Astrophysics of Galaxies
Spatially-Resolved Spectra of Diffuse Galactic Light using 10.8 M DESI Sky Fibers
Andrew K. Saydjari, Bruce T. Draine, Timothy D. Brandt et al. (+49 more)
Using 10.8 million “blank” sky spectra from the DESI Year 3
dataset, we measure the diffuse
galactic light (DGL) spectrum in the optical at spectral resolution $R \sim 4000$ by correlating with far-infrared emission from IRAS. Subdividing the sky into 54 deg$^2$ pixels (HEALPix, NSIDE = 8), we map the variation of the DGL correlation spectrum and nebular emission lines across the DESI footprint in the high-
Galactic-latitude sky. The increased data volume over previous SDSS-based analyses enables several new detections in the DGL, including scattering both onto and out of the line of sight from neutral interstellar sodium and potassium. We further detect direct emission from ro-vibrational transitions of molecular hydrogen in the near-infrared with an absolute radiance of $0.65\substack{+0.13 \\ -0.12}\times10^{-9}~{\rm erg\, cm^{-2}\,s^{-1}\,sr^{-1}}$, roughly consistent with theoretical expectations, but with an apparent ortho-to-para line ratio that is lower by a factor of $0.60\substack{+0.28 \\ -0.27}$. We confirm previous detections of extended red emission (ERE) in the DGL and map its spatial variation. Our spatially resolved DGL maps provide important observational constraints for the radiative transfer efforts that are now possible with recent 3D models of the Milky Way.
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All authors Andrew K. Saydjari, Bruce T. Draine, Timothy D. Brandt, Edward F. Schlafly, Arjun Dey, Douglas P. Finkbeiner, J. Aguilar, S. Ahlen, C. Allende Prieto, A. Anand, F. Beutler, D. Bianchi, D. Brooks, A. Carnero Rosell, T. Claybaugh, A. de la Macorra, P. Doel, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, Satya Gontcho A Gontcho, G. Gutierrez, J. Guy, K. Honscheid, T. Karim, D. Kirkby, A. Kremin, O. Lahav, A. Lambert, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, E. Paillas, W. J. Percival, I. Pérez-Ràfols, F. Prada, C. Ravoux, G. Rossi, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, R. Sharples, J. Silber, M. Siudek, G. Tarlé, B. A. Weaver, R. Zhou
Disordered Systems and Neural Networks
Fractal Confinement and Magnetic Self-sabotage of Current Flow: Electrons Near the Metal-insulator Crossover in a 2D $\delta$-layer
Xinghai Zhang, Matthew S. Foster and Markus Mueller
We study low-$T$ transport and itinerant magnetism in 2D $\delta$-doped
semiconductors. Large-scale Hartree-Fock calculations with random hoppings and repulsion $U_0$ reveal two transport regimes near a critical density. The conductivity $\sigma(T)$ initially increases as $T$ drops below $U_0 / 10$. However, at $T \sim U_0/100$, a tiny density of
magnetic moments forms, driving an insulating downturn. Fractal wavefunctions locally amplify
magnetic interactions, initially concentrating currents into branched filaments, but ultimately choking them off via dynamic SU(2)
symmetry breaking.
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Cosmology and Nongalactic Astrophysics
AXIS Could Have Accessed Dark Matter Decays
Joshua W. Foster, Inci Karaaslan, Gordan Krnjaic et al. (+1 more)
The Advanced X-ray Imaging Satellite (AXIS) was a mission concept designed to improve upon the sensitivity and spatial resolution of the Chandra X-ray Observatory and XMM-Newton. Although AXIS was not selected for implementation, the concept study defined a mature instrument design with low-background, arcsecond imaging over the $0.3$-$10$ keV energy range, a large effective area, and a wide field of view. These capabilities provide a useful
benchmark for the dark matter decay sensitivity of future X-ray observatories. We estimate the reach of a future AXIS-like instrument for narrow
photon lines from decaying keV-scale dark matter, including
axion-like particles and sterile
neutrinos. For
Galactic center observations, we find projected lifetime sensitivities of order $10^{31}$ s, improving upon existing limits by up to an order of magnitude over part of the keV mass range.
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All authors Joshua W. Foster, Inci Karaaslan, Gordan Krnjaic, Nimrod Shapir
Astrophysics of Galaxies
Magnetic destabilisation in disc galaxies: Filament/feather formation
Raghav Arora, Oscar Agertz, Christoph Federrath et al. (+1 more)
Gas gravitational instability plays a crucial role in secular
galactic evolution, but the role played by
magnetic fields in mediating this instability - despite their dynamical relevance and ubiquity - is still not understood. To investigate this question we conduct a parameter study using numerical simulations of 3D isolated disc
galaxies that are initialized in
equilibrium, but have a range of initial magnetisation, quantified by $\beta \in \{0.1, 0.5, 1, 10, 100, \infty\}$, where $\beta$ is the ratio of thermal to
magnetic pressure. We analyse how
magnetic field strength influences the formation of dense filaments and feathers driven by gravitational instability. The simulations show that filament growth rate and spacing are significantly altered by dynamically strong fields ($\beta \lesssim 10$), and that these effects depend on the value of $\beta$ and strength of shear in the disc.
Magnetic fields either stabilise or destabilise, with destabilisation dominating in regions with low $\beta$, and low shear. This makes the destabilisation particularly important in
dwarf galaxies with low-shear rotation curves. Filament spacings are similarly affected differently in different
galactic regions, depending upon the local field strength and shear. Our results are in good agreement with predictions from the magneto-Jeans mechanism.
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All authors Raghav Arora, Oscar Agertz, Christoph Federrath, Mark R. Krumholz
High Energy Physics (Theory)
Reimagining Gravity: Generalized Symmetries, Double Copy, and Spinning Black Holes
Joon-Hwi Kim
General relativity is a century-old subject. Yet modern explorations through generalized
symmetries, scattering amplitudes, and effective field theory have raised open problems, motivating a reassessment of conventional views on gravitation, spacetime, and
spin. First, do generalized
symmetries exist in dynamical
gravity as a low-energy EFT? Second, is there a field-theoretic explanation for the tree-level double copy relationship between general relativity and Yang-Mills theory? Third, what are the exact equations of motion or Lagrangians of four-dimensional spinning black holes in external fields, in point-particle effective theory? In this dissertation, three different perspectives on
gravity are developed to shed light on each of these puzzles. In Part I, we view
gravity as a gauge theory of Lorentz group to establish a one-form
symmetry of dynamical
gravity. In Part II, we investigate how far
gravity can be viewed as a gauge theory of diffeomorphisms, in connection with color-kinematics duality and double copy. In Part III, we view four-dimensional
gravity as a nonlinear interaction between self-dual and anti-self-dual parts. We apply this view to the derivation of four-dimensional spinning black hole solutions as well as their dynamics in point-particle effective theory. First, we derive a new self-dual black hole metric from classical double copy and show that the Kerr metric represents a pair of self-dual and anti-self-dual Taub-NUT solutions, elevating the Newman-Janis
algorithm to a rigorous derivation. Second, we propose a dynamical probe counterpart of Newman-Janis
algorithm. We give a Lagrangian derivation of spinning black hole Compton amplitudes that exhibit correct factorizations and are free of spurious poles for all helicity configurations while developing a
chiral formalism that manifests and maximally utilizes the simplicity of the self-dual sector.
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High Energy Physics (Theory) · Cross-listed from math.AG
Singular Points on Positroid Varieties and Planar N=4 Supersymmetric Yang-Mills Theory
Joseph Fluegemann
Positroid varieties $\Pi_f$ provide a decomposition of the Grassmannian $Gr(k,n)$; they can be enumerated using bounded affine permutations ($f$) which have bijections with a number of interesting combinatorial objects. Furthermore, (the nonnegative part of) positroid varieties parameterize the space that is integrated over when calculating amplitudes in planar N=4 supersymmetric Yang-Mills theory. The main question we answer in this thesis is whether a positroid variety $\Pi_f$ has any
geometric singularities. We show that it is sufficient to check singularity at the $T$-fixed points ($\lambda$) and we can obtain the multiplicity at these points $\lambda$ by calculating the equivariant
cohomology of $\Pi_f$ restricted to the point. We give 2 ways of doing this: (1) A diagrammatic way using affine pipe dreams and (2) A computational method. For (2), we have written code that does the computation and outputs the multiplicity (files at josephflueg.github.io). We have included tables listing the multiplicities of all the points on positroid varieties up to $n=6$. We also describe an ordering on pairs $(\Pi_f,\lambda)$ given by deletion/contraction that interacts nicely with smoothness, and describe the relationship between affine pipe dreams and finite pipe dreams. In Part II of this thesis connects with physics of planar N=4 SYM. We briefly introduce
quantum field theory, leading singularities, and positroids in N=4 SYM. We then explain Britto-Cachazo-Feng-Witten (BCFW) recursion and the BCFW bridge decomposition of an on-shell diagram. We describe how to build an on-shell diagram on a pipe dream using BCFW bridges. Finally, we work out some combinatorics related to inverse soft factors for on-shell diagrams and explore whether singularities in positroid varieties have relevance to amplitudes. This is a revised version of my thesis originally written in August 2024.
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Physics and Society
The scales of urban mobility shape socioeconomic mixing
Andrew Renninger, Egor Kotov and Carmen Cabrera
Urban daily mobility determines how far we travel and whom we encounter through the city. As local-living and polycentric planning gain popularity, a key question is whether more localised mobility can preserve the socioeconomic mixing that cities enable. Yet systematic evidence on how different scales of movement contribute to experienced social exposure remains limited. Here, we use anonymised GPS traces from ~20 million devices across 226 functional urban areas in France, Germany and the UK to decompose everyday mobility into three scales - proximal, medial and distal - and link these to the socioeconomic composition of destinations. Proximal trips remain similar in length across neighbourhoods, whereas medial and distal trips lengthen toward the periphery. Distal trips account for 33% of travel but facilitate 42% of inter-group encounters; reallocating them to local movement reduces experienced mixing by up to one third. These findings reveal a trade-off between shorter travel and integrated urban living.
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Mesoscale and Nanoscale Physics
Statistical Properties of a Fluctuation-Driven Nanomechanical Duffing Resonator
Monan Ma, Nathan Welles, Johnathon Barbish et al. (+5 more)
We investigate the fluctuating nonlinear dynamics of multiple modes of a nanomechanical doubly clamped beam resonator. Each mode is driven by Gaussian force noise centered around the resonance; the mode response is monitored while the force magnitude is increased, inducing a transition from harmonic to the nonlinear Duffing regime. To characterize the dynamics, we introduce an effective temperature based on the mode fluctuation amplitude. As the nonlinearity becomes prominent at large amplitudes, we observe a reduction in the effective thermal energy and a crossover in response statistics from Gaussian to platykurtic, consistent with the dynamics expected in a Duffing potential.
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All authors Monan Ma, Nathan Welles, Johnathon Barbish, Ismet I. Kaya, M. Selim Hanay, Oleksiy Svitelskiy, Mark R. Paul, Kamil L. Ekinci
Quantum Gases
Emergent hydrodynamic response and dynamical backreaction: Magnon bound-state propagation in a Bose-Hubbard fluid
Andrés N. Cáliz, Arnau Riera, Enrique Rico et al. (+2 more)
We study the nonequilibrium response of a one-dimensional Bose-Hubbard medium to a two-
magnon bound state propagating along an attractive XXZ chain. A Holstein-type displacement coupling makes the
magnon density act both as a local chemical-potential perturbation and as a source of
bosons. We derive a long-wavelength hydrodynamic description of the density and phase fluctuations and test it against
matrix-product-state simulations of the full coupled dynamics. The theory predicts a comoving near-field deformation together with retarded density waves confined to a sound cone. In the Mott regime, the deformation remains localized around the moving pair. In the compressible regime, two counterpropagating fronts detach and approach the semiclassical sound velocity, recovered from the
equilibrium density with no fitted parameters. The coupling also induces a dynamical backreaction that slows the bound state and broadens its
magnon-density profile. The comparison delimits where hydrodynamics stays quantitative once the probe reacts back on the medium.
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All authors Andrés N. Cáliz, Arnau Riera, Enrique Rico, João Barata, Marcin Płodzień
Materials Science
Charge-State Dependence of Electronic Excitations in keV Ions Transmitted Through Solids Probed by Ion-Photon Coincidence Measurements
Kevin Vomschee, Radek Holeňák, Svenja Lohmann et al. (+2 more)
Investigating the electronic excitations caused by light keV ions in matter contributes to a better understanding of materials modification such as space weathering or
plasma-wall interactions in fusion reactors as well as improved materials analysis methods such as low or medium energy ion scattering. This study investigates the dependence of specific excitations in keV He projectiles, the most common projectile employed in these analytical methods, on the kinetic energy of the ion. We report on
photon emission at energies >10eV emitted by projectiles excited upon transmission through different sample systems. We separate exit charge states and report on measurements of ion-
photon pairs in coincidence, i.e. we can link a
photon to the specific ion emitting it. From these measurements we extracted charge state resolved
photon yields and obtained a deep insight into the electronic excitation occurring. Our results show that the electronic excitation of the helium projectile is largely material independent and rising strongly with the kinetic energy of the projectile. The
photon yields are in good agreement with a common excitation model initially developed for beam foil spectroscopy. We hence extend the validity of this model to higher
photon energies and different sample materials. We further provide a detailed analysis of the employed coincidence approach and necessary corrections to the raw data, as the methodology has a broad applicability in fundamental research and materials analysis.
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All authors Kevin Vomschee, Radek Holeňák, Svenja Lohmann, Eleni Ntemou, Daniel Primetzhofer
Strongly Correlated Electrons
Interaction corrections to topological density three-point functions in two-dimensional Fermi liquids: a coadjoint orbit perspective
Akshay Pal, Andrew Lucas and Umang Mehta
Density three-point correlations are known to probe the
topology of the
Fermi sea in two-dimensional noninteracting systems. Here, we study how these correlations are modified by interactions using the coadjoint-orbit effective field theory. A key advantage of the coadjoint-orbit formulation is that it provides a systematic way to incorporate generalized Landau interactions in terms of bosonized degrees of freedom, mapping fermionic loop contributions onto simpler tree-level diagrams. We show that, for a general isotropic dispersion $\epsilon(p)$, even at linear order in the generalized Landau interaction, $\mathcal{O}(\mathcal{F}^{(2,0)})$, there exists a contribution proportional to the band
curvature $\epsilon''(p_F)$ that changes the nonanalytic structure of the free density three-point correlation function. This contribution introduces a distinct nonanalytic structure beyond that found in either the noninteracting case or an interacting Galilean-invariant system, showing that interaction effects can modify the
topology-detecting density three-point correlation.
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High Energy Astrophysical Phenomena
A Similarity Theorem and Its Breakdown in Atomic Black Hole Accretion
Marcus DuPont
Inferring black-hole mass and growth from radiation processed by dense atomic gas requires connecting the emitting atmosphere to its feeding flow. We derive an exact similarity for point-mass
accretion and use its limits to identify spectral information and dynamical consistency tests. At fixed temperature and composition, scaling mass, radius, and time together while scaling density inversely preserves the dimensionless flow, optical depths, and normalized spectra within a specified class of two-body microphysics, radiation, and boundary laws. Luminosity scales with mass, and the full atomic cooling curve is retained. Within this class the fixed-velocity power-law rescaling is unique. Density-sensitive populations and thermal radiation break the
symmetry; public models of Little Red Dots illustrate the resulting density information. Even with luminosity and density normalization known, a prescribed spherical inflow retains an exact degeneracy between central mass and inward drift. A proposed feeding model nevertheless supplies growth and inventory tests. For point-mass Bondi feeding at fixed ambient sound speed, luminosity and its conversion to retained growth determine the ratio of adjustment to growth time independently of black-hole mass. For the critical isothermal Bondi profile with full retention, comparable times require gas mass comparable to the hole's mass. More generally, steady spherical continuity links luminosity and gas transit time to a required reservoir mass and minimum radial column. Lower retention slows growth while leaving this inventory unchanged at fixed supply and transit time.
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Fluid Dynamics · Cross-listed from math.AP
Bounds for inertialess dynamo
Ali Arslan and Hezekiah Grayer II
We derive necessary conditions for instantaneous dynamo action for rotating convection. A magnetohydrodynamic model is considered in two settings: the rapidly rotating plane layer where inertia and viscosity are absent, and at an arbitrary rotation rate where viscosity is finite. In contrast to kinematic dynamo bounds, the
evolution of the
magnetic field is coupled via an inertialess force balance. The buoyancy-driven part of the flow $\mathbf{u}^{\mathrm{A}}$ in the event of dynamo action must in fact satisfy, for $3\leq p \leq \infty$ $$ Rm\, A_p\| \mathbf{u}^{\mathrm{A}}\|_{L^p} \geq 1 $$ where $A_p$ is an explicit constant, and $Rm$ is the
magnetic Reynolds number. In the inviscid model, $\mathbf{u}^{\mathrm{A}}$ depends only on the horizontal gradients of the vertical primitive of temperature. A refinement via the poloidal-toroidal decomposition allows us to replace $L^p$ in our constraint with an anisotropic norm for $L^{\infty}_z \dot{H}^1_{x,y}$. For the viscous model, we also derive necessary conditions for the growth of
magnetic enstrophy and a combined thermo-
magnetic energy. One branch of our constraints implies that the scaling $Ra_\nu \gtrsim Ek^{-3/2}$ is necessary for dynamo action, where $Ra_\nu$ is the classical Rayleigh number and $Ek$ is the Ekman number.
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Materials Science
Layer-Controlled Intermolecular Coupling and Many-Body Effects in C$_{60}$ Films
Hai-Lan Luo, Weitang Li, Luca Moreschini et al. (+4 more)
Crystalline C$_{60}$ is a molecular solid whose electronic properties emerge from the interplay of intermolecular hopping, electron correlations, and electron-vibration coupling. Unlike moir$\rm\acute{e}$ van der Waals
heterostructures, where interaction strength is commonly tuned by twist angle, molecular materials offer a complementary route in which layer number, molecular orientation, and substrate registry provide experimentally accessible control parameters. Here we present a systematic thickness-dependent angle-resolved photoemission study of C$_{60}$ films, spanning the monolayer to the bulk limit. The HOMO-derived band exhibits a non-monotonic
evolution: the intermediate-thickness film shows larger bandwidth, reduced effective mass, and pronounced gap-like and sub-band features. The experimental trends, together with Holstein-model simulations, point to strengthened effective intermolecular electronic coupling and enhanced electron-
phonon-induced spectral renormalization in the intermediate-thickness regime. These results identify a dimensional crossover in C$_{60}$ films and establish layer number as an effective knob for engineering electronic structure and many-body interactions in molecular thin films.
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All authors Hai-Lan Luo, Weitang Li, Luca Moreschini, Jonathan Denlinger, Zhigang Shuai, Claudia Ojeda-Aristizabal, Alessandra Lanzara
Lattice Field Theory
Renormalization-guided cascade upscaling for lattice field generation
Anna Hasenfratz, Ethan T. Neil, Letizia Parato et al. (+1 more)
We introduce a renormalization-group (RG) guided machine-learning
algorithm for
lattice field generation based on approximate inversion of an RG transformation. A “perfect blocking” construction supplies equilibrated long-distance modes, while a conditional normalizing flow reconstructs short-distance details and brief rethermalization removes residual errors. In 2D $\phi^4$ theory at criticality, a flow trained at $L\le32$ is reused recursively in cascades reaching $L=2048$ with correct long-distance physics.
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All authors Anna Hasenfratz, Ethan T. Neil, Letizia Parato, Noah Schwartz
Lattice Field Theory
Renormalization-guided inverse blocking for lattice field generation: construction and validation
Anna Hasenfratz, Ethan T. Neil, Letizia Parato et al. (+1 more)
We propose an
algorithm for generating
lattice field configurations based on the approximate inversion of a renormalization-group blocking transformation. We optimize the blocking transformation using a “perfect blocking” condition so that the blocked
lattice distribution is well approximated by a simple coarse action. The blocking is separated into an invertible smoothing transformation followed by decimation. Machine learning, in the form of a conditional normalizing flow, is used to reconstruct the short-distance degrees of freedom removed by the decimation. A short fine-action rethermalization then removes the residual mismatch. Because the coarse ensemble supplies the long-distance modes, the same blocking transformation and conditional flow can be reused recursively on larger
lattices, producing a cascade of configurations from an initial small-volume ensemble. We test the method in two-dimensional $\phi^4$ theory with $\lambda=1$ at criticality and demonstrate stable cascade upscaling from $16^2$ to $2048^2$
lattices on local computational resources. Controlled rethermalization tests show that short-distance mismatches relax rapidly, whereas a deliberately introduced mismatch in the relevant thermal direction relaxes much more slowly. The construction uses ingredients that admit natural extensions to higher-dimensional systems and, ultimately, to gauge and fermionic degrees of freedom.
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All authors Anna Hasenfratz, Ethan T. Neil, Letizia Parato, Noah Schwartz
Quantum Physics
How Long-Range Tails Reshape Non-Hermitian Spectra
Ding Gu, Zhanpeng Fu, Yu-Min Hu et al. (+1 more)
Exponentially decaying long-range hoppings are ubiquitous in realistic tight-binding models and are often truncated to obtain a finite-range description. We show that this approximation can fail dramatically in non-Hermitian systems under open boundary conditions: an infinitesimal long-range hopping can nonperturbatively reconstruct the spectrum and eigenstates of a short-range non-Hermitian system. The mechanism is controlled by a competition between the decay length of infinitesimal long-range hoppings and the localization length of non-Hermitian skin modes, leading to a sharp transition as the decay rate is tuned. In one dimension, we show that a squeezed generalized Brillouin zone (GBZ) replaces the original GBZ of the short-ranged
Hamiltonian, yielding the reconstructed open-boundary spectrum. In two or higher dimensions, we formulate a squeezed amoeba formulation describing the reconstructed spectral density. We further show that long-range hoppings can qualitatively reshape Green's function, which can be readily detected in experiments.
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All authors Ding Gu, Zhanpeng Fu, Yu-Min Hu, Zhong Wang
Statistical Mechanics
Solvable relaxation in discrete unitary systems: Ruelle-Pollicott resonances and CMV matrices
Urban Duh, Friedrich Hübner and Marko Žnidarič
Leading
eigenvalues of the truncated propagator, known as Ruelle-Pollicott (RP) resonances, are an elegant way of addressing the dynamics of
unitary many-body systems. We study
unitary propagators in their canonical form, known in the mathematical literature as the CMV
matrices, and obtain a number of exact results for RP resonances and the associated norm-diverging eigenvectors. For the simplest CMV class describing a unilateral shift with an
impurity, motivated by operator dynamics in dual-
unitary circuits, we obtain closed-form results and in particular show that the three independent ways of obtaining RP resonances – the truncated propagator, analytic continuation of the resolvent, and the rigged
Hilbert space approach – all give the same results. In more realistic CMV
matrices, in which shift-like operator dynamics characteristic of chaotic systems is only asymptotic, we rely on the rich theory of orthogonal
polynomials on the unit circle and identify two phases. In the first phase, relaxation occurs due to local operators effectively evolving into increasingly nonlocal ones with negligible backflow. Especially interesting is the second phase, which, surprisingly, exhibits faster relaxation because of contributions from the backflow of large operators. Additionally, in the second phase, RP resonances are not equal to the
eigenvalues of the truncated propagator, instead, they are “hidden” within a ring of ill-conditioned
eigenvalues.
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Mesoscale and Nanoscale Physics
Super-resolution Control of Individual Two-dimensional Quantum Emitters
Bosai Lyu, Valeria Vento, Ludivine Fausten et al. (+8 more)
Localized interlayer
excitons in semiconducting transition-metal dichalcogenide heterobilayers are
quantum emitters with a static electric dipole moment, making them excellent nanoscale charge sensors to probe correlated
quantum phases in a proximal layer. These emitters are electrically tunable and inherit
spin-valley selection rules, yet their deterministic spatial control remains challenging due to subwavelength confinement. Here, we present a platform that combines cryogenic optical spectroscopy with scanning probe microscopy to investigate trapped interlayer
excitons in MoSe$_2$/WSe$_2$
bilayers. By exploiting tip-induced local Stark shift, we achieve super-resolution of emitters separated by a few tens of nanometers and demonstrate deterministic control of individual charge states, including trion formation. Time-resolved measurements reveal tip-induced modification of the electromagnetic
vacuum around individual emitters, and thus control of their radiative emission. Our multi-point charge sensing platform with optical readout is particularly well-suited for future study of fractionalization and anyon dynamics in semiconducting fractional Chern
insulators.
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All authors Bosai Lyu, Valeria Vento, Ludivine Fausten, Daniel Suarez-Forero, Klevis Domi, Kenji Watanabe, Takashi Taniguchi, Alberto Morpurgo, Iaroslav Gaponenko, Patrycja Paruch, Ajit Srivastava
Quantum Physics
Carli Bruinsma, Pietro M. Posta, Joppe Stokvis et al. (+2 more)
Quantum Fourier transforms (QFTs) are essential primitives in
quantum algorithms. While abelian groups admit efficient QFT
circuits, with
circuit size
polynomial in the logarithm of the group order, efficient constructions are known for relatively few non-abelian families. We develop two new approaches to QFT
circuit construction, based on Mackey theory and Clifford theory, respectively, and use them to show exponential improvement in
circuit cost for specific group families. Using the Mackey-theoretic approach, we obtain explicit
quantum circuits for the QFT over $\mathrm{GL}_2(F_q)$ that scale polynomially in $\log q$, rather than polynomially in $q$. Using the Clifford-theoretic approach, we obtain QFT
circuits for wreath products $F\wr S_n$, whose cost depends on the cost of a QFT over $F$ and the size of its representation registers. This removes the restriction $|F|=\operatorname{poly}(n)$ required by previous generic constructions and can yield exponential improvements when $F$ itself has an efficient QFT. Together, these methods provide new systematic tools to construct QFTs for broad classes of finite groups.
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All authors Carli Bruinsma, Pietro M. Posta, Joppe Stokvis, Dmitry Grinko, Maris Ozols
Quantum Physics
Learning to Decode Concatenated Quantum Codes with Hierarchical Message Passing
Jiahui Wu, Chao Zhang, Zipeng Wu et al. (+1 more)
We introduce a neural message-passing framework for decoding general concatenated stabilizer codes. Soft beliefs propagate bidirectionally across concatenation levels, and lightweight neural networks learn only to aggregate incoming messages. For the concatenated $[[15,7,3]]$
quantum Hamming code, the resulting decoder achieves substantially higher thresholds than the state-of-the-art bidirectional hard-decision decoder under both bit-flip and depolarizing noise. In particular, the depolarizing pseudo-threshold nearly doubles, from $6.5\%$ to $12.3\%$. For many-hypercube codes, a decoder fine-tuned on
circuit-level errors in Knill's teleportation-based error correction can achieve lower logical-CNOT failure rates than their dedicated decoder, using a fixed number of message-passing iterations instead of extensive combinatorial search. Our framework provides a generic decoding tool for exploring the design space of concatenated codes, including non-CSS constructions, toward low-overhead fault tolerance.
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All authors Jiahui Wu, Chao Zhang, Zipeng Wu, Shilin Huang
Quantum Physics
Quantum Fourier transform for the symmetric group
Carli Bruinsma, Dmitry Grinko and Maris Ozols
Quantum Fourier transforms (QFT) for general groups were recognized to be fundamental already early in the field. A canonical example of non-abelian QFT for the symmetric group was outlined by Beals (1997). Later, a more detailed analysis of this
algorithm was carried out by Kawano and Sekigawa (2016). In this paper, we revisit that construction. After a careful analysis, we revise their gate complexity to $\widetilde{\mathcal{O}}(n^{3.5})$ and
circuit depth to $\widetilde{\mathcal{O}}(n^3)$. Moreover, we observe that their construction is not optimal in the choice of transversal elements, so we propose simpler realization of the symmetric group QFT.
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Superconductivity
A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities
Matthias Liepe Michelle M. Kelley, Sean Deyo, Nathan Sitaraman et al. (+4 more)
Experiments on superconducting cavities have found that under large RF fields the quality factor can improve with increasing field amplitude, a so-called “anti-Q slope.” We numerically solve the Bogoliubov-de Gennes equations at a superconducting surface in a parallel
magnetic field, finding at large fields there are surface quasiparticle states with energies below the bulk superconducting gap that emerge and disappear as the field cycles. Modifying the standard two-fluid model, we introduce a “three”-fluid model where we partition the normal fluid to consider continuum and surface quasiparticle states separately. We compute dissipation in a semi-classical theory of conductivity, where we provide physical estimates of elastic scattering times of Bogoliubov quasiparticles with point-like
impurities having potential strengths informed from complementary ab initio calculations of
impurities in bulk niobium. We show, in this simple yet effective framework, how the relative scattering rates of surface and continuum quasiparticle states can play a role in producing an anti-Q slope while demonstrating how this model naturally includes a mechanism for turning the anti-Q slope on and off.
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All authors Matthias Liepe Michelle M. Kelley, Sean Deyo, Nathan Sitaraman, Danilo B. Liarte, Tomás Arias, James P. Sethna, Thomas Oseroff
Quantum Physics
Exact quantification of nonlocal magic
Piotr Sierant
Magic, or nonstabilizerness, is the resource that lifts Clifford
circuits to universal
quantum computation and has become a standard diagnostic of many-body states. For a state shared between two parties, however, a basic question has remained open: how much of the magic resides in the correlations between the parties rather than in their local bases? Isolating this nonlocal magic requires minimizing over all local bases, an optimization that has so far resisted exact solution. Here we solve it for the stabilizer fidelity: the nonlocal magic of every pure multiqubit state is the distance of its
entanglement spectrum from the closest spectrum of Bell pairs. The same quantity governs an apparently unrelated task: a family of states universally embezzles
entanglement under local operations and classical communication if and only if its nonlocal magic diverges. The deciding property is not the amount of
entanglement but the way the
entanglement spectrum spreads its weight across factor-of-two windows of rank, so that critical chains and random-singlet states, with identical logarithmic
entanglement scaling, carry unbounded and vanishing nonlocal magic, respectively. Nonlocal magic thereby becomes an operationally meaningful property of
quantum correlations, directly accessible to tensor-network simulations and, through
entanglement spectroscopy, to experiments.
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High Energy Physics (Theory)
The Lagrangian Amplituhedron
Syl Tom Krovi and Ran J. Tessler
The article constructs the Lagrangian analog of the amplituhedron, studies its
geometric properties and BCFW decompositions.
Exactly Solvable and Integrable Systems
An Extended 2+1-Dimensional Gardner Equation: On Moving Boundary Problems Solvable via Ermakov-Painlevé II Symmetry Reduction
Colin Rogers and Sandra Carillo
A class of moving boundary problems of Stefan-type for an extension of the 2+1- dimensional Gardner equation is shown to be amenable to exact solution by application of a Ermakov- Painlevé II
symmetry reduction.
Soft Condensed Matter
Machine learned designs of functional colloidal foldamers
Ryan van Mastrigt and Zorana Zeravcic
A
protein's function follows from the structure it adopts, and in some cases which structure that is depends on the pathway taken. In programmable matter the target is fixed before assembly, and whatever else forms is treated as error. Here we show that pathways themselves form a design space. Using reinforcement learning, we fold model DNA-coated droplet chains into rigid two-dimensional geometries, uncovering two classes of pathways: downhill, in which bonds are only added, and detour, in which bonds are broken and remade before the target is reached: for some the only route that exists. Coarse-graining pathways by interactions gives experimentally realizable protocols. Some produce one geometry, others several: structures sharing a detour route can be cycled between, while those that coexist assemble into superstructures inaccessible to a uniform product. Function emerges from the pathways rather than being designed. Designing the process instead of the components could give colloidal materials that reconfigure on demand.
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Earth and Planetary Astrophysics
ExoMOD II. A Statistical Model of Transit Timing Variations in Kepler Multi-Planet Systems
David Nesvorny, Daniel A. Yahalomi, David Kipping et al. (+2 more)
In Paper I (Nesvorný et al. 2026), we forward modeled transit observations of the Kepler
telescope to characterize the orbital properties of close-in planetary systems. The new population model, ExoMOD, was calibrated on Kepler's DR25 data. Here we use ExoMOD to statistically predict Transit Timing Variations (TTVs) from gravitationally interacting
planets in the close-in systems, and compare these predictions with TTVs actually detected in the Kepler data. We find that
planet-
planet interactions are not expected to produce significant short-period TTVs, $P_{\rm TTV}/P_{\rm orb}<10$, where $P_{\rm TTV}$ and $P_{\rm orb}$ are the TTV and orbital periods, often enough to explain the short-period TTV signals inferred from the Kepler data. Most measured short-period signals must therefore have a different origin. The statistics of long-period TTVs – likely arising from the gravitational interaction between
planets – indicates that single transiting
planets have TTV-inducing companions nearly as often as doubles, thus ruling out multiplicity distributions with a prevalence of intrinsic singles. The fraction of
planets with measured long-period TTVs increases to $\simeq 15$-18% for observed multiplicities $m \geq 3$, suggesting a change in the orbital architecture. High-multiplicity planetary systems have low gap complexities and probably retained a
memory of their formation conditions. Ultimately, our work aims at developing a more informative feedback between observations and
planet formation theories.
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All authors David Nesvorny, Daniel A. Yahalomi, David Kipping, Cristian Beauge, Sarah C. Millholland
Earth and Planetary Astrophysics
ExoMOD I. A Forward Model for the Orbital Architecture of Kepler Multi-Planet Systems
David Nesvorny, Daniel A. Yahalomi, David Kipping et al. (+1 more)
Transit observations only detect
planets with favorable, near edge-on orientation of orbits as seen by a distant observer, which leaves much freedom for various interpretations in terms of the underlying planetary system architecture. Here we forward model transit observations of the Kepler
telescope to characterize the orbital properties of close-in planetary systems. We make sensible choices about the underlying distributions of
planet radii, masses and orbital periods, parameterize the orbital excitation with the Angular Momentum Deficit (AMD), and adopt an accurate method to account for transit detection. The fits to Kepler's DR25 data are executed with MultiNest. We find that the orbital period distributions of Kepler singles and multis are statistically different from each other – possibly a consequence of Kepler's observational baseline. The observed gap complexity distribution is reproduced when
planets in high multiplicity systems ($m \geq 5$) are assigned ideally correlated period ratios. The high-multiplicity systems probably retained a
memory of their formation conditions. The gap complexity metric also helps to constrain the AMD distribution. We find that systems with positive radius monotonicities typically harbor smaller
planets, as expected if the radius monotonicity is influenced by non-detections. A FGK
dwarf in the Kepler field should host $\simeq 2.4 \pm 0.2$
planets on average with radii $0.5 < R_{\rm pl}/R_\oplus < 7$ and orbital periods $3<P_{\rm orb}<300$ d. For a detected planetary system, there is roughly a 50% chance that Kepler transit observations missed at least one inner or intermediate-period
planet.
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All authors David Nesvorny, Daniel A. Yahalomi, David Kipping, Cristian Beauge
Materials Science
Switchable chiral antiferromagnetism through nonlinear magnetic susceptibility
Hua Chen and Philipp Gegenwart
Antiferromagnets (AFM) have attracted considerable
attention in recent years because a number of nontrivial, technologically relevant properties associated with time-reversal
symmetry (TRS) breaking are discovered in many materials. However, time-reversal (TR) partners of AFM states are generally challenging to be selected deterministically except in a few cases with nonzero net magnetization. Recently, it has been shown that the TR partners of the kagome
spin ice ground state in HoAgGe with strictly zero net magnetization can be selected through a nonlinear
magnetic susceptibility $\chi^{(1)}$. In this work, we generalize this scenario to a broad class of
chiral AFM with zero net magnetization but field-switchable ground states through $\chi^{(1)}$. After a general discussion of $\chi^{(1)}$ and its
symmetry constraints, we first present a first-principles formalism for calculating it including both mean-field and self-consistent corrections, and then apply the approach to the noncollinear AFM family Mn$_3X$N ($X=$ Ni, Ag, Ga, Zn, Sn) in the $\Gamma_{5g}$ phase. An intuitive picture of the origin of $\chi^{(1)}$ in similar noncollinear AFM is illustrated using 3-sublattice toy model. The model also predicts a nontrivial temperature dependence of $\chi^{(1)}$ due to competitions between the longitudinal and transverse single-
spin susceptibilities. Our work shows that nonlinear susceptibility can serve as a general protocol for accessing and switching TR partners in fully compensated AFM.
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