements at the seam to maintain the minimum CNOT depth. Through this seam construction, we confine the elevated link error at the seam, protecting the bulk from higher error rate. We also give a custom detector annotator for such seams that can find the detector space, annotate detectors in the Stim
circuits, and ensure that they are suitable to use by matching decoders. We implement our construction for the logical Pauli-$XX$ measurement
lattice surgery and a cross-shaped spatial junction and sweep the link error rate from $10$ times to $100$ times a fixed bulk error rate, and show that our construction gives the lowest and most stable logical error rate than the other frameworks compared here.
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Quantum Physics
Good Quantum Locally Testable Codes from Product Expansion
Mitali Bafna, Anqi Li and Quynh T. Nguyen
We construct
quantum locally testable codes (LTCs) with constant rate, distance, soundness and locality under a variant of a product expansion
conjecture of Bafna and Vyas about Reed-Solomon codes. In particular, we use the high-dimensional expansion framework of Dinur, Lin and Vidick for constructing
quantum LTCs, instantiated with the non-Abelian cubical complexes of Rungtanapirom, Stix and Vdovina. Our code is obtained by equipping the complex with carefully chosen Reed-Solomon local codes whose
symmetries are compatible with those of the complex.
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Soft Condensed Matter
Entropy-Driven Initiation and Cytoskeletal Viscoelasticity in Endocytosis: An Onsager Variational Framework
Jinjie Liu, Zhongcan Ouyang and Hao Wu
Receptor-mediated endocytosis requires a particle to approach the
cell membrane to within a few nanometers before ligand–receptor binding can occur. Existing continuum models often start from an already established contact and do not explicitly describe how crowding particles on the extracellular side influence the distribution of the particle near the membrane. We examine entropic depletion forces as one possible nonspecific contribution to this initial approach. For ideal depletants, the Asakura–Oosawa excluded-volume construction gives an exact depletion potential for the planar geometry before contact. The potential and force vanish continuously at the onset of excluded-volume overlap. This interaction provides a possible contribution to membrane proximity before specific binding, while its extension to curved wrapping geometries requires additional approximation. Within a reduced continuum model, we combine depletion attraction, ligand–receptor binding, membrane deformation, and cytoskeletal viscoelastic dissipation. The viscoelastic contact is formulated through a hereditary integral and a standard linear solid. The kinetic model gives a conditional minimum ligand density for complete engulfment, a finite particle-size window, and a stiffness-dependent upper limit. When the stationary radius lies inside the domain of finite positive wrapping times, the estimated wrapping time has a minimum at a radius that decreases with increasing binding energy density. At fixed viscosity and other independent parameters, the same time approximation predicts slower wrapping as
cell stiffness increases. The two positive roots defining the size window merge at a limiting parameter value, which characterizes closure of the admissible size interval. Depletion attraction is interpreted as one possible contribution to particle-membrane association
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Materials Science
Three-Dimensional Imaging of High-Density Dislocation Networks and Their Interactions using Multislice Electron Ptychography
Eegene Chung, Anand Ithepalli, Naomi Pieczulewski et al. (+6 more)
Development of novel devices often involve combining functional materials and substrates, each chosen for particular physical properties such as low-loss or thermal conductivity. This, however, can introduce a large
lattice mismatch and high density of structural defects that may limit device performance and reliability by trapping charge or creating leakage pathways. Such is the case for integrating superconducting TiN with a low-loss sapphire substrate. Here we resolve and image the resulting misfit, screw, and threading dislocations in epitaxial TiN on sapphire using the depth-sectioning capabilities of multislice electron ptychography. We find misfit dislocations spaced ~1.6 nm apart and track out-of-plane crossings of misfit dislocations as well as their transitions to threading dislocations, details which are obscured in conventional defect-imaging methods. The ability to correlate specific dislocation types and their interactions in extremely small volumes and at high densities is valuable for understanding structure-property relations even in modern, scaled devices.
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All authors Eegene Chung, Anand Ithepalli, Naomi Pieczulewski, Chia-Hao Lee, Steven Zeltmann, Keun-Yeol Park, Celesta S. Chang, Debdeep Jena, David A. Muller
High Energy Physics (Theory)
Quasinormal modes and quantum black hole interiors
Chiara Coviello, Ansh Gupta, Robie A. Hennigar et al. (+2 more)
Quasinormal modes (QNMs) of black hole perturbations in the large overtone limit, namely, asymptotic QNMs, are highly sensitive to a black hole's interior geometry. We probe the singularity structure of a class of exact (2+1)-dimensional
quantum black hole solutions to semi-classical
gravity by computing their asymptotic QNM spectra. We do this using methods of complex analysis in which the radial coordinate is analytically continued to the complex plane. The leading order QNM frequencies all fit the generic form $\omega=(\text{offset})+n(\text{gap})$, for overtone number $n$, which we also confirm numerically. Under a general assumption about the global Stokes
topology of the complexified radial coordinate, we show how to reconstruct the scaling exponent of more general (spacelike or timelike) black hole singularities from the offset. We then compute subleading corrections to the asymptotic QNMs, from which we provide a robust method for extracting the scaling of the metric function near the singularity. Our findings exemplify the transition between "Kasner eons", successive regimes encountered on approach to a spacelike singularity, as non-perturbative
quantum effects become dominant. For charged
quantum black holes, the asymptotic QNMs exhibit a crossover between two regimes in which the neutral and charge contributions to the metric function dominate, respectively. Within the crossover region, the QNMs develop an oscillatory behavior that may be a signature of the inner horizon.
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All authors Chiara Coviello, Ansh Gupta, Robie A. Hennigar, Kai Shi, Andrew Svesko
Mesoscale and Nanoscale Physics
The Role of Electron Correlations in Chirality Induced Spin Selectivity of Molecular Junctions
A. Konidena, J. Fransson and L. Kantorovich
The Non-
Equilibrium Green's Function (NEGF) approach is applied to a chain of Hubbard atoms in a helical geometry sandwiched between two leads, one of which is
magnetic, to assess what role the electronic correlation effects within the molecule may play in explaining the Chirality Induced
Spin Selectivity (CISS) effect. The correlation effects are treated at the level of the self-consistent second Born approximation. Two chiralities, Laevorotatory (L) and Dextrorotatory (D), of the helix, are discussed. Further, we account for
spin-orbit coupling (SOC) within the chains using a simplified model of Kane and Mele that exploits next-nearest neighbour interactions intrinsic to a curved geometry. The interaction with the leads is considered within the Wide Band Approximation. We consider the ratio, U/t, of the Hubbard constant U to the hopping t between atomic sites along the chain of up to two, but found very little
spin polarisation in our calculations. Even though the
spin polarisation factor defined as a relative difference between the largest and smallest total current is found for both enantiomers practically the same, the orientation of the tip's polarisation required to reach the largest and smallest currents for the two enantiomers differed. It is also found that the qualitative agreement with observations can only be achieved if we account, self-consistently, for the second order of the perturbation theory. The distribution of the
spin populations on the chain atoms for different U/t ratios is also discussed. This study concludes that even though accounting for electron-electron interactions are important in understanding
spin selectivity within molecular junctions, they cannot be made solely responsible for the high
spin polarisation factors observed in experiments.
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Space Physics
First Observation of a Polar Coronal Hole-like Fast Solar Wind Stream in the Sub-Alfvénic Solar Corona: an Analysis of Turbulence Properties
Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus et al. (+2 more)
Parker
Solar Probe, near its 23rd perihelion in March 2025, sampled an extended interval of sub-Alfvénic
solar wind likely originating from a large equatorial coronal hole. At heliocentric distances of approximately 10
solar radii, with speed mostly above 400 km/s, this interval is a first example of “polar coronal hole-like (PCH-l) fast"
solar wind observed in the sub-Alfvénic
solar corona. We characterize the
turbulence properties of this unique interval using Parker
Solar Probe measurements. Despite being sampled well inside the nominal Alfvén surface, the
turbulence appears to be already well developed while remaining strongly transverse and highly imbalanced, exhibiting a large cross helicity. These observations provide new constraints on the development and
evolution of
solar wind
turbulence within the lower corona.
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All authors Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus, Yeimy J. Rivera, Samuel T. Badman
Chaotic Dynamics
The cubic discriminant as an organizing principle for Duffing dynamics
Patrycja Jaros and Przemyslaw Perlikowski
We present an analytical organizing principle underlying the dynamics of the periodically forced Duffing oscillator. In the massless limit the system reduces to a time-dependent cubic equation whose discriminant and Jacobian classify the canonical Duffing regimes and determine the number and stability of instantaneous
equilibria. For the double-well oscillator, the same construction gives an exact forcing threshold $F_{\mathrm{bif}}$ separating intra-well and inter-well dynamics. We show that this algebraic quantity governs the finite-mass dynamics far beyond the singular limit from which it originates: the boundary between intra-well and inter-well motion converges to $F_{\mathrm{bif}}$ as $m\to0$, and the families of pitchfork bifurcations responsible for asymmetric inter-well states accumulate at a common point. Numerical simulations further show how the discontinuous jumps of the degenerate model are regularized at finite mass into short oscillatory transients that shrink as $m\to0$. These results reveal the massless Duffing equation as the organizing center of the full finite-mass dynamics and establish a direct link between the algebraic structure of the degenerate problem and the global bifurcation structure of the oscillator.
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Astrophysics of Galaxies
JWST Observations of Starbursts: The motion of dust - PAH kinematics of M82 and NGC 253 with JWST/MIRI spectroscopy
Fergus R. Donnan, Karin Sandstrom, Alberto D. Bolatto et al. (+27 more)
We present an analysis of
dust kinematics in the local starburst
galaxies M82 (NGC 3034) and NGC 253 using Polycyclic Aromatic Hydrocarbon (PAH) features observed with JWST/MIRI spectroscopy. We are able to produce high-quality velocity maps of the 5.2 $\mu$m, 6.2 $\mu$m, and 11.3 $\mu$m PAH features, as well as numerous lines of molecular gas via H$_2$ rotational transitions and ionized gas from [NeII] and H recombination lines. Given the field of view and inclination, we trace a rotating disk in M82 where we observe a steep rise in the velocities followed by flattening, typical of
galaxy rotation curves. In NGC 253, however, the 6.2 $\mu$m and 11.3 $\mu$m PAH features trace the launching region of the
outflow, firmly within the starburst region. We find the ionized gas also shows
outflow contributions in NGC 253 while the warm molecular gas is dominated by rotation. Additionally, the molecular gas
outflow velocities are lower than the ionized gas, with the 11.3 $\mu$m PAH feature consistent with the ionized gas rather than the molecular gas. We therefore suggest that PAHs are more closely associated with the ionized gas rather than the molecular at the base of the
galaxy outflow, where larger scale imaging shows comparable morphology between PAHs and HI. The 6.2 $\mu$m PAH feature has an even higher
outflow velocity for both
galaxies, possibly suggesting preferential ionization of the PAHs within the faster-moving hot phase of the base of the
outflow.
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All authors Fergus R. Donnan, Karin Sandstrom, Alberto D. Bolatto, Bruce T. Draine, Sara E. Duval, Ralf S. Klessen, Elisabeth A.C. Mills, Helena M. Richie, J.D.T. Smith, Sylvain Veilleux, Patricia A. Arens, Leindert A. Boogaard, Serena A. Cronin, Daniel A. Dale, Kimberly L. Emig, Rodrigo Herrera-Camus, Thomas S.-Y. Lai, Sebastian Lopez, Laura Lenkić, Rebecca C. Levy, Divakara Mayya, David S. Meier, Kaitlyn E. Sheriff, Utsav Siwakoti, Evan Skillman, Elizabeth Tarantino, Yu-Hsuan Teng, Vicente Villanueva, Fabian Walter, Paul P. van der Werf
Quantum Physics
Evidence for a low-gap component in compressively stressed niobium thin films
J.T. Paustian, Maciej Olszewski, Kiichi Okubo et al. (+6 more)
We investigate the microwave response of sputtered Nb films as a function of biaxial film stress. Although transport measurements show nearly identical superconducting transition temperatures ($9.0\pm 0.2$K) and residual resistance ratios across the stress series, microwave resonators fabricated from highly compressive films exhibit enhanced temperature-dependent loss and larger frequency shifts. A conventional single-phase Mattis–Bardeen description yields an effective critical temperature of $2.4\pm0.2$K, approximately a factor of four below the value obtained from transport measurements. We show that the data are instead consistent with the presence of an additional low-gap component whose contribution increases with compressive stress. These results show that conventional transport measurements can overlook stress-dependent low-energy excitations that strongly influence microwave performance.
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All authors J.T. Paustian, Maciej Olszewski, Kiichi Okubo, Lingda Kong, B.L.T. Plourde, Ethan G. Arnault, Caleb W. Fink, Valla Fatemi, Ivan V. Pechenezhskiy
Quantum Physics
A quantum lower bound for path finding in welded trees
Joseph Carolan, Andrew M. Childs, Matthew Coudron et al. (+1 more)
In the welded tree problem, an
algorithm is tasked with navigating a graph formed from two binary trees joined at the leaves through a “weld” of connecting edges. A
quantum walk can navigate from root to root exponentially faster than any classical
algorithm. However, known efficient
quantum algorithms cannot find a path between the roots, as recording the path destroys constructive interference and thus the speedup. We prove that this is inherent: any
quantum algorithm needs exponentially many queries to find a path between the roots of an independently matched welded tree graph. This provides an example of a problem that a
quantum computer can solve exponentially faster than any classical
algorithm by exploring exponentially many paths in superposition, but where it is provably intractable to find any such path. The proof uses compressed permutation oracles to record the progress of a
quantum algorithm as it queries the graph. We show that the compressed database remains path-free up to a small error. By controlling such errors and bounding the progress of the
algorithm with each compressed oracle query, we show that $\Omega(2^{n/12})$ queries are required to find a path in a height-$n$ tree with constant success probability.
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All authors Joseph Carolan, Andrew M. Childs, Matthew Coudron, Amin Shiraz Gilani
Physics and Society
Normalized fractional Hirsch Index and Modified Pareto Law
Asim Ghosh and Bikas K. Chakrabarti
The Hirsch index (introduced in 2005) has been a very successful scientometric author-level measure for the publication impact inequalities among the authors. However, it does not have any upper bound and statistically it grows in proportion to the square root of the number of publications by the author. Social scientists, on the other hand, measure the economic performance of different countries (having different wealth amounts and populations etc.) using inequality indices like the Gini index (since 1912) etc., which are normalized quantities (independent of the country's total wealth or the population size). We show here that a normalized fractional Hirsch index, giving the fraction of total citations earned by fraction of those successful papers published by the author, can even indicate that typically about $14\%$ of the top cited papers earn about $86\%$ of citations for very successful scientists (like the 95 Nobel Laureates considered here). This is similar to Pareto's 80-20 law (since 1896) and agrees more precisely with those observed for self-organized sandpile models, where typically $86\%$ of the avalanche masses are dissipated through $14\%$ of the largest avalanches as the piles approach their respective self-organized critical points.
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Mesoscale and Nanoscale Physics
Nonlinear Spin Polarization Enables Néel Order Switching in Centrosymmetric Altermagnets
Sunit Das, Sayan Sarkar and Amit Agarwal
Deterministic electrical switching of the Néel order remains challenging in centrosymmetric altermagnets, where linear current-induced
spin polarization is forbidden by inversion
symmetry. Here, we establish a nonlinear route to Néel order control.
Spin group
symmetry shows that, in the nonrelativistic limit, the nonlinear
spin polarization is constrained along the Néel vector, with a staggered response allowed in $8$ of the $10$ nontrivial
spin-Laue groups. Although this Néel
spin polarization is torque-inactive by itself, finite
spin-orbit coupling can generate an additional uniform component transverse to the Néel vector. Using a minimal model for the $d$-wave altermagnet FeSb$_2$, we demonstrate the coexistence of the nonrelativistic staggered response with an SOC-induced uniform transverse component. Landau-Lifshitz-Gilbert equation-based macro-
spin simulations reveal that the transverse component alone produces oscillatory dynamics, whereas its cooperative action with the staggered response enables deterministic $180^\circ$ reversal. We further show that changing the electric field orientation reverses the staggered
spin response and selects the switching direction, while the opposite Néel states can be distinguished by their anomalous
Hall response. Our results establish a nonlinear electrical write-read scheme for centrosymmetric altermagnets.
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Quantum Physics
When are bosonic Gaussian states classical to learn?
Senrui Chen, Antonio Anna Mele, Francesco Anna Mele et al. (+1 more)
A fundamental question in physics is: When does classical behavior emerge from
quantum systems? Bosonic Gaussian states provide a natural setting to explore this
quantum-classical boundary, as they capture both the classical field behavior and the intrinsic
quantum nature of light. Here, we address this problem from a learning-theoretic perspective by asking: When are bosonic Gaussian states classical to learn? That is, under what conditions (if any) can an n-mode bosonic Gaussian state be learned with as few samples, and with operations as simple, as are needed to learn a classical 2n-variate Gaussian distribution? We establish a smooth crossover in learnability governed by the state's thermal fluctuations: - Cold Gaussian states are non-classical to learn: When the covariance
matrix satisfies $\Sigma\le(\frac12+O(\frac1n))I$, i.e. close to the
vacuum covariance,
tomography under single-copy (i.e., non-entangled) measurements fundamentally requires $\Omega(n^3)$ copies, strictly exceeding the sample complexity $\Theta(n^2)$ of learning classical Gaussian distributions. We show that this hardness persists even when few-copy entangled measurements are allowed. - Warm Gaussian states are classical to learn: When thermal fluctuations exceed the
vacuum noise, parameterized by $\Sigma\ge(\frac12+\nu)I$ for any parameter $\nu>0$, we prove that single-copy
tomography requires $N=\Theta\left(n^2\min(n,1+\nu^{-1})\right)$ copies. This bound is tight and is achieved by simple, non-adaptive, unentangled heterodyne measurements. Crucially, for $\nu=\Omega(1)$, the sample complexity drops to $\Theta(n^2)$, matching the classical case. Our results tightly characterize a
quantum-to-classical crossover in the learnability of bosonic Gaussian states, reveal a novel connection between fundamental physics and statistical learning theory, and have implications for real-world sensing experiments.
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All authors Senrui Chen, Antonio Anna Mele, Francesco Anna Mele, John Preskill
Strongly Correlated Electrons
Real-Frequency Diagrammatics with Pole Representations
Rayan Farid, Lei Zhang, Aiman Al-Eryani et al. (+2 more)
Finite-temperature many-body theories are typically formulated in imaginary time, where they are amenable to efficient numerical treatment. However, the extraction of spectral properties from the imaginary axis is difficult and requires numerical analytic continuation, while a direct formulation on the real axis requires prohibitively expensive numerical quadrature. In this paper, we represent the objects of many-body perturbation theory using systematically improvable pole and moment expansions and develop the corresponding framework for evaluating diagrammatic contributions directly on the real axis. We introduce a controlled recompression procedure that prevents the proliferation of poles under algebraic and diagrammatic operations. We
benchmark the approach on paradigmatic
quantum impurity problems and apply it to self-consistent calculations of the uniform electron gas. The resulting spectral quantities converge systematically towards numerical accuracy. This work provides a practical framework for controlled and systematically improvable calculations of spectral quantities within diagrammatic many-body theories, including self-consistent conserving approaches.
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All authors Rayan Farid, Lei Zhang, Aiman Al-Eryani, Agnieszka Jażdżewska, Emanuel Gull
High Energy Physics (Phenomenology)
Model-Independent Sideband Constraints on Inelastic Dark Matter at the LZ High-Recoil Candidate
David Delepine and Shaaban Khalil
The LUX-ZEPLIN experiment has reported one
nuclear-
recoil event at $248\pm23_{\rm stat}\pm23_{\rm sys}\,{\rm keV}$ in a $2.84\,{\rm tonne\text{-}year}$ exposure, with a local significance of $3.4\sigma$. Inelastic (endothermic) dark matter is a natural candidate: its kinematic threshold suppresses low-energy
recoils and shifts the signal toward higher
recoil energies. We perform a model-independent analysis of the LZ data using two sidebands, without specifying an ultraviolet completion, so our results apply broadly to inelastic dark matter with coherent
spin-independent
nuclear scattering. For each $(m_\chi,\delta)$ we compute $N_{\rm low}/N_{\rm sig}$ and $N_{\rm hi}/N_{\rm sig}$—predicted count ratios in the sidebands $[14,225)\,{\rm keV}$ and $(271,800]\,{\rm keV}$ relative to the signal region $[225,271]\,{\rm keV}$. The two ratios vary in opposite directions with $\delta$ and are simultaneously optimized at a unique splitting $\delta^\star$. For $m_\chi=1\,{\rm TeV}$, $\delta^\star=339\,{\rm keV}$ with a combined Poisson tension of $\approx1.9\sigma$; over $500\,{\rm GeV}$–$3\,{\rm TeV}$, the tension at $\delta^\star$ rises from $\lesssim1.3\sigma$ to $\approx2.5\sigma$. Additional suppression arises from the Helm form factor: $|F_{\rm Xe}^{\rm Helm}|^2\simeq3\times10^{-4}$ at $248\,{\rm keV}$, near its second diffraction zero. A dedicated LZ search over $271<E_R<800\,{\rm keV}$ would provide a decisive test of inelastic dark matter with $\delta\gtrsim330\,{\rm keV}$.
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Astrophysics of Galaxies
The molecular gas of four ram pressure stripped galaxies in the core of the Hydra I cluster
Clara C. de la Casa, Kelley M. Hess, Nikki Zabel et al. (+15 more)
We present new CO(1-0) measurements from ALMA and new HI measurements from MeerKAT in four ram pressure stripped (RPS)
galaxies in the core of the Hydra I cluster: NGC 3312, NGC 3314a, NGC 3314b and LEDA 753342. These deep data, with compatible spatial resolution in CO and HI ($\sim15''$, $\sim$4 kpc), help increase the low statistics of
galaxies observed in CO at extreme infall stage for probing how molecular and atomic gas behave under high ICM pressures. We studied the cold gas morphologies of these
galaxies, and found asymmetries in their detected CO disks with respect to their HI and optical disks. No stripped CO was found in the tails, which could support the scenario that H$_2$ displays morphological and velocity asymmetries in the disks before being stripped. We then compared the H$_{2}$/HI ratios and H$_{2}$ vs. HI deficiencies between the four Hydra I
galaxies, the xCOLDGASS sample dominated by field
galaxies and VIVA-VERTICO Virgo RPS
galaxies. LEDA 753342 ($\rm log~M_{\star}/M_{\odot} = 8.6$) is below the
stellar mass limit of the reference samples ($\rm log~M_{\star}/M_{\odot} = 9$), but its $\rm M_{H_2}/M_{HI}$ and cold gas deficiencies are compatible with lower
stellar mass field and Virgo cluster
galaxies. NGC 3312 and NGC 3314a are in an intermediate stage between field
galaxies and more advanced RPS Virgo
galaxies. NGC 3314b is more consistent with Virgo
galaxies more advanced in RPS, than with field
galaxies. We reason that LEDA 753342 is at a very early stage of RPS, that NGC 3314a and NGC 3312 are at a similar timescale of early but very active RPS with differences potentially due to unequal initial total baryonic mass and infall angles, and that NGC 3314b is the latest stage in RPS in the sample. These
galaxies display RPS across different evolutionary stages, and suggest that RPS starts affecting the CO reservoir before it starts being stripped from the
galaxy.
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All authors Clara C. de la Casa, Kelley M. Hess, Nikki Zabel, Emanuela Pompei, Yara L. Jaffé, Nazir Makda, Julia Healy, Johanna Hartke, Lourdes Verdes-Montenegro, Enrichetta Iodice, Sarah Blyth, Ralf Kotulla, Marie-Lou Gendron-Marsolais, Renée C. Kraan-Korteweg, Brenda Namumba, Amidou Sorgho, Roger Ianjamasimanana, John S. Gallagher
High Energy Physics (Experiment)
Extending the reconstruction of displaced tracks at CMS during the HL-LHC with Line Segment Tracking
Jade Chismar
The upgrade of the Large
Hadron Collider (LHC) to the High-Luminosity LHC (HL-LHC) will greatly increase the average number of simultaneous
proton-
proton interactions per bunch-crossing (pileup), and will place significant demands on computing resources for the reconstruction of charged-particle tracks. Line Segment Tracking (LST) is a novel, highly parallelizable
algorithm that can run efficiently on GPUs and has been integrated into the CMS software to enable the reconstruction of displaced tracks in the high pileup scenarios of the HL-LHC. The LST
algorithm is designed to build track candidates using only outer tracker hits, naturally allowing for high acceptance of displaced track signatures. In the HL-LHC tracking reconstruction sequence without LST, displaced tracking ends at a radial displacement of the track origin of approximately 8 cm. The usage of LST in track reconstruction enhanced efficiency for displaced tracks, extending the acceptance in radial displacement from the track origin by more than a factor of 4. In this work, we introduce a new LST object, the quadruplet (T4), defined as a linked pair of triplets with a common line segment, targeting displaced track signatures. We present the performance of this improved implementation of the LST
algorithm in several physics scenarios, extending the displaced-track acceptance from 40 cm to 60 cm in radial displacement compared to LST without T4s.
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Mesoscale and Nanoscale Physics
Benchmarking the generalized Kadanoff-Baym ansatz and second-order adiabatic expansion using time-dependent spintronic effects: Spin pumping, torque, and inertia
Jalil Varela-Manjarres, Nicole Sofia Salazar-Delgado and Branislav K. Nikolic
The generalized Kadanoff-Baym ansatz (GKBA) [P. Lipavský et al., Phys. Rev. B 34, 6933 (1986)] has emerged as a popular and numerically efficient
algorithm for simplification of nonequilibrium Green's function (NEGF)-based calculations of time-dependent
quantum transport. For systems that can be split into classical and
quantum degrees of freedom, another popular simplifying strategy is adiabatic expansion (AE) of NEGF [N. Bode et al., Phys. Rev. Lett. 107, 036804 (2011); S. Deghi et al., Phys. Rev. B 110, 115409 (2024)] in terms of the velocity of classical degrees of freedom, such as localized
magnetic moments (LMMs) in spintronics or coordinates of
nuclei in nanoelectronics. Here we compare GKBA and second-order AE with numerically exact
benchmarks for two-terminal junctions whose central region hosting
quantum electrons and classical LMMs is attached to two semi-infinite normal metal leads. Three simple models are employed to exhibit cornerstone time-dependent effects in spintronics—
spin pumping and
spin-transfer torque (STT), as well as
magnetic inertia as a recently explored phenomenon. We find that GKBA fails to describe pumping of
spin current by precessing LMMs, or STT vectors, and thereby induced LMM dynamics. Conversely, the second-order AE matches numerically exact
benchmarks for both effects remarkably well, thereby also revealing the essentially nonadiabatic nature of
spin pumping. Thus, AE opens a path toward an accurate description of STT-driven magnetization dynamics, including combination with first-principles
Hamiltonians, while incurring a fraction of the cost of time
evolution of full NEGF. However, despite including terms up to the second time derivatives of LMMs into AE, this approach fails to capture fast nutational oscillations on top of the precessional motion of LMMs as the hallmark of
magnetic inertia.
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Quantum Physics
Parallelizable and addressable transversal non-Clifford gates on good quantum LDPC codes
Yiming Li, Zimu Li, Zhengyi Han et al. (+1 more)
We achieve linearly many parallelizable and addressable transversal logical multi-controlled-Z gates with asymptotically optimal parameters simultaneously on good
quantum low-density parity check codes and
quantum locally testable codes, by applying the gate framework of [arXiv:2604.01874] to good qLTC constructions. To establish the nontriviality of the logical operation, we express the cup product pairing as a coefficient in a product of Moore determinants and prove that this coefficient is nonzero. Moreover, we use the
symmetries of the covering spaces to construct large spaces of cocycles. By multiplying the initial cocycles by suitable elements of these spaces, we obtain linearly many independent pairings, each selected by a corresponding cycle constructed using Poincaré duality. This yields linearly many parallelizable and addressable multi-controlled-Z gates and enables asymptotically constant-overhead magic state
distillation with good qLDPC codes.
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All authors Yiming Li, Zimu Li, Zhengyi Han, Zi-Wen Liu
Optics
Structured detection beyond spatial imaging
Bruno K. Nowak and Shu-Wei Huang
In a point-scanning microscope, detection through a pinhole improves resolution and replacing the pinhole with a detector array provides redundant encoding of the object spectrum, enabling correction of nonidealities in the imaging system or further resolution improvements, for instance. Here, we show that the mathematical principles underlying structured detection are not intrinsically spatial and therefore structured detection may be used for imaging distributions in other physical domains, such as time, frequency, and velocity space. We numerically illustrate this generality by applying structured detection to an electromagnetic distribution in time using four-wave mixing (FWM). The resulting image reconstructions outperform the temporal equivalent of confocal detection, even as the FWM models are made more realistic and shot noise is considered.
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Fluid Dynamics
Experimental observations of sub-threshold triadic resonances in internal wave beams
Laura J. Irvine, Katherine M. Grayson, Andrew G. W. Lawrie et al. (+1 more)
This work examines sub-threshold triadic responses to a
vortex-ring-induced perturbation of an internal
gravity-wave field, using sparsity-promoting dynamic mode decomposition (spDMD) to diagnose wave structures from experimental observations. Compared with a standard approach to dynamic mode decomposition (DMD) that selects modes by truncation of the singular value spectrum, spDMD, an alternative approach that instead seeks to minimise reconstruction error, is shown here to robustly identify previously indistinguishable oscillatory signals of high frequency in cases of both triadic resonance instability (TRI) and sub-threshold sustained triadic response (STR). These signals are consistent with wave–wave interaction products composed of a primary internal wave with frequency $\omega_0$, and secondary TRI waves with frequencies $\omega_1$ and $\omega_2$ respectively, leading to signals with frequencies $\omega_3 = \omega_0 + \omega_1$ and $\omega_4 = \omega_0 + \omega_2$. We show that these signals satisfy conditions for resonance, but fail to satisfy the dispersion relation for internal waves, indicating that they are confined, non-propagating oscillatory signals rather than freely propagating internal waves. A hierarchical analysis of wave–wave interactions provides evidence that feedback between both branches of the TRI secondary waves gives rise to these signals. Whilst we expect our observations to generalise to many classes of wave–wave interaction, we cannot exclude the possibility that the particular observations we make in the laboratory may arise due to reflections of the primary wave from a free surface. However, beneath strongly density-stratified regions of the ocean we would expect to find these interaction pathways faced with the same
geometric configuration, so we are confident our findings will transfer directly to the natural environment.
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All authors Laura J. Irvine, Katherine M. Grayson, Andrew G. W. Lawrie, Stuart B. Dalziel
Materials Science
Disentangling Surface Charge and Electrolyte Effects on Interfacial Water at Electrified Pt(111)
Thorben Eggert, Lang Li, Yair Litman et al. (+3 more)
The structure of interfacial water at electrified metal electrodes is known to affect electrocatalysis, and experiments highlight its sensitivity to electrolyte ion identity and applied bias. To disentangle generic charge-controlled structural changes from ion-specific effects, we compare ab initio molecular dynamics water structures at electrified Pt(111) generated with two very different biasing schemes: an explicit ion imbalance in the double layer and homogeneously distributed partially charged hydrogen atoms. Despite these distinct counter-charge representations, both approaches yield a consistent average response of the first water
bilayer, in particular of the chemisorbed first layer, when compared on a common surface-charge scale. Method-dependent differences, in particular those associated with explicit electrolyte ions, become apparent only in more local structural descriptors. The hydrogen-bond
topology reveals charge-dependent chain-to-ring rearrangements, with explicit ions enhancing ring populations near the potential of zero charge. Layer-resolved vibrational density of states (VDOS) assigns the strongest O-H stretching perturbation to chemisorbed first-layer water and identifies high-frequency signatures of ion-coordinated water, while computed vibrational sum-frequency generation (VSFG) spectra show that the physisorbed, electrolyte-facing region is particularly sensitive to the counter-charge representation. These results suggest that surface charge controls the average structural response, whereas electrolyte ions and their solvation shells become visible only when locally refined descriptors are investigated or probed, e.g. the H-bond network
topology and vibrational fingerprints of the interfacial
bilayer.
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All authors Thorben Eggert, Lang Li, Yair Litman, Karsten Reuter, Nicolas G.Hoermann, Clotilde S. Cucinotta