Strongly Correlated Electrons
Direct minimization versus iterative embedding in the ghost-Gutzwiller method: a comparative study of magnetism in Mott insulators
Antonio Maria Tagliente, Ivan Pasqua and Michele Fabrizio
Accurately describing a hypothetical
symmetry-invariant Mott
insulator presents a long-standing ing challenge in iterative
quantum embedding methods. We address this issue within the ghost- Gutzwiller method, which can be solved either through an iterative
embedding scheme, analogous to dynamical mean-field theory, or by directly minimizing its variational energy functional. Across the Mott transition of the single-band Hubbard model, these formally equivalent approaches behave very differently: the iterative scheme is computationally efficient but fragile, necessitating ad-hoc recipes in the Mott phase that fail in a Zeeman field, leading to a discontinuous energy and a spurious fully-polarized
insulator. Direct minimization avoids these artifacts, stabilizing a genuinely paramagnetic solution. Conversely, when
symmetry breaking is allowed, as in an
antiferromagnetic phase, the iterative scheme yields the correct solution, closely aligning with dynamical mean-field theory. Our findings delineate the conditions under which the iterative
embedding can be trusted and when direct minimization is instead required.
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Quantum Physics
Improved Methods for Determining Quantum Error Correcting Code Performance and Fault Tolerance
Michael Mullan, Matthew Weippert and Winton Brown
One of the central challenges in
quantum error correction is determining the performance of a code in the low-error regimes needed to implement utility-scale computations. While performance at these error rates is not amenable to direct Monte Carlo simulation, it can be extrapolated from simulations at higher logical error rates, assuming the logical error rate scales predictably with increasing distance or decreasing physical error rate. However, the expected scaling depends sensitively on the minimum weight of uncorrectable error patterns. In many cases, the minimum weight is unknown since it depends not only on the theoretical code distance, but also on details of the implementation. Markov chain Monte Carlo (MCMC) methods, as adapted to
quantum error correction by Bravyi and Vargo, provide a way to estimate logical failure rates in these low-error regimes via simulation. While offering significant gains over Monte Carlo, the described Metropolis
algorithm makes small changes to the current logical failure patterns which results in slow convergence. In this paper, we argue that typical failure patterns include a large number of easily correctable errors that coexist alongside a malignant core. This observation motivates two new approaches to better evaluate code performance. First, we describe a
pruning algorithm designed to obviate these correctable errors and focus on the problematic low-weight core. Second, we develop a novel family of Metropolis-Hastings
algorithms, referred to as subregion MCMC. This technique is parameterized by the fraction of the error pattern that is resampled at each step, effectively interpolating between Monte Carlo and single step MCMC. We show that a judicious choice of this parameter results in far faster convergence than prior work.
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Cosmology and Nongalactic Astrophysics
Shear-kSZ: A New Estimator for the Matter-Electron Power Spectrum from kSZ Tomography and Weak Lensing
Boryana Hadzhiyska
We propose a new
estimator of the electron–matter power spectrum, $P_{me}(k)$, which correlates the kinematic Sunyaev–Zel'dovich (kSZ) temperature with the product of the line-of-sight velocity field and the weak-
lensing convergence. Like the stacked kSZ
estimator, it factorizes into a calibratable velocity kernel times $P_{me}(k)$, but it probes the full matter distribution rather than the gas around a biased tracer. It therefore measures the baryonic suppression of the matter power spectrum, $S(k)$, one of the dominant astrophysical systematics for Stage-IV
cosmic shear. We derive an analytic expression for the
estimator, validate it against simulations at the per-cent level, and show that its parity structure cancels
cosmic microwave background (CMB) foregrounds. We forecast the detectability with a realistic pipeline: velocities reconstructed from the simulated tracers, with and without photometric-
redshift errors; the kSZ signal of all the ionized gas along the line of sight; a CMB map with Simons Observatory (SO) noise; and LSST source samples free of intrinsic
alignments. A DESI-like spectroscopic sample at $0.5<z<1$ over the $20\%$ of the sky that DESI, LSST and SO share gives a $4$–$7\sigma$ detection. Photometric
redshifts cost only $5$–$10\%$ of the significance, so LSST can supply its own velocity tracers over its full overlap with SO: with tracers at $0.1<z<1.3$ and five source samples we find $10\sigma$ in an end-to-end simulation, and $13\sigma$ with Advanced SO (16$\sigma$ if extending to $z < 1.5$). This corresponds to a few-per-cent measurement of $S(k)$ at $k\simeq1$–$4\,h\,{\rm Mpc}^{-1}$, the scales that matter most for
cosmic shear.
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Superconductivity
Momentum Structure of Superconductivity and Sublattice Effects from Quasiparticle Interference in CsV$_3$Sb$_5$
Aaron G. Greenberg, Xinze Yang, Junze Deng et al. (+11 more)
Quantum interference encoded in the sublattice texture of kagome Bloch wavefunctions has been widely invoked as a route to correlated states, including
chiral charge order, unconventional superconductivity, and their possible intertwining in pair-density-wave (PDW) states. Using sub-Kelvin scanning tunneling microscopy, we conducted spectroscopic mapping of the kagome material CsV$_3$Sb$_5$ with high energy resolution and dense energy sampling through the superconducting gap. Quasiparticle interference (QPI) analysis, aided by ab initio and
symmetry calculations, reveals an isotropic superconducting gap on the
Fermi surfaces derived from V $M_z$-even ($M_z^+$) $d$ orbitals, thereby constraining possible gap
symmetries and limiting any gap anisotropy to the remaining V $M_z$-odd ($M_z^-$) and Sb $p_z$ bands. Meanwhile, the CDW-peak-selected d$I$/d$V$ spectra closely track the spatially averaged density of states and show no distinct enhancement restricted to subgap energies, which do not support an additional PDW modulation within our sensitivity. Finally, the selective absence of specific QPI scattering vectors points to a spectroscopic sensitivity to sublattice character on the
Fermi surface. Together, these results provide a clearer experimental picture of the low-energy electronic structure relevant to kagome superconductivity in CsV$_3$Sb$_5$.
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All authors Aaron G. Greenberg, Xinze Yang, Junze Deng, Pranab Kumar Nag, Kirsty Scott, Yi Jiang, Haoyu Hu, Chandra Shekhar, Dong Chen, Claudia Felser, Santiago Blanco-Canosa, Päivi Törmä, B. Andrei Bernevig, Eduardo H. da Silva Neto
Quantum Physics
Parity-Based Time-Bin Encoding Enabling SWAP Between Polarization and Time-Bin Qubits
Adam Sultan and Connor Kupchak
Multi-degree-of-freedom photonic
quantum processing requires routing between degree-of-freedom (DOF)
qubit encodings on a single
photon. A SWAP between polarization and time-bin
qubits is an advantageous primitive for such architectures, however conventional early/late time-bin encoding does not support bidirectional logical time-bin flips from late to early which limits the ability to implement certain
quantum operations. We introduce a parity-based time-bin encoding in which logical $\ket{0}_T$ and $\ket{1}_T$ correspond to even and odd multiples of a spacing $\Delta t$, so that a physical delay of $\Delta t$ implements $\ket{0}_T \leftrightarrow \ket{1}_T$. This encoding is the enabling ingredient that makes a polarization-controlled delay line implement $\mathrm{CNOT}_{P \rightarrow T}$ and aligns naturally with periodic refractive index modulation for $\mathrm{CNOT}_{T \rightarrow P}$. Composing three such CNOT operations sequentially results in a deterministic SWAP between polarization and time-bin degrees of freedom. We quantify how EOM voltage errors reduce the polarization-flip probability and estimate timing requirements from modulator switching, detector resolution, and timing jitter, giving an illustrative timing budget.
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Cosmology and Nongalactic Astrophysics
The art of simulating the early Universe. Part III: Scalar-Gauge-Fluid Dynamics
Daniel G. Figueroa, Kenneth Marschall, Antonino S. Midiri et al. (+1 more)
We discuss
lattice methods for the simulation of fluid dynamics in the early Universe. This review represents a third entry in the monographic series on
lattice cosmology techniques~\cite{Figueroa:2020rrl,Baeza-Ballesteros:2025tme}, which previously covered canonical and non-canonical field theory dynamics. Here, we first review the continuum theory of fluid dynamics in flat spacetime, and then in an FLRW background. We consider conservation and non-conservation forms of the equations of motion for fluids in isolation or coupled to scalar and/or gauge fields, and either fully relativistic or subrelativistic regimes of fluid bulk motion. After reviewing basic
lattice concepts, we introduce detailed discretization schemes for fluid dynamics in expanding backgrounds for: $i)$ isolated perfect fluids, $ii)$ isolated imperfect (viscous) fluids, $iii)$ fluids coupled to gauge fields, and $iv)$ fluids coupled to scalar fields. Our
evolution algorithms accommodate self-consistent expansion sourced by all scalar, gauge, and fluid sectors, preserving gauge invariance to machine precision in some cases. We also review
lattice methods to set up the initial conditions for fluids, and the implementation of gravitational wave dynamics sourced by all scalar, gauge, and fluid degrees of freedom. This document represents the theoretical basis for the scalar-gauge-fluid module that will be publicly released as part of ${\mathcal C}{\tt osmo}{\mathcal L}{\tt attice}~{\tt v3.0}$ after publication of this monograph, check http://www.cosmolattice.com for updates.
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All authors Daniel G. Figueroa, Kenneth Marschall, Antonino S. Midiri, Alberto Roper Pol
Applied Physics · Cross-listed from cs.AR
Investigating reservoir computing for branch prediction in pipelined processors using emerging CMOS memristor devices
Harvey Samuel George Johnson and Sendy Phang
This project aimed to develop a novel reservoir compute (RC) implementation framework targeting high-speed operation and integration with CMOS digital logic. With the target workload of branch prediction (BP) for multistage pipelined central pro-cessing unit (CPU) cores. For this, a novel memristor based RC design framework was developed within the context of the workload requirements. This was then implemented in simulation using industry standard modelling
languages of System Verilog (SV) and Verilog-AMS (VAMS).The developed RC design framework was subsequently verified using a basic sequence detection task before further benchmarking for its effectiveness at BP. The developed RC framework was tested using the Dhrystone performance
benchmark, while targeting the RISC-V RV64GC instruction set architecture (ISA). Conducted testing demonstrates that RC shows great promise for ap-plication to BP and is capable of achieving impressive overall prediction accuracy. However, testing also shows that further refinement of the developed RC design framework is necessary to address shortfalls in the adaptability of the proposed RC system. As comparison against the state of the art TAGE predictor showed the proposed RC design framework to be 15x slower to adapt to changes in branching behaviour.
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Plasma Physics
SPECTRE: A robust solver for 3D equilibria with arbitrary topology
E. Balkovic, J. Loizu, E. Lanti et al. (+6 more)
We present SPECTRE, a new
equilibrium code based on the Multi-Region relaxed MHD model for robustly calculating 3D
equilibria with general
magnetic topology, allowing for flux surfaces,
magnetic islands, and chaos. The code builds on a previous MRxMHD solver, SPEC, but performs significantly better thanks to a new formulation of force, the use of a stable trust-region-based least squares minimization scheme, as well as several additional features. SPECTRE is verified through application to configurations with known
equilibrium solutions, in
vacuum and with finite beta, both in the fixed boundary and the free boundary mode. Notably, these include
vacuum equilibria of a quasi-axisymmetric (QA) device in fixed-boundary mode, and of W7-X in the free-boundary mode, along with a classical stellarator finite-beta free-boundary case. Finally, the solver is applied to a modern optimized finite-beta quasi-isodynamic (QI) configuration, where we demonstrate calculation of a strongly-shaped
equilibrium with a core island which is in agreement with a HINT calculation.
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All authors E. Balkovic, J. Loizu, E. Lanti, C. Smiet, C. Lazzati, R. Ramasamy, A. Goodman, J. Geiger, J. P. Graves
High Energy Physics (Theory)
Quantum Field Theory Of Cosmological Perturbations Induced By Ultralight Dark Matter
Tomislav Prokopec and Marco Vecchioni
The growth of
primordial perturbations during the matter-dominated era is primarily driven by dark matter. Ultralight scalar fields (ULDM) are a promising candidate for this role, conventionally modeled as operating in a classical, high-occupation regime. In this work, we develop a first-principles field-theoretic framework to investigate the impact of ULDM on linear cosmological perturbations during matter domination, explicitly retaining its
quantum nature. Deriving a closed equation for the graviton field dynamics, we compute and regularize its source terms for a generic Gaussian initial state of the ULDM field within the adiabatic (WKB) approximation, employing the middle-point working assumption for non-local terms. After gauge-fixing we find that, contrary to previous claims, the classical condensate of ULDM has no influence on gravitational wave propagation. However, the time-dependent graviton effective mass induced by
quantum pressure of the squeezed state can drive parametric resonance in specific
primordial gravitational wave modes. We demonstrate this growth is negligible for non-relativistic ULDM at matter-radiation equality under the assumption of a power-law squeezing spectrum for masses in the range $m \sim 10^{-21}{-}10^{-24}$ eV.
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General Relativity and Quantum Cosmology
Quadrupolar tidal effects destroy the integrability of black hole geodesics: analytic proof and numerical evidence of chaos
Paul Ramond
In general relativity, the motion of a test mass around a rotating black hole is described by Kerr geodesics. Owing to the
symmetries of the Kerr spacetime, these geodesics possess four constants of motion, rendering the associated
Hamiltonian system integrable. This integrability underlies much of the analytical framework used to model asymmetric-mass-ratio inspirals, key sources for future gravitational-wave detectors. Real compact bodies, however, are not test masses: their internal structure couples to the background
curvature. In this work, we show that a non-spinning body endowed with a tidally induced quadrupole admits no deformation of the geodesic Carter constant that remains conserved, for generic
tidal couplings and generic Kerr
spin. Consequently, the leading-order
tidal dynamics is generically non-integrable. The proof is analytic and relies on two key ingredients: a covariant
Hamiltonian formulation of
tidal dynamics on the same phase space as the geodesic problem, valid in arbitrary background spacetimes, and a novel relation between
curvature tidal scalars and the geodesic Carter constant derived from the algebraic and Killing
symmetries of Kerr spacetime. We complement this result with numerical diagnostics of the tidally perturbed dynamics, including Poincaré sections, Lyapunov exponents, and escape-time maps. These reveal chaotic structures in phase space, such as
stochastic layers, sensitivity to initial conditions, and fractal basin boundaries, consistently with the analytic non-integrability result.
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Plasma Physics
Divertor topology and vacuum vessel design for stellarators
Andrew Giuliani, Raffael Wendlinger, Misha Padidar et al. (+4 more)
We present stellarator optimization
algorithms for designing the edge
magnetic structure in
vacuum fields, together with the
vacuum vessel. First, we introduce a numerical method that robustly computes periodic-orbit fixed points of any type (
elliptic,
hyperbolic, or
parabolic), which could form the basis of a divertor. To couple divertor and
vacuum vessel design, we introduce parametric families of
vacuum vessels for which point-to-vessel distances, and their derivatives, can be computed efficiently. The resulting
algorithms use signed distance functions to enforce coil-vessel clearance while allowing coils to be placed on or off the vessel. Using these methods, we jointly optimize modular coils and the
vacuum vessel to realize a wide range of
magnetic topologies for diverting exhaust, including standard X-point divertors, and single- and double-null configurations. For the first time, we show that precise snowflake divertors can be achieved in stellarators. Using this framework, we generate a number of quasi-axisymmetric stellarator designs with compatible
vacuum vessels and diverse divertor architectures, which we consider to be candidates for a next-generation
STAR Lite prototype.
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All authors Andrew Giuliani, Raffael Wendlinger, Misha Padidar, Robert Davies, Shibabrat Naik, Calvin Lowe, Georg Harrer
Quantum Physics
Hardware-efficient erasure-error detection with an integer fluxonium
Junyoung An, Helin Zhang, Jeffrey M. Gertler et al. (+13 more)
Erasure-error detection can improve the efficiency of
quantum error correction by revealing the times and locations of their error events. In this work, we demonstrate erasure conversions and mid-
circuit erasure detections in a single integer fluxonium, in which the states $\mathrm{|g\rangle, |f\rangle}$ encode the logical states and $\mathrm{|e\rangle}$ encodes the erasure state. The integer fluxonium suppresses direct $|\mathrm{f} \rangle \rightarrow |\mathrm{g} \rangle$ transitions and allows the dominant $|\mathrm{f} \rangle \rightarrow |\mathrm{e}\rangle$ transitions to be converted into detectable erasures. Furthermore, we identified a design space that nullifies the resonant-frequency shift between the two logical states, enabling ancilla-free mid-
circuit erasure checks using the same resonator employed for final readout. By discarding the detected erasure events, we achieved an 8.4-fold increase in the $|\mathrm{f}\rangle$ state lifetime, a 1.38-fold increase in the Hahn-echo time, and a reduction of single-
qubit gate error from 0.061(2)% to 0.030(5)%. Our results establish integer fluxonium as a hardware-efficient platform for erasure-error detection and conversion, while identifying the improvements required to realize an effective erasure
qubit with high erasure bias.
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All authors Junyoung An, Helin Zhang, Jeffrey M. Gertler, Kate Azar, Renée DePencier Piñero, Michael Gingras, Junghyun Kim, Bethany M. Niedzielski, Ilan T. Rosen, Mollie E. Schwartz, Joel Î-j. Wang, Terry P. Orlando, Jeffrey A. Grover, Max Hays, Kyle Serniak, William D. Oliver
Mathematical Physics · Cross-listed from math.AP
Integral Representations for Interface Problems for the Barenblatt-Sobolev-Galpern Pseudoparabolic Equation
Andreas Chatziafratis, Sergey A. Rukolaine and Elias C. Aifantis
We obtain novel integral representations, expressed as contour integrals in the complex
Fourier plane, for the solution of fully nonhomogeneous initial-boundary-value as well as interface problems for the Barenblatt-Zheltov-Kochina pseudo-
parabolic equation of Sobolev-Galpern type formulated on the real line, half-line and finite interval. This fundamental partial differential equation (PDE) of mathematical physics emerges in a wide variety of natural phenomena and applied sciences including continuum mechanics, thermodynamics, chemical engineering, solid-state electronics, semi-conductor devices, battery research, and nanotechnology. A suitable implementation of a modern methodology, known as Unified Transform Method, is in force throughout this study, with particular challenges arising due to the higher-order mixed-derivative term of the PDE and the generality of the problems under consideration altogether. The boundary and interface conditions appear to be non-standard but are naturally dictated by the structure of the PDE itself. Our explicit analytical formulae directly lend themselves to future explorations of the solutions' qualitative properties such as asymptotic behavior, spatio-temporal dynamics, regularity and well-posedness. This work is expected to be of utility also in the investigation of nonlinear counterparts as well as towards the study of phase-transition phenomena and free-boundary problems, where the interface evolves dynamically according to energy balance laws.
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Quantum Physics
The Keyl-Werner algorithm is not optimal for spectrum estimation
Angelos Pelecanos, Jack Spilecki, Ewin Tang et al. (+1 more)
We give an
algorithm which, given $n = O(d^2 \cdot (\log\log(d)/\log(d))^2)$ copies of $\rho$, estimates the
eigenvalues of $\rho$ to constant error in total variation distance. Thus, we can learn the
eigenvalues of a
quantum state with fewer copies than the $\Theta(d^2)$ needed to run full state
tomography. This is the first improvement to spectrum estimation over the influential Keyl-Werner
algorithm, which uses $n = \Theta(d^2)$ copies, thereby resolving a question raised by Keyl and Werner in 2001 and refuting a 2016
conjecture of Wright. Our main technical tool is a new
tomography guarantee, where the error of
tomography in a particular direction $|w\rangle$ scales with $\langle w | \rho |w\rangle$ for all directions simultaneously. From this stronger "relative-error" bound, we recover better
algorithms for principal component analysis in Bures distance and
tomography in $\chi^2$-divergence as corollaries.
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All authors Angelos Pelecanos, Jack Spilecki, Ewin Tang, John Wright
Quantum Physics
Ky Fan majorization for binary tensor products
Michael M. Wolf and Yuanheng Zhou
We provide a short proof of a Ky Fan-type majorization relation for the singular values of a sum of binary tensor products of
matrices. This generalizes Alhejji's result (arXiv:2410.18254) from two summands to arbitrary sums and from positive
matrices to arbitrary
matrices. As an application, we show a majorization relation between the singular values of a completely positive map and those of its Kraus operators.
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Strongly Correlated Electrons
Interaction-induced sign reversal of the orbital magnetic susceptibility in Chern insulators
Ke Huang and Xiao Li
It has been well established that the orbital magnetization of interacting electrons can be simply evaluated by applying the single-particle formula to self-consistent HF bands. However, we show that such procedure fails qualitatively for orbital
magnetic susceptibility, especially in topological systems: in a Chern-insulating phase of twisted MoTe$_2$, the interaction-induced correction reverses the sign of the susceptibility. This result follows from an algebraic framework that solves the HF problem at finite
magnetic field, where noncommuting canonical momenta obstruct a direct calculation: a reverse Peierls substitution maps every
magnetic-translation-invariant operator to a unique bivariate function, converting the finite-field self-consistency into a function equation that can be expanded systematically in $B$. At first order, this yields a linear equation for the field-induced change $\delta X$ of the Fock potential, leading to an intrinsically interaction-induced susceptibility in addition to a single-particle-like one. The framework reproduces the Středa formula for
insulators, and an auxiliary-
Hilbert-space construction carries it to periodic and moiré systems. Finite-field HF calculations in a gapped Dirac model and in the twisted-MoTe$_2$ Chern
insulator confirm the theory quantitatively.
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Quantum Physics
Razvan Stanescu and Hugo Ribeiro
High-fidelity
quantum control relies on accurate models of driven dynamics. We examine this re- quirement for single-
qubit gates in superconducting transmons by comparing control pulses derived from the standard Duffing approximation and from a
Hamiltonian constructed by diagonalizing the transmon eigenbasis. Using the same correction-pulse construction for both models, we show that correction fields derived from the Duffing approximation can substantially reduce the gate error pre- dicted by that model while remaining less effective when combined with an independently calibrated baseline pulse in the diagonalized-transmon model. In the fast-gate regime, such transferred correc- tions can even fail to improve over the uncorrected diagonalized-transmon baseline. We show that small model-dependent differences in both the energy spectrum and the representation of the drive operator can compound during driven
evolution, resulting in different predicted error generators and correction pulses. A mismatch in the accumulated AC Stark phase provides one illustrative di- agnostic of this dynamical model dependence. We further demonstrate that the model
Hamiltonian informs the choice of control framework: Omitting relevant leakage pathways or higher-order error channels can lead to an overly restricted correction strategy. Including these channels motivates an extended correction framework that improves the gate performance using the same physical control resources.
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Materials Science
Formation of $\mathrm{L}1_2$-ordered $\gamma'$-$\mathrm{Ni}_3\mathrm{Al}$ precipitates in ternary Cu-Ni-Al alloys modelled using an ab initio concentration wave theory and atomistic simulations
Christopher D. Woodgate, Hubert J. Naguszewski, Samuel L. Deacon et al. (+4 more)
Precipitation-strengthened Cu-Ni-Al
alloys are of interest for technological applications because coherent, $\mathrm{L}1_2$-ordered $\gamma'$-$\mathrm{Ni}_3\mathrm{Al}$ precipitates can confer high mechanical strength while allowing the material to retain many of the good transport properties characteristic of elemental Cu. In this work, we study the thermodynamics and phase stability of the pseudobinary $\textrm{Cu}_x (\textrm{Ni}_{3/4} \textrm{Al}_{1/4})_{1-x}$ system, $0 \leq x \leq 1$. We use a computational modelling framework combining first-principles electronic structure calculations with a concentration wave analysis from which atom-atom effective pair interactions are extracted for use in atomistic Monte Carlo simulations. Our modelling reveals three distinct, composition-dependent regimes of phase behaviour, in qualitative agreement with the experimentally determined phase diagram. At low Cu content, Cu is soluble in the $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$ phase, with a single identifiable phase transition corresponding to chemical ordering between Ni and Al. At intermediate compositions, this high-temperature ordering is followed at lower temperatures by phase separation of Cu and $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$. Finally, at high Cu content, $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$ precipitates directly from the solid solution, with no clearly identifiable secondary transition. We relate these phase transformations to features of the underlying electronic structures of the considered
alloys. Overall, this work demonstrates a computationally efficient workflow capturing both chemical ordering and coherent precipitation in multicomponent substitutional
alloys, with relevance to the study of phenomena such as precipitation strengthening.
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All authors Christopher D. Woodgate, Hubert J. Naguszewski, Samuel L. Deacon, Mathys P. Potel, Ján Minár, David Quigley, Julie B. Staunton
Quantum Gases
Engineering SU($N$)-Symmetric Hubbard Models with Microwave-Shielded Dipolar Molecules
Jing-Lun Li, Ragheed Alhyder, Andreas Schindewolf et al. (+3 more)
Ultracold polar molecules provide strong, long-range interactions that microwave shielding makes tunable and nearly
nuclear-
spin independent, giving an emergent SU($N$)
symmetry. However, extended Hubbard models of polar molecules in optical
lattices lack, so far, controllable finite on-site interactions, a key ingredient of strong correlated physics. We show that tuning the Rabi frequency of the microwave coupling can bring two individual molecules (monomers) on neighboring
lattice sites into resonance with a field-linked dimer (doublon) on one of the sites, enabling coherent doublon–monomer-pair conversion. In this model, we characterize the key Hubbard parameters and the dimer lifetime, demonstrating that the on-site and off-site interactions can be tuned nearly independently through the microwave amplitude and orientation, respectively. Our results provide a roadmap for implementing SU($N$)-symmetric extended Hubbard models with controllable doublon fluctuations, providing access to
quantum-simulation in the strongly dipolar regime.
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All authors Jing-Lun Li, Ragheed Alhyder, Andreas Schindewolf, Kaden R. A. Hazzard, Mikhail Lemeshko, Georgios M. Koutentakis
Superconductivity
Dual Enhancement of Superconductivity in FeSe/SrTiO3 via Orbital and Correlation Synergy
Guihao Jia, Jingming Yan, Yucong Peng et al. (+5 more)
In iron-based
superconductors, the dz2 orbital band typically resides far below the
Fermi level and has not been considered to participate in Cooper pairing. Here, using monolayer FeSe/SrTiO3 as a model system, we demonstrate that tip-induced tensile strain controllably shifts the dz2 band toward the
Fermi level, driving a two-stage enhancement of superconductivity. In-plane
lattice expansion first enhances electronic correlation, amplifying superconductivity in the initial stage. As strain further increases, the upward-shifted dz2 band hybridizes with the dxy band, reconstructing the pairing-active d-orbital bands and inducing a secondary, stronger gap enhancement. Collectively, these two stages enlarge the superconducting gap from 17.8 to 23.6 meV. Throughout this process, invariant
Fermi wave vectors confirm that the enhancement originates from band renormalization and reconstruction rather than carrier doping. Our work establishes a route to tailor superconducting states via strain-activated electronic correlations and band engineering, and reveals a previously unrecognized orbital-selective pairing mechanism with broad implications for correlated multiband
superconductors.
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All authors Guihao Jia, Jingming Yan, Yucong Peng, Shendong Su, Pei Ouyang, Xiaopeng Hu, Qi-Kun Xue, Wei Li
Mathematical Physics · Cross-listed from math.NA
Numerical approach to the London Equation of superconductivity
Nicolás Barnafi, Ignacio Labarca-Figueroa and Carlos Román
In this work, we propose a general discretization strategy for solving the London equation for type-II
superconductors in the whole space $\mathbb{R}^3$. To compute the
magnetic field $H_0$, we reformulate the problem for the
magnetic potential as a transmission problem and discretize it through a nonstandard FEM-BEM coupling. This formulation accounts for both the bounded interior domain and the unbounded exterior domain without introducing an artificial truncation. We then compute the vector field $B_0$, which arises from the Helmholtz-Hodge decomposition of the
magnetic potential in the superconducting sample. This field enters the isoflux problem, which identifies the curves along which
vortex nucleation first becomes energetically favorable in the Ginzburg–Landau model of superconductivity. We recast the equations for $B_0$ using the mixed formulation of Kikuchi, in which the divergence-free constraint is imposed weakly, and discretize the resulting problem using a classical $H(\operatorname{curl})$-conforming finite element discretization. We validate our discretization strategy through convergence tests and conclude with an application to the isoflux problem. For a ball under a constant applied
magnetic field, the unique maximizer is the diameter aligned with the field. For ellipsoids under a constant applied
magnetic field aligned with their major axis, our computations provide numerical evidence of a different behavior in sufficiently elongated, cigar-shaped geometries: off-axis competitors reminiscent of U-shaped
vortex configurations attain a larger isoflux ratio than the major axis. Since the major axis is therefore not a maximizer, any off-axis maximizer generates, by rotational
symmetry, a continuous family of equivalent configurations, implying non-uniqueness and the presence of a degenerate rotational direction in the isoflux problem.
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Atomic Physics
Tackling the uncertainty of the nuclear-polarization correction to the bound-electron $g$ factor by means of the nuclear Skyrme interaction
Arnab Choudhury and Igor A. Valuev
The Coulomb part of the leading-order
nuclear-polarization correction to the bound-electron $g$ factor of hydrogenlike ions is investigated in a microscopic approach from the
nuclear point of view. To this end, the effective Skyrme force is employed to model nucleon-nucleon interactions, with the energies and the reduced transition probabilities of collective
nuclear excitations being obtained in the Hartree-Fock-based random-phase approximation. These
nuclear parameters serve as input for the
nuclear-polarization correction, evaluated via effective self-energy diagrams where the
photon propagator is modified by a
nuclear-polarization insertion. A diverse set of Skyrme parameterizations is probed for $^{40}\text{Ca}^{19+}$, $^{60}\text{Ni}^{27+}$, $^{90}\text{Zr}^{39+}$, and $^{120}\text{Sn}^{49+}$, and the results are compared to the common approach involving experimental
nuclear data and estimates based on energy-weighted sum rules. As a result, tighter constraints on the theoretical uncertainties of the
nuclear-polarization corrections are obtained, providing key input for high-precision measurements of the bound-electron $g$ factors of heavy hydrogenlike ions.
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Materials Science
No band gap, no problem: Defects in InAs using a band-avoiding occupation-constrained density functional theory
Peter A. Schultz, Arthur H. Edwards, Evan M. Anderson et al. (+2 more)
Density functional theory (DFT) underestimates the experimental band gap—the infamous band gap problem. As the band gap defines the energy scale of defect levels, this complicates computation of charge transition energies for atomic defects. In the extreme case of narrow-gap
semiconductors, the DFT band gap collapses to zero, seemingly precluding quantitative predictions of defect levels. We present a band-avoiding occupation-constrained DFT (ba-occ-DFT) approach that prevents spurious occupation of band-edge states and enables reliable total energy calculations of atomic defects. Application to indium arsenide (InAs) shows that ba-occ-DFT circumvents the band gap problem, separates band-edge errors from defect level calculations, and enables rigorous defect level predictions in a narrow-gap
semiconductor despite a zero DFT band gap.
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All authors Peter A. Schultz, Arthur H. Edwards, Evan M. Anderson, Anthony C. Knighton, Leopoldo Diaz
Quantum Physics
Native CCZ Gate with Fluxonium Qubits and a Microwave-Driven Coupler
Grigoriy S. Mazhorin, Tatyana A. Chudakova, Alena S. Kazmina et al. (+12 more)
Native multi-
qubit gates could reduce the overhead associated with decompositions into single- and two-
qubit operations, but whether they can simultaneously provide high fidelity, simple control and robustness against parasitic interactions in scalable architectures remains unclear. Here we experimentally realize a 65-ns native controlled-controlled-phase operation, locally equivalent to the Toffoli gate, with a fidelity of 99.39(5)% in a three-
qubit processor unit based on fluxonium
qubits coupled via a microwave-driven transmon coupler. The implemented operation would require CZ fidelities of approximately 99.94% if realized through a conventional decomposition. The gate is implemented with a single control pulse, that relies on a simple calibration procedure yielding coherence-limited performance. This processor unit naturally extends to scalable two-dimensional layouts with low parasitic interactions. Altogether, these results establish native multi-
qubit gates as a viable hardware-efficient primitive for scalable superconducting
quantum processors.
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All authors Grigoriy S. Mazhorin, Tatyana A. Chudakova, Alena S. Kazmina, Nikolai G. Berezkin, Arina V. Zotova, Artyom M. Polyanskiy, Nikolay N. Abramov, Mikhail A. Tarkhov, Alexander M. Mumlyakov, Igor V. Trofimov, Elizaveta A. Krivko, Nikita Yu. Rudenko, Maxim V. Chichkov, Vladimir I. Chichkov, Ilya A. Simakov
Fluid Dynamics
A New Paradigm for 3D Turbomachinery Design: Generative Diffusion Model Based Framework with Direct Geometry Encoding
Yingfan Geng, Jinhong Wang, Lazaros Papachristodoulou et al. (+2 more)
The aerodynamic design of turbomachinery is critical to the performance of the overall energy system, yet it is challenging due to the complex non-linear flow physics and the presence of multiple-target design compromises. Denoising
diffusion model, as one of the leading approaches in generative machine learning, has shown its advantages of high design solution accuracy and diversity in many engineering applications. In this study, we bring it to the 3D inverse design problem of turbomachinery, using centrifugal compressors as a classic representative, to demonstrate the new methodology for complex geometry designs. A
diffusion model-centred design framework has been developed in this study. By specifying the desired design condition (mass flow rate and rotational speed) and targeted performance (pressure ratio and efficiency), the trained
diffusion model returns directly the 3D compressor geometry that satisfies the condition inputs. Compared to traditional deterministic forward design approaches, the proposed method not only generates accurate geometry solutions to inverse design problems, but also enables effective exploration of the entire design space, providing a diverse set of candidate solutions. In addition, this paper presents the first study to directly train on 3D blade geometry coordinates rather than parametrised representations, demonstrating the feasibility of coordinate-based learning while enabling a highly flexible framework applicable to a wide range of designs. The trained
diffusion model achieves excellent design capability, with solution accuracy up to 99% and unfeasible designs less than 1%. Furthermore, the solution diversity of the trained
diffusion model is also quantitatively verified by means of comparing the distribution of the solution sets generated from the
diffusion model and from direct sampling of physical parameters.
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All authors Yingfan Geng, Jinhong Wang, Lazaros Papachristodoulou, Sibo Cheng, Teng Cao
Mesoscale and Nanoscale Physics
Angular Momentum Transfer in Magnetic Weyl Semimetal Spheres
Adriano Biondo and Francesco M. D. Pellegrino
In this work, we investigate the problem of electromagnetic angular momentum within the framework of topological materials, described by
axion electrodynamics. Specifically, we calculate the electromagnetic angular momentum for a spherical sample of
magnetic Weyl semimetal in the presence of a point charge. We then analyze how, by moving the point charge quasi-statically, the angular momentum stored in the electromagnetic field can be converted into mechanical angular momentum of the sphere. Finally, we derive analytical expressions for the resulting angular velocity and angular displacement, demonstrating that the effect is enhanced in the Weyl semimetal compared with a topological
insulator.
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Soft Condensed Matter
Twist-driven helical flattening in nematic elastomer cylinders
Alexia Chatzitheodorou and Christian D. Santangelo
Liquid Crystal elastomers (LCEs) deform anisotropically along a prescribed nematic director field, making them promising candidates for programmable shape change. Existing studies have primarily focused on either director patterns on flat sheets or simple patterns on curved geometries, leaving the case of a non-trivial director on a non-trivial geometry still largely unexplored. Many biological systems, however, have both complex geometries and complex helical fiber architectures. To explore the interplay between director and underlying geometry, we use a non-Euclidean plate theory for nematic elastomers with a through-thickness twisted director to develop an effective 2D model. With a fixed twist angle, our model shows an anomalous coupling between mid-surface
curvature and director twist. This emergent term arises from the interplay between orientational order and elasticity, and dominates traditional bending contributions. To illustrate the general theory, we study the stability of cylindrical shapes with through-thickness twist. We find that the cylinder is unstable to a long-wavelength helical flattening mode and determine the critical parameter for the onset of instabilities.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG
Equilibrium Training of Energy-Based Models with Parallel Trajectory Tempering
Nicolas Béreux, Aurélien Decelle, Cyril Furtlehner et al. (+1 more)
Energy-Based Models (EBMs) provide an interpretable framework for generative modeling of scientific data, but poor Markov Chain Monte Carlo mixing often limits their reliability. We introduce a training
algorithm based on Parallel Trajectory Tempering (PTT), which exploits the continuity of the optimization path to maintain
equilibrium sampling throughout learning. This enables stable and fast training on highly
multimodal and data-scarce scientific
datasets. Combined with reservoir sampling and adaptive optimization, PTT has a computational cost comparable to Persistent Contrastive Divergence, making it a practical replacement for standard training methods. It also provides direct estimates of thermalization times,
equilibrium samples from trained models, and accurate log-likelihoods at essentially no additional cost. Experiments on Restricted Boltzmann Machines show that PTT consistently outperforms existing EBM training approaches. On discrete tabular data, it also surpasses state-of-the-art deep generative models, yielding higher-quality samples and greater robustness to overfitting and limited data. Our results make
equilibrium maximum-likelihood training of EBMs practical and computationally efficient.
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All authors Nicolas Béreux, Aurélien Decelle, Cyril Furtlehner, Beatriz Seoane
Quantum Physics
Adaptive Multi-Backend Simulation of Near-Clifford Quantum Circuits via Spatial Stabilizer-Frame Partitioning
Héctor J. García
We present an exact amplitude simulator for Clifford+T
quantum circuits that combines a Feynman path sum across a balanced
qubit bipartition with stabilizer-frame simulation on each half. The construction extends prior stabilizer-based Schrödinger-Feynman methods in three directions: recursive multilevel bipartition into a binary tree, automatic fallback to dense state-vector simulation when a leaf's stabilizer frame would exceed its
memory ceiling, and a cost-model-driven partition selector that replaces the standard cut-count minimization heuristic. We show cut-count minimization is an unreliable proxy in practice: a globally cleaner partition can reduce cross-cut count yet increase wall-clock time, because it imbalances T-gate density across halves and inflates per-half stabilizer-frame size. Our cost model substitutes the stabilizer-frame bound 2w for the dense 2n ceiling per side and explicitly models per-amplitude readout cost; isolating that term uncovered a quadratic-asymptotic inefficiency in the leaf simulator's end-of-path amplitude extraction, fixed by replacing it with an existing O(F * s * n) single-amplitude inner product. On a structured hierarchical n=16
benchmark the recursive simulator beats monolithic stabilizer-frame simulation by 92x to 17,645x, wins by 79x per path against a dense half-state-vector baseline under an identical cut, and beats a production state-vector simulator end to end by up to 47.9x (median ~5x). On
adversarial random Clifford+T
circuits the dense state vector wins past a crossover near n/2 cross-cut gates – the regime the cost model identifies. The dominant cost, the cross-cut Feynman sum, is embarrassingly parallel with constant inter-worker communication, unlike recent
matrix-product-state stabilizer-tensor methods whose inner contraction loop is sequential.
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Physics and Society · Cross-listed from q-fin.ST
Where does the criticality live? Early-warning signals are event-heterogeneous across seven crypto-perpetual liquidation cascades
Ramon Marc Garcia Seuma
Do crypto perpetual-futures crashes carry a reproducible early-warning fingerprint of a critical transition, and in which state variable? We study seven major BTC liquidation cascades (2022-2025, including the record 19B USD event of 10 October 2025) using minute-level price and 5-minute leverage/order-flow data. On detrended residuals we compute rolling variance and lag-1 autocorrelation and test their pre-cascade trend with the Kendall-tau statistic, sweeping 39 analysis configurations per variable per event. No variable is event-invariant. Price carries the critical-slowing-down signature in five of seven events but is silent in exactly the two sudden-news (tariff) shocks, suggesting a two-type structure: endogenous-buildup versus exogenous-shock cascades. The October 2025 event, whose in-sample analysis suggests the signature lives in leverage rather than price, turns out to be the outlier, not the rule. The one regularity surviving all events with data is a compression of taker order-flow variance, which passes a 300-onset placebo test (Fisher-combined p ~ 5e-6) but is a population-level precursor, not a per-event alarm. Single-event critical-slowing-down claims in crypto derivatives are therefore fragile by construction. We argue the pattern of failures is itself diagnostic: slowing down is absent exactly where the destabilising mechanism is most abrupt, as one would expect if these cascades are discontinuous, shock-driven transitions rather than critical ones.
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