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Monday 7 September

Quantum Gases

Limit Cycles in a Photonic Dimer with Tuneable Non-Hermitian Interactions

Kevin J. H. Peters, Peter Schnorrenberg, Daniel Ehrmanntraut et al. (+2 more)

Interactions govern the emergence of collective behaviour in classical and quantum many-body systems. While conservative interactions are well known to generate nonlinear phenomena ranging from self-trapping to pattern formation, it remains largely unexplored whether purely dissipative – i.e., non-Hermitian – interactions can give rise to similarly rich dynamics and nontrivial system states. Here, we experimentally realise tuneable non-Hermitian interactions in two coupled condensates of light confined within a dye-filled double-well microcavity. Local coupling to molecular reservoirs generates the effective dissipative photon interactions. We show that the interplay between coherent tunnelling and interactions stabilises limit-cycle oscillations, a hallmark of nonlinear dynamics traditionally associated with Hermitian nonlinearities. By tuning the reservoir coupling, we map out the dynamical phase diagram comprising stable fixed points and limit cycles, thereby demonstrating direct control over the interaction strength. Our experimentally validated model reveals both supercritical and subcritical Hopf bifurcations, giving rise to hysteresis, bistability and excitability. These results validate dissipative interactions as a mechanism for organising collective nonlinear dynamics in driven-dissipative systems and pave the way towards exploring nonequilibrium many-body physics through controlled dissipation.
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All authors Kevin J. H. Peters, Peter Schnorrenberg, Daniel Ehrmanntraut, Nikolas Longen, Julian Schmitt

Mesoscale and Nanoscale Physics

Steady reservoir-mediated self-trapping of polariton condensates

Pavel N. Kozhevin, Oleg I. Utesov, Igor S. Aranson et al. (+2 more)

Nonequilibrium bosonic condensates of exciton-polaritons generated by tightly focused incoherent optical beams are typically expected to form a stationary ballistically expanding state with the notable exception of experimentally observed compact self-trapped states [Phys. Rev. Lett. 123, 047401 (2019)]. We show that the back-action of the condensate on the optically pumped excitonic reservoir via bosonic stimulated scattering can cause local reservoir depletion, producing a steady condensate confined in a self-induced potential trap. Notably, this self-trapped state is formed by persistent converging rather than radially expanding polariton currents and exists even below the conventionally defined condensation threshold. This state remains steady over nanosecond-scale times and is eventually ejected from the self-induced trap due to a bullet-type instability, enabling spiking neuromorphic dynamics in networks of polariton condensates.
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All authors Pavel N. Kozhevin, Oleg I. Utesov, Igor S. Aranson, Sergey V. Koniakhin, Anton V. Nalitov

Quantum Physics · Cross-listed from cs.CC

Accelerating Fourier–Motzkin elimination: redundancy removal and the choice of variable elimination order

Shashaank Khanna

Fourier-Motzkin elimination computes an inequality description of the projection of a polyhedron onto a subset of its coordinates by eliminating one variable at a time. It is used in several areas of optimisation and computer science, and it is a standard way of obtaining the entropic constraints of a causal structure, where the marginalisation over the latent variables produces such a projection. Its limitation is the growth of the intermediate systems of inequalities, which can be doubly exponential in the number of eliminated variables even though the projection itself grows only as a single exponential. In practice the computational overload of the method therefore depends on two choices: how the redundant inequalities are removed after each step, and the order in which the variables are eliminated. We consider both. We first show, by an explicit example, that Imbert's redundancy test cannot be interleaved with redundancy removal by linear programming. We show that the two methods, however, can be combined soundly if the derivation records used by Imbert's test are re-initialised after every step at which linear programming is used. We then propose a rule for choosing the elimination order of the variables that gives a significant computational advantage, however, at the cost of increased resource usage. We demonstrate this advantage on some random polytopes, where the rule reduces the running time by factors of between 6 and 25 compared with the same elimination under a fixed order. For entropic descriptions of causal structures, with more than 250 inequalities and more than 100 variables to eliminate, our rule keeps the number of inequalities handled at each step one to two orders of magnitude lower than a fixed order.
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Fluid Dynamics · Cross-listed from cs.LG

Structured Extrema Errors in Classical Surrogates for Viscous Burgers: A Physics-Consistent Interpretation

Youssef Oubari

We study the local errors of classical machine-learning surrogate models, which approximate the time evolution of the one-dimensional viscous Burgers equation. Four models are compared on the same prediction task, using the spatial grid values directly: radial basis function (RBF) kernel ridge regression (KRR), linear Ridge, ExtraTrees, and Random Forests. Across all four models, the one-step residual, defined here as the true value minus the predicted value at each grid point, forms clear curved branches near predicted maxima and minima. A more detailed analysis of KRR shows that these errors are much more strongly related to the second spatial derivative, which measures local curvature, than to the first spatial derivative. Near a smooth extremum, predicted value and curvature form a local two-branch fold. Under our local curvature-based model of the residual, this fold predicts a leading-order near-parabolic relation between predicted value and residual. This geometric result motivates a direct test of the Burgers advection (transport) and diffusion (smoothing) terms. For KRR and Ridge, regression tests on held-out trajectories, a control that breaks the spatial alignment of the diffusion term, and a spectral test of high-frequency content are consistent with insufficient viscous smoothing at moderate and high viscosity. In this case, the surrogate retains more small-scale structure than the true future state. The same physical explanation is much weaker for the tree models. Finally, a correction that uses only predicted quantities reduces both one-step error and error during recursive rollout, where each prediction is used as the next input.
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Strongly Correlated Electrons

Vertical quantum confinement in bulk MoS$_2$

Jairo Obando-Guevara, Álvaro González-García, Marcin Rosmus et al. (+5 more)

We experimentally observe quantum confinement states in bulk MoS$_2$ using Angle-Resolved Photoemission Spectroscopy (ARPES). The band structure at the $\overline{\Gamma}$ point reveals quantum well states (QWSs) linked to vertical quantum confinement of the electrons, confirmed by the absence of dispersion in k$_z$ and a strong intensity modulation with photon energy. Notably, the binding energy dependence of the QWSs vs $n$ does not follow the quadratic dependence of a two-dimensional electron gas. Instead, a linear behaviour is observed that is consistent with a parabolic-like quantum well. This confinement arises from the mechanical exfoliation preparation method, which leads to the detachment of a multilayer stack from the underlying bulk. This is confirmed by Density Functional Theory (DFT) calculations. The quantum confinement in bulk-like MoS$_2$ not only offers the opportunity to explore intersubband transitions to exploit optical properties but also provides a means to study fundamental quantum phenomena in multilayer stacks of different thicknesses.
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All authors Jairo Obando-Guevara, Álvaro González-García, Marcin Rosmus, Natalia Olszowska, César González, Miguel Ángel González-Barrio, Antonio Tejeda, Arantzazu Mascaraque

Mathematical Physics · Cross-listed from math.AP

A counterexample to Kenig's conjecture for the Laplace double-layer operator

Matthew J. Colbrook and Siavash Sadeghi

We disprove Kenig's 1994 spectral-radius conjecture for the double-layer operator in every dimension $d\ge2$. For every $t>1/2$ sufficiently close to $1/2$, we construct a bounded simply connected Lipschitz domain with connected boundary such that the double-layer operator on $L^2$ with respect to the surface measure has $\pm \mathrm{i} t$ in its Fredholm essential spectrum. In particular, the essential spectral radius is greater than $1/2$. In the plane, the boundary may be chosen differentiable everywhere and smooth away from a single point. Our planar construction develops a refinement mechanism that produces unbounded growth of adjoint resolvent solutions with fixed forcing while keeping the graph slopes uniformly bounded. A closed recursion for the density and its image under an auxiliary singular integral reduces the growth estimate to a certified inequality for Hermitian $2\times2$ matrices. The certificate uses continuous estimates, exact rational arithmetic and rigorous interval enclosures. Localisation and rescaled graph insertions then produce a weakly null sequence of normalised approximate eigenvectors for the adjoint double-layer operator on one bounded boundary. A compact intertwining relation on Cartesian products of the planar domain with cubes gives the higher-dimensional examples without changing the spectral parameter.
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Quantum Physics · Cross-listed from cs.CC

Promises should be taken seriously: On relativization with promise problems

David Miloschewsky, Supartha Podder and Dorian Rudolph

Relativization is concerned with comparing computational models with black-box access to an oracle. For promise problems, black-box access is not canonical due to inputs outside of the promise being unconstrained. We study two semantics for such access. Under robust queries, a machine must correctly answer regardless of the completion of the problem,, while loose access requires that the internal choices of a machine do not change based on off-promise queries. Our first result separates the language and promise settings. Namely, we construct an oracle $O$ such that $\mathsf{P}^O = \mathsf{BQP}^O = \mathsf{AWPP}^O$, but $\mathsf{PromiseBQP}^O\not\subseteq\mathsf{PromiseP}^O_{\mathsf{/poly}}$. In particular, $\mathsf{BPP}^O = \mathsf{BQP}^O$, but $\mathsf{PromiseBQP}^O \neq \mathsf{PromiseBPP}^O$, showing that results for languages need not transfer to promises. Next, we use loose queries to strengthen the upper bound on the Quantum-Classical Polynomial Hierarchy from $\mathsf{P}^{\mathsf{PP}^{\mathsf{PP}}}$ to $\mathsf{QCPH} \subseteq \mathsf{BP\cdot PP} \subseteq \mathsf{PromiseBPP}^{\mathsf{PP}}$. The same proof also shows $\mathsf{PP}^\mathsf{PromiseBQP} = \mathsf{PP}$. Additionally, we show that $\mathsf{PromiseBQP}$, even when given quantum advice, is self-low under robust queries. Finally, we exhibit an obstruction to transferring language-level counting results to promise classes. Although $\mathsf{AWPP}$ and $\mathsf{APP}$ are low for $\mathsf{PP}$, a corresponding promise analogue would collapse the counting hierarchy as $\mathsf{GapP} \subseteq \mathsf{FP}^{\mathsf{PromiseAWPP}}$. This motivates the introduction of $\mathsf{PromisePostBQP^*}$, which restricts $\mathsf{PostBQP}$ to input-indepencent postselection. By showing that it is low for \PP, we obtain $\mathsf{PP}^{\mathsf{PromiseYQP^*}} = \mathsf{PP}$.
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High Energy Physics (Phenomenology)

Recent applications of the gradient flow

R. Harlander and A. Shindler

The gradient flow provides a gauge- and O(4)-invariant ultraviolet regulator for QCD. This opens new opportunities for combining non-perturbative lattice calculations with perturbative results, in particular in the context of an operator-product expansion (OPE). We review the concepts behind this and argue that, within the operator basis of a given OPE, the flow-time dependence of the conversion between flowed and regular Wilson coefficients is exact at each perturbative order. Recent applications to parton distribution functions, heavy-meson observables, quark masses, and gradient-flow definitions of the strong coupling are discussed. Finally, the perturbative formulation of the Ricci flow in quantum gravity and its application to the study of non-Gaussian fixed points is reviewed.
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Optics

Spectro-temporal shaping of broadband optical wavepackets via programmable on-chip photonics

Bruno P. Chaves, Jérémy Saucourt, Van Thuy Hoang et al. (+9 more)

The ability to precisely shape the properties of light over multiple degrees of freedom constitutes the foundation of modern photonic architectures. Broadband sources with addressable spectro-temporal content are for instance critical for applications spanning biomedical imaging, material processing, lidar, and ultrafast spectroscopy, but also key enabling technologies in quantum information processing, high-capacity communications, and optical computing. Yet, flexible and adjustable spectro-temporal shaping so far remains a significant challenge, as it requires the simultaneous manipulation of both frequency and temporal domains across broad spectral bandwidths and extended timescales, from femtoseconds to nanoseconds. Importantly, conventional approaches to spectro-temporal processing typically rely on bulky and complex optical systems that lack scalability and flexibility, ultimately hampering their utility for applications requiring addressable multiphotonic processes. Here, we present a framework for spectro-temporal wavepacket control over a broad bandwidth, merging programmable integrated photonics with high-speed optical characterization. Leveraging machine leaning for tailoring nonlinear pulse propagation, we experimentally report scalable and on-demand shaping of broadband ultrafast pulse patterns. We demonstrate the efficacy of our method through reconfigurable power across 400 nm bandwidth with picosecond resolution, with promises for applications where precise control over light is paramount, in particular those needing versatile and controllable multiphoton excitations.
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All authors Bruno P. Chaves, Jérémy Saucourt, Van Thuy Hoang, Alexis Bougaud, Yassin Boussafa, Erwan Ferrandon, Sai T. Chu, Brent E. Little, David J. Moss, Roberto Morandotti, Vincent Couderc, Benjamin Wetzel

Solar and Stellar Astrophysics

SN 2024afyu interpreted as a Pair Instability Supernova

P. J. Pessi, S. Barmentloo, Ł. Wyrzykowski et al. (+63 more)

Pair-instability supernovae (PISNe) are the predicted explosions of very massive stars triggered by electron-positron pair production. Numerous transients have been proposed as PISN candidates, yet none has provided unambiguous confirmation of this explosion mechanism. The predicted strengths of nebular emission lines offer a powerful means of testing the PISN scenario. We investigate the nature of SN 2024afyu, a nearby (z = 0.0085), long-lived (trise = 85 +- 11.7 days) SN with peculiar spectral evolution, with the aim of identifying its powering mechanism. We analyse multi-band photometry and optical and near-infrared spectroscopy from shortly after explosion to the nebular phase (around 500 days past peak). Besides early appearance of [Ca II] features, we identify a number of sulfur and silicon emission lines, for which we estimate electron temperatures and elemental masses. SN 2024afyu has an inferred 56Ni mass of around 0.4 to 1.0 solar masses and an inferred sulfur mass of the order of 3 solar masses, substantially larger than expected for conventional core-collapse explosions. SN 2024afyu is photometrically similar (although fainter, M_Peak(r) = -18.9 +- 0.04 mag) but spectroscopically distinct to other proposed PISNe. Yet, existing PISN models broadly reproduce several key characteristics, including the overall spectral appearance and broad photometric evolution. SN 2024afyu is a strong PISN candidate, since alternative scenarios would struggle to explain the combination of broad light curve, large intermediate-mass-element abundance, and general spectroscopic evolution. The discrepancies between the observations and currently available theoretical models highlight the need for new PISN calculations spanning a wider range of progenitor masses, metallicities, mixing prescriptions, and circumstellar environments.
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All authors P. J. Pessi, S. Barmentloo, Ł. Wyrzykowski, S. Schulze, J. Sollerman, A. Gangopadhyay, P. J. Mikołajczyk, S. Rose, K. Kotysz, C. Fremling, A. Jerkstrand, R. Lunnan, L. Yan, C. Fransson, J. L. Wise, M. Dubey, K. Misra, A. P. Cotter, D. Athanasopoulos, A. Bochenek, M. Bronikowski, U. Burgaz, W. Burzynski, J. M. Carrasco, E. Concepcion, C. Galdies, A. F. Gillan, A. Gkini, E. Gkiokas, E. Głowacki, F-J. Hambsch, J. Japelj, N. Karaman, P. King, S. Kurowski, C. Liu, M. Maskoliunas, Z. McGrath, M. Mihelčič, M. Nikolajuk, W. Ogloza, E. Pakštienė, U. Pylypenko, A. Pucek, N. Rehemtulla, R. M. Rich, A. O. Simon, A. Singh, C. Skoglund, E. Stonkute, Y. Stsefanenka, P. Szober, K. Tsalapatas, B. F. A. van Baal, C. Ventura, K. Vrontaki, A. Wozniak, J. Zdanavicius, S. Zola, E. C. Bellm, J. Castaneda Jaimes, M. J. Graham, G. Helou, F. J. Masci, J. N. Purdum, R. Riddle

High Energy Physics (Theory)

Wilson loops, M2-branes and strings

Alexia Nix

We establish a universal approach for studying the semiclassical quantization of both probe M2-branes and fundamental strings in asymptotically AdS$_{4}$ backgrounds. On the field theory side, their partition functions are dual to the vacuum expectation value of half-BPS Wilson loops of a class of three-dimensional $\mathcal{N}\geq 2$ Chern-Simons-matter theories. Utilizing this universal approach we arrive at novel predictions for the semiclassical behaviour of the Wilson loop or upon availability match our results with the previously obtained expressions via supersymmetric localization. We also show that the correct choice of holographic ensemble suggests that the semiclassical quantization of probe M2-branes yields the full perturbative answer in the rank of the gauge group $N$ for the dual Wilson loop. 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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Strongly Correlated Electrons

Hysteretic Coherence Collapse Across the First Order CDW Transition in 1T-TaS2

Turgut Yilmaz, Anil Rajapitamahuni, Asish K. Kundu et al. (+2 more)

The first order phase transition between the nearly commensurate (NC-CDW) and commensurate (C-CDW) charge density wave phases in 1T-TaS2 underpins its exotic electronic behavior, yet the spectroscopic evolution of the low energy electronic structure across this transition remains crucial to understand. Using angle resolved photoemission spectroscopy (ARPES), we investigate the low temperature C-CDW phase, characterized by a flat band commonly associated with the lower Hubbard band and a distinct in-gap state located closer to the Fermi level. Photon energy dependent measurements distinguish these two low energy features through their different spectral weight evolution. Temperature dependent ARPES across heating and cooling cycles reveals that the in-gap state undergoes an abrupt collapse upon heating into the NC-CDW phase and re-emerges sharply upon cooling back into the C-CDW phase. This pronounced thermal hysteresis provides direct spectroscopic evidence of the first order nature of the transition. Furthermore, the disappearance and recovery of the in-gap state closely track the corresponding changes in resistivity, highlighting its intimate connection to the electronic reconstruction across the C-CDW/NC-CDW phase transition.
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All authors Turgut Yilmaz, Anil Rajapitamahuni, Asish K. Kundu, Menka Jain, Elio Vescovo

High Energy Physics (Theory)

Spherical DAHA as an algebra of framed BPS states

Kunal Gupta and Pietro Longhi

Line operators of 4d $\mathcal{N}=2$ theories of class $\mathcal{S}$ of type $A_{N-1}$ in a half Omega background provide a physical model for $SL_N$ skein algebras. In this paper we extend this correspondence to $GL_N$ skein algebras and prove that the $GL_2$ skein algebra of the punctured torus is isomorphic to the $GL_2$ spherical double affine Hecke algebra ${{\mathbf{S}\ddot{\mathbf{H}}}}^{q,t}_2$. The construction is based on $\mathfrak{q}$-nonabelianization for the $SU(2)$ $\mathcal{N}=2^*$ gauge theory, which realizes the skein algebra as a quantum torus algebra associated with the Seiberg-Witten curve. Different regions of the Coulomb branch yield distinct presentations of ${{\mathbf{S}\ddot{\mathbf{H}}}}^{q,t}_2$. These range from the Macdonald $q$-difference module in Fenchel-Nielsen (weak coupling) charts to cluster-type realizations in Fock-Goncharov (strong coupling) charts. Transitions between these descriptions are governed by the vanilla BPS spectrum of the $\mathcal{N}=2^*$ theory via framed wall-crossing, which provides a unified physical framework for several representations of spherical DAHA.
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High Energy Physics (Experiment)

Solid-state nuclear magnetic resonance search for axion-like dark matter with broadband SQUID magnetometry

Andrew J. Winter, János Ádám, Deniz Aybas et al. (+5 more)

We report the results of an experimental search for ultralight axion-like dark matter in the mass ranges 19.5–20.5 and 21.5–22 neV. The Cosmic Axion Spin Precession Experiment-electric probes the axion-nuclear electric dipole moment coupling. We perform solid-state nuclear magnetic resonance on $^{207}$Pb spin ensembles which reside in a polarized ferroelectric crystal. The background axion-like dark matter field induces an oscillating torque on the $^{207}$Pb spins via the electric dipole moment coupling $g_{d}$. The experiment is calibrated with pulsed magnetic resonance measurements covering two frequency bands (4.6–5.0 and 5.2–5.3 MHz) that correspond to the axion Compton frequencies associated with the identified axion mass ranges. By sweeping the leading magnetic field applied to the sample, we are able to detect the $^{207}$Pb nuclear magnetic resonance in these frequency ranges using a superconducting quantum interference device, inductively coupled to the sample with a broadband circuit. We establish the upper bounds $|g_{d}| < 4\times 10^{-4}$ GeV$^{-2}$ with 95% confidence in these frequency bands. Our results demonstrate the detection and small-tip angle calibration of low-field $^{207}$Pb nuclear magnetic resonance, allowing for sensitivity to axion-like dark matter in the nanoelectron-volt axion mass range.
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All authors Andrew J. Winter, János Ádám, Deniz Aybas, Dmitry Budker, Derek F. Jackson Kimball, Surjeet Rajendran, Arne Wickenbrock, Alexander O. Sushkov

Physics and Society

Latent geometry organizes higher-order interactions

Berné L. Nortier, Jasper van der Kolk, Robert Jankowski et al. (+4 more)

Higher-order structures offer a natural representation of complex systems that involve interactions between groups of different sizes. A widespread feature of their higher-order structure is nestedness, whereby interactions involving smaller groups are contained within larger ones. Yet, why interactions of different orders organise into nested structures remains largely unexplained. Here, we introduce an analytically tractable geometric model of higher-order networks in which a single latent geometric space couples interactions across orders, leading to the spontaneous emergence of nestedness. We show analytically and numerically that nestedness undergoes a transition between a nested geometric regime, where it remains finite in the thermodynamic limit, and a regime where it vanishes with system size. In this regime, we uncover a weakly geometric range characterized by an anomalously slow finite-size decay, allowing substantial nestedness to persist in finite systems even when its asymptotic value vanishes. Finally, with a single geometric coupling parameter, the model reproduces the nestedness profiles observed in real-world hypergraphs across different domains. Our results reveal latent geometry as a simple organising principle underlying the nested organisation of higher-order interactions.
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All authors Berné L. Nortier, Jasper van der Kolk, Robert Jankowski, Simon Dobson, M. Ángeles Serrano, Federico Battiston, Marián Boguñá

Classical Physics

Conformal Symmetry and Planck's Thermal Radiation in Classical Physics

Timothy H. Boyer

Thermal radiation is discussed for a classical scalar field. Dilation and acceleration appear in conformal symmetry, and so are treated in connection with zero-point radiation and equilibrium thermal radiation. Classical zero-point radiation is completely invariant under dilation in a inertial frame. However, in a Rindler frame, zero-point radiation takes a different form which is related to Planck's thermal spectrum with temperature T related to acceleration. Traditionally, zero-point radiation is said to take a thermal (Unruh) form in a Rindler frame. However, the classical viewpoint indicates that zero-point radiation in a Rindler frame requires a divergent frequency spectrum and so is not thermal radiation. The Unruh form suggests an additional classical thermal spectrum satisfying the Stefan-Boltzmann relation.
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High Energy Physics (Experiment)

Real-time lepton identification at LHCb in Run 3 using Lipschitz neural networks

Adrian Casais Vidal, Kate A. Richardson, Maarten Van Veghel et al. (+3 more)

The LHCb physics program in Run 3 relies critically on the efficient real-time selection of events containing muons and electrons, which are key signatures in a wide range of heavy-flavor and exotic decay processes. The LHCb Run 3 detector now operates with a fully software-based trigger that processes the complete detector readout at the LHC bunch-crossing rate, with the first trigger stage executed on GPUs. In this environment, particle-identification algorithms must achieve high efficiency and background rejection while satisfying stringent constraints on throughput and memory footprint. We present algorithms for muon and electron identification in the LHCb Run 3 GPU trigger based on Lipschitz-constrained neural networks. Separate networks are developed for muons and electrons and are trained using simulated events. Their performance is evaluated relative to the previous baseline algorithms, demonstrating improved discrimination across a wide range of kinematic regions while remaining compatible with the requirements of real-time GPU execution.
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All authors Adrian Casais Vidal, Kate A. Richardson, Maarten Van Veghel, Marco Santimaria, Marianna Fontana, Mike Williams

Statistical Mechanics

Tensor network investigation of the monomer-dimer model on the honeycomb lattice

De-Zhang Li, Jie Liu and Xin Wang

The monomer-dimer model is one of the most well-known unsolved lattice models. In this paper we study the monomer-dimer model on the honeycomb lattice using the tensor network method, in the case that the dimer and monomer activities are 1. The monomer-dimer configurations are exactly mapped into the ground states of the antiferromagnetic Ising model on the Kagomé lattice in the critical field $H_{\rm{ex}}=4J$, and the tensor network is constructed based on the local ground states of each Ising triangle. The VUMPS approach is employed to contract the tensor network, providing a high-precision result of the monomer-dimer problem. We also revisit the edge coloring problem on the honeycomb lattice and discuss its relationship to the monomer-dimer model. Finally we formulate the monomer-dimer problem in the language of the sixteen-vertex model, and discuss the non-integrability of the general monomer-dimer model and the integrability of the pure dimer model.
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Quantum Physics

A Novel Steganography Scheme Using Quantum Hilbert Transform

Nitin Jha and Abhishek Parakh

The main goal of steganography is to transmit hidden messages in legitimate-looking communication messages. Phase-domain information hiding, however, has not been fully explored for quantum systems. This work introduces a finite-dimensional Quantum Hilbert Transform (QHT) as a unitary phase operator based on the Quantum Fourier Transform. Using this construction, we develop a QHT-based quantum steganography scheme that embeds classical bits as weak signed phase perturbations of quantum cover states. Bob recovers the hidden message through binary state discrimination, block aggregation, and classical error-correcting decoding.
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Quantum Physics

Few-Body Decay Dynamics in Colloidal CsPbI3 Quantum-Dot Clusters

Emma Daggett, Christian M. Lange, Nicholas Favate et al. (+7 more)

Colloidal perovskite quantum dots combine bright emission with the ability to self- assemble into closely spaced structures, enabling radiative dynamics to be studied from isolated emitters to few-dot clusters. Here, we characterize CsPbI3 perovskite quan- tum dots from isolated emitters to self-assembled clusters containing up to ten dots. We estimate the number of emitters in each cluster using a combination of photon autocorrelation, blinking statistics, and emission brightness. Compared with isolated dots, clusters containing two or more emitters exhibit biexponential decay, with a short lifetime that decreases with emitter number and an additional long-lived component. Photon-correlation Fourier spectroscopy shows that the single-dot emission remains far from the lifetime-limited regime. Nevertheless, we observe emitter-number-dependent decay dynamics even in this low-coherence regime. Together, these measurements es- tablish self-assembled perovskite quantum-dot clusters as a platform for studying how collective optical behavior emerges between the single-emitter and ensemble limits
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All authors Emma Daggett, Christian M. Lange, Nicholas Favate, Ankit Kundu, Ishita Agarwal, Arya D. Keni, Adhyyan S. Mansukhani, Christina W. Li, Libai Huang, Jonathan D. Hood

Quantum Physics

Riemannian optimization for linear optical problems

Pablo V. Parellada

Many applications of linear optics in quantum science involve searching for some optimal configuration of a multiport interferometer. For example, to find heralded state preparations, one can optimize the interferometer to maximize the fidelity and success probability of the state preparation. In this paper, we derive a closed analytical formula for the Riemannian gradient of any differentiable function defined over the interferometer unitaries. We use this gradient in Riemannian optimization algorithms, such as gradient descent or BFGS, to find the optimal setup of the interferometer. As an interesting use case, we search for linear optical state preparations, improving some of the success probabilities reported in the literature for NOON or photon catalysis preparations. Finally, we show that our optimizer is orders of magnitude faster than other methods in the literature, opening the door for solving linear optical problems involving more modes and photons.
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Applied Physics

Wave-based reading of mechanical memory in multistable mass-in-mass metamaterials

Audrey Watkins, Giovanni Bordiga, Vincent Tournat et al. (+1 more)

Mechanical metamaterials with integrated bistable elements have emerged as promising platforms for mechanical information storage, where transitions between stable states encode information as mechanical bits. While it has been shown that information can be written into such metamaterials by applying global inputs, existing readout strategies rely predominantly on visual inspection. Here, we experimentally demonstrate a mass-in-mass bistable metamaterial with state-dependent stiffness that enables both writing and reading of mechanical information using only boundary-applied dynamic excitations. We further show that such metamaterial architecture functions as both a mechanical sensor of input amplitude and a reconfigurable wave-control device. Together, these results highlight the versatility of bistable metamaterials as multifunctional platforms that integrate mechanical memory, sensing, and adaptive wave manipulation.
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All authors Audrey Watkins, Giovanni Bordiga, Vincent Tournat, Katia Bertoldi

Lattice Field Theory

Gauge field digitization in the Hamiltonian limit

Attila Pasztor and David Pesznyak

Quantum computers can circumvent the numerical sign problem in gauge theories at finite density or in real time. Quantum simulations of gauge theories require a finite-dimensional representation of continuous gauge fields. Replacing a continuous gauge group by a finite subgroup can substantially reduce the required quantum resources, but introduces digitization errors that must be controlled in the Hamiltonian, or continuous-time, limit. Previous studies, using the isotropic Euclidean lattices showed that the freezing transition of the discrete subgroup can make it a bad approximation for the continuous group at large Euclidean couplings. Here, we study the digitization of U(1) by its Z($N$) subgroups in 2+1 dimensions using anisotropic Euclidean lattices. We derive the trajectories of the spatial and temporal gauge couplings along which the Hamiltonian limit is approached at fixed Hamiltonian coupling. While the temporal coupling exhibits power-law scaling in the continuous U(1) theory, it grows only logarithmically for finite Z($N$). Using classical lattice simulations and exact diagonalization, we verify that these trajectories reproduce the corresponding Hamiltonian theories. We find that the freezing transition persists in the Hamiltonian limit of discrete gauge groups and that finite-$N$ theories can differ substantially from U(1) even outside the frozen regime, in contrast to the behavior on isotropic Euclidean lattices, where for small couplings, the discrete group provides a very accurate approximation of the continuous group. Our results provide a classical benchmark for quantifying the systematic errors due to gauge-field digitization in quantum simulations.
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General Relativity and Quantum Cosmology

Nonradial oscillations of realistic anisotropic neutron stars: Polar modes

L. M. Becerra, José F. Rodríguez-Ruiz, E.A. Becerra-Vergara et al. (+1 more)

In this work, we study the polar perturbations of static, spherically symmetric neutron stars with anisotropic pressure in full general relativity, including linear-order perturbations of both the metric and the fluid. We calculate the $f$-mode frequencies and the corresponding damping times using a consistent treatment of the perturbation of the radial vector $k^\alpha$. In particular, its Lagrangian perturbation $\Delta k^\alpha$ is determined by the metric perturbations and the fluid Lagrangian displacement and is constrained to the $(\tilde{u},\tilde{k})$ plane, where $\tilde{u}^\alpha$ is the normalized fluid four-velocity. This constraint introduces an additional dynamical degree of freedom into the perturbation equations. Considering three equations of state and the Horvat and Bowers-Liang prescriptions for pressure anisotropy, we find that the $f$-mode frequency increases with stellar mass, ranging from $1$ to $3$~kHz, while the damping time decreases, ranging from $0.5$ to $1.25$~s. Increasing anisotropy, in the sense of tangential pressure exceeding radial pressure, generally lowers the oscillation frequency, while its effect on the damping time depends on the anisotropy prescription: the damping time decreases with increasing anisotropy for the Horvat model but increases with increasing anisotropy for the Bowers-Liang model. We further find quasi-universal relations between the real and imaginary parts of the $f$-mode frequency, $M\omega_R$ and $M\omega_I$, and the stellar compactness $\mathcal{C}=M/R$, which are largely insensitive to the equation of state. Polynomial fits to these relations achieve an accuracy better than $10\%$, providing a simple phenomenological framework for constraining neutron-star pressure anisotropy through future asteroseismology observations.
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All authors L. M. Becerra, José F. Rodríguez-Ruiz, E.A. Becerra-Vergara, F. D. Lora-Clavijo

Quantum Physics

Measurement-induced remote activation of nonclassicality

Sudip Chakrabarty

Nonclassicality, defined through nonpositivity of quasiprobability distributions such as the Wigner and Kirkwood-Dirac distributions, underlies key quantum advantages. We show that it can be remotely activated: local measurements by a correlated partner alone can drive a party whose reduced state is classical into a genuinely nonclassical conditional state. For two-qubit systems we obtain closed forms for the maximal single-branch effect and for its probability-weighted average under the best two-outcome projective measurement, the latter proven optimal over all measurements when the shared state carries no local bias. Local noise on the steered party, evaluated relative to its own noise-updated reference basis, can enhance the effect when non-unital and misaligned with that party's axis, whereas no unital channel ever helps. This nonclassicality is shown to unlock, for the same reference observable, anomalous weak values unavailable to the unsteered state under arbitrary postselection. An exactly solvable hybrid qubit-oscillator model shows the same mechanism generates Wigner negativity. These results identify measurement-induced steering as an operational resource for remotely activating nonclassicality.
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General Relativity and Quantum Cosmology

NRSur7dq4v2: A multi-domain precessing surrogate model with improved accuracy

Abhishek Ravishankar, Vijay Varma, Scott E. Field et al. (+5 more)

Numerical relativity simulations provide the most accurate waveforms for binary black hole coalescences, but are prohibitively expensive for direct use in gravitational-wave data analysis. Surrogate models overcome this cost, and NRSur7dq4 is commonly used in parameter estimation for this reason. However, there is evidence in the literature that NRSur7dq4's accuracy could be improved in the merger-ringdown portion of the waveform, which is particularly important for the analysis of high-mass binary black hole events. Motivated by these observations, we construct NRSur7dq4v2, a multi-domain extension of NRSur7dq4 in which overlapping temporal subdomains allow tighter, independent error control over the inspiral and merger-ringdown portions of the waveform before they are smoothly combined. To assess the new model's performance in the merger-ringdown regime, we infer the mass and spin of the remnant black hole from quasi-normal fits to the ringdown portion of the surrogate waveform. We find that NRSur7dq4v2 produces significantly improved remnant mass and spin estimates, with gains of roughly factors of $3$ to $10$ over NRSur7dq4. Compared to NRSur7dq4, NRSur7dq4v2 also includes modes up to $\ell=5$, includes more accurate modeling of certain subdominant modes, and introduces a runtime model-complexity feature that gives users direct control over the tradeoff between evaluation cost and accuracy. Finally, alongside the model development, we have optimized the gwsurrogate package to achieve a fourfold speedup for precessing surrogates. The resulting precessing surrogates called through gwsurrogate are now slightly faster than their LALSimulation counterparts.
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All authors Abhishek Ravishankar, Vijay Varma, Scott E. Field, Keefe Mitman, Nils Deppe, Leo C. Stein, Michael Boyle, Mark A. Scheel

High Energy Physics (Theory)

ABJM/BMN Index Matching in the Plane-Wave Limit

Chi-Ming Chang and Kangning Liu

We establish coefficientwise equality between the refined supersymmetric indices of ABJM theory and the BMN matrix model in the plane-wave limit at every fixed positive Chern-Simons level k. For multi-membrane families with fixed multiplicities, and hence fixed finite ABJM gauge rank, the equality holds as all longitudinal momenta tend to infinity with their pairwise differences fixed. Scalar-dressed equal-flux ABJM monopoles correspond to BMN vacua of fuzzy-sphere membranes: multiplicities count coincident membranes, whereas flux magnitudes give the momentum per membrane along the M-theory circle. At the index level, the associated Higgs residues yield a diagonal-holonomy integral for the ABJM plane-wave contribution, whose monopole-harmonic kernel agrees with the BMN matrix-harmonic kernel up to the finite BMN upper-spin cutoff. At finite momentum, the full index difference splits into the non-plane-wave remainder and the harmonic tail above this cutoff. Increasing k shifts the former to higher fugacity grade without changing the surviving kernel or the cutoff contribution. This gives a coefficientwise, multi-membrane extension of the earlier single-membrane index relation.
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Solar and Stellar Astrophysics

Precise physical and kinematical parameters of massive eclipsing binaries in the Small Magellanic Cloud

M. Kaya, Ö. Çak{\i}rl{\i}, B. Hoyman et al. (+3 more)

The formation of massive stars serves an important field of study, requiring research into whether these stars need to form together within clusters of low-mass stars or if they are able to form independently. Currently, there has been an increase in the number of massive stars found far from clusters in the Milky Way (MW) and Small Magellanic Cloud (SMC). The existence of isolation and composition in binary systems is an uncommon phenomenon among massive stars, and their rare occurrence presents valuable insights that are regarded as evidence in this field. This research looks for ways to increase the catalogue of identified massive stars in eclipsing binaries, particularly those that show significant indications of isolation. For the definition of the first step, we are analysing the eight double-lined spectroscopic binaries in the SMC, as detailed in the OGLE variable star catalogues, with the goal of identifying their astrophysical properties. Later, we examine the expected locations and characteristics of binary stars thought to be part of a cluster, using absolute parameters and a cross-validation approach to determine the connection between kinematic analysis and these parameters. If the kinematic connection with the cluster and the physical parameters match precisely with the cluster's isochrone, such stars could act as reliable standard candles for determining the cluster's distance and age.
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All authors M. Kaya, Ö. Çak{\i}rl{\i}, B. Hoyman, O. Özdarcan, T. Yontan, R. Canbay

Quantum Physics

Quantifying Margenau–Hill Nonclassicality

Sudip Chakrabarty

Quasiprobability distributions offer a useful way of describing nonclassical features of quantum systems through their departure from classical probability theory. In this work, we investigate the quantification of nonclassicality associated with the Margenau–Hill quasiprobability (MHQ) distribution using its moments, without requiring reconstruction of the full distribution. First we introduce the logarithmic MHQ negativity as a quantifier of nonclassicality, and then derive a hierarchy of rigorous lower bounds in terms of low-order moments. Within the resulting hierarchy, the fourth-moment bound is the strongest among the bounds based on even moments. For qubits, we further derive a tight upper bound on the exact MHQ negativity and identify the corresponding extremal state. We also obtain an optimal positivity threshold based on the fourth moment for arbitrary pairs of qubit observables. Finally, we show that the relevant moments admit exact multicopy representations, providing a route to their estimation using interferometry or classical shadow techniques. Our results establish a moment-based framework for extracting quantitative information about MHQ negativity from a finite set of low-order observables.
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Astrophysics of Galaxies

The Role of Dark Matter in Driving Disk Perturbations: Application to LMC-SMC Like Galaxy Interactions

Himansh Rathore, Hayden R. Foote, Gurtina Besla et al. (+6 more)

Dark-matter (DM) models predict that satellite galaxies distort their host's DM halo. As such, both the satellite and the distorted halo can perturb the host's stellar disk. The LMC-SMC system is a nearby $\sim1:10$~mass-ratio binary with a well-constrained orbit and well-characterized LMC disk perturbations. Hence, the system offers unique opportunities to test DM theory, provided the impact of halo torques on the LMC's disk can be characterized along with the SMC's torques. We use halo Basis Function Expansions (BFEs) of an N-body simulation of an isolated LMC-SMC-like interaction to quantify the time-dependent torques exerted on the LMC's disk by the SMC and the LMC's DM halo. We find that the halo torques arise from the quadrupole halo distortion, and the inner (R$<6$ kpc) LMC disk warps are the most promising probe of this quadrupole. For the first time, we construct a BFE to quantify the LMC's disk perturbations resulting from the SMC and halo torques. We find that the LMC's disk is significantly perturbed prior to the Clouds' Milky Way infall, possessing warps with a mean vertical extent of $\sim1$ kpc. Finally, we apply multi-channel singular spectral analysis (mSSA) to the time-series of the disk BFE coefficients, halo quadrupole, and the LMC-SMC orbit. mSSA successfully separates the temporal evolution of the LMC warps into components correlated with the halo versus the SMC. Our framework identifies correlated evolution between the LMC's halo distortions and the LMC's disk perturbations, enabling the Clouds to be a precision laboratory for DM physics.
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All authors Himansh Rathore, Hayden R. Foote, Gurtina Besla, Silvio Varela-Lavin, Nicolas Garavito-Camargo, Martin D. Weinberg, Facundo A. Gomez, Kathryne J. Daniel, Chervin F.P. Laporte