Statistical Mechanics · Cross-listed from quant-ph
Divergence Geometry of Quantum Multi-Mpemba Effects
Domingos S. P. Salazar
Two
quantum states may relax toward the same steady state, yet the one that starts farther away can overtake the closer one. This is the
quantum Mpemba effect. The same pair can reverse order more than once, but these crossings may depend on the divergence used to compare them. We ask which crossings persist for every normalized operator-convex Petz divergence. Because each such divergence is a positive average of one-parameter $\chi^2$ kernels, the problem reduces to the sign of one profile across the full kernel range. Alternating sign margins guarantee repeated family-wide reversals, while finite dimension yields a
polynomial positivity test. A simple real slow mode fixes the common late-time order; near stationarity, coherence between unequal-
eigenvalue sectors makes the order divergence dependent. In a trapped-ion qutrit ideal model, the reported preparation shows divergence-selective crossings. A nearby preparation is a candidate for at least two family-wide reversals.
Read the full abstract ▾
Materials Science · Cross-listed from physics.ins-det
Development of Neutron Transmutation Doped Germanium (NTD-Ge) for Cryogenic Applications
Kangkang Zhao, Mingxuan Xue, Haiping Peng et al. (+10 more)
This paper presents the systematic fabrication and characterization of cryogenic thermometers based on
neutron transmutation-doped germanium (NTD-Ge). High-purity (10N) germanium samples were irradiated by thermal
neutrons with different fluences at the China Advanced Research Reactor (CARR). After irradiation and a six-month cooling-down period, positron annihilation lifetime spectroscopy and temperature-dependent
Hall effect measurements were performed to characterize irradiation-induced defects and carrier concentrations in the NTD-Ge samples. Utilizing standard
semiconductor fabrication techniques, point electrodes were deposited onto the processed samples to fabricate functional NTD-Ge cryogenic thermometers. The low-temperature resistance performance of the devices was characterized down to 20 mK on a millikelvin range cryogenic test platform. The measured temperature dependence of resistance follows Mott's law, showing excellent agreement across the full measured range. The extracted T0 is consistent with expectations. These results collectively verified both the applicability of the thermometers in cryogenic system and the reliability of the fabrication procedure.
Read the full abstract ▾
All authors Kangkang Zhao, Mingxuan Xue, Haiping Peng, Deyong Duan, Yunlong Zhang, Yi Li, Junfeng Yang, Xintan Deng, Hongjun Zhang, Huaichang Ran, Sicheng Wen, Xiaolian Wang, Zizong Xu
Materials Science · Cross-listed from physics.comp-ph
Predictive beam-lattice reduction for higher-order topological modes in a 2D SSH phononic crystal
Eloi Perez Compte, Michele Brun, Giorgio Carta et al. (+3 more)
We develop a mechanically faithful reduced model for a two-dimensional topological phononic
crystal composed of rigid square masses connected by slender elastic ligaments. Exploiting Euler Bernoulli beam theory, we derive a Hermitian 12 degree of freedom dynamical
matrix that retains in-plane translations, rotations, and ligament eccentricity. This reduction captures effects that are absent from scalar mass spring SSH models while remaining computationally much more tractable and more easily interpretable than full finite element simulations. Dimerizing the ligament widths produces a mechanical 2D SSH
lattice with a full band gap and a quantized bulk polarization. The sign of the dimerization controls the transition from trivial to non trivial phases, while ligament eccentricity provides an additional purely
geometric mechanism for changing the
topology. Ribbon and finite
cell calculations predict in gap edge and corner modes, quantified by localization measures and confirmed by finite element simulations. Measurements on 3D printed samples show an evanescent response in the trivial structure and enhanced boundary/corner response in the non trivial structure within the predicted gap. The results provide a validated route for designing topological elastic metamaterials using a continuum informed discrete model rather than either idealized mass spring networks or brute force numerical optimization.
Read the full abstract ▾
All authors Eloi Perez Compte, Michele Brun, Giorgio Carta, Nicola M. Pugno, Antonio S. Gliozzi, Federico Bosia
Statistical Mechanics
Memory with Onsager-Casimir symmetry: Rotating particle in a viscoelastic fluid
Debankur Das, Niloyendu Roy, Niklas Windbacher et al. (+2 more)
We study the
stochastic dynamics of a rotating Brownian particle in a non-Markovian fluid. Experimentally, we find that rotation enhances the long-time diffusivity of the particle and generates time-antisymmetric cross-correlations between orthogonal displacement components in the plane perpendicular to the rotation axis. To rationalize these observations, we introduce a minimal linear model in which a tracer is coupled to a slow bath degree of freedom and rotation enters through an advective coupling. Eliminating the bath variable yields a generalized Langevin equation with a non-reciprocal
memory kernel. This kernel rotates in time, forming a logarithmic spiral, and it obeys Onsager-Casimir
symmetry under reversal of the rotation vector, and the corresponding fluctuation-response relation. From the latter we obtain a
geometric construction that links two-time cross-correlations to the transverse response of the particle in bulk. Unlike the ordinary Einstein relation, this relation involves the antisymmetric sector of the response. Our experiments and theory are in qualitative agreement, establishing rotating colloids in viscoelastic fluids as a minimal realization of Onsager-Casimir
symmetry in time-nonlocal
stochastic dynamics
Read the full abstract ▾
All authors Debankur Das, Niloyendu Roy, Niklas Windbacher, Clemens Bechinger, Matthias Krüger
Superconductivity
Ferroelectric superconductivity in noncentrosymmetric metals
Jason G. Kattan and T. Pereg-Barnea
It has recently been shown in experiments that certain materials can display both superconductivity and ferroelectricity, contrary to a long-standing
conjecture that these two phenomena are incompatible, or at least unrelated. In this work we study superconductivity in ferroelectric metals, using a formalism of ionic polarization fields coupled to itinerant electrons, both of which are treated at the microscopic level. The ferroelectric order manifests as a spontaneous polarization that may be uniform or spatially modulated, and fluctuations of the polarization mediate interactions between the electrons. The polarization fluctuations give rise to attractive interactions that can lead to Cooper pairing in certain
lattice configurations, analogous to the nonpolar
phonons in conventional BCS theory. Working with a simplified BCS model, we derive conditions under which superconductivity can coexist with and even emerge from ferroelectricity.
Read the full abstract ▾
Materials Science
Transient Liquid Phase Bonding of NiTi Using Cu- and Nb-base Interlayers
Zhaoxi Cao, Samuel Price, Alessandra Crippa et al. (+3 more)
Transient
liquid phase (TLP) bonding was examined as an approach for joining NiTi to achieve a high joint efficiency while minimizing chemical variance within the joint region. Two bonding interlayer chemistries (Cu-base and Nb-base) were identified by screening thermodynamic criteria for TLP in ternary
alloys using the CALPHAD method. These two systems were then experimentally evaluated with respect to their impact on solidification kinetics, microstructure in the joint region, and performance during quasistatic and cyclic tensile loading. For both interlayer chemistries, the composition profile and microstructure in the joint region confirmed an isothermal solidification mechanism. In addition, the joints were found to be fully dense and contain at most 1.2% intermetallic phases. Tensile testing showed excellent load transfer across the joints with approximately 4% recoverable strain and martensite onset stresses reaching 94% and 89% of the unbonded, annealed NiTi values for Cu-base and Nb-base interlayers, respectively. Lastly, a stable superelastic response was observed under cyclic loading for both bond chemistries, with spatial variation in the strain
evolution linked to enhanced stiffness and hardness in the joint region arising from the substitutional Cu and Nb solutes, as confirmed via nanoindentation. This study demonstrates that TLP bonding of NiTi can produce high-strength and nearly intermetallic-free joints without sacrificing functional performance, such as the superelastic response.
Read the full abstract ▾
All authors Zhaoxi Cao, Samuel Price, Alessandra Crippa, John P. Reidy, Gianna M. Valentino, Ian McCue
Soft Condensed Matter · Cross-listed from physics.bio-ph
Noise-induced stability of insect swarms
Justin Faber, Annabelle Boots and Dolores Bozovic
Flying insect swarms exhibit cohesion without the local velocity
alignment observed in flocks of birds or schools of fish. The interaction rules and channels of communication between insects that lead to collective behavior have not yet been determined. We propose a theoretical model based on acoustic communication between swarm members, where each individual is attracted to a weighted mean field of its neighbors. We demonstrate that this simple framework can describe a wide range of swarming dynamics, including a phenomenon where pairs of insects break free from the swarm in a helical orbit around each other. Counterintuitively, our numerical model suggests that
stochastic noise enhances the stability of an insect swarm, as it interferes with pair formation. Finally, we demonstrate that a specific species of malarial mosquito produces swarms that reside on the edge of a transition to instability. Our study shows that fairly simple local interaction rules can be sufficient to describe the collective behavior of swarming biological systems.
Read the full abstract ▾
Materials Science · Cross-listed from physics.optics
Hybrid BaTiO3/TiO2 Metasurface for Efficient Gigahertz-Speed Free-Space Electro-Optic Modulation
Zhongpeng Sun, Kerolos M. A. Yousef, Michael Domm et al. (+13 more)
Free-space electro-optic modulators are key to emerging photonic systems, yet their performance remains limited by trade-offs between modulation efficiency, bandwidth, and device aperture. Here we report a hybrid BaTiO3 (BTO)/TiO2 metasurface for large-aperture, efficient, gigahertz-speed free-space electro-optic modulation. Combining scalable BTO film growth by
radio-frequency magnetron sputtering with mature TiO2 nanofabrication, we pattern the metasurface in TiO2 on an unetched BTO layer. The resulting devices support guided-mode resonances with quality factors exceeding 1300 and an optical confinement factor of ~0.8, while the continuous BTO layer makes efficient use of the applied voltage, together maximizing the overlap between the optical and driving fields within the BTO. A device with a 0.3 mm x 0.3 mm metasurface achieves a transmittance modulation efficiency of ~0.020 per volt and a -3 dB electro-optic bandwidth of ~0.8 GHz, with an effective Pockels coefficient of ~151 pm/V for the BTO. This establishes a scalable route to high-performance free-space electro-optic modulators for
LiDAR, free-space optical communication, and reconfigurable optical computing.
Read the full abstract ▾
All authors Zhongpeng Sun, Kerolos M. A. Yousef, Michael Domm, Agham Posadas, Xudong Li, Marcus Ossiander, Maryna L. Meretska, Yiwei Ju, Isabel Barth, Jason Tischler, Theodore P. Letsou, Moaz Waqar, Amirhassan Shams-Ansari, Xiaoqing Pan, Alexander A. Demkov, Federico Capasso
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Elasto-hydrodynamics of droplet-pool-interactions
Md Sultan and Purbarun Dhar
In Newtonian fluids, impact of a droplet on a
liquid pool births a cavity, crown, capillary waves, and Worthington jet. The corresponding hydrodynamic events for elastic or Boger fluids, however, remain an uncharted domain of comprehension and exploration. We thoroughly investigate, via experiments, theory, and simulations, how elastic energy storage, fluid relaxation, and competitive inertio elasto capillarity govern the spatio temporal
evolution of the cavity, the crown, and the ensuing Worthington jet in polymeric elastic fluids. The events are systematically explored over a wide range of impact Weber and Deborah numbers, considering varied Newtonian and elastic fluid droplet pool combinations, and revealing new, and distinct morphological regimes compared to Newtonian counterparts. We illustrate that these new findings are purely driven by fluid elasticity, and not by viscosity or interfacial tension. We derive a theory for cavity radius
evolution, using energy conservation within potential-flow framework. We show that 30-40 % of the droplets kinetic impact energy may be stored as elastic energy by the stretching
polymer chains during cavity expansion. Appealing to the FENE P model, we derive a theory for the temporal
evolution of the radius of the elongated Worthington jet. We show that in elasto capillary regime, competitive elastic and capillary stresses lead to exponential decay of the jet radius. The role of elastic stresses and the local velocity field in governing cavity
evolution, morphology, and jet formation are further elucidated through computer simulations. Our findings significantly advance the uncharted paradigm of interplay between inertia, capillarity, and elasticity in droplet-pool interaction elastohydrodynamics.
Read the full abstract ▾
Materials Science
Resonant Raman spectroscopies beyond density-functional theory
Aleksandr Poliukhin, Corto Babs Aubry, Lorenzo Bastonero et al. (+1 more)
Resonant Raman spectroscopy probes, in a single measurement, how electrons and
phonons couple in a material. Density-functional theory (DFT) typically reproduces well
phonon frequencies, but resonant Raman intensities hinge on electron-
phonon matrix elements and electronic transitions that are far more sensitive to the underlying exchange-correlation approximation. However, electron-
phonon coupling has so far been accessible only through linear-response theories developed for a handful of semilocal DFT methods, leaving the sensitivity of resonant Raman intensities to the electronic-structure approximation essentially unexplored. Here, we introduce a general finite-difference framework that can compute resonant Raman tensors for any electronic-structure method capable of delivering forces,
eigenvalues, and wavefunctions of pristine and displaced configurations. We apply the formalism to
graphene and monolayer MoS$_2$, using hybrid functionals or meta-GGAs, and show that these approaches systematically enhance electron-
phonon couplings relative to semilocal DFT, reflecting reduced dielectric overscreening. A decomposition of the Raman tensor shows that accurate intensities require electronic
eigenvalues and electron-
phonon matrix elements to be treated consistently at the same level of theory. Among the approaches tested, hybrid functionals provide the best overall agreement with experiment. Because the framework needs only quantities every electronic-structure code already produces, it opens the door to systematic, beyond-DFT Raman characterization or benchmarking against experiments, especially for 2D materials.
Read the full abstract ▾
All authors Aleksandr Poliukhin, Corto Babs Aubry, Lorenzo Bastonero, Nicola Marzari
Strongly Correlated Electrons
Interplay of spin-orbit coupling, crystal field splitting and correlations: a ghost rotationally invariant slave boson treatment
Xue Sun, Walber Hugo Brito, Andreas Gleis et al. (+4 more)
We investigate the interplay of
spin-orbit coupling,
crystal field splittings, and electronic correlations in the $t_{2g}$ Hubbard-Kanamori model within the recently formulated ghost rotationally invariant slave-
boson method (GRISB). In particular, we study a tight binding model of Sr$_2$RuO$_4$ with parameters extracted from density functional theory and linearized quasiparticle self-consistent GW (LQSGW) calculations; we study the behavior of different physical quantities as the number of ghosts increases to examine the convergence of GRISB to dynamical mean field theory (DMFT) and experimental results; and we leverage the ability of GRISB to investigate the model over a wide range of parameters at low temperature. In particular, we examine both static and dynamical observables driven by the
spin orbit coupling (SOC) and study how they vary as a function of the Hubbard $U$ and Hund's coupling $J$. GRISB converges quickly for most of these observables, and the calculations reveal the following: $U$ enhances the
spin-orbit coupling while $J$ suppresses it. We also study the shape of the
Fermi surface within different methodologies, and examine the Lifshitz transition which takes place as a function of strain in this material.
Read the full abstract ▾
All authors Xue Sun, Walber Hugo Brito, Andreas Gleis, Ran Adler, Tsung-Han Lee, Gabriel Kotliar, Corey Peters
Statistical Mechanics · Cross-listed from physics.ao-ph
From Flight Logs to Atmospheric Science: Paragliders as Convection Sensors for Identifying Thermal Predictors
César Hernández-Aguayo, Matthieu Cristelli and Michael Benzaquen
Atmospheric thermal convection drives boundary-layer dynamics and vertical exchange of heat, moisture, and momentum, yet fundamental questions about thermal structure remain open due to limited in situ observational coverage. We introduce a novel high-resolution observational
dataset for atmospheric convection based on paragliding flight logs collected over metropolitan France during 2017-2024. Paragliders probe thermal updrafts by circling within them while carrying GPS variometers that record position and altitude; each climbing segment samples the vertical velocity field within a thermal column. Aggregated across 1.47 million climbing segments from 110,730 flights, this
dataset provides unprecedented spatial coverage and temporal resolution. To demonstrate the value of this observational resource, we extract three physically distinct observables from climbing segments and characterize their dependence on terrain, season, time of day, cloud state, and soil moisture. Coupling the paragliding observations with global atmospheric reanalysis data (ERA5, 0.25 degrees hourly) through a regression framework against 118 physically interpretable predictors, we identify leading atmospheric predictors of these observables. The empirical relationship between ceiling height and temperature-dew point depression matches the theoretical lifting condensation level scaling with striking precision supporting our methodology. Boundary-layer height emerges as the leading independent predictor of both ceiling height and thermal strength across all terrains and seasons, while vertical-velocity variability is controlled by surface heat-flux and wind variables. Taken together, our results highlight the utility of crowdsourced flight-log data for investigating atmospheric convection.
Read the full abstract ▾
Superconductivity
Analytical Charge Density Profile of Vortex Core in Weak-Coupling Superconductor
Chi-Ken Lu
Self-consistent Bogoliubov-de Gennes calculations have long shown that solving the Poisson equation inside a superconducting
vortex turns a one-signed charge depletion into a modulation that alternates in sign with period $\pi/k_F$. We give an elementary account of that result. Taking the Caroli-de Gennes-Matricon bound states in a step-like gap, we show that the normalization of the bound-state spinor is nearly independent of angular momentum, which collapses the mode sum into closed form. Inside the core the
vortex winding removes one Bessel channel from a completeness sum, so the density vanishes on the
vortex line and carries Friedel-like oscillations of wavevector $2k_F$; outside it the sum gives a $1/r$ envelope decaying over a coherence length, with a residual ripple. The bound-state charge does not integrate to zero, so neutrality obliges the extended states to compensate it exactly. That compensation is complete at long wavelength but fails at the diameter of the
Fermi circle, and what survives is a sign-alternating $2k_F$ modulation reduced only by $4k_F^2/(4k_F^2+k_{TF}^2)$, a factor lying between one-half and three-quarters for any metal. The oscillation is therefore not a delicate effect but a consequence of neutrality and the inefficiency of screening at large momentum transfer: in the screened total the smooth terms cancel and only the ripple is left.
Read the full abstract ▾
Statistical Mechanics · Cross-listed from quant-ph
Dissipation in Periodically Driven Quantum Systems: Partial Secularization and Thermodynamic Consistency
Luísa T. Tude, Carlos Ortega-Taberner, Roberta Zambrini et al. (+1 more)
Periodically driven open
quantum systems are central to
quantum thermodynamics and
quantum control. These systems are typically described using Floquet-Born-Markov master equations, derived with the use of a full secular approximation, and whose thermodynamic implications are often overlooked. In this context, we show that such a strong secular approximation may lead to unphysical predictions for steady state energy currents. We then demonstrate that a coarse-grained formulation of the master equation can regularize these issues while yielding completely positive dynamics and consistent energy currents. The coarse-graining time has a clear physical interpretation, as it defines the temporal resolution at which a Markovian master equation can describe the
evolution of the periodically driven system. We show the consistency and validity of our approach by comparing to an exact non-Markovian simulation in paradigmatic examples: a driven two-level system and a three-level maser coupled to hot and cold thermal reservoirs. Our work provides a practical framework for correctly applying the secular approximation in periodically driven-dissipative systems and for assessing the accuracy of master equations of the GKSL form.
Read the full abstract ▾
All authors Luísa T. Tude, Carlos Ortega-Taberner, Roberta Zambrini, Gonzalo Manzano
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Marked vertex search on disordered graphs with Rosenzweig-Porter phases
Sabyasachi Chakraborty, Tilen Cadez, Sonjoy Majumder et al. (+1 more)
Quantum marked vertex search
algorithms are known to outperform their classical counterparts, yet their behavior in the presence of disorder remains largely unexplored. Here, we address this gap by studying marked vertex search on disordered random graphs. To introduce disorder, we implement the Rosenzweig-Porter (RP) model, a random
matrix ensemble with tunable ergodic, non-ergodic extended, and localized phases, on Erdős-Rényi (ER) graphs. This produces a doubly random system where ER graph connectivity randomizes which interactions exist, while RP disorder controls their strength and `on-site' potentials, providing a two-parameter framework to study
quantum dynamics on disordered networks. First, we show that the characteristic Wigner-Dyson-to-Poisson spectral crossover of the RP ensemble survives under graph constraints across the sparse-to-dense range, and we derive an analytical estimate for the finite-size localization boundary that shifts systematically with the graph edge probability $p$, consistent with a resonant-hybridization argument. Thereafter, using this disordered graph ensemble, we study the marked vertex search problem and find that search performance tracks the underlying
quantum phase directly. Counterintuitively, the ergodic phase, despite supporting fast transport, yields lower success probability than the localized phase, which achieves high success probability at the cost of significantly longer search times. These results establish a direct and quantitative link between random
matrix disorder on graphs and the performance of continuous-time
quantum walk search, and suggest that disorder, rather than being merely an obstacle, can be exploited as a tunable parameter in
quantum search protocols.
Read the full abstract ▾
All authors Sabyasachi Chakraborty, Tilen Cadez, Sonjoy Majumder, Rohit Kishan Ray
Mesoscale and Nanoscale Physics
Ion Flow under an Applied Electric Field in Semiconducting and Metallic Carbon Nanotubes
J. B. Sokoloff
Measurements made by Li, et. al., showed that the flow rates of potassium ions through 11nm long, subnanometer diameter, metallic and semiconducting carbon nanotubes under an applied electric field are almost the same. In contrast, measurements of the electrical conductivity of potassium chloride solution through 100 long metallic and semiconducting carbon nanotubes with diameters between 2.6-5.4nm by Cui, et. al., show that the ionic conductivity in the semiconducting nanotubes is larger than that of the metallic nanotubes. Possible theoretical origins of these differences are explored in this article.
Read the full abstract ▾
Strongly Correlated Electrons
Chiral Magnon Mixing by Symmetry-Breaking in Collinear Ferrimagnets
Dhurba R. Jaishi, Tyler J. Slade, S. X. M. Riberolles et al. (+8 more)
Magnons in ferromagnets possess
spin angular momentum defined by right-handed precession of the moment around the magnetization direction. In antiferromagnets with no net magnetization, left-and right-handed
magnons are degenerate in the absence of an applied field. Ferrimagnets possess uncompensated
magnetic sublattices, which should natively possess right-and left-handed
magnons where their energy is split by the internal molecular field. Here, we show that RMn6Sn6 (R = Tb, Er) ferrimagnets possess right and left-handed
magnon bands that cross at finite momentum (k) within the basal plane, defining modes with opposite dynamical chirality. Depending on the
symmetry of the ferrimagnetic order, which may be manipulated by varying the rare-earth
magnetic anisotropy or with applied field, the band crossing may remain a nodal line or may be gapped. The gapped modes contain hybridized
chiral excitations whose chirality becomes k-dependent.
Read the full abstract ▾
All authors Dhurba R. Jaishi, Tyler J. Slade, S. X. M. Riberolles, Bing Li, Tianxiong Han, D. M. Pajerowski, D. L. Abernathy, Barry Winn, Melissa Graves-Brook, B. G. Ueland, R. J. McQueeney
Statistical Mechanics · Cross-listed from quant-ph
Phase transitions in quantum-circuit compilation
Andrea De Girolamo, Davide Rattacaso, Simone Notarnicola et al. (+2 more)
Quantum-
circuit compilation aims at finding an optimized realization of a target
circuit under given constraints, e.g., the minimization of hardware-induced errors and the
unitary-equivalence of the
circuit. We connect the compilation process with the thermodynamics of a many-body
spin system:
circuit infidelity plays the role of the energy function and low-temperature states correspond to compiled
circuits. In the paradigmatic case where crosstalk between parallel gates is present, we find a phase transition between a disordered phase and an
antiferromagnetic brick-wall phase, compatible with the Ising universality class. At larger crosstalk, we observe a $\mathbb{Z}_3$-ordered regime, suggesting that increasingly serial compiled
circuits are associated with emergent $\mathbb{Z}_n$-ordered phases. When the
unitary-equivalence constraint is removed, these phases disappear, showing that the equivalence between
circuits underlies the emergent criticality and constitutes a source of complexity in
quantum-
circuit compilation and, more generally, in equivalence-constrained optimization. Finally, we observe that the Kolmogorov complexity of the
circuit enhances the emergence of ordered phases.
Read the full abstract ▾
All authors Andrea De Girolamo, Davide Rattacaso, Simone Notarnicola, Ilaria Siloi, Simone Montangero
Materials Science
Configuration averaging of X-ray absorption spectra of disordered systems within the augmented-space full multiple-scattering formalism
Maurizio Benfatto
We present a formulation of the full multiple-scattering theory of X-ray absorption spectroscopy (XAS) for disordered systems based on the augmented-space method of Mookerjee. Both substitutional (chemical) and thermal (vibrational) disorder are cast, on the same footing, as exact
matrix elements of a non-random operator acting on an enlarged
Hilbert space. The configuration-averaged scattering-path operator is thereby obtained by inverting a non-random secular
matrix, with no expansion in scattering paths, without recourse to the single-site approximation and without any assumption on the shape of the disorder distribution. This is what the quantitative analysis of the near-edge region requires: XANES lies where the multiple-scattering series does not converge, so that a treatment of disorder tied to a path expansion is unavailable there. The inversion is carried out by a continued-fraction (Lanczos) recursion, which accesses the required
matrix element without constructing the full configuration basis or diagonalising the augmented operator. The operator Debye-Waller factor of the harmonic theory is recovered as the Gaussian special case, and anharmonic disorder is included with no additional machinery, through the moments of a non-Gaussian displacement distribution. Where the series does converge, the construction also settles a question of principle: for statistically independent site variables, replacing each t-
matrix by its configuration average is exact only for scattering paths in which every site occurs once, and for paths that revisit a site we obtain the exact second-order correction.
Read the full abstract ▾
Disordered Systems and Neural Networks
Bharadwaj Chowdary Mummaneni and Bo Xing
Predicting a
nuclear magnetic resonance (NMR) spectrum from first principles requires propagating a
quantum state of dimension $2^N$ for $N$ coupled
spins, which becomes intractable beyond larger $N$. We
benchmark Neural
Quantum States (NQS), a class of variational
quantum states expressed as an artificial neural network, as an alternative representation for this problem. Using two propagation methods, the Time-Dependent Variational Principle (TDVP) and projected time-dependent Variational Monte Carlo (p-tVMC), we compute the $^1$H spectra of four ($2 \to 5$
spins) experimentally parameterized molecules. TDVP reproduces all line positions and intensities with average spectral mean squared errors of $<10^{-3}$; p-tVMC reproduces the same features, with accuracy determined by its per-step optimization parameters. One dominant obstacle to larger systems is the steep growth of the number of integration steps with spectral bandwidth, which can be removed by propagating in the interaction frame of the chemical-shifted
Hamiltonian. Retaining the same accuracy, this reduces the number of integration steps roughly eightfold for the 3-
spin system and by at least an order of magnitude for the 4- and 5-
spin systems, and it enables a 14-
spin molecule (sucrose) to be accurately propagated via Monte Carlo sampling.
Read the full abstract ▾
Strongly Correlated Electrons
Shape of Wigner Crystals and Hole Self-Doping in a Mexican-Hat Dispersion
Minho Luke Kim and Xiao-Gang Wen
We study Wigner
crystals (WCs) induced by a strong Coulomb interaction from the ring-like
Fermi surface of a Mexican-hat dispersion $\epsilon_k= c_2k^2+c_4k^4$. We design orbital shape in order to minimize the energy of the WC, and find that a low ground-state energy requires an orbital shape with a depletion of electrons near $k=0$. To capture the Coulomb-induced correlations, we include a Jastrow factor as well as a factor describing the correlation between electrons and doped vacancies. Using variational Monte Carlo calculations, we calibrate the effective band parameters $c_2$ and $c_4$ to reproduce the two transitions observed experimentally as the electron density is lowered: from a
spin-valley-polarized
Fermi liquid with a disk-like
Fermi surface, to one with a ring-like
Fermi surface, and finally to a WC. We find that, even with an optimized orbital shape that depletes electrons near $k=0$, a WC with hole self-doping near $k=0$ can still be energetically favorable near the WC transition, provided that the electron-vacancy correlation is included. We also estimate the dispersion of the doped hole.
Read the full abstract ▾
Quantum Gases · Cross-listed from hep-th
Dynamics of nucleation in thermal phase transitions
Oliver Gould, Joonas Hirvonen, Andrey Shkerin et al. (+1 more)
We study dynamical effects during nucleation in thermal first-order phase transitions in field theory. Focusing on the classical regime of the decay of a metastable state, we present the general formula for the thermal decay rate including the dynamical prefactor and give a recipe for its systematic evaluation. We describe the physical mechanism which reduces the actual thermal decay rate with respect to the statistical rate obtained in
equilibrium theory. We also discuss the thermality conditions ensuring the existence of a steady-state thermal rate, in which case our formula is exact up to exponentially small corrections. We show that it reproduces the known results for the nucleation rate in
stochastic mechanics and field theory, and allows us to unify and go beyond them. We illustrate this in real-time numerical simulations of simple field theory models. We observe significant non-perturbative contributions which can dominate the dynamical prefactor in weakly-coupled field theories at moderate exponential suppression of the decay rate. We explore the connection of these non-perturbative effects to oscillons. Notably, our numerical method requires exponentially less computing time than direct simulations of decays and is thus applicable to systems with arbitrarily strong exponential suppression. Finally, we discuss small or poorly thermalized systems when the thermality conditions are violated and the steady-state rate does not exist.
Read the full abstract ▾
All authors Oliver Gould, Joonas Hirvonen, Andrey Shkerin, Sergey Sibiryakov
Strongly Correlated Electrons
Ahmed Abouelkomsan, Filippo Gaggioli, Daniele Guerci et al. (+1 more)
Experiments on rhombohedral
graphene have uncovered an extraordinary wealth of correlated
quantum phases - from
chiral superconductors to electronic
crystals - all within a single family of atomically thin materials. Here, we introduce a simple indicator, derived from the noninteracting band dispersion, that identifies strongly correlated regions in the phase diagram of rhombohedral
graphene as a function of carrier density and displacement field. We develop a neural-network variational Monte Carlo method, combined with Hartree-Fock theory, to solve the interacting ground states. Our calculation reveals a variety of electron
crystals with no classical analog. These include, at increasing density: Wigner
crystal, self-doped Wiger
crystal, as well as ”anticrystal”, a
lattice of holes in an electron
liquid. We discuss their experimental manifestations and possible connection to superconductivity.
Read the full abstract ▾
All authors Ahmed Abouelkomsan, Filippo Gaggioli, Daniele Guerci, Liang Fu
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Realization of a Quantum Topological Photon Pump
Qianao Yue, Bernardo Barrera, Martin Ritter et al. (+4 more)
Topological pumps transfer charge or energy at quantized rates determined solely by band
topology, independent of the details of the control fields.
Photon pumps operating on this principle could enable the robust preparation of non-classical states in a
quantum cavity, even in the presence of control imperfections, but have not been directly observed. We present the first experimental observation of a topological
photon pump, using a transmon
qubit coupled to a microwave cavity. The pump operates in the
quantum regime, pumping up from the
vacuum state up to $\approx 7$
photons, and produces demonstrably non-classical cavity states for the first few cycles.
Read the full abstract ▾
All authors Qianao Yue, Bernardo Barrera, Martin Ritter, David M. Long, David A. Lane, Anushya Chandran, Alicia J. Kollár
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Optimal Decoding for Measurement-Based GHZ State Preparation: The Maximum-Utility Decoder
Misha Yutushui, Theo Haas and Simon Trebst
The meticulous preparation of macroscopic Greenberger-Horne-Zeilinger (GHZ) states provides a foundational resource for
quantum technologies such as metrology, cryptography, and fault-tolerant codes. While state-of-the-art measurement-based protocols offer efficient low-depth execution, their performance can be bottlenecked by conventional decoders, such as minimum weight perfect matching (MWPM) or even maximum-likelihood decoding (MLD), which optimize for $binary$ logical recovery and fail to maximize the $continuous$ long-range order characteristic of a GHZ state for two-dimensional geometries. Here we overcome this limitation by framing the decoding problem as minimum
Bayesian risk inference, introducing a general paradigm that maximizes the expected ${utility}$ of the decoded state. Implementing this maximum-utility approach, we construct an
algorithm that achieves the highest possible per-shot decoded
quantum order and thereby establish an optimal decoding strategy for measurement-based GHZ state preparation. To improve its computational efficiency, we design a scalable two-stage decoder, which first encodes the syndromes into the edge weights of MWPM and then refines the result with a convolutional neural network trained to maximize the expected utility, at a fraction of the cost of the optimal decoder. Remarkably, we find that the first stage alone$\unicode{x2014}$which makes the matching aware of the gauge choice at no cost beyond bare MWPM$\unicode{x2014}$already performs near-optimally up to the largest sizes we study, $N=256\times256$, closing up to $87\%$ of the gap between the bare-MWPM and optimal decoding thresholds. Generalizing MWPM and MLD, the maximum-utility decoder (MUD) establishes a versatile framework that can be explicitly tailored to the operational demands of specific experiments by redefining the utility function.
Read the full abstract ▾
Disordered Systems and Neural Networks
An asymptotically solvable model of many-body critical phases: mobility edges, scars, and inverted scars
Yi-Ting Tu, Zi-Jian Li and Sankar Das Sarma
While the prethermal regime of random many-body localized (MBL) systems is dominated by accidental many-body resonances, another class of resonances, originating from the underlying potential structure, is expected in large-size deterministic systems. It is known that this class of resonances can lead to single-particle critical phases that are neither localized nor extended, but the consequences in interacting systems remain unclear. In this work, we construct an asymptotically solvable model of a one-dimensional nearest-neighbor interacting
spin chain, whose spatial structure induces a hierarchy of mirror-like many-body resonances. We derive two phases in the thermodynamic limit, characterized by the satisfaction and violation of a version of the weak eigenstate thermalization hypothesis (ETH). While these two phases are similar to the usual MBL and ETH phases, there exist rare eigenstates that behave like the opposite phase, interpreted as many-body scars and inverted scars. Surprisingly, the two phases can be separated by a finite-temperature phase transition, corresponding to a thermodynamic many-body mobility edge, which was often believed to be impossible. Our results also suggest the existence of delocalized rare regions in an otherwise-localized interacting Aubry-André model, even if there are no low-disorder regions like those in random systems. This challenges the common belief that there is no avalanche instability in quasiperiodic MBL.
Read the full abstract ▾
Soft Condensed Matter
A Synthetically-accessible Universe of Chemically Recyclable Polymers
Anagha Savit, Wei Xiong, Harikrishna Sahu et al. (+3 more)
Polymers synthesized via ring-opening polymerization (ROP) of cyclic monomers represent an important class of materials due to their chemical recyclability and possible insertion in several critical applications. We present a
dataset of 1 million synthetically realizable ROP
polymer structures generated through a combination of Virtual Forward Synthesis (VFS) and
polymer expert
language models and qualified by stringent chemical heuristics. VFS is used to generate ROP
polymers by applying known reactions to existing monomers. The
polymer foundation models polyBART and POLYT5 further enable the generation of ROP candidates, with polyBART exploring its learned latent space and POLYT5 producing candidates via sequence-to-sequence generation. The resulting ROP
polymers are subjected to robust filtering criteria to ensure novelty, validity and overall data quality through a combination of automated validation pipelines and a comprehensive set of chemist-informed heuristic rules introduced in this work for the first time. We hope that this
dataset will serve as a valuable resource for downstream sustainable applications.
Read the full abstract ▾
All authors Anagha Savit, Wei Xiong, Harikrishna Sahu, Shivank S. Shukla, Will R. Gutekunst, Rampi Ramprasad
Materials Science
Vibrational spectroscopy identifies the bond asymmetry of hexagonal diamond
Li Zhu
Bulk hexagonal diamond has been synthesized by independent routes, but its structure remains contested: the two recent refinements disagree even on the sign of the difference between its two inequivalent bond lengths, 238~mÅ apart, and both depart from an earlier 2003 refinement. Here we test the competing structures with first-principles
lattice dynamics. Relaxed hexagonal diamond has an interlayer bond longer than the intralayer bonds by 24~mÅ in both functionals, an effect of its eclipsed conformation that scales with polytype hexagonality. The bright zone-center $A_{1g}$ mode gauges the interlayer bond at $\approx\!-2{,}100$~\icm~Å$^{-1}$, and neither refined coordinate reproduces the full pattern of measured modes. The only structure matching the twinned sample's three bands requires tens-of-gigapascals confining stress and
lattice constants excluded by its own diffraction. Raman spectroscopy and diffraction jointly select a small positive bond asymmetry: inverting the spectrum of the phase-pure sample gives $\OB-\OA=24\pm3$~mÅ (95% interval), and two determinations on separate samples give $+33\pm8$ and $+60\pm45$~mÅ. The 1{,}529~\icm{} feature cannot be assigned to homogeneous ideal 2H diamond, and the local HRTEM observation remains an open puzzle.
Read the full abstract ▾
Materials Science
Wrinkling of Randomly Heterogeneous Film-Substrate Systems
Xinyu Xing, Liyu Zhong, Feng Deng et al. (+1 more)
Wrinkling instabilities in stiff films on compliant substrates are strongly affected by spatial fluctuations in film stiffness. We develop a homogenized instability theory for one-dimensional film–substrate systems with random bending stiffness. The heterogeneous stability equation is reformulated as a Lippmann–Schwinger equation for the
curvature field, and a strong-contrast expansion is derived using a local–nonlocal kernel decomposition and a cavity-field formulation. Truncation at third order yields an effective polarizability and a Dyson-type dispersion relation for predicting the critical load and wavenumber. The stiffness is modeled as an exponentially mapped Gaussian random field, allowing the required two- and three-point connected statistics to be obtained analytically. The theory is validated against generalized
eigenvalue calculations and
Fourier spectral simulations. Increasing stiffness contrast lowers the critical load and shifts the instability toward higher wavenumbers, producing shorter wrinkles. At weak contrast, the threshold follows the universal scaling $N_c^{(0)}-N_c\sim\varepsilon^2$, whereas at moderate and strong contrast the third-order approximation is more accurate than the second-order theory. Wavelength selection is controlled by the ratio of the dominant material wavelength $\lambda^\ast$ to the harmonic-mean reference wavelength $\lambda_H$. For $\lambda^\ast/\lambda_H<1$, the harmonic-mean model accurately predicts the wrinkle wavelength. The framework provides a mechanics-based tool for reliability assessment and design of statistically heterogeneous film–substrate systems.
Read the full abstract ▾
All authors Xinyu Xing, Liyu Zhong, Feng Deng, Sheng Mao
Materials Science
AC Field-driven orientational crossover and energy dissipation in suspended magnetic nanoparticles
Iago López-Vázquez, Siraj Ul Haq, Kazuya Okada et al. (+4 more)
By combining the Landau–Lifshitz–Gilbert equation with Brownian rotational dynamics of
magnetic nanoparticles (MNPs), we theoretically investigate the role of particle rotation through easy-axis reorientation in
magnetic fluid hyperthermia (MFH). Our results reveal a field-driven crossover in the stationary orientation of the easy axes, from predominantly perpendicular to predominantly parallel or antiparallel to the applied field as the field amplitude increases. Although the precise crossover field depends on particle size and excitation frequency, it occurs at approximately $0.5H_k$, where $H_k$ is the uniaxial anisotropy field. These orientational regimes are directly linked to the underlying microscopic dynamics and the associated MFH performance through the occurrence of switching and non-switching hysteresis cycles, predominantly associated with Néel magnetization reversal and Brownian particle rotation, respectively. The relative importance of these dissipation mechanisms also depends on frequency: at $f=1$ MHz, Brownian heating dominates at low field amplitudes, whereas Néel heating dominates at high fields. By contrast, at $f=100$ kHz, both contributions remain comparable over most of the investigated field range.
Read the full abstract ▾
All authors Iago López-Vázquez, Siraj Ul Haq, Kazuya Okada, Sergiu Ruta, Roy W. Chantrell, Òscar Iglesias, David Serantes