Papers

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Physics

Thursday 8 October

Plasma Physics

Reaching high fusion gain with grams of spin-polarized fuel

J. F. Parisi

Building on recent ignition-access work of Delgado-Aparicio, Ono, and Menard, we show that even a single-use, gram-scale quantity of spin-polarized fuel (SPF) is useful for increasing fusion power and gain in magnetic confinement fusion machines such as tokamaks and stellarators. While fueling a fusion power plant continuously with SPF requires $\sim$kilograms per day, far beyond present capabilities, a single-use short pulse of SPF allows a fusion plasma to cross into a high-gain regime, and stay there, even after switching back to regular unpolarized fuel. With continuous polarized fueling, polarization also makes high-gain plasmas easier to control: a resonant wave that depolarizes the fuel lowers the reactivity quickly, on a much faster timescale than transport. Grams of polarized fuel can therefore improve plasma performance and open a path to scaling SPF sources and usage, from small first experiments to continuous fueling.

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Quantum Physics

2 Fast 2 Surgery: Fast surgery on QLDPC codes with $\tilde{O}(n(k + d))$ space overhead

Nouédyn Baspin

We show that the fast surgery framework of Baspin-Berent-Cohen can be instantiated using at most $\tilde{O}(n(k + d))$ ancilla qubits, improving on the previously achievable $O(n\cdot k \cdot d)$ overhead. This result also establishes that fast surgery can be performed at a cost comparable to the $\tilde{O}(nk)$ overhead required for regular surgery. We build the surgery ancilla by first starting with a dense, but expanding system; and then applying expansion-preserving sparsification methods from gauging and code embeddings.

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Quantum Physics

Analog quantum simulation of $\phi^4$ field theory with a superconducting transmission line

Ilan T. Rosen, Neill C. Warrington, Max Hays et al. (+4 more)

Understanding the dynamics of interacting quantum fields remains a fundamental challenge. We propose a superconducting transmission line for analog quantum simulation of $(1+1)$-dimensional $\phi^4$ field theory. The transmission line comprises fluxonium-like circuit elements whose continuous and unbounded phase variables encode a scalar field without Hilbert-space truncation. Their anharmonic potentials provide strong interactions. Tuning the circuit parameters provides access to two distinct regimes. In the first, the transmission line emulates $\phi^4$ field theory with a single-well potential. We confirm this correspondence through lattice Monte Carlo calculations of the low-energy spectra of both the circuit and lattice $\phi^4$ theory. This regime enables scattering experiments between counter-propagating particle wave packets. The second parameter set yields a double-well potential that emulates $\phi^4$ theory in the symmetry-broken phase and hosts degenerate vacua. Interfaces between the two vacua form topological kinks, and the transmission line can simulate kink-antikink collisions. We present state preparation and measurement protocols for both collision experiments, enabling spatially resolved, real-time studies of particle and soliton scattering in an interacting quantum field theory.

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All authors Ilan T. Rosen, Neill C. Warrington, Max Hays, Christopher McNally, Joshua Lin, Stephen Sorokanich III, Julian Bender

Statistical Mechanics

High-resolution mapping of the phase boundary of the honeycomb-lattice Blume–Capel ferromagnet

Eluiz C.M. Filho and Claudio J. DaSilva

We present a high-resolution numerical study of the spin-1 Blume–Capel ferromagnet on the honeycomb lattice ($z=3$). Wang–Landau estimates of the joint density of states $\Omega(E_1,E_2)$, combined with field mixing, are used to map the first-order transition line and locate the tricritical point at $(\Delta_t,T_t)=[1.4819(2),\,0.4022(7)]$. Histogram reweighting of Metropolis simulations for $L=36$ and $48$ provides an independent consistency check, with a crossing temperature near $0.4039$, compatible with the Wang–Landau extrapolation. From the field-mixing analysis we obtain $r=-1.586(19)$, while the slope of the multicanonical coexistence line yields the consistent and more precise estimate $r=-1.587(5)$. Normalizing by the zero-temperature field $\Delta_0=zJ/2$, the available honeycomb, square, triangular, and simple-cubic estimates cluster near $r/\Delta_0\simeq-1.06$, corresponding to a magnitude about $6\%$ larger than the mean-field value $-1$; no systematic dependence on coordination number or dimensionality is resolved over the range examined. Finite-size scaling of $\sigma_Q$ gives $y_t=1.795(7)$, consistent with the tricritical Ising value $9/5$, while the fourth-order cumulant scaling is compatible with $y_g=4/5$. Deep in the first-order regime, the cumulant approaches the expected two-phase limit $U_Q\to2/3$. Multicanonical simulations up to $L=64$, using weights constructed directly from the Wang–Landau density of states for $L\le24$ and rescaled and refined for larger systems, yield an interface-tension exponent $\mu=1.265(26)$, consistent with the tricritical prediction $(d-1)/y_g=5/4$. Finally, we map the continuous branch of the phase boundary from the same density-of-states data, obtaining $T_c(\Delta=0)=1.157$; estimates sufficiently close to the tricritical point are affected by crossover from Ising to tricritical scaling.

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Materials Science

Bond-Switching Reconstruction in Bare Ti3C2 MXene

Kui Lin

MXene properties are typically tuned through composition, surface termination, and intercalation, while the metal-carbon framework topology is considered fixed. Here, we demonstrate that this framework can reconstruct. Unconstrained relaxations of biaxially strained bare Ti3C2 yield a dynamically stable polymorph, N, featuring a 15-atom primitive cell, six distinct Ti-C bond classes, and 2.55 Å Ti-Ti pairs. The coherent transformation pathway crosses an 8.47 eV barrier per cell but first reaches another reconstructed minimum, N', lying 1.08 eV below N, revealing a family of bond-switched networks. Phase N lies 7.58 eV per cell above the parent. Reverse barriers along the calculated pathway are 1.50 and 1.98 eV per cell for N and N', respectively. Reconstruction quenches the parent spin polarization, yielding a nonmagnetic metal with a nearly fourfold increase in Fermi-level density of states. Bader and electron-localization analyses suggest charge redistribution from C toward Ti associated with Ti-Ti pairing. In multilayers, reconstructed layers form interlayer Ti-C bonds. A 10% biaxial tension halves the phase-energy difference, and pressure reverses phase ordering near 85 GPa. These results establish bond-switching reconstruction as a mechanically controllable structural degree of freedom in MXenes.

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Plasma Physics

Beam filamentation instability drives deuterium-tritium fusion with polarized neutron emission

Guanqi Qiu, Deji Liu, Dongchi Cai et al. (+3 more)

Filamentation instabilities are generally regarded as detrimental to fast-electron transport in fusion plasmas because they increase beam divergence and redistribute deposited energy. Here, we use two-dimensional particle-in-cell simulations coupled to a spin-dependent deuterium-tritium fusion module to investigate whether filamentation can instead transfer energy from counterstreaming electrons to prepolarized fusion ions. The simulations show that magnetic filaments, together with longitudinal inductive and transverse charge-separation electric fields, accelerate initially stationary deuterons and tritons to energies at which fusion reactions occur. Over the parameter range examined, the calculated neutron yield increases with the saturated magnetic-field energy. The model further predicts anisotropic, spin-resolved neutron emission. The direction of maximum neutron polarization is approximately perpendicular to the dominant deuterium-tritium collision direction and evolves with the angular distribution of the reacting ions. These results suggest that beam filamentation can couple relativistic-electron energy to fusion ions and that polarized neutron emission may provide a reaction-weighted signature of the underlying plasma dynamics.

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All authors Guanqi Qiu, Deji Liu, Dongchi Cai, Ronghao Hu, Zheng Gong, Xueqing Yan

Other Condensed Matter

Three-dimensional dopant distribution from a single, out-of-focus spectroscopic image

Michael Deimetry, Timothy Petersen, Matthew Weyland et al. (+1 more)

Increasing miniaturization of nanoscale devices makes determining the three-dimensional distribution of dopants increasingly important. In out-of-focus spectroscopic scanning transmission electron microscopy images, we show that dopant atoms appear as disks with radii relating to dopant depth, allowing the three-dimensional distribution of dopants to be determined from simple geometric analysis of a single out-of-focus image. Through numerical experiments on Si-doped graphene we validate statistical detection and Bayesian inference methods to quantify confidence and uncertainties while making the analysis more robust at lower dose. We present proof-of-concept experimental data from an Fe-doped spinel, retrieving dopant depth to within around 2 nanometres.

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All authors Michael Deimetry, Timothy Petersen, Matthew Weyland, Scott Findlay

General Relativity and Quantum Cosmology

Accounting for detector calibration uncertainty in black-hole ringdown analysis

Rowina S. Nathan, Shingo Hido, Neil Lu et al. (+3 more)

Detector calibration systematics can bias measurements of a remnant black hole's mass and spin, producing spurious evidence against general relativity if unaccounted for. The ringdown phase in the gravitational-wave signal produced by a binary black-hole merger encodes the remnant properties: at sufficiently late times, the signal is well described by a superposition of quasinormal modes, each with a frequency and damping time set only by the remnant mass and spin. Here we present two complementary approaches for analyzing the ringdown portion of the data to estimate the remnant mass and spin in the presence of a nonnegligible detector calibration error, using the quasinormal-mode rational filter (QNMRF). With a well-measured error, we apply the best-estimated calibration correction to the strain before conducting the standard analysis; with an unknown error, we instead jointly sample the remnant mass, spin and the frequency-dependent calibration error, marginalizing over an uncertainty prior. By injecting the numerical-relativity waveform SXS:BBH:0305 into colored detector noise, at a full-signal matched-filter signal-to-noise ratio of $\sim60$ and with simulated calibration errors of $\pm25\%$ in magnitude and $\pm25^\circ$ in phase, marginalizing over the calibration uncertainty recovers the true mass and spin within the 90% credible interval, whereas the estimated values are biased if the calibration errors are ignored. We apply the method to GW250207, an event recorded while the Hanford detector response was not well characterized, and recover a remnant consistent with the inspiral-merger-ringdown prediction using the ringdown portion alone, both by correcting for a best-estimated calibration error and by marginalizing over a broad uncertainty prior.

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All authors Rowina S. Nathan, Shingo Hido, Neil Lu, Mallika R. Sinha, Sizheng Ma, Ling Sun

Nuclear Theory

$\boldsymbol{\textit{Ab initio}}$ $n\alpha$ scattering using the Efros method

Mamoon A. Sharaf, Weijie Du, Peng Yin et al. (+2 more)

We present the first $\textit{ab initio}$ many-body application of the Efros method for scattering utilizing the harmonic oscillator expansion of the continuum wave function. We select single-channel $n\alpha$ scattering and, using low-lying eigenstates from no-core shell model (NCSM) calculations, we obtain well-converged scattering results that are in reasonable agreement with experiment. The results demonstrate that the Efros method is computationally practical and promising for further $\textit{ab initio}$ many-body studies of nuclear reactions.

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All authors Mamoon A. Sharaf, Weijie Du, Peng Yin, Andrey M. Shirokov, James P. Vary

Cosmology and Nongalactic Astrophysics

Galaxy Clustering Can Reveal Host-Galaxy Properties of Binary Black Hole Mergers

Daiki Watarai, Hayato Imafuku and Fumihiro Chuman

Galaxy clustering encodes information about the host galaxies of binary black hole (BBH) mergers even when individual hosts remain unidentified, because the distribution of neighboring galaxies depends statistically on the host-galaxy population. We construct event-level host-type likelihoods from host-conditioned galaxy-count distributions within gravitational-wave localization regions and combine them to infer the fractions of BBH mergers hosted by different galaxy populations. The framework applies to common and rare galaxy populations without prescribing formation efficiencies or merger delay-time distributions. Using measured star-forming and quenched galaxy clustering, idealized one-year forecasts assuming all mergers occur in quenched galaxies yield median one-sided 90% lower credible limits of 0.19, 0.48, and 0.92 on the quenched-host fraction for O5, post-O5, and third-generation networks. These forecasts illustrate the potential for host-galaxy population inference before the third-generation detector era.

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Instrumentation and Detectors

Enhanced micrometre spatial resolution and usable photon flux for hybrid pixel detectors via deep-learning-based X-ray localization

Xiangyu Xie, Anna Bergamaschi, Martin Brückner et al. (+30 more)

Micrometre spatial resolution is achieved for X-rays with the MÖNCH detector, a charge-integrating hybrid pixel detector with a 25 {\mu}m pixel pitch, by exploiting charge sharing between neighbouring pixels. The conventional analytical interpolation method, however, relies on a global mapping derived from the charge-sharing statistics and is applicable only to isolated single-photon clusters, which limits both the achievable resolution and the usable photon flux. To overcome these limitations, we trained deep learning models to localize single-photon and pile-up events based on high-fidelity simulation data. For knife-edge measurements at 12 keV and a low occupancy of 0.74% (photons per pixel and frame), where single-photon events dominate, the proposed method reaches a of the edge spread function of 1.36 {\mu}m, compared with 1.54 {\mu}m for the conventional eta interpolation. We demonstrate experimentally that resolving up to three photons per cluster raises the reconstruction efficiency from 59% to 93% at a 2.4{\times} higher occupancy of 1.81%, while preserving a of 1.39 {\mu}m.

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All authors Xiangyu Xie, Anna Bergamaschi, Martin Brückner, Maria Carulla, Tomáš Celko, Roberto Dinapoli, Simon Ebner, Simone Emiliani, Khalil Daniel Ferjaoui, Erik Lars Fröjdh, Viveka Gautam, Dominic Greiffenberg, Shqipe Hasanaj, Viktoria Hinger, Marius Hürst, Vadym Kedych, Thomas King, Shuqi Li, Carlos Lopez-Cuenca, Leonid Lunin, Federica Marone, Alice Francesca Mazzoleni, Davide Mezza, Scharon Moses, Konstantinos Moustakas, Aldo Mozzanica, Jonathan Franklin Mulvey, Martin Müller, Christian Ruder, Bernd Schmitt, Saverio Silletta, Dhanya Thattil, Jiaguo Zhang

Statistical Mechanics

A general framework for crystallization in maximal hard-core models

Alexander Barg, Qidong He and Geyang Wang

We study general maximal hard-core models on periodic lattice-type graphs. While for standard models, phase coexistence may arise for high activity, for maximal models this behavior may occur also for sufficiently low activity values. Relying on the concept of volume allocation, we develop a unified set of assumptions that imply the Peierls condition, a convergent cluster expansion for the partition function, and hence the conclusions of Pirogov-Sinai theory for this class of models. We further check these assumptions for a number of examples including standard lattice-type periodic graphs, proving crystallization for both high and low activity. We also derive estimates for the values of activity that bound the phase coexistence regions in the phase diagram, rewriting for this purpose the proof of a technical result in the derivation of Pirogov-Sinai theory.

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Lattice Field Theory

Hamiltonian framework for Chiral Gauge Theories on a Disk Boundary

Srimoyee Sen

I propose a Hamiltonian framework for chiral gauge theories (CGT) based on a Euclidean formulation which uses 2n dimensional chiral fermions on the boundary of a 2n+1 dimensional disk. In the original Euclidean formulation, boundary gauge fields were extended into the bulk using $2n + 1$ dimensional gauge field equations of motion (EOM) which creates a bottleneck for constructing a Hamiltonian. I present an alternate proposal for extending the gauge fields into the bulk that is compatible with both a Hamiltonian framework and a Euclidean path integral. Applying this to Abelian gauge fields produces exact expressions of interior fields as a functional of the boundary fields, which can be directly used in a Hamiltonian formulation. Euclidean analysis of the new gauge field extension shows that it can preserve the non-perturbative content of the original construction, including the behavior of topological charge, associated chiral fermion zero modes and an absence of the strong CP problem when applied to the Standard Model. This construction opens up a route to a Hamiltonian treatment and future quantum simulation of CGTs on a disk boundary.

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Fluid Dynamics

Geometric Mechanics of Real-Space Energy Transfer in Turbulence

Weijie Zhang and Hanxun Yao

How the local energy transfer across scales in turbulence is encoded in the instantaneous deformation of fluid elements remains a fundamental question. We exploit the spherical geometry of the real-space energy cascade at length scale $\ell$. An exact derivation shows that it can be decomposed locally by strain self-amplification and vortex stretching, with a coefficient equal to the specific moment of inertia $2/5(\ell/2)^2$ of a spherical fluid neighborhood. Direct numerical simulations show that this contribution captures the dominant local transfer and defines a statistical boundary separating forward- and inverse-cascade events. A further longitudinal and transverse decomposition reveals that the longitudinal transfer underlying Kolmogorov's $4/5$ law is governed solely by strain self-amplification, whereas vortex stretching enters through the transverse component. These results establish a purely mechanical connection between turbulent energy cascade and the local rotational and deformational dynamics of fluid elements.

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Quantum Physics

Demonstration of subspace-search variational quantum eigensolver using photonic orbital angular momentum qudits

Kang-Min Hu, Myung-Hyun Sohn, Yong-Su Kim et al. (+3 more)

Accurate excited state energies are essential for interpreting fluorescence and photochemical processes, yet variational quantum eigensolvers (VQEs) on noisy intermediate-scale quantum (NISQ) hardware have largely been confined to ground states. Subspace-search VQE (SSVQE) offers a NISQ-friendly route to excited states without ancilla-based overlap measurements, however it has lacked an experimental demonstration since it requires the coherent preparation and manipulation of multiple orthogonal basis states under a shared variational unitary. Here we realize SSVQE on a photonic platform by encoding orthogonal qudit states in the orbital angular momentum of single photons and optimizing a shared variational circuit. We estimate excited state energies for a four-dimensional $\rm{HeH^+}$ molecule and an eight-dimensional Heisenberg chain, thereby demonstrating scalable excited state eigensolving in a high-dimensional Hilbert space. Our results establish photonic qudits as a resource-efficient pathway to excited state quantum simulation.

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All authors Kang-Min Hu, Myung-Hyun Sohn, Yong-Su Kim, Kwang Jo Lee, Hyun Woo Kim, Hyang-Tag Lim

Atmospheric and Oceanic Physics

A Graph Neural Network for Global Daily Fire Radiative Power Prediction at Medium-Range Lead Times

Li Zhang, Jun Wang, Isidora Jankov et al. (+6 more)

Skillful prediction of biomass-burning activity several days in advance is important for air-quality forecasting and aerosol prediction. Two operational constraints motivate this work. First, the GBBEPx satellite fire radiative power (FRP) product used to initialize NOAA's GEFS-Aerosols is available with about a 1.5-day latency, so each forecast cycle relies on the most recently available, but already outdated, fire observations. Second, these fire inputs are then held fixed throughout the subsequent 5-day operational forecast, or 7 days in the GSL experimental system, effectively assuming no evolution in fire activity. We develop a data-driven model that predicts global FRP one to seven days ahead from the most recent available observations. The model adapts a spatiotemporal graph neural network using reanalysis meteorology, land-cover and vegetation information, recent fire history, and GBBEPx FRP as the training target. It is trained on 2020-2022 data and evaluated for 2023-2024. The model reproduces the global seasonal cycle and substantially outperforms persistence. At 0.1$^\circ$ resolution, mean squared error is reduced by 32% at one-day lead and 43% at seven days in 2023, and by 24% and 40% in 2024. At 1$^\circ$ resolution, the critical success index ranges from 0.32 to 0.60. Detection skill declines only modestly with lead time, whereas intensity skill degrades more rapidly. Large fires are detected reliably, but their radiative power is systematically underestimated. These results demonstrate useful predictability of fire activity several days ahead and identify intensity calibration and small-fire placement as the main remaining challenges before predicted FRP can support operational aerosol forecasts.

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All authors Li Zhang, Jun Wang, Isidora Jankov, Yongxin Liu, Gonzalo A. Ferrada, Ravan Ahmadov, Ligia Bernardet, Haonan Chen, Shobha Kondragunta

Mathematical Physics · Cross-listed from math.OA

Three-Point Trace Positivity:Schatten Norm Compression and Interpolating Metrics

Trung Dung Vuong and Hiroyuki Osaka

Let $(\mathcal N,\nu)$ be a finite tracial von Neumann algebra and set $\mathcal{K}_r(P,Q)=\nu((P^{1/2}QP^{1/2})^r)$. We prove that $$ [\mathcal{K}_r(P_i,P_j)]_{i,j=1}^3\ge0, \qquad 1/2\le r\le1. $$ The range $1/2<r<1$ is new even for matrices, and order three is sharp for $1/2\le r<1$. This single mechanism resolves two problems. First, if $(\mathcal R,\omega)$ is finite tracial and $H=[H_{ij}]_{i,j=1}^3\in M_3(\mathcal R)_+$, then $$ [\omega(|H_{ij}|^p)]_{i,j=1}^3\ge0, \qquad 1\le p\le2, $$ settling the Lin–van den Driessche conjecture on Schatten norm compression. Second, for a semifinite tracial von Neumann algebra $(\mathcal M,\tau)$, define $$ d_t(A,B)^2=\frac{\tau(A)+\tau(B)}2- \|B^{t/4}A^{t/4}\|_{2/t}^{2/t}. $$ We prove that $d_t$ is a complete metric on $L^1(\mathcal M,\tau)_+$ for $1\le t\le2$, including the previously open range $1<t<2$ between the Hellinger and Bures endpoints, and that $$ d_t\text{ is a metric on }L^1(\mathcal M,\tau)_+ \quad\Longleftrightarrow\quad t\in[1,2]\ \text{or}\ \mathcal M\text{ is abelian}. $$ Its topology and Cauchy sequences agree with those of $L^1$. The same classification holds for unital tracial $C^*$-algebras and, with the known $t=0$ obstruction, resolves Problem~2 of Komálovics and Molnár.

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Classical Physics

A Shape-Preserving Shell Theorem

Penelope Messinger, Stephany M. Rodriguez and Trung V. Phan

We identify all radial interaction potentials that generalize Newton's exterior shell theorem, for which a uniformly distributed spherical shell is indistinguishable from a point-source up to strength renormalization and radial rescaling. We call these shape-preserving shell interactions, extending Gurzadyan's cosmological theorem which considers strength renormalization alone. We further expand the theory from monopolar to multipolar sources and establish the corresponding classification in arbitrary spatial dimensions. We find potential families beyond the spherical property subclass and show that the classifications for multipolar shape-preserving interactions form a nested hierarchy, with each lower-rank class being a subset of the next higher-rank class.

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Wednesday 7 October

Quantum Physics

Can the Quantum Fisher Effective Dimension Judge a Hybrid Quantum Neural Network?

Md Masum Mia, Amith Khandakar and Mohamed Arselene Ayari

Hybrid quantum neural networks (QNNs) pair a classical feature extractor with a variational quantum circuit, and the effective dimension of the circuit's quantum Fisher information matrix (QFIM) is widely used to assess such models. This scalar is often interpreted as an indicator of trainability or accuracy, although these readings are rarely tested under controlled conditions. We therefore investigate what it actually measures. We define the effective dimension as the participation ratio of the QFIM diagonal, which lies between one and the parameter count, and we evaluate it across two image datasets, four frozen backbones including a random-projection control, four circuit depths on eight qubits, and three seeds. During training, the effective dimension remains well below the parameter count, and its correlation with test accuracy ranges from -0.72 to +0.87, changing sign across seeds in half of the configurations. Increasing depth activates a larger share of the circuit directions, from 0.38 to 0.91 of the parameter count, while the initialization gradient variance remains between 1e-5 and 1e-4, so no barren plateau (BP) appears at eight qubits. At a fixed circuit, the four backbones share an initial effective dimension of 6 to 9, even though CIFAR-10 accuracy ranges from 23.14% to 86.44%. These results show that the effective dimension characterizes circuit geometry rather than model quality. We conclude with a practical protocol that assigns each diagnostic to the question it can answer.

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Mathematical Physics · Cross-listed from math.DG

An Explicit Bound for the First Dirichlet Eigenvalue via Two Moments

Thomas Schürmann

Let $(M^n,g)$, $n\ge2$, be a compact connected Riemannian manifold with smooth nonempty boundary, $\operatorname{Ric}_M\ge(n-1)Kg$ for $K>0$, and nonnegative outward boundary mean curvature. We derive an explicit algebraic lower bound $B_\eta$ for the first Dirichlet eigenvalue from Kasue's mixed inradius model. With $R$ the inradius and $s=4KR^2/\pi^2$, the bound involves one square root and approximates the model eigenvalue with relative error $O_n(s^4)$ as $s\downarrow0$ for fixed $n$. The construction uses the first two moments of a positive representation of the averaged model potential and a sharp pointwise corrector estimate. For the chosen spectral transfer, the first two moments determine an optimal bound. We also show that the model eigenvalue is the geometric infimum at fixed $(n,K,R)$. For $0<s<1$, it is approached by smooth collapsing balls with sectional curvature at least $K$ and totally geodesic boundary. At the maximal inradius, the model value is attained by the round hemisphere. The bound strictly improves the variance refinement throughout $0<s\le1$. We also give a direct algebraic comparison with an optimized power-test benchmark.

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Quantum Physics · Cross-listed from cs.DS

Grover Search for a Threshold-Fraction Variant of the Travelling Salesman Problem: A Circuit-Level Construction

Aayra Dhindsa Sawkmie

The Travelling Salesman Problem (TSP) is a classic combinatorial optimisation problem which is NP-hard in optimisation form and NP-complete as a decision problem. The standard question asks for the shortest tour that visits every city exactly once and returns to the origin. This paper studies a threshold-fraction variant, which we call the robust TSP, formulated as a promise problem: given a distance threshold $K$ and a promised fraction $p$, decide whether at least a fraction $p$ of all tours have total length at most $K$, or whether no such tour exists. We show that Grover's quantum search algorithm decides this problem using $O(1/\sqrt{p})$ oracle queries, independent of the number of cities $N$, with each query implemented by a quantum circuit of polynomial size in $N$. For any fixed robustness level $p$, the total runtime is therefore polynomial in $N$. Measured in oracle queries, the quantum algorithm offers a quadratic improvement in the dependence on $1/p$ over classical random sampling, which needs $\Theta(1/p)$ samples; because each quantum query is costly, however, it is faster in total running time only when $p$ is very small (roughly below $N^{-4}$), where the number of queries is no longer constant. We describe the problem formulation, detail the oracle construction (edge-length loading, sequential quantum addition, and threshold comparison), and analyse the query complexity to achieve the required result.

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Physics and Society

Voluntary nonpharmaceutical intervention as a feedback-evolving game

Ryuichi Kumata, Hiromu Ito and Masato Yamamichi

Nonpharmaceutical interventions (NPIs), such as mask wearing, can reduce epidemic spread, but their effectiveness depends on whether people adopt and sustain them. The incentive to adhere changes with infection risk and with the behavior of others. Yet it remains unclear how epidemiological protection and social reinforcement determine the strategic structure of infection control, and how epidemic feedback changes that structure over time. Here, we develop a socio-epidemiological model in which prevalence changes behavioral incentives while adherence changes transmission, separating private protection from source control and incorporating conformity. At a given prevalence, private protection favors adherence, source control creates opportunities for free-riding, and conformity reinforces whichever behavior is already common, generating distinct adherence games. Because adherence reduces transmission and prevalence, the population can move between these games as the epidemic unfolds. This feedback can stabilize partial adherence, create alternative behavioral norms, or generate recurrent epidemic-behavior cycles. Moreover, interventions with the same population-level effect on transmission at a given adherence level can produce different long-term outcomes when protection is distributed differently between the individual and others. Thus, voluntary infection control is a feedback-evolving game whose outcome depends not only on epidemiological efficacy but also on who is protected and how behavior is socially reinforced.

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Chemical Physics

Looking Under the Streetlight: Evaluation in Generative Molecular Dynamics

Simon Olsson, Frank Noé, Grant M. Rotskoff et al. (+1 more)

This position paper argues that the generative molecular dynamics (GenMD) community is not properly evaluating its progress: current evaluations let a model match what is reported while being arbitrarily wrong on what was claimed, which risks over-claiming advantage over classical baselines. This reflects a structural misalignment between common evaluation practices and the scientific tasks the field sets for itself. The reason is that the ground truth—exhaustive molecular dynamics on the systems of interest—is computationally costly, and this cost is what motivates the field. With ground truth inaccessible, evaluation drifts toward convenient proxies, and the resulting norms entrench easily. We identify misaligned evaluation patterns that persist as a community-level equilibrium, and propose concrete observables, reporting standards, and benchmark designs, both computational and experimental, that better reflect what GenMD aspires to deliver. Our aim is to give the field shared language and tools for evaluation that match its scientific ambitions before today's conventions calcify into norms.

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All authors Simon Olsson, Frank Noé, Grant M. Rotskoff, Kresten Lindorff-Larsen

Chaotic Dynamics

A Second-Order Asymptotic Expansion for Nonlinear Filtering in the Lorenz–63 System

Masahiro Kurisaki and Kota Takeda

A challenge in nonlinear filtering is to incorporate nonlinear effects into approximations of the conditional mean while retaining a finite-dimensional recursive algorithm. We derive a second-order asymptotic expansion of the filtering mean with respect to the system-noise intensity. We apply this expansion to the Lorenz–63 model, a prototypical three-dimensional chaotic dynamical system. The first-order approximation is computed using a Kalman–Bucy filter for the system linearized around the deterministic reference trajectory. The second-order correction incorporates the Hessian of the Lorenz–63 drift and is computed through a closed recursive system with 3+9+18=30 independent scalar components. The full system, including the reference trajectory and the first-order mean and covariance, has 42 independent scalar components. To support stable tracking of chaotic trajectories over long time intervals, we introduce recentering of the expansion and redistribution of Gaussian components between expansion orders. In the numerical experiments, we compare the proposed algorithm with an ensemble transform Kalman filter (ETKF) as a practical benchmark and a particle filter (PF) as a numerical reference. Under the full-observation settings, the proposed algorithm achieves a lower root-mean-square error relative to the truth and a smaller distance to the 10,000-particle PF reference than the 20-member ETKF. These results suggest that the proposed second-order extension of Kalman filtering has the potential to balance filtering accuracy and computational cost.

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Quantum Gases

Spinodal-controlled freeze-out and nucleation at the first-order superfluid-supersolid transition of a dipolar gas

Wai Kui Wong

Dipolar quantum gases in elongated traps become supersolid through a transition that is continuous at intermediate density but first order at low and high density; at the continuous point, ramps of the scattering length follow Kibble–Zurek scaling. We study ramps across the first-order superfluid–supersolid transition of $^{164}$Dy in an infinite tube using the three-dimensional extended Gross–Pitaevskii equation with truncated-Wigner noise. With quantum noise only, the uniform superfluid survives the metastable window and transforms after its spinodal, where the roton softens. For onsets occurring during the linear ramp, the delay measured from this spinodal has a fitted exponent $\zeta = 0.36 \pm 0.02$, close to the continuous-transition result and the mean-field value $1/3$. Reverse ramps show a comparable delay beyond the fold of the crystal branch, producing dynamical hysteresis. Initial thermal noise with nominal temperatures of 2.5–10 nK produces crystalline regions inside the metastable window during holds, with faster nucleation closer to the spinodal and at higher initial temperature. In ramps at 5 nK, thermal fluctuations cross onset thresholds near $f_s = 1$ early, whereas the bulk of the crystal still forms after the zero-temperature spinodal with a similar scaling. Without a heat bath these effective rates depend on preparation: ramps crossing the window at the same rate nucleate early in 2 of 32 or 11 of 16 realizations depending on their starting point. At low density, slower ramps select larger spacings in a crystal of separated droplets, and droplets survive far above the transition on reverse ramps. A Maxwell construction gives a coexistence window $0.04 a_0$ wide around the first-order transition point, in which localized states exist; in the simulated tube they lie above the homogeneous states. At the continuous point there is no coexistence.

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General Physics

On the notion of kinetic energy in a spacetime of maximal proper acceleration

Ricardo Gallego Torromé

It is shown in this work that in spacetimes of maximal proper acceleration there are situations where a particle decelerates and simultaneously increases its kinetic energy. To illustrate the effect, a classical $1$-dimensional electric cavity-like scheme is discussed. The gain in kinetic energy by deceleration suggests an equivalence between velocity and acceleration from the energetic point of view. Such an equivalence is stated in a form resembling Born reciprocity principle but formulated in the framework of higher order jet spacetime geometry. We also show the existence in the theory of a dynamical superluminal sector for point particles with positive mass and characterized by superluminal speed and a proper acceleration larger than the maximal proper acceleration. Therefore, the speed of light and the maximal proper acceleration become only separation conditions at the classical level of the two dynamical sectors.

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High Energy Physics (Experiment)

Short-Baseline Near Detector (SBND): Design and Initial Performance

SBND Collaboration: P. Abratenko, R. Acciarri, C. Adams et al. (+351 more)

The Short-Baseline Near Detector (SBND) is a 112 tonne active mass liquid argon time projection chamber (LArTPC) situated in the Booster Neutrino Beam at Fermilab, forming part of the Short-Baseline Neutrino (SBN) Program. SBND began operation in 2024 and has since accumulated the world's largest sample of neutrino-argon interactions. This paper describes the as-built detector and presents performance results from the first year of beam operation. All detector systems performed at or above design requirements. The liquid argon purity achieved an electron lifetime exceeding 30ms, ten times the design requirement, for more than 95% of Run 1. The TPC wire plane readout achieved noise levels at the theoretical minimum for the given wire geometry (an average of 388e$^-$ for the 4m long collection plane wires) with 99.3% of readout channels live. Together, the liquid argon purity and TPC performance are enabling extremely clean event reconstruction in the SBND TPC. The photon detection system, consisting of passive reflectors and multiple active components (PMTs and X-ARAPUCAs), has achieved a light yield exceeding 10 photoelectrons per MeV throughout the detector volume and a timing resolution of a few nanoseconds, sufficient to resolve the 19ns bunch structure of the Booster Neutrino Beam. A nearly 4$\pi$ cosmic ray tagger system surrounds the TPC to mitigate cosmic backgrounds in neutrino and BSM physics analyses. The data acquisition system has demonstrated stable performance up to an event rate of 8Hz, and a data collection efficiency of 98.6% was achieved throughout SBND's first neutrino run in 2025. These results demonstrate that SBND represents the state of the art in multi-tonne-scale LArTPC detector performance.

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All authors SBND Collaboration: P. Abratenko, R. Acciarri, C. Adams, T. Alafaro, L. Aliaga-Soplin, R. Alvarez-Garrote, J. Ameel, D. Andrade Aldana, C. Andreopoulos, A. Antonakis, L. Arellano, J. Asaadi, W. Badgett, L. Bagby, S. Balasubramanian, D. Barker, A. Barnard, C. Barnes, N. Barros, A. Basharina-Freshville, V. Basque, J.R. Bateman, M.C. Bazetto, A. Beever, B. Behera, E. Belchior, O. Beltramello, M. Betancourt, A. Bhat, K. Biery, M. Bishai, A. Bitadze, A. Blake, B. Bogart, J. Boissevain, C. Bonifazi, J. Book Motzkin, G. Botogoske, D. Brailsford, A. Brandt, J. Bremer, S. Brickner, T. Brooks, M.B. Brunetti, G. Buccino, A. Bullock, G.A.N. Buzzard, L. Camilleri, D. Caratelli, D. Carber, B. Carlson, M.F. Carneiro, M. Cascella, R. Castillo Fernandez, F. Cavanna, M. Chalifour, P. Chambouvet, A. Chan, A. Chappell, H. Chen, S. Chung, D. Cianci, M.F. Cicala, R. Coackley, L. Cooper-Troendle, J.I. Crespo-Anadon, E. Cristaldo, C. Cuesta, Y. Dabburi, O. Dalager, M. Dall'Olio, R. Darby, I. de Icaza Astiz, M. Del Tutto, S. Dennis, V. Di Benedetto, S. Dixon, M. Donnachie, Z. Djurcic, V. do Lago Pimentel, S. Dominguez-Vidales, R. Doubnik, M. Dubnowski, K. Duffy, S. Dytman, A. Elvin, A. Ereditato, E. Espinoza, J. Estrada, J.J. Evans, A.C. Ezeribe, C. Fan, J. Farrell, A. Filkins, B. Fleming, W. Foreman, D. Franco, H. Frandini, J. Freestone, G. Fricano, J. Fried, D. Friend, I. Furic, A.P. Furmanski, T. Gamble, S. Gao, D. Garcia-Gamez, S. Gardiner, G. Ge, M. Geynisman, I. Gil-Botella, S. Gollapinni, M. Goodman, O. Goodwin, P. Green, H. Greenlee, W.C. Griffith, R. Guenette, P. Guzowski, L. Hagaman, T. Ham, A. Hamer, P. Hamilton, R. Hanni, K. Hardin, B. Harris, S. Hentschel, A. Hergenhan, M. Hernandez-Morquecho, C. Hilgenberg, C. Hill, A. Hoffman, P. Holanda, A. Holin, B. Howard, B. Howe, J. Howell, J. Hrivnak, C. James, C. James, T. Johnson, R.S. Jones, M. Jung, T. Junk, Y.-J. Jwa, D. Kalra, G. Karagiorgi, L. Kashur, K.J. Kelly, W. Ketchum, M.J. Kim, M. King, J. Klein, L. Kotsiopoulou, S. Kr Das, I. Kreslo, T. Kroupova, S. Kubecki, V.A. Kudryavtsev, F. Kumar, M. Langstaff, J. Larkin, K. Laureto, H. Lay, R. LaZur, G. Leigh, I. Lepetic, J.-Y. Li, K. Lin, B.R. Littlejohn, F. Liu, L. Liu, S. Lockwitz, D. Lorca, W.C. Louis, G. Lukhanin, X. Luo, A.A. Machado, P. Machado, G. Mahler, S. Manohari Kancharla, S. Marcocci, C. Mariani, F. Marinho, J. Marshall, L. Martinez, C. Martin-Morales, A. Mastbaum, K. Mavrokoridis, N. McConkey, B. McCusker, J. Mclaughlin, V. Meddage, D. Mendez, I. Mercer, T. Mettler, T. Miao, M. Micheli, G. Miller, D. Mishins, K. Mistry, D. Mladenov, A. Mogan, J. Molina, D. Montanari, M. Mooney, A.F. Moor, G. Moreno-Granados, F. Morgadinho-Inacio, C.A. Moura, J. Mousseau, J. Mueller, S. Mulleriababu, J. Najdzion, R. Natieli de Oliveira, A. Navrer-Agasson, M. Nebot-Guinot, M. Nessi, V.C.L. Nguyen, S. Ni, T. Nichols, F. Nicolas-Arnaldos, B. Norris, R. Northrop, J. Nowak, S.B. Oh, O. Olorife, N. Oza, L. Pagliuso, O. Palamara, N. Pallat, V. Pandey, A. Papadopoulou, H.B. Parkinson, J. Pater, J. Paton, L. Paulucci, Z. Pavlovic, D. Payne, L. Pelegrina-Gutierrez, O.L.G. Peres, R. Pfaff, F. Pietropaolo, J. Plows, J. Poirot, I.D. Ponce Pinto, A. Popov, F. Psihas, D. Pushka, G. Putnam, X. Qian, Y. Qie, V. Radeka, E. Raguzin, R. Rajagopalan, P. Ratoff, H. Ray, B. Rebel, R. Rechenmacher, M. Reggiani-Guzzo, F. Resnati, D. Rivera, A. Roberts, M. Roda, O. Rodrigues, J. Romeo-Araujo, M. Ross-Lonergan, N. Rowe, P. Roy, M. Rumore, A. Sanchez-Castillo, P. Sanchez-Lucas, G. Savage, G. Scanavini, A. Scarff, A. Scherf, D.W. Schmitz, A. Schneider, A. Schukraft, F. Schwartz, W. Scofield, H. Scott, E. Segreto, Z. Semovski, J. Sensenig, M. Shaevitz, R. Sharankova, S. Shetty, K. Shiba, P. Singh, B. Slater, J. Smith, M. Soares-Nunes, M. Soderberg, S. Soldner-Rembold, F. Spagliardi, M. Spanu, J. Spitz, N. Spooner, M. Stancari, A. Stefanik, G.V. Stenico, T. Strauss, P. Sutcliffe, K. Sutton, A.M. Szelc, W. Tang, C. Thorn, C. Thorpe, J. Tillman, A. Timilsina, D. Torretta, D. Totani, M. Toups, C. Touramanis, M. Tripathi, S. Tufanli, L. Tung, E. Tyley, S. Unnikrishnan G.A. Valdiviesso, R. Van de Water, A. Vazquez-Ramos, A. Verdugo de Osa, B. Villa Ferre, L. Wan, M. Weber, H. Wei, Z. West, T. Wester, A.J. White, A. Wilkinson, P. Wilson, T. Wongjirad, E. Worcester, M. Worcester, M. Wright, W. Wu, S. Yadav, E. Yandel, T. Yang, G. Yarbrough, L. Yates, S. Yebes, J. Yu, B. Yu, H. Yu, V. Zamazal, B. Zamorano, A. Zeglam, J. Zennamo, J. Zhang, C. Zhang, M. Zhao, M. Zuckerbrot

Quantum Physics

Fast entanglement generation via cavity-mediated nematic tensor dynamics

Stuart J. Masson

Many-body entanglement in atomic ensembles offers the potential for enhanced sensing devices. Entanglement can be generated by interfacing atoms with a cavity. Traditional methods use effective two-level systems isolated from more complex atomic level structures. However, alternative strategies allow entanglement to be generated in atoms confined to a single hyperfine manifold. These strategies enable entanglement in ways fundamentally not available to two-level systems but feature extremely slow dynamics due to requiring strongly off-resonant laser fields. Here, I show that equivalent squeezing dynamics can be achieved much closer to resonance, offering entanglement generation over a hundred times faster than typical experiments. Furthermore, the Hamiltonian can be used to speed up the creation of maximally entangled states via adiabatic passage.

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Astrophysics of Galaxies

NGC 6426: Colour-Magnitude diagram and variable star population as indicators of metallicity, distance, and age

A. Arellano Ferro, R. Michel, D. Deras et al. (+3 more)

We present new VI CCD photometry of the globular cluster NGC 6426. The membership status of all point sources and, in particular, of all the variables in the field of view is discussed, including four recently detected variables. The double mode nature of variables V3 and V9 is confirmed and their periods are calculated. The presence of a cluster member anomalous Cepheid (V17) is reported. Employing only likely members we produce a decontaminated colour-magnitude diagram (CMD) differentially dereddened, which enables us to compare it with theoretical predictions and to study the variable stars distribution. The mean cluster metallicity and distance were calculated via the RR Lyrae V-band light curve Fourier decomposition and an I-band calibration of the Period-Magnitude-Metallicity relation. Further, a comparison using a Bayesian approach between theoretical isochrones of Dartmouth Stellar Evolution Database (DSED), with a deep HST CMD, gave us independent estimates of distance modulus, metallicity, colour excess, and cluster age.

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All authors A. Arellano Ferro, R. Michel, D. Deras, M. Vaca Montejano, S. Muneer, I. Bustos Fierro

Atomic Physics

Disorder-induced nuclear-transition doublet at nominally cubic $^{229}$Th sites

Andrei Derevianko

The $^{229}$Th nuclear clock transition is inhomogeneously broadened even at sites of nominally cubic symmetry, where the electric-field gradient of the ideal lattice vanishes. We show that dilute static point-defect disorder produces a doublet with a zero at the quadrupole-free frequency. The doublet is symmetric in the isotropic approximation; size misfit point defects introduce a small lobe asymmetry without removing the zero. Charged and size-misfit defects share inverse-cube scaling and an approximately common normalized profile, whose width separates into a host-controlled background and a term linear in the $^{229}$Th density. In a heavily doped $^{229}$Th:CaF$_2$ crystal [Nature 657, 626 (2026)], the thorium-linked contribution is comparable to the measured 1.1 MHz width; in a lightly doped crystal [arXiv:2606.08870], the 0.9 MHz width bounds the host background. Neither spectrum shows the predicted dip, which points to the presence of extended defects in both crystals. If the predicted dip is resolved, it can provide a nuclear-clock discriminator referenced to the quadrupole-free nuclear transition frequency.

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