Strongly Correlated Electrons
Ferromagnetic ordering in Hubbard models
Wojciech Niedziółka and Jacek Wojtkiewicz
One of the long-standing and only partially solved problems of theoretical condensed matter physics and mathematical physics is to demonstrate that ground states of some of the versions of the Hubbard model can exhibit a
ferromagnetic ordering. It has long been speculated that the opportunity crucial for the occurrence of ferromagnetism is the structure of the
lattice on which the Hubbard model is formulated \cite{TasakiMB}. As a consequence, while on simple cubic
lattices no
ferromagnetic ordering seems to be possible, it can naturally arise, even for low densities of
magnetic moment carriers, on so-called frustrated
lattices. We investigate the problem of ground state
ferromagnetic ordering with the use of the formula for ground-state energy of interacting
fermions as the first term of `density expansion', proven rigorously by Lieb, Seiringer and Solovej \cite{
fermi exact} in continuum and by Giuliani \cite{hub exact} for the simple cubic
lattice. Assuming that analogous expansion holds also for certain another
lattices we apply this formula to five frustrated
lattices – among them to the face-centered cubic one. The hypothesis is confirmed: most of examined models formulated on frustrated
lattices do indeed have
ferromagnetic ground states already for densities being moderate or even low. Although the approach adopted cannot be treated as a rigorous proof that the ground state is
ferromagnetic, the results obtained here strongly indicate that it can be the case. Moreover, as in some cases FM occurs at low densities, one can hope that it would be possible to prove convergence of the density expansion and prove rigorously the occurrence of `wealthy ferromagnetism' in these cases.
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Quantum Physics
Repetition-code-based readout error detection and correction across hardware platforms and generations
Csaba Czabán, Orsolya Kálmán, Sergey N. Filippov et al. (+1 more)
Readout errors are one of the dominant sources of noise in current
quantum processors, limiting both expectation-value estimation and sampling-based applications. Since they affect only the classical measurement outcomes, they can be addressed using classical coding techniques: immediately before measurement, each data
qubit is redundantly encoded with ancilla
qubits, and the resulting bit string is decoded either by post-selection or by majority voting. Unlike conventional readout error mitigation, which corrects only aggregate quantities such as expectation values, this approach operates on individual measurement shots and can therefore produce approximately corrected samples. We present a systematic cross-platform and cross-generation experimental evaluation of repetition-code readout error detection and correction. We
benchmark the same protocol on IBM Heron r1-r3 superconducting processors and Quantinuum H1 and H2 trapped-ion processors while independently varying the code distance, hardware generation, and encoding layout. We find that both error detection and correction improve readout fidelity on every device and generation tested, even as the unencoded baseline improves substantially across successive hardware releases. At the same time, the value of additional redundancy depends strongly on the underlying hardware. On superconducting processors, the extra gate errors introduced by the encoding rapidly offset its benefits, whereas on trapped-ion processors the much lower gate error rates allow larger code distances to remain advantageous.
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All authors Csaba Czabán, Orsolya Kálmán, Sergey N. Filippov, Zoltán Zimborás
Physics and Society
Pulses, waves, and cascades in collective migration dynamics
Niraj Kushwaha, Woi Sok Oh and Edward D. Lee
Decisions to migrate depend on others' decisions. Dependence can produce nontrivial dynamics. We propose a minimal migration model that accounts for social influence alongside individual heterogeneity in mobility as migrants move from region to region. In special locations of parameter space, migrant flows dramatically and spontaneously fluctuate. Such aspects mimic observed fluctuations in migration statistics and thus show how large fluctuations in data can reflect more than response to events like armed conflict and natural disasters. Correspondingly, the impact of exogenous factors can be confounded with the results of collective decisions.
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Quantum Physics
Provably Efficient Learning of Fermionic Correlations under Particle-Number Symmetry
Yuki Koizumi, Kaito Wada, Toshinori P. Takama et al. (+1 more)
Predicting local fermionic correlations is a central task in
quantum many-body physics, as these correlations encode many physically relevant local observables. The ubiquitous particle-number
symmetry imposes strong structural constraints on
quantum states, suggesting that local correlations should be learned with fewer samples than by
symmetry-agnostic approaches. However, it has remained unclear whether such a provable advantage exists in collective learning of local correlations. Here, we develop a framework of number-conserving fermionic-shadow
tomography based on random orbital rotations. We prove that, for every given order $k$, we can simultaneously estimate all $k$-body fermionic correlations of an $N$-mode $\eta$-particle state with a given variance $\varepsilon^2$ using only $O_k(\eta^k/\varepsilon^2)$ samples, which are independent of the system size $N$. We further establish a matching information-theoretic lower bound $\Omega_k(\eta^k/\varepsilon^2)$ for any adaptive protocol based on single-copy measurements, showing that the $(\eta^k,\varepsilon)$-dependence is optimal up to constants depending only on $k$. Furthermore, numerical studies show a 20-fold query reduction for one-body correlation estimation at $N=200$, $\eta=20$, and $\varepsilon=10^{-2}$, compared with the best alternative including Heisenberg-limited estimation methods. Relative to fermionic Gaussian-
unitary shadows, sample costs for the square-
lattice Fermi-Hubbard model at $N=288$ are reduced by factors of $148$ for energy density and $161$ for
spin structure factor estimation. For molecular energy derivatives with respect to atomic coordinates, our method reduces sample requirements by factors of $53$ for $\mathrm{Cr}_2$ and $18.5$ for $[\mathrm{Fe}_2\mathrm{S}_2]^{2-}$ at $N=128$. These results demonstrate the practical advantage of particle-number
symmetry for fermionic observable estimation.
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All authors Yuki Koizumi, Kaito Wada, Toshinori P. Takama, Nobuyuki Yoshioka
High Energy Physics (Theory)
A thermal representation for conformal ladder integrals
Anastasios C. Petkou
I discuss the recently discovered representation of conformal four-point ladder integrals in terms of the thermal free energy of free massive scalar fields. These integrals satisfy a novel second-order differential equation in even dimensions $D$ at arbitrary loop order $L$. I also present a simple derivation of the all-loop resummation of conformal ladder integrals for arbitrary $D$. Possible connections to the thermal bootstrap, multiloop calculations, integrability, AdS/CFT and string theory are briefly discussed. This is a proceedings contribution to the Athens Workshop in Theoretical Physics: 10th Anniversary, held at the National and Kapodistrian University of Athens on December 17–19 2025.
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General Relativity and Quantum Cosmology
Efficient Eccentric Effective-One-Body Dynamics via Near-Identity Averaging Transformations
Philip Lynch, Alessandra Buonanno, Aldo Gamboa et al. (+1 more)
Next-generation gravitational-wave detectors, such as LISA, the Einstein
Telescope, and
Cosmic Explorer, will require accurate and efficient models of long-lived black hole binary signals, including those with significant eccentricity. A challenge for eccentric effective-one-body models is the cost of resolving rapidly oscillating orbital dynamics over the inspiral, particularly for low-mass and large-mass-ratio systems. We address this by recasting the nonspinning eccentric effective-one-body equations of motion in terms of osculating orbital elements and then applying near-identity averaging transformations to eliminate the fast orbital-timescale structure during the inspiral. Each order in this procedure suppresses the oscillatory behavior by one factor of the ratio of orbital to radiation-reaction timescales. The resulting averaged dynamics are evolved on the radiation-reaction timescale, and then the system is mapped back to the full EOB dynamics for the final transition to plunge. This reduces the cost of the inspiral dynamics by up to two orders of magnitude, eliminating this as the primary bottleneck for long waveforms. The overall waveform-generation speedup spans $1.5 - 8 \times$, motivating the development of more efficient waveform-generation methods. We also validate the accuracy of the method by comparing waveforms generated from the averaged and full effective-one-body dynamics across a broad region of parameter space for moderate to large eccentricities. Carrying out this averaging procedure to next-to-next-to-leading order is needed to accurately model comparable-mass binaries, yielding mismatches $\leq 8.05 \times 10^{-5}$. These results establish near-identity averaging as a practical route to efficient eccentric effective-one-body inspirals, and provide a foundation for further extensions to low-eccentricity and spinning waveform models.
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All authors Philip Lynch, Alessandra Buonanno, Aldo Gamboa, Maarten van de Meent
Quantum Physics
Untangling QLDPC Codes with Biased Noise Ancilla
Runjiang Bi, Kathleen Chang and Shruti Puri
Remarkable technical progress has made high-rate, high-distance,
quantum low-density parity-check codes (QLDPC) promising candidates for scalable
quantum computing. However, it is hard to design low-depth syndrome extraction
circuits that do not spread errors from ancilla
qubits to multiple data
qubits, also known as hook errors, for general QLDPC codes. Additionally, widely used decoders for these codes based on belief propagation are impaired due to short loops in the Tanner graph. Here, we investigate a hardware-aware approach to avoid these hooks and loops using biased noise ancillas. Using examples of bicycle bivariate codes and a cyclic hypergraph product code, which have been widely considered for practical application, we show that the effective fault-distance of the conventional syndrome extraction
circuit can be significantly higher and the number of short loops can be significantly lower when the ancillas are subject to phase-flip errors only, compared to when they are also subject to bit-flip errors. This can result in almost an order of magnitude improvement in the logical error rate at
circuit noise of $2\times 10^{-3}$ and when bit-flip errors in the ancilla are 50 times less likely than phase-flip errors. Our work demonstrates a significant and practical
quantum error correction advantage with biased noise
qubits in which full-bias cannot be maintained.
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Mesoscale and Nanoscale Physics
Microfabricated Au and Au/graphene bilayer platelets for levitation experiments
Sunghyun Kim, Joyce E. Coppock and B. E. Kane
We describe a fabrication process for preparing
liquid suspensions of micron-scale Au and Au/
graphene bilayer platelets using thin-film deposition, optical lithography, ion milling, hydrofluoric acid (HF) substrate etching, and release from the substrate into a
liquid suspension. Residual HF is removed through repeated centrifugation, decanting, and dilution cycles. The resulting suspension is characterized by electrospray deposition onto a secondary substrate, followed by electron and atomic force microscopy. The deposited platelets exhibit minimal aggregation, and the overall platelet yield reaches up to 30% of the platelets originally patterned on the wafer. Lateral force microscopy further confirms that the Au/
graphene bilayer remains intact throughout fabrication, release, and electrospray deposition. This process provides a practical route for preparing high-quality platelet suspensions for levitated nanoparticle experiments and other applications requiring suspensions of two-dimensional nanostructures.
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Quantum Gases
Equilibrium and non-equilibrium phases of microwave-dressed polar molecules beyond rotational symmetries
Matteo Ciardi, Andreas Schindewolf, Tim Langen et al. (+1 more)
Recent experiments on molecular droplets have opened a new frontier of self-organization in strongly dipolar
quantum matter. Microwave-dressing of polar molecules permits to tune both the strength and the angular structure of long-range interactions, potentially promoting a rich spectrum of
quantum phases, from superfluid droplets with varying geometry and insulating or supersolid droplet arrays to strongly correlated
crystals of individual molecules. Using path-integral Monte Carlo simulations of large molecular ensembles, we demonstrate that experimentally observed droplet arrays emerge as a metastable non-
equilibrium state from the quenching of a gas-droplet phase transition under entirely broken rotational
symmetry of the microwave-induced interaction potential. We moreover find that a crystalline phase of molecules, predicted for antidipolar interactions, is absent under conditions of recent experiments. This is traced back to the lack of angular
symmetry in currently employed microwave-dressing, which qualitatively reshapes the many-body energy landscape and cannot be captured by effective scalar interaction parameters. Our results provide the first direct comparison of ab initio simulations and experiments and establish interaction anisotropy as a key aspect of molecular
quantum gases.
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All authors Matteo Ciardi, Andreas Schindewolf, Tim Langen, Thomas Pohl
Materials Science
Excitons in Large Disordered Boron-Nitride Layer using Linear-Scaling Bethe-Salpeter Simulations
Thomas Galvani, Lorenzo Sponza, Hakim Amara et al. (+2 more)
We introduce a real-space, linear-scaling Bethe-Salpeter framework that enables excitonic spectroscopy in large and possibly disordered boron-nitride-derived systems. Thanks to the use of a sublattice-resolved perturbative decoupling that maps localized electron-hole pairs onto a sparse tight-binding model, we implement the Kernel
Polynomial Method to compute absorption spectra with O(N) cost. To illustrate the capabilities of our method, we apply it to Anderson-disordered monolayer hexagonal boron nitride with up to $10^{5}$ orbitals. The method reveals a disorder-induced asymmetric broadening of bright
excitons, a crossover from quadratic to linear
redshift of the main absorption peak, and Anderson localization of the
exciton center of mass. This approach extends excitonic calculations beyond the reach of conventional ab initio Green's function methods (GW approximation and Bethe-Salpeter equation), opening optical spectroscopy to large-scale, disordered, moiré, quasicrystalline, and structurally complex
quantum materials.
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All authors Thomas Galvani, Lorenzo Sponza, Hakim Amara, Sylvain Latil, Stephan Roche
Pattern Formation and Solitons
Kinetic equations for a two-dimensional soliton gas
Gino Biondini, Thibault Bonnemain, Benjamin Doyon et al. (+2 more)
We formulate a general system of kinetic equations for a non-stationary two-dimensional gas of elastically interacting line
solitons and apply it to the description of a
soliton gas governed by the Kadomtsev-Petviashvili II (KPII) equation. We then verify the predictions of the kinetic theory in two analytically tractable problems: the oblique interaction of a KPII line
soliton with a one-dimensional
soliton condensate of the Korteweg-de Vries equation, and the interaction of a trial KPII
soliton with a monochromatic KPII
soliton gas. In both cases, we compare the analytical results with direct numerical simulations obtained by constructing two-dimensional
soliton gases via exact KPII $N$-
soliton solutions for large $N$, using appropriately chosen random distributions of
soliton parameters. The comparison demonstrates excellent agreement, thereby providing strong validation of the proposed kinetic theory of 2D non-
equilibrium soliton gases.
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All authors Gino Biondini, Thibault Bonnemain, Benjamin Doyon, Gennady El, Giacomo Roberti
Quantum Physics
Revisiting crossed-correlated baths in open quantum systems simulated by HEOM or T-TEDOPA
Brieuc Le Dé, Etienne Mangaud, Alex W. Chin et al. (+1 more)
Excited-state dynamics of open
quantum systems is analyzed by the hierarchical equations of motion (HEOM) or the thermalized time-evolving density operator with orthogonal
polynomials algorithm (T-TEDOPA) method when a discrete $ab$ $initio$ linear vibronic model is parametrized by continuous temperature-dependent spectral densities leading to crossed correlation functions, i.e. correlated fluctuations of the energy gap collective modes. We focus on a conical intersection involving two collective modes tuning the energy of each excited state and we revisit the transformation of the initial correlated tuning baths to de-correlated shared baths in order to reduce the computational resources. While a completely frequency-dependent transformation poses problems for HEOM, we find that in some particular cases, an optimal approximate frequency-independent transformation may be derived. On the contrary, T-TEDOPA is very efficient and allows to use this frequency-dependent transformation at the price of managing long-range couplings in the tensor chain. An illustrative application is shown by using the linear vibronic coupling model of a planar symmetrical (phenylethynyl)benzene dimer.
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All authors Brieuc Le Dé, Etienne Mangaud, Alex W. Chin, Michèle Desouter-Lecomte
Quantum Physics
Bridging the NISQ and Fault-Tolerant Regimes: Generative-ML-Assisted Quantum Selected CI for Molecular Simulations
Anurag K. S. V.
Calculation of binding energies for
protein-ligand molecular systems requires accurate treatment of the electronic structure, a
quantum chemistry problem that scales exponentially on classical hardware, while current
quantum hardware remains too noisy for the required
circuit depths. This report presents a hybrid
quantum-classical workflow performed on the Fujitsu FX700 ideal state-vector simulator using QARP that addresses two structural inefficiencies in
quantum-sampling-based diagonalization workflows. First, we integrate the Linear Scaling CNOT UCCSD (LCNot-UCCSD) ansatz into the QSCI framework, replacing the $\mathcal{O}(N^6)$ CCSD parameter initialization of the competing LUCJ ansatz approach with $\mathcal{O}(N^4)$ MP2-amplitude initialization. Second, we introduce QSCI-RBM, a variant that replaces the configuration recovery of the SQD framework with a Restricted Boltzmann Machine (RBM) acting as a compact generative subspace expansion model. Both are evaluated on eight different molecules in STO-3G across 14 controlled artificial error levels with 100 independent runs each, validated on potential energy surface scans of the N$_2$ molecule in cc-pVDZ, and embedded within DMET to treat the FDA-approved antiviral Amantadine (C$_{10}$H$_{17}$N, 11 DMET fragments) and the active region of the SARS-CoV-2 main protease complexed with its covalent inhibitor Carmofur (PDB: 7BUY, C$_{15}$H$_{28}$N$_4$O$_5$S, 10 fragments). To our knowledge, this is the first deployment of LCNot-UCCSD within QSCI on a
quantum computing simulator, and the first DMET-QSCI(LCNot-UCCSD)-RBM application to an industry-relevant
protein-ligand system. By utilizing a fraction of the classical computing resources required by the current state-of-the-art work by Cleveland Clinic, RIKEN, and IBM
Quantum, this approach enables more efficient and economical drug discovery simulations for the industry.
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Solar and Stellar Astrophysics
Wave-Driven Mixing Enhanced by Rotation in Red Giant Branch Stars
Simon Blouin, Paul R. Woodward, Pavel A. Denissenkov et al. (+2 more)
Stars like our Sun expand as they exhaust their core hydrogen fuel, becoming red
giants that eventually reach sizes up to 100 times their original radius. These
giants have long presented a puzzle: they show systematic changes in their surface chemical composition that can only be explained by the transport of material from their
nuclear-burning interior to their surface. The challenge is that this transport must somehow cross a stable layer that acts as a barrier between the
star's outer convective envelope and its
nuclear-burning interior. The convective motions in the envelope create internal waves that propagate through this barrier layer, but on their own these waves produce very little material transport. Here we show through high-resolution three-dimensional hydrodynamical simulations that
stellar rotation dramatically amplifies how effectively these waves can mix material across this barrier. We find that the mixing rates can exceed those in non-rotating
stars by over 100 times, increasing with faster rotation rates. This enhanced mixing provides a natural explanation for the observed chemical signatures in typical red
giants. The amplification of wave-driven mixing by rotation may have implications beyond red
giants to other types of
stars.
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All authors Simon Blouin, Paul R. Woodward, Pavel A. Denissenkov, Praneet Pathak, Falk Herwig
Materials Science
Synthesizability and Mechanical Properties of High-Entropy Borides: First-Principles and Machine Learning Studies
Luke Moore, Ethan Fox, Bria Storr et al. (+4 more)
We perform density functional theory (DFT) calculations to investigate five-metal high-
entropy borides (HEBs) in the hexagonal AlB$_2$ structure, considering all 126 possible elemental combinations among the nine group 4-6 transition metals (Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W). The
entropy forming ability (EFA) descriptor is employed to evaluate their single-phase synthesizability, and the resulting EFA predictions show good agreement with the experimental data for selected HEBs. Mechanical properties are computed using special quasi-random structures. Several mechanically unstable compounds – primarily those containing Cr – are also predicted to be less synthesizable. Machine learning (ML) models are developed to analyze the results. This combined ab initio and ML study provides a systematic roadmap for identifying mechanically superior single-phase HEBs.
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All authors Luke Moore, Ethan Fox, Bria Storr, Jayden R. Palomino, Shane A. Catledge, Yogesh K. Vohra, Cheng-Chien Chen
Quantum Gases
Finite-size effects in Schulz-Shastry-Luttinger models for determining anyonic signatures in 1d spin chains
B. Perković, M. Bonkhoff and T. Posske
We study finite-size properties of Schulz-Shastry-Luttinger
liquids to reveal anyonic signatures, realized as low-energy excitations on top of the helical ground state in saturated
spin-1/2 zigzag chains. The model features asymmetric and marginal couplings of density and phase gradients and belongs to the Schulz-Shastry class. We investigate periodic and Dirichlet boundary conditions and discuss its diagonalization as well as its stability. Although Dirichlet boundary conditions require a fine-tuning of coupling constants and universal parameters, only their magnitude is restricted for cyclic systems. We derive boundary characteristic quantities like Friedel oscillations and persistent currents. Finally, we discuss the bulk and boundary behavior of the longitudinal
spin correlations including subleading corrections.
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General Relativity and Quantum Cosmology
Evaluating the Fourier Approximation in Pulsar Timing Array Analysis
Yongqi Zhang, Hayden Scholz, Ken D. Olum et al. (+53 more)
Pulsar timing arrays search for
stochastic processes such as gravitational waves by comparing pulse time of arrival data for millisecond
pulsars to expectations from a background with a given power spectral density (PSD). To make the analysis computationally tractable, the
Bayesian likelihood is usually computed using an approximation in which the signal is taken to be a sum of
Fourier modes appropriate to the total time of observation, even though the true signal is not periodic. We study the difference between likelihoods computed with this
Fourier approximation method for power law spectra and those computed exactly (or using more-closely spaced frequencies as a proxy for the exact result) in the NANOGrav 15-year
dataset. We find that the true marginal likelihoods for power-law PSDs are on average about half as large as the likelihoods computed using the
Fourier approximation. This could lead to an error of a factor of two in model comparison. However, in the important comparison of uncorrelated vs. Hellings-Downs correlated models, a very similar correction appears in both, so the model comparison is essentially unaffected. We also compare parameter estimation results for power law PSDs, finding little difference between the methods. We briefly discuss spectra with sharper features, for which the approximation could be much worse.
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All authors Yongqi Zhang, Hayden Scholz, Ken D. Olum, Lucas Steinberger, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Paul R. Brook, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Justin A. Ellis, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Jeffrey S. Hazboun, Ross J. Jennings, Megan L. Jones, David L. Kaplan, Matthew Kerr, Michael T. Lam, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Alexander McEwen, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Cherry Ng, David J. Nice, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Ann Schmiedekamp, Carl Schmiedekamp, Brent J. Shapiro-Albert, Ingrid H. Stairs, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Stephen R. Taylor, Michele Vallisneri, Rutger van Haasteren, Haley M. Wahl
Soft Condensed Matter
Role of Single Chemical Heterogeneities in Generating Anisotropic Tactile Sensitivity and Soft Sliding Friction Phenomena
Kayla A. Hepler, Leanne Ton and Charles B. Dhong
Physical heterogeneities in the context of sliding friction, such as a human finger exploring an object, have been well studied, yet the behavior of chemical heterogeneities in mesoscale soft sliding remains underexplored, despite the similar prevalence of chemical and physical variations in real systems. Here, we experimentally characterized the friction of a planar soft elastic probe sliding across a single chemical heterogeneity that was formed at the interface of two silanes on silicon wafers. By constructing phase maps across multiple loads and velocities, we quantified the occurrence of several frictional phenomena at and around the chemical edge, including stiction spike formation, edge slope direction, baseline shifts, and baseline drift, and quantified their sliding direction-dependent formation. We found that chemical heterogeneities made by more disparate materials (butyl- and aminopropyl-terminated) exhibited several phenomena that were more often direction-independent compared to chemical heterogeneities formed from more similar materials (butyl- and hexyl-terminated). We attributed this directional asymmetry to elastic body effects. In subsequent human testing (n=36), we observed that humans also exhibited directional-dependent accuracy (66.7% versus 38.9%) on one pair (butyl- and hexyl-terminated) but not the other (77.8% versus 75%), which in the context of our phase maps, suggests that the slope of the friction force when sliding over a chemical edge is important for generating a clear edge of a tactile feature, rather than the differences in simple material properties or other friction phenomena.
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Fluid Dynamics · Cross-listed from math.AP
Higher Order Convergence for the Sharp Interface Limit of 3D Navier–Stokes/Allen–Cahn Systems
Helmut Abels, Mingwen Fei, Yadong Liu et al. (+1 more)
We show convergence of solutions to a Navier–Stokes/Allen–Cahn system as the interfacial thickness $\varepsilon>0$ tends to zero for well-prepared initial data as long as the limit system possesses a sufficiently smooth solution. The limit system consists of a two-phase Navier–Stokes system separated by a sharp interface in the presence of surface tension coupled to a convective mean
curvature flow equation. In comparison to previous results we obtain improved convergence estimates for higher-order norms. These enable us to prove convergence in the case of three space dimensions and non-constant viscosity, which was unknown before. The convergence results relies crucially on uniform higher-order estimates for the associated linearized Navier–Stokes/Allen–Cahn system in suitably weighted $L^2$-Sobolev spaces. Here a novel problem-adapted weight proportional to the sum of $\varepsilon$ and the distance to the sharp interface of the limit, which gives improved and sharp estimates, is an important new ingredient. This approach can be potentially adapted to other sharp interface limits as well.
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All authors Helmut Abels, Mingwen Fei, Yadong Liu, Maximilian Moser
Mathematical Physics
A Kac system interacting with two heat reservoirs: the shearing case
Federico Bonetto and Matthew Powell
We study a system formed by $M$ particles moving in 3 dimensions and interacting with two heat reservoirs, each with $N\gg M$ particles. The system and the reservoirs interact via random collisions and thus evolve via a Kac-type master equation. The initial state of the reservoirs is given by two non-centered Maxwellian distributions; they have temperature $T_+$ and $T_-$ and have average velocity $\vec p_+$ and $\vec p_-$, respectively. We prove that, for times shorter than $\sqrt{N}/M$, the interaction with the two reservoirs is well-approximated by the interaction with two shearing dynamic Maxwellian thermostats (i.e. heat reservoirs with $N=\infty$). As a byproduct of our analysis, we obtain a uniform in time approximation when $T_+=T_-$ and $\vec p_+=\vec p_-$.
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Cosmology and Nongalactic Astrophysics
Universal distance modes from DESI BAO and Type Ia supernovae: what do cosmological rulers actually measure?
Matias Zaldarriaga
We use an SVD decomposition of the low-
redshift distance measurements from DESI BAO and three Type Ia
supernova compilations to identify the leading linear directions probed by the data and to localize the tension with the LCDM CMB-anchored predictions. The leading direction V_0 – whose data amplitude we denote c_0 – is, to high accuracy, a measurement of Omega_m h^2: the projection of the data on V_0 probes essentially this one CMB-derived parameter combination. BAO constrains this parameter more tightly than the CMB itself; the three SN compilations do not. In every extension of LCDM we consider, the leading measurable direction remains V_0, and it is where most of the tension with the CMB resides. In the w0-wa extension a second direction V_1 becomes measurable and provides an independent test of dynamical dark energy; the data show no significant tension in this direction. The only other beyond-LCDM extension that opens a genuinely new measurable direction is spatial
curvature, and only marginally and only for BAO; both measurable directions then independently prefer positive spatial
curvature, though the second direction is poorly constrained.
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Quantum Physics
Working With Measurement-Based Computations on Qudits
Piotr Mitosek and Miriam Backens
Measurement-based
quantum computing is a universal model of
quantum computation in which successive product measurements of an entangled resource state drive the computation. The non-deterministic nature of measurements necessitates adaptivity to ensure an overall deterministic computation. Flow structures characterise cases in which such an adaptive correction procedure is possible. Recently, flow has been defined in a setting where the resource states are
prime-dimensional qudit graph states rather than the usual
qubit graph states. Yet, this qudit flow definition is more burdensome to work with than analogous definitions for
qubits. Here, we give a simpler definition of qudit flow and consider various useful properties of this flow, drawing on results for the
qubit case. In particular, we show how to focus qudit flow and argue that focused flow is canonical. We improve the previous algebraic formulation to capture focused flow and use it to obtain an O(n^3) flow-finding
algorithm (where n is the number of qudits), matching the best known complexity for
qubit flows and improving on the previous O(n^4) result for qudits. Furthermore, we explore multiple flow-preserving transformations, thus opening a pathway to using flow for optimisation. These transformations include pivoting, removal and insertion of certain types of vertices, and reversibility of flow. Lastly, we propose an algorithmic approach to generating large qudit computations with flow, for testing or machine learning.
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Nuclear Theory
Nonequilibrium Andreev transport at the QGP-2SC interface
Tingyu Zhang, Honoka Hoshino, Hiroyuki Tajima et al. (+2 more)
We discuss a nonequilibrium Andreev reflection at an interface between
quark-
gluon plasma (QGP) and two-
flavor color superconducting (2SC)
quark matter. Based on the Schwinger-Keldysh framework and a relativistic tunneling model, we evaluate the momentum-resolved tunneling current generated by a chemical-potential bias between the QGP and 2SC phases. We find that the Andreev reflection appears as at the fourth order of the tunneling strength, in which an incident
quark in QGP is converted into a reflected hole, while a Cooper pair is injected into the 2SC condensate. We show that the Andreev reflection is enhanced when the bias becomes comparable to the gap and is suppressed in the supergap region, which is similar to that in superconducting materials. The present formulation provides a field-theoretical pathway to strongly-correlated transport across dense-matter interfaces relevant to nonequilibrium dynamics in compact
stars.
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All authors Tingyu Zhang, Honoka Hoshino, Hiroyuki Tajima, Motoi Tachibana, Mariusz Sadzikowski
Quantum Physics
Staged Hybridisation for Visual Quantum Reinforcement Learning via Knowledge Distillation
Javier Lazaro, Juan-Ignacio Vazquez and Pablo Garcia-Bringas
Visual environments are a demanding setting for
quantum reinforcement learning (QRL): high-dimensional observations, unstable RL optimisation, and constrained variational
quantum circuits (VQCs) are difficult to train jointly. This paper studies knowledge
distillation (KD) as a staged hybridisation strategy for visual QRL. Instead of training a hybrid visual
agent end-to-end from pixels, we first train a classical visual teacher, freeze its encoder as a feature interface, and distil the teacher's policy behaviour into compact downstream heads. These heads can be classical or VQC-based, enabling small
quantum-compatible students to be evaluated under the same frozen representation as compact classical controls. We evaluate the pipeline on CartPole Pixels and Acrobot Pixels. The results show that staged KD enables shallow VQC heads to acquire non-trivial visual-control behaviour in settings where direct pixel-based training would be substantially more difficult. Angle-encoded VQC heads retain near-teacher performance, while amplitude-encoded heads push compactness to an extreme regime, at the cost of greater fragility, stronger budget sensitivity, and higher simulation time. Overall, staged KD reframes visual QRL as a compact-head learning problem, opening a practical route for training small
quantum-compatible policies outside the standard end-to-end RL loop.
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Nuclear Theory
Nuclear Mass Models with Deformation Optimized and Diagnosed by Bayesian Analysis with Markov Chain Monte Carlo
Xiangnan Lee, Yi Hua Lam, Zi-Ao Zhang et al. (+1 more)
We employ a full
Bayesian analysis with adaptive Metropolis-Hastings Markov chain Monte Carlo (BA-MCMC) sampling to systematically study the posterior probability distributions of the strengths of energy terms in optimized
nuclear mass models of Bethe-Weizsäcker variants. Strong correlations of some energy terms for some mass models are revealed through the parameter degeneracy diagnosis. We analyze selected refined models to determine parameter degeneracies while proposing a new macroscopic-microscopic mass model, BWL, which considers quadrupole and high-multipole deformation and shell corrections. All mass models in this work are analyzed and optimized through the BA-MCMC method. Compared with 2242 precise experimental binding energies of AME2020, BWL produces a root-mean-square deviation of 759 keV, particularly improving the description of masses in the light-
nuclei and actinide regions. BA-MCMC offers robust inference on parameter degeneracy while providing an optimization method for future
nuclear mass models.
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All authors Xiangnan Lee, Yi Hua Lam, Zi-Ao Zhang, Jayke Ren
Fluid Dynamics
Electrophoretic motion of a liquid droplet with Brinkman-screened internal hydrodynamics
Sutapa Mandal and Subrata Majhi
We develop a theory for the electrophoresis of a spherical porous
liquid droplet with prescribed uniform surface charge. The exterior electrokinetics is governed by the Poisson-Nernst-Planck-Stokes equations, while the internal
liquid motion is described by the Brinkman-Debye-Bueche equation. A regular perturbation expansion in the applied electric field reduces the governing equations to coupled radial ordinary differential equations. In the Debye-Hückel regime, we derive a closed-form mobility expression valid for arbitrary Debye layer thickness. The analysis shows that the porous interior modifies clean-droplet electrophoresis through a single Brinkman-screened hydrodynamic resistance, yielding a continuous transition between clean-droplet and rigid-particle limits. Numerical solutions beyond the low-potential regime reveal a non-universal role of permeability: increasing the Darcy number can either suppress or enhance the mobility. This reversal is determined by the sign of the interfacial-velocity mode, which is governed by the competition between tangential Maxwell traction and hydrodynamic shear generated by electric-double-layer distortion. Dielectric polarization, surface charge and double-layer thickness can reverse the internal circulation, while the Darcy number controls how strongly this circulation is transmitted through the porous interior. This permeability sensitivity is especially pronounced for highly polarizable droplets in the thin-double-layer regime. The theory provides a basis for tuning electrokinetic transport of soft porous droplets in microfluidic and biomedical technologies.
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Mesoscale and Nanoscale Physics
GaAs/AlAs Acoustic Nanocavities for Coherent GHz-THz Phonon Engineering
S. Sandeep, E. R. Cardozo de Oliveira, E. Mehdi et al. (+1 more)
The controlled confinement of high-frequency acoustic
phonons in
semiconductor nanostructures has emerged as a key ingredient for functional nanophononic and hybrid
quantum technologies. In this Review, we summarize recent advances that have established GaAs/AlAs acoustic nanocavities as a versatile and scalable platform for GHz-THz
phonon engineering. Compared with alternative nanophononic platforms, GaAs/AlAs offers a particularly favorable combination of mature epitaxial growth, strong photoelastic coupling, and simultaneous optical-acoustic mode colocalization across the GHz-THz regime. We focus on distributed Bragg reflector (DBR)-based architectures, with particular emphasis on micropillar resonators enabling three-dimensional
phonon confinement and strong colocalization of acoustic and optical fields. Recent developments in ultrafast optical techniques, including picosecond ultrasonics and Brillouin scattering, have provided unprecedented access to
phonon dynamics, coherence, and dissipation at the nanoscale. These advances, combined with strong optophononic coupling, have enabled efficient coherent generation, detection, and manipulation of confined acoustic modes. We discuss key performance metrics, integration strategies, and remaining challenges, notably in acousto-optic transduction efficiency and scalable electrical control. Finally, we outline near-term perspectives for nonlinear phononics, hybrid
quantum systems, and integrated phononic
circuits, positioning GaAs/AlAs
heterostructures as a robust and scalable platform for next-generation nanophononic functionalities.
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All authors S. Sandeep, E. R. Cardozo de Oliveira, E. Mehdi, N. D. Lanzillotti-Kimura
Optics
Quantization and Biphoton Statistics of k-Gap Solitons in Nonlinear Photonic Time Crystals
Liang Zhang, Chenhao Pan and Yiming Pan
Nonlinear photonic time
crystals (PTCs) can support
solitons inside momentum k gaps, where the amplification of k gap modes is saturated by Kerr nonlinearity, forming spatially homogeneous but temporally localized excitations. Yet their
quantum nature remains unclear. Here we quantize nonlinear k gap dynamics of PTCs and show that k gap
solitons are represented by biphoton Fock ladder states. K gap amplification drives two-mode squeezing of the biphoton, while Kerr nonlinearity generates an anharmonic potential along the biphoton Fock ladder that balances this squeezing process, creating a finite biphoton number turning point and giving rise to
quantum collapse and revival dynamics and nonclassical phase space interference. We further analyze how
photon loss and dephasing reshape the biphoton statistics of quantized k gap
solitons. Our results establish a biphoton Fock space description of k gap
soliton quantization and provide a framework for studying
quantum nonlinear excitations and entangled light generation in photonic time
crystals.
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General Relativity and Quantum Cosmology
The Role of the Volume in Black Hole Thermodynamics
William Ballik
Gibbons et al. [arXiv:hep-th/0408217] found the energy $E$ of Kerr–anti-de Sitter black holes by integrating the first law of black hole thermodynamics. They found that $E$ corresponds to the Ashtekar–
Magnon–Das (AMD) energy associated with an asymptotically nonrotating frame, whereas the AMD “energy” which I will call $F$ associated with an asymptotically rotating frame does not satisfy the first law. In Cvetič et al. [arXiv:1012.2888], the first law was extended by interpreting $E$ as an enthalpy and $\Lambda$ as being proportional to a pressure. The term conjugate to the pressure was then interpreted as the “thermodynamic volume” $V_{th}$. Associated with the first law (with varying pressure) is a Smarr relation for $E$. The Smarr relation for $F$ also exists, and the term conjugate to the pressure in that Smarr relation is the “
geometric volume” $V_{geo}$, shown in [arXiv:1310.1935] to be equal to the vector volume $V_C$ of the black hole. To address why it is necessary to use $E$ rather than $F$ to have a viable first law but $V_C$ appears naturally in the Smarr relation associated with $F$ rather than $E$, I adapt Barnich and Compère [arXiv:gr-qc/0412029], by defining a conserved quantity $H^I_\chi$ associated with Killing vector $\chi$. $E$ and $F$ are given by $H^I_\xi$ and $H^I_\beta$ respectively where $\xi$ is asymptotically hypersurface-orthogonal and $\beta$ is proportional to the divergence of the Principal Conformal Killing–Yano tensor $\boldsymbol{h}$. I show that the first law will be satisfied by $H^I_\chi$ if both $\chi^a$ and the background anti-de Sitter metric have unvarying components, which holds for $\xi^a$ but not $\beta^a$, explaining why the first law works for $E$ but not $F$. I show that $V_C$ appears in the $\beta$-associated Smarr relation due to simplifications related to $\boldsymbol{h}$.
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Cosmology and Nongalactic Astrophysics
Rapid Hubble constant inference from GW170817 using GPU-accelerated nested sampling: prior sensitivity and the limits of post-hoc reweighting
Ming Han Yang, Metha Prathaban, David Yallup et al. (+1 more)
The bright-siren measurement of the Hubble constant from GW170817 (Abbott et al. 2017) assumes that switching from a volumetric to a uniform-in-$d_L$ luminosity-distance prior can be implemented by post-hoc reweighting of the baseline samples, rather than by re-running the inference under the target prior. Using a GPU-native heterodyned nested sampling pipeline that completes the full $n_{\rm live}=5000$ analysis in about 13 min on a single A100, we recompute the GW170817 $H_0$ posterior under four prior variants for the modern aligned-
spin tidal waveform IMRPhenomXAS_NRTidalv3. Switching from the volumetric to a uniform-in-$d_L$ distance prior raises the high-tail probability $P(H_0>120\,\mathrm{km/s/Mpc})$ from 0.017 to 0.159 when imposed during sampling and shifts the weighted-median $H_0$ from 77.6 to 87.6 km/s/Mpc, while the binned MAP stays at 70.5 km/s/Mpc: both the tail and the bulk move under a change of prior that leaves the mode in place. Post-hoc reweighting of the baseline samples to the same target prior recovers only $P=0.041$ in the tail, approximately 17% of the directly sampled shift. The three prior variants that carry an independent nested sampling evidence agree to $\Delta\ln Z\lesssim 1.8$, so the data show at most a weak preference among the distance priors; the tail and bulk shifts are therefore properties of the prior, not a data update. Targeted mode-isolated runs reveal a $(d_L,\iota)$ bimodality whose high-$H_0$, low-$d_L$ branch (Mode B; $|\ln\mathcal{B}_{\rm B/A}|<1$) the volumetric prior assigns negligible mass: this is the mechanism behind the reweighting deficit. The reweighted posterior has a lower effective sample size than the baseline, independently flagging the coverage failure. The runtime budget makes full-sample prior-sensitivity reruns the default robustness tool for bright-siren cosmology, replacing post-hoc reweighting.
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All authors Ming Han Yang, Metha Prathaban, David Yallup, Will Handley