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Physics

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Saturday 25 July

General Relativity and Quantum Cosmology

Optical Appearance of a Rotating Black Hole in Nonlinear Electrodynamics Surrounded by Thin Accretion Disks

Abdul Malik Sultan, Manahil Ali, Muhammad Israr Aslam et al. (+1 more)

This work investigates the optical appearance of a rotating black hole (BH) in nonlinear electrodynamics (NED) using two illumination models, namely a celestial sphere and a thin accretion disk. The BH images are constructed using a backward ray-tracing method together with a fisheye camera model. We examine the effects of the electric charge $Q$ and the NED parameter $\beta$ on the event horizon, shadow, photon ring, and optical appearance for both prograde and retrograde accretion flows. The results indicate that an increase in $\beta$ leads to a larger shadow radius with reduced distortion, whereas increasing $Q$ decreases the shadow size and enhances its deformation. These features are further quantified through the shadow radius and distortion parameter. We also analyze the direct and lensed images of the thin accretion disk, together with their corresponding redshift distributions and emission bands. The redshifted emission is found to dominate the observed images, while the blueshifted region is confined to the vicinity of the photon ring. Our results demonstrate that both $Q$ and $\beta$ leave distinct signatures on the optical appearance of rotating NED BHs, providing useful insights for future high-resolution observations.
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All authors Abdul Malik Sultan, Manahil Ali, Muhammad Israr Aslam, Zi-Chao Lin

Atomic Physics

Protocols of coherent motion control for an interaction-driven Rydberg gate

Valentin Magro, Wojciech Adamczyk and Sylvain de Léséleuc

Generating entanglement between two Rydberg atoms is at the core of neutral-atom quantum computers. Current two-qubit gates operate in the Rydberg-blockade regime, in which the full strength of the van der Waals interaction between the two Rydberg atoms is not directly exploited, to avoid sensitivity to the position noise of the tweezer-trapped atoms, at the cost of a longer time spent in the Rydberg state. Here, we propose a set of techniques based on coherent control of the atomic motion obtained by combining optical tweezers and a two-dimensional optical lattice, and a sequence of multiple on/off pulses. The protocols keep the two-qubit gate error contribution from position noise below $10^{-4}$, heat the atom by less than~$\Delta n = 0.01$, while being robust to alignment errors of the potential up to $50$~nm and thermal excitation up to $\bar{n} = 3$. This toolbox opens the path for new two-qubit Rydberg gates directly, or partially, driven by the interaction, in which the atoms spend only $\sim 10$~ns in the Rydberg state, minimizing the increasingly dominant error source originating from its finite lifetime.
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Instrumentation and Methods for Astrophysics

Output-Stage Design Optimization for High-Sensitivity SiSeRO CCDs and SiSeRO Active Pixel Sensors

Tanmoy Chattopadhyay, Sven Herrmann, Kevan Donlon et al. (+16 more)

The Single electron Sensitive Read Out (SiSeRO) technology is a new device class designed to support the needs of future X-ray and optical astronomical telescopes that will require fast, low-noise, megapixel spectro-imagers. Developed at MIT Lincoln Laboratory, in collaboration with Stanford University and MIT, the first generation SiSeRO-CCD (charge-coupled device) prototypes achieved a charge/current conversion gain of 700$-$800 pA per electron, an equivalent noise charge (ENC) of around 3.5 electrons root mean square (RMS), and a full width half maximum (FWHM) energy resolution of approximately 130 eV at 5.9 keV at a readout speed of 625 kpix/s. Utilizing Repetitive Non-Destructive Readout (RNDR), these same devices also demonstrated sub-electron noise performance (ENC$<$0.5 electrons RMS) at a readout speed of 10 kpix/s. We present the results of device simulations for next-generation SiSeRO CCD output stages that optimize the sensing transistor and its internal gate geometry to enhance noise and speed performance. Further, the goal is to develop a SiSeRO active pixel sensor (APS) that combines the proven X-ray performance of CCDs with the architectural advantages of an APS. Enabling this requires substantial design updates, for example, incorporating two SiSeRO amplifiers side by side on each pixel and shuffling the charge between them to support RNDR. We discuss our device simulation framework and design parameter optimization in the first-generation SiSeRO devices.
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All authors Tanmoy Chattopadhyay, Sven Herrmann, Kevan Donlon, Ilya Prigozhin, Peter Orel, Steven W. Allen, Marshall W. Bautz, Michael Cooper, Catherine E. Grant, Beverly LaMarr, Christopher Leitz, Eric D. Miller, R. Glenn Morris, Abigail Y. Pan, Tonya L. Peshel, Artem Poliszczuk, Gregory Prigozhin, Haley R. Stueber, Keith Warner

Mathematical Physics

$\mathcal{P}(\Phi)_2$ Theory from many-body quantum Gibbs states

Phan Thành Nam, Zhilin Yang and Xiangchan Zhu

We derive the $\mathcal{P}(\Phi)_2$ measure on the two-dimensional unit torus as the rigorous limit of many-body quantum Gibbs states. In particular, the quantum model corresponding to the $\Phi^{2p}_2$ measure is formulated in the grand-canonical ensemble with a general symmetric $p$-body interaction potential which is not required to have a factorized form. Unlike in the $\Phi^4_2$ case investigated by Fröhlich–Knowles–Schlein–Sohinger in \cite{FKSS25}, in the treatment of higher-order interactions, Wick renormalization generates a full hierarchy of lower-order interactions which we organize systematically using a graphical formalism. One key ingredient of our analysis is a logarithmic stability estimate for both the nonlocal Hartree functional and the many-body Hamiltonian that is uniform in the interaction range, allowing us to use the positivity of the leading $p$-body interaction to control all lower-order terms generated by the Wick counterterms.
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Quantum Physics

Digital techniques for the frustrated Ising ring: the role of counter-diabatic terms

Kiran Thengil, Vincenzo Roberto Arezzo and Giuseppe E. Santoro

We investigate the role of local counter-diabatic (CD) terms in enhancing the performance of discrete-time digital protocols for a frustrated Ising ring, a system with an exponentially small spectral gap that acts as a bottleneck for conventional quantum annealing. The techniques investigated range from a digitised version of a fixed-schedule protocol, including lowest-order analytical CD terms, all the way to a full-fledged Quantum Approximate Optimisation Algorithm (QAOA), including variational CD terms (DC-QAOA). By analyzing the resulting residual energy, we show that DC-QAOA combined with Chopped RAndom Basis (CRAB) quantum control techniques for optimizing the circuit parameters, can outperform all the other strategies. By monitoring the ground-state population during the dynamics we learn that DC-QAOA finds effective shortcuts towards the target state through intermediate excited states, a process that is unexpectedly enhanced by the inclusion of local CD unitaries. Our results highlight the importance of flexible variational control of CD dynamics and demonstrate that digital optimization can explore operator dynamics that remain inaccessible to standard analytical CD constructions.
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Materials Science

Imaging of van der Waals Materials via Standing-Wave Photoemission Microscopy: Depth-Resolved Electronic Structure of WS2

J. R. Paudel, R. Muzzio, M. E. Matzelle et al. (+13 more)

Two-dimensional van der Waals materials promise electronic, optoelectronic, and quantum technologies, yet depth-resolved characterization remains challenging. Here, we demonstrate standing-wave photoemission electron microscopy (SW-PEEM) for Angstrom-scale spectromicroscopy of monolayer WS2 on a W/C multilayer substrate. Tuning the X-ray standing wave through the monolayer yields a chemical depth profile and valence-band modulation with enhanced sensitivity to the top and bottom sulfur layers. X-ray optical modeling determines the structure and field distribution. The measurements reveal an ~0.2 eV shift in sulfur-derived valence-band spectral weight between measurements with enhanced sensitivity to the top and bottom sulfur layers. This shift is unlikely to arise from strong direct substrate hybridization and is instead consistent with sulfur-related surface species, as supported by calculations using a representative elemental-sulfur model. These results establish SW-PEEM as a non-destructive depth-resolved probe, highlighting its potential to probe interfacial coupling, chemical reconstruction, and emergent states in van der Waals and moiré systems.
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All authors J. R. Paudel, R. Muzzio, M. E. Matzelle, S. Sheikh, A. Fadul, A. Tiwari, F. Salmassi, E. Gullikson, K. M. McCreary, B. T. Jonker, J. Nieminen, C. M. Schneider, F. Kronast, A. Bansil, J. Katoch, A. X. Gray

High Energy Physics (Phenomenology)

Properties of $\Omega_{ccb}$ and $\Omega_{bbc}$ baryons in a quark-diquark model

Chaitanya Anil Bokade and Bhaghyesh

In this work, we investigate the mass spectra and radiative transitions of $\Omega_{ccb}$ and $\Omega_{bbc}$ baryons within a relativistic screened potential model using the quark-diquark approximation to capture key aspects of their internal structure. The model describes the $S$-, $P$-, and $D$-wave excitations, provides corresponding mass predictions, and offers a comparison with other theoretical approaches. Our findings suggest that excitations involving the diquark occur at lower energies than those requiring relative motion between the quark and diquark, challenging conventional assumptions about the rigidity of heavy diquark systems. Analysis of radiative decays of these states, shows that spin-flip transitions within the same orbital multiplet are suppressed, while transitions involving orbital or radial changes dominate with significantly larger widths. The model offers subtle distinctions in excitation dynamics and highlights its value for future studies and for interpreting potentially upcoming experimental results on triply heavy baryons.
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Quantum Physics

The Ruskai-Audenaert conjecture & equipartitions of positive operators

Niranjan Kumar and Michael M. Wolf

Several open problems in quantum information theory can be formulated as equipartition problems for positive operators, asking for a decomposition into bounded-rank positive parts under uniform constraints. The existence problems for SIC-POVMs and MUBs are of this type, as is the Ruskai-Audenaert conjecture. We first show that certain problems of this form can be attacked using equivariant cohomology, and then present new results on the Ruskai-Audenaert conjecture. In its weak form, this conjecture asserts that every quantum channel admits a convex decomposition into a minimal number of generalized extreme points; in its strong form, one with equal weights. We prove the strong conjecture in all dimensions for a set of channels of nonzero measure, including all cq- and qc-channels, as well as for all channels with qubit inputs. We also prove the weak conjecture for all qutrit channels, along with further results on convex decompositions of quantum channels.
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Atomic and Molecular Clusters

Size characterization of neutral rare-gas clusters based on time-resolved polarization anisotropy measurements

Arne Morlok, Grzegorz Kowzan, Yilin Li et al. (+3 more)

The size determination of neutral clusters is experimentally challenging. In particular, weakly-bound rare-gas clusters tend to fragment upon ionization, resulting in systematic errors in cluster size studies. In contrast, characterization of the temporal polarization anisotropy dephasing provides a soft detection scheme for cluster size estimation, which avoids fragmentation of the clusters. Here, we present a systematic experimental study of argon and neon clusters in the size range of 50 to 10.000 atoms using this technique. In order to extract the mean cluster sizes from the data, we present an efficient analytical model of the polarization anisotropy dephasing of an ensemble of doped clusters. The approach shows remarkable sensitivity to small changes in the mean cluster size of just a few tens of atoms and allows us to refine the widely used Hagena scaling law for the estimation of rare-gas cluster sizes.
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All authors Arne Morlok, Grzegorz Kowzan, Yilin Li, Ulrich Bangert, Frank Stienkemeier, Lukas Bruder

Astrophysics of Galaxies

HETDEX: Star Formation Stochasticity Diagram of Lyman Alpha Emitting Galaxies at Cosmic Noon Confirms Three Archetypes

Nicole Firestone, Eric Gawiser, Kartheik G. Iyer et al. (+14 more)

In this work, we aim to measure the star formation stochasticity of Lyman Alpha Emitting Galaxies (LAEs) at Cosmic Noon. We identify 270 LAEs from the HETDEX Survey in the COSMOS field with rest-UV-through-NIR photometry from CANDELS\null. For each LAE, we perform non-parametric gaussian-process star formation history (SFH) reconstruction using the Dense Basis method. Our HETDEX LAE sample is described well by the three SFH archetypes defined for ODIN LAEs in Firestone et al. 2025 with comparable frequency: First Burst, Dominant Burst, and Nondominant Burst. The rapidly rising Star Formation Rates (SFRs) of First Burst LAEs are not adequately represented in traditional SFR$_{100}-M_*$ diagrams, where SFR$_{100}$ is averaged over the most recent 100Myr. This motivates the usage of SFR$_{10}-M_*$, where SFR$_{10}$ is averaged over the most recent 10Myr. We introduce the Star Formation Stochasticity Diagram, a diagnostic tool that probes variations in galaxies' SFRs across cosmic time. By eliminating the confounding factor of redshift evolution, we are able to employ a gaussian mixture model to decompose our ratio of short- vs.long-term SFR into statistically motivated sub-populations. This agnostic component decomposition reveals three populations consistent with the empirical LAE SFH archetypes. We can, therefore, summarize the overall stellar mass assembly of LAEs with this ratio, even without viewing their full star formation histories.
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All authors Nicole Firestone, Eric Gawiser, Kartheik G. Iyer, Charlotte Olsen, Antara Basu-Zych, Adam Broussard, Peter Kurczynski, Kyoung-Soo Lee, Erin Mentuch Cooper, Robin Ciardullo, Daniel J. Farrow, Steven L. Finkelstein, Caryl Gronwall, Ho Seong Hwang, Byeongha Moon, Shun Saito, Donald P. Schneider

Solar and Stellar Astrophysics

High-resolution spectroscopy of the bipolar proto-planetary nebula Hen 3-1475, the Garden Sprinkler Nebula

Ana Valeria Beltrán-Sánchez, Miriam Peña and Mudumba Parthasarathy

A detailed analysis of high-resolution spectra in the optical and near-infrared range of the central zone of the proto-planetary nebula Hen 3-1475, obtained in 2006 and 2024, is conducted. The spectrum primarily revealed stellar emission of H Balmer and Paschen series, lines of iron (Fe I, Fe II, and [Fe II]), and other significant lines of He I, Ca II, [Ca II], and O I. Several multiplets of Fe II, the H Balmer series, Ca II H and K, Na I D and He I lines exhibit P-Cygni profiles and bump-like features, which are clear indicators of strong stellar winds. The terminal velocity of the winds was calculated, reaching values up to ~ 800 km/s. [Fe II] and Fe I lines were used as gas density indicators. In these observations, no photoionized nebular lines of planetary nebulae were identified, suggesting that the central star has not reached the temperature required to photoionize the nebula. A comparison between the observations from 2006 and 2024 reveals some few significant differences, being the most important the probably ejection of a new jet emerging from the central zone and the detection of a broad component adjacent to H \alpha, probably originating from emission associated with a jet at 700 km/s. High-spectral resolution observations of the knot NW1 obtained on August 2024, are also presented. This knot shows a typical spectrum of shocked gas. The emission of this knot has changed, presently not showing [O III] 5007 and other ionized lines that were reported in 2006.
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Earth and Planetary Astrophysics

Asymmetrical shape of the Near-Infrared K 4p-5s doublet perturbed by He and H2

N.F. Allard and J.F. Kielkopf

The goal of this paper is to provide an exhaustive study of the K 4p-5s doublet at 1.243/1.252~$\mu$m perturbed by He and H$_2$ in physical conditions of brown dwarfs. This work is applicable to analysis of the ESO SupJup Survey's J-band spectra such as for Luhman~16. Line profiles of this doublet computed within a unified line-shape theory exhibit a blue asymmetrical behavior. This effect is of increasing importance with He and H2 density, and as a result, the full treatment of the infrared K doublet reveals strong effects on its opacity outside the impact approximation. For a He and H2 perturber density larger than $10^{19}$~cm$^{-3}$ (0.4 bar) the impact approximation breaks down and is not applicable to calculate the shape of the line profiles and their line core parameters.
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Superconductivity

Evolution of the electronic and superconducting properties of Re-based quinary high-entropy alloys under chemical and physical pressure

Thiagarajan Maran, Yoshiya Uwatoko, Sathea Suweatha M N et al. (+4 more)

We report a comparative study of chemical- and physical-pressure effects on the electronic and superconducting properties of the Re-based quinary high-entropy alloys (HEAs) [Nb0.67-xRex][TiZrHf]0.33 (x = 0.10, 0.20, and 0.56). Increasing Re concentration suppresses the superconducting transition temperature Tc from 5.4 to 3.9 K while producing positive, composition-dependent cocktail-effect ratios. Field-dependent transport and magnetization establish all three compositions as strongly type-II superconductors and identify x = 0.20 as the most distinctive composition, with the largest upper critical field and Ginzburg-Landau parameter and a Maki parameter close to unity. Most importantly, the pressure coefficient of Tc changes sign across the bcc-hcp structural change: dTc/dP is positive for the bcc x = 0.10 and 0.20 samples, with values of approximately 0.018 and 0.053 K/GPa, respectively, but negative for the hcp x = 0.56 sample, with a value of approximately -0.033 K/GPa. This systematic contrast within a single chemically related alloy series establishes a robust structure-associated superconducting response and identifies crystal structure as a key organizing variable under compression. Metallic transport and superconductivity remain robust up to approximately 8 GPa in all three compositions. These results reveal that chemical substitution and hydrostatic compression are complementary but nonequivalent routes for tuning superconductivity in Re-based HEAs.
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All authors Thiagarajan Maran, Yoshiya Uwatoko, Sathea Suweatha M N, Sonika Jangid, R.P. Singh, Arumugam Sonachalam, Sathiskumar Mariappan

Materials Science

Hydrogen-Induced Sign Reversal in Magnetic Hysteresis Evolution of CoPd Alloys and Co/Pd Multilayers

S. S. Das and A. Gerber

Hydrogen absorption in magnetic thin film nanostructures can modulate their electronic, magnetic, and transport properties by modifying the electronic structure and lattice strain. However, the influence of composition and nanostructuring on these two competing effects is not well understood. We systematically investigate hydrogen-induced magnetic hysteresis in Co$_x$Pd$_{100-x}$ alloys, [Co(0.1 nm)/Pd(d)]$_{15}$, and [Co(0.2 nm)/Pd(d)]$_{15}$ multilayers, using extraordinary Hall effect characterizations (EHE) in air and 4% H$_2$/N$_2$ mixture. We show that the hydrogen-induced response is not universal, but depends strongly on composition and layer thickness. This reflects competition between Pd-related electronic effects and magnetoelastic anisotropy. In Pd-rich CoPd alloys and Co(0.2 nm)/Pd multilayers, hydrogen initially contracts the hysteresis loops at low Co fractions, followed by loop expansion above x ~ 40%. This contrast results from competition between suppression of Pd-induced magnetization through Pd-4d band filling and hydrogen-driven anisotropic strain that strengthens magnetoelastic anisotropy in Co-rich samples. In contrast, in ultrathin [Co(0.1 nm)/Pd(d)]$_{15}$ multilayers, hydrogen induces a weak, non-monotonic but generally expanding loop behaviour across x = 15-60%, indicating a dominant role of interfacial magnetic connectivity and strain-mediated magnetoelastic anisotropy in the ultrathin limit. Furthermore, we observe a hydrogen-induced reversal of the EHE loop polarity near the crossover regime, reflecting a change in the dominant EHE scattering mechanisms, thus providing an additional degree of magnetic tunability by hydrogen. These results demonstrate that hydrogen can selectively tune the magnetism of CoPd nanostructures via composition-controlled electronic and magnetoelastic effects, offering insights for hydrogen-responsive spintronic and sensing devices.
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Materials Science

Ferroelastic exciton splitting in hybrid perovskite nanowalls

Afreen, J. Delgado-Alvarez, H. Krishna Mishra et al. (+9 more)

Hybrid metal-halide perovskites are soft semiconductors in which electronic excitations are strongly influenced by lattice distortions and structural phase transitions. An important open question is whether ferroelastic symmetry breaking merely broadens optical resonances or instead modifies excitonic states through exciton-lattice coupling. Here, we address this question using highly aligned MAPbI3 nanowalls fabricated by glancing-angle deposition, enabling symmetry-selective coupling between ferroelastic texture, structural anisotropy, and a well-defined optical axis. Combining temperature-dependent photoluminescence, X-ray diffraction and polarization-resolved ultrafast transient absorption spectroscopy, we observe a polarization-selective excitonic splitting in the orthorhombic phase at 5 K, characterized by orthogonal optical selection rules and a 45 meV energy separation. Near 160 K, where orthorhombic and tetragonal phases coexist, a lower-energy lattice-coupled excitation emerges 58 meV below the centre of the anisotropically split excitonic structure, consistent with coupling between excitonic and lattice-dressed states. At higher temperatures, these excitations progressively acquire lattice-dressed character accompanied by reduced optical anisotropy. A symmetry-guided effective Hamiltonian captures the evolution from anisotropically split excitons to coupled excitonic and lattice-dressed states across the structural transition. Our results show that ferroelastic texture and phase coexistence can modify exciton-lattice coupling, providing a route to symmetry-selective optical responses in soft polar semiconductors.
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All authors Afreen, J. Delgado-Alvarez, H. Krishna Mishra, J. Castillo-Seoane, Koustav Maiti, Pravrati Taank, A. Borras, A. Barranco, Surajit Saha, Priya Mahadevan, J. R. Sanchez-Valencia, K. V. Adarsh

Quantum Physics

Loss and distinguishability effects in heralded entangled state generation with Gaussian resources

Yun-Long Cao, Xiao-Ye Xu, Wiwittawin Sukmas et al. (+2 more)

The effects of optical loss and photon distinguishability on the heralded generation of entangled states based on Gaussian resources are quantitatively investigated. By incorporating mode-dependent loss and the statistical characteristics of partially distinguishable photons into a phase-space representation, an efficient numerical framework is established to optimize target-state fidelity and success probability, with a specific focus on the enhancement triggered by non-Gaussian operations such as photon addition and subtraction. The numerical optimization results indicate that a non-vacuum post-selection strategy within a dual-rail encoding framework, combined with the simultaneous tuning of squeezing parameters and the interferometer network, effectively suppresses vacuum noise, enabling the generation of high-fidelity Bell, GHZ, and W states under realistic experimental constraints. The results show that introducing non-Gaussian operations can successfully enhance the state generation performance under realistic imperfections analogous to the enhancements observed under ideal conditions. This study demonstrates that experimental imperfections primarily scale down the success probability rather than fundamentally compromising the state fidelity, providing practical design guidelines for scalable state engineering on integrated photonic platforms.
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All authors Yun-Long Cao, Xiao-Ye Xu, Wiwittawin Sukmas, Chuan-Feng Li, Guang-Can Guo

Quantum Physics

Characterizing Arbitrary Lindbladian Dynamics with a Few Pauli Measurements

Taiqi Zhou and Weiyuan Gong

Quantum devices are open systems whose dynamics interleave coherent evolution with dissipation, and benchmarking, error mitigation, and error correction all rest on a faithful model of both. Existing characterization protocols either assume prior knowledge of the interaction and noise structure, or demand ancillas, entangled probes, or mid-circuit control, or capture only the Pauli-diagonal part of the noise. Here, we present a protocol that reconstructs an arbitrary sparse Markovian generator, including every Hamiltonian together with the jump operator coefficients, using only product Pauli state preparation, single uninterrupted forward evolutions, and product Pauli measurements. Given a sparsity budget $M_0$ and a strength bound $\Gamma$ of the Lindbladian, every coefficient is learned to precision $\epsilon$ from $\widetilde{O}(\Gamma^2M_0^2/\epsilon^4)$ experiments and $\widetilde{O}(\Gamma M_0^2/\epsilon^2)$ total evolution time, with both supports identified from data without locality assumptions. The protocol runs at a logarithmic number of positive evolution times on a hardware clock lattice and is provably robust to calibrated state-preparation and measurement errors.
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Space Physics

For SIRs, CIRs, and Beyond: Polarization Ratio to Feature Location

Curt A. de Koning, Dusan Odstrcil, Sarah Gibson et al. (+3 more)

The Polarimeter to UNify the Corona and Heliosphere (PUNCH) mission will remotely observe solar wind transients with high signal-to-noise ratio, high-cadence, high-resolution polarized white-light images. Using different polarization states, an important PUNCH data product will be polarization ratio images. In the small-Sun limit, and using two simple line-of-sight density distributions with a finite angular width that can approximate a stream or corotating interaction region (SIR/CIR), we analytically investigate how the polarization ratio will provide three-dimensional location information and what the uncertainty in this estimated location is.
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All authors Curt A. de Koning, Dusan Odstrcil, Sarah Gibson, Craig DeForest, Vic Pizzo, Christopher J. Scott

Mathematical Physics

Nonlocal Cubic Density Gibbs Measures from Bosonic Gibbs States with Three-Body Interactions

Hao Liang

We study the high-temperature mean-field limit of grand-canonical bosonic Gibbs states on the torus with renormalized nonlocal three-body interactions. In dimensions two and three, we construct the limiting nonlinear classical Gibbs measure and prove convergence of the relative free energy and of the reduced density matrices of every fixed order; in three dimensions, a smallness condition on the interaction is imposed. The proof combines the density-channel representation of the interaction with a coherent-state variational method based on the upper-symbol representation of the free Gibbs state. The same framework also contains, as a special case, the homogeneous positive-type model studied by Lewin, Nam, and Rougerie (2021).
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Quantum Physics

Revisiting the invariant ring of two-qubit mixed states

Bing Xie and Lin Zhang

Local unitary equivalence serves as the cornerstone for classifying entanglement in bipartite quantum systems. Mathematically, it reduces to the study of polynomial invariants of the density matrix under the action of local unitary groups. The collection of all such polynomial invariants forms a ring, known as the invariant ring. However, identifying the complete generators of the invariant ring is the central issue. In 2007, for the two-qubit system, King et al fully characterized the structure of the invariant ring and determined its Cohen–Macaulay decomposition. In this paper, we revisit their work, with a focus on the computation of the Molien series and the construction of invariants. On one hand, we rigorously derive the Molien series via explicit contour integration over the maximal torus, filling in all previously omitted computational steps. On the other hand, we systematically construct all invariants using a graphical method, and then reduce the candidate set by applying various identities and algebraic relations, obtaining a generating set consisting of 21 invariants. This paper aims to make this important result more widely accessible to researchers in quantum information and invariant theory through the above discussions.
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Quantum Physics

Parameter Calibration for Reduced-Bandwidth Two-Photon Waveguide-QED Simulations

Romain Piron and Akihito Soeda

Waveguide-QED platforms represent one potential approach to scalable quantum technologies, but their simulation remains computationally demanding due to the large number of frequency modes required to describe traveling photons. In practice, increasing the simulated bandwidth rapidly raises the numerical cost, leading to a trade-off between accuracy and tractability. The existing approaches formulated in time-domain indirectly control this trade-off through the choice of time step, which obscures the connection between discretization parameters and the represented spectral window. In this work, we introduce an end-to-end framework to explicitly control the effective bandwidth in waveguide-QED simulations of two-photon scattering. We show that truncating the frequency domain requires consistent shifts of the model parameters, and derive a systematic calibration procedure that preserves the physical accuracy of the reduced model. This enables tuning the central frequency and the bandwidth of the numerical spectrum, leading to a several-fold reduction in the Hilbert space dimension while maintaining physical accuracy. We discuss the limitations of this calibration and relate the finite-bandwidth viewpoint to time-domain discretizations.
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Earth and Planetary Astrophysics

Metal-Silicate Segregation During Planetary Accretion: Limited Iron Emulsification through intermediate Impacts

L. Honarbakhsh, G. Morra, P. Mora et al. (+1 more)

In this study, we investigate the post-collisional evolution of an impactor's iron core within a fully molten magma ocean using 2D numerical simulations with a novel Rothmann-Keller multiphase Lattice Boltzmann Method. The impactor's core diameter ranges from $152\;\text{km}$ to $552\;\text{km}$, with aspect ratios from $0.75$ to $5$. At Reynolds numbers up to $10^4$, our models reveal significant deformation and progressive fragmentation of the impactor into an iron cloud down to the smallest scale (several kilometers) that our method allows, which is then dispersed throughout the magma ocean by turbulent flow. We determined entrainment coefficients for a range of intermediate impactor sizes with various shapes, finding that larger impactors consistently exhibit higher entrainment coefficients. By extrapolating our mixing data, we anticipate incomplete iron-silicate mixing for kilometer-scale impactors in a real magma ocean, qualitatively consistent with previous predictions of partial equilibration. Additionally, our models highlight the mid- to lower magma ocean depths as critical zones for further iron fragment breakups and material transfer in the magma ocean.
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All authors L. Honarbakhsh, G. Morra, P. Mora, CRM. Jackson

High Energy Physics (Theory)

Overcrowding and the Finite-$N$ Hilbert Space

Robert de Mello Koch, Anik Rudra and Augustine Larweh Mahu

Finite-$N$ trace relations reorganize the Hilbert space of gauge-invariant operators beyond the freely generated large-$N$ description. We study this structure using the Hironaka decomposition of the invariant ring of $d$ Hermitian $N\times N$ matrices. We first prove that the primary invariants may always be chosen to be homogeneous single-trace operators. We then show that, for any such choice, a nontrivial secondary invariant must appear by degree $L_{N,d}=2\log_d N+\log_d\log_d N+\mathcal{O}_d(1)$, which is parametrically below the first universal trace identity at degree $N+1$. This is a global overcrowding effect: exponentially many independent short single traces compete for only $1+(d-1)N^2$ algebraically independent coordinates. The overcrowding scale matches the fastest scrambling times expected for fast scramblers. We argue that this agreement of scales is not accidental: overcrowding provides a microscopic algebraic picture of scrambling in matrix models. Low-rank examples show that secondary invariants can distinguish configurations with identical primary data and, for suitable dynamics, label semiclassical sectors connected by instantons. These results identify the Hironaka decomposition as a natural framework for organizing perturbative and intrinsically finite-$N$ information in collective descriptions of gauge theories.
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General Relativity and Quantum Cosmology

Qualitative Shadow Anomaly as a Smoking-gun Signature of Nonmetricity

Zi-Chao Lin, Hao Yu, Yu-Xiao Liu et al. (+1 more)

In general relativity and its metric-formalism extensions, the innermost stable circular orbit and the photon ring of a charged black hole contract as the charge increases. In this paper, we discover a qualitative anomaly that violates this universal behavior, serving as a smoking-gun signature of geometric nonmetricity. By considering a minimal coupling between the bosonic field and the independent affine metric, we demonstrate that nonmetricity induces an effective geometric force that triggers a trajectory expansion of both massless and massive bosons with increasing black hole charge. This qualitative inversion directly imprints onto the black hole shadow, lifting the degeneracy between metric-affine gravity and general relativity. Using Eddington-inspired Born-Infeld gravity as a concrete implementation, we show that next-generation horizon-scale imaging can resolve this signature, probing a complementary high-energy window up to the $10^{5}_{~}\,\text{TeV}$ scale.
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All authors Zi-Chao Lin, Hao Yu, Yu-Xiao Liu, Jin Li

Astrophysics of Galaxies

PhotoIFU: NIRCam as a Photometric Integral Field Unit for Mapping Feedback in Galaxies

Yongda Zhu, Marcia J. Rieke, Courtney Carreira et al. (+25 more)

We present PhotoIFU, a workflow that uses deep multi-band imaging as a low-resolution photometric integral field unit. Applied to PSF-matched JWST/NIRCam imaging, PhotoIFU treats each spatial pixel as a coarse SED element and fits the pixel SEDs with Prospector to map resolved stellar-population and ISM-related properties. We apply this approach to three galaxies at $z=1.3$–3.7 in JADES: two systems with extended ionized line emission and one post-starburst galaxy with an exceptionally strong neutral outflow. Pixel-by-pixel SED fitting gives maps of stellar-mass surface density, specific star formation rate, dust attenuation, gas-phase metallicity, and recent star-formation history. We find that regions selected from the extended-emission or outflow geometry occupy distinct parts of the resolved SED-property distribution compared with the full host. In the systems with extended ionized emission, these regions are generally less dusty, consistent with ionized emission being observed along dust-poor, low-column-density pathways through the host. In the neutral-outflow system, the selected regions show enhanced recent star formation, suggesting that compact rejuvenation may mark the aftermath of an earlier energetic phase. These results show that galactic outflows and extended emission-line structures can be spatially associated with measurable differences in resolved host-galaxy stellar populations and ISM-related properties. PhotoIFU provides an imaging-based method for resolved SED mapping of feedback-related structures in larger galaxy samples where full spectroscopic integral-field mapping is unavailable.
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All authors Yongda Zhu, Marcia J. Rieke, Courtney Carreira, Yang Sun, Zhiyuan Ji, Jianwei Lyu, Christina C. Williams, Stacey Alberts, Feng Yuan, Yuxuan Zou, Yurina Nakazato, Andrew J. Bunker, Sandro Tacchella, Fengwu Sun, George H. Rieke, Eiichi Egami, Jacopo Chevallard, Kevin Hainline, Zheng Ma, Pablo G. Pérez-González, Pierluigi Rinaldi, Bruno Rodríguez Del Pino, Tristen Shields, Meredith Stone, Christopher N. A. Willmer, Zihao Wu, Minghao Yue, Junyu Zhang

Space Physics · Cross-listed from stat.ML

Covariance-Boosted Gaussian Processes for Spatiotemporal Irregularities

Jeremy Ovadia

Nonstationary Gaussian process (GP) models are powerful tools for capturing input-dependent variability by adapting to observed data. However, with limited sampling and highly parameterized covariance structure, they are often prone to overfitting and overconfident uncertainty estimates, potentially leading to misleading predictions in safety-critical applications. Motivated by ionospheric modeling for satellite-based augmentation systems (SBAS), this paper proposes a Covariance-Boosted Gaussian Process (CBGP) framework centered upon boosting covariance priors to discover nonstationary latent functions for signal and observation variation that capture irregularities in the input domain. An additional layer of GP modeling of "partially-whitened" observations guides latent function relative error estimation that is used to iteratively update weak priors in a gradient descent-like procedure. Following boosting, restrictions are imposed upon prior covariances to prevent overfitting while posterior uncertainties are inflated to prevent model overconfidence. CBGP model efficacy and robustness are demonstrated through out-of-sample testing of both simulated and real-world applications that meet a three-nines integrity standard. The modeling of an extensive ionospheric storm dataset over South America suggests accurate and reliable means to compute SBAS ionospheric corrections in the most challenging space weather environment using regional models that are more informed and responsive than local fitting performed by currently-operating SBAS.
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Optics

Investigating planar Proca metamaterials in nonlinear (2+1)-Electrodynamics

Widervan de Deus Morais, Stamatios Strikos, Ronaldo Thibes et al. (+1 more)

The present work pursues the investigation of the physics of a planar electromagnetic system incorporating nonlinear effects, as well as de Broglie-Proca and Chern-Simons mass terms in vacuum, which can be tuned to describe new planar metamaterials (MTMs) potentially suitable for technological applications. As a result, we observe interesting effects generated by a spatially dispersive profile that emerges from non-linearity. This characterizes the three-dimensional QED vacuum as a nonlocal metamaterial. The constitutive relations are derived, and the dielectric function of the metamaterial (MTM) exhibits spatial dispersion due to the Chern-Simons mass. The dispersion relations are analyzed in terms of applied external electromagnetic fields and both the de Broglie-Proca and Chern-Simons mass parameters. We also notice that, in the special case in which only a background magnetic field is present, this field gives no contribution neither to the dielectric function nor to the spatial dispersion profile, as is the case when both the electric and magnetic fields are present.
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All authors Widervan de Deus Morais, Stamatios Strikos, Ronaldo Thibes, José Abdalla Helayël-Neto

Physics and Society

An index to quantify scientific debt

N. Zen

I propose the index $z$, defined as $z=\sum\limits_{i=1}^{n} \mathrm{IF}_{i}$, where $\mathrm{IF}_{i}$ is the impact factor of the journal in the publication year of the $i$-th retracted paper. Whereas the $h$-index is a forward-looking measure of scientific achievement, the $z$-index quantifies scientific debt. The quantity $h-z$ may provide a more balanced assessment of scientific value.
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Materials Science · Cross-listed from cs.IR

VecTree-RAG: An Agentic Retrieval-Augmented Generation Framework Combining Vector and Tree Retrieval for Efficiency and Accuracy

Xinyan Zhong, Yuwei Shi, Yuqi Wei et al. (+3 more)

Scientific question answering requires a retrieval system to solve two distinct problems: identifying which papers are relevant and locating the supporting evidence within those papers. Conventional retrieval-augmented generation typically addresses both through similarity search over fixed-length passages, flattening document structure and separating scientific claims from their methodological and argumentative context. We present VecTree-RAG, an agentic framework that assigns these tasks to complementary retrieval mechanisms. Vector search ranks compact document and section representations across the corpus, whereas reasoning-guided traversal of source-verified section trees localizes evidence within shortlisted papers. Full text is retained in a page store and exposed progressively only after structural localization. We evaluate VecTree-RAG on 300 QASPER questions, an open-access subset of 54 LitQA2 questions, and 49 multi-document MOSAIC questions. Compared with Dense RAG, reranked Dense RAG, RAPTOR, and Search-o1, VecTree-RAG obtained the highest observed answer score on all three benchmarks, reaching 0.800 LLM-judge correctness on QASPER, 0.925 accuracy on LitQA2, and a 0.547 composite score on MOSAIC. On QASPER, its evidence-page precision was 0.274, compared with 0.046–0.071 for the baselines. LitQA2 ablations further showed that the complete vector–tree architecture required fewer inference tokens than variants without tree navigation or corpus-level vector routing. These results indicate that vector retrieval narrows the corpus-level search space and tree navigation concentrates reading on structurally relevant evidence. Although multi-turn inference remains more expensive than single-call retrieval, VecTree-RAG provides a structure-aware and traceable architecture for scientific literature question answering.
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All authors Xinyan Zhong, Yuwei Shi, Yuqi Wei, Chen Shen, Tianhang Zhou, Zhenghao Wu

Materials Science

Uncertainty-quantified $J$-integral computation for quasicontinuum and finite element methods

Sai Harshith Badi, Stephen M. Whalen, Ronald E. Miller et al. (+1 more)

The $J$-integral is a fundamental concept in fracture mechanics, quantifying the energy release rate that drives crack propagation. While extensively implemented in finite element (FE) codes and adapted for atomistic calculations, its application within multiscale frameworks bridging atomistic and continuum formulations remains unexplored. This work presents a rigorous implementation and validation of the $J$-integral within the three-dimensional quasicontinuum (QC3D) method, computed under plane strain assumptions, using continuum fields (stress, strain energy density) derived from the interatomic potential via the Cauchy-Born rule. The implementation is validated against linear elastic fracture mechanics (LEFM) theory and the virtual crack extension (VCE) method across three regimes: (1) small-strain linear elasticity, with a prescribed anisotropic $K$-field displacement applied throughout; (2) the same field evaluated through the nonlinear Cauchy-Born constitutive relation, without atomic relaxation; and (3) the same relation with atomic relaxation enabled, allowing the crack-tip region to equilibrate. Excellent agreement is shown throughout. We further introduce a Markov chain Monte Carlo framework to statistically quantify the uncertainty of $J$-integral results for a given mesh and integration domain, applicable to conventional FE methods as well. Predictive capability is demonstrated via a QC3D simulation of a three-point bending test of silicon, where the computed critical energy release rate agrees closely with the Griffith criterion. This work establishes a reliable framework for evaluating crack driving forces in multiscale fracture simulations with quantified uncertainty, enabling large-scale fracture simulations while resolving atomistic mechanisms at the crack tip.
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All authors Sai Harshith Badi, Stephen M. Whalen, Ronald E. Miller, Ellad B. Tadmor