Statistical Mechanics · Cross-listed from physics.soc-ph
Exact Scaling Theory of Social Tipping Phenomena in Finite Populations
Bianca Y. S. Ishikawa and José F. Fontanari
Granovetter's threshold model provides a classical framework for social mobilization, where collective action spreads through cascades as individuals join once movement size reaches their personal threshold. Here, we characterize social tipping points-the minimum seed required for global mobilization-using the initial fraction of instigators, $\rho_0$, as a control parameter. For a finite population of size $N$ with Beta-distributed thresholds $(\alpha, \beta)$, we present an exact analytical study of the cascade dynamics. By evaluating the asymptotic active fraction $\rho_\infty$, we map the thermodynamic phase diagram separating partial cascades ($\rho_0 \le \rho_\infty < 1$) from complete mobilization ($\rho_\infty = 1$), revealing continuous and discontinuous transition lines that meet seamlessly at a critical endpoint. For interior-peaked distributions ($\alpha > 1, \beta > 1$), the regimes are separated by a hybrid phase transition combining a first-order discontinuity with second-order bottleneck singularities. Combining exact finite-$N$ combinatorial formulations with large-deviation theory, we establish how finite-size fluctuations smooth these singularities. For power-law thresholds ($\alpha > 1, \beta = 1$), the critical scaling window shrinks as $N^{-1/3}$, while the expected inactive fraction vanishes as $N^{-1/3}$ at criticality. For interior-peaked distributions ($\beta > 1$), the order parameter is bimodally distributed: realizations either achieve full mobilization or stall near a bottleneck $\rho^*$. Excluding fully mobilized trajectories, $\rho^* - \langle \rho_\infty \rangle$ vanishes as $N^{-1/4}$ and the scaling window compresses to $N^{-1/2}$. Together, these results establish an exact finite-size scaling theory for threshold-driven tipping phenomena.
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Soft Condensed Matter
A molecular perspective on the yield and flow of polymer glasses: The role of enhanced segmental dynamics during active deformation
M.D. Ediger and Kelly Hebert
The mechanical properties of
polymer glasses are often critical in determining the best material for a particular application. Extremely stiff materials (high modulus) may be important for some applications while avoiding catastrophic failure due to fracture (high toughness) may be more important for others. The mechanical properties of a
polymer glass will depend upon both molecular structure and many experimental variables, including temperature and the mode of deformation (tension, compression, or shear). In this chapter we discuss the mechanical response of
polymer glasses from a molecular perspective. In particular, we consider how deformation changes the rate at which
polymer segments rearrange and how this in turn influences the mechanical response of the material. It will be shown that this focus on the changes in dynamics provides an understanding of many important features of
polymer glass deformation. Of course, it is also true that the structure of a
polymer glass must be altered by nonlinear deformation. Although not a major focus, we will make some comments about these structural changes at the end of this chapter.
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Soft Condensed Matter
Highly organized smectic-like packing in vapor-deposited glasses of a liquid crystal
Ankit Gujral, Jaritza Gomez, Jing Jiang et al. (+6 more)
Glasses of a model smectic
liquid crystal-forming molecule, itraconazole, were prepared by vapor deposition onto substrates with temperatures ranging from Tsubstrate = 0.78 Tg to 1.02 Tg, where Tg = 330 K is the glass transition temperature. The films were characterized using x-ray scattering techniques. For Tsubstrate near and below Tg, glasses with layered smectic-like structures can be prepared and the layer spacing can be tuned by 16% through choice of Tsubstrate. Remarkably, glasses prepared with Tsubstrate above Tg exhibit much higher structural organization than a thermally annealed film. These results are explained by a mechanism based upon preferred molecular orientation and enhanced molecular motion at the free surface, indicating that molecular organization in the glass is independent of the anchoring preferred at the substrate. These results suggest new strategies of optimizing molecular packing within active layers of organic electronic and optoelectronic devices.
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All authors Ankit Gujral, Jaritza Gomez, Jing Jiang, Chengbin Huang, Kathryn A. OHara, Michael F. Toney, Michael L. Chabinyc, Lian Yu, M.D. Ediger
Superconductivity
A non-local power-law baseline for transient flux penetration in YBCO films: parameter degeneracy and constitutive limitations
O. A. Hernández-Flores, C. Romero-Salazar and F. Pérez-Rodríguez
We assess whether a non-local thin-film model with a bounded, constant-exponent power law can reproduce high-speed magneto-optical measurements of transient flux penetration in a $3\times3$~mm$^2$ YBa$_2$Cu$_3$O$_{7-\delta}$ film. The model is solved forward in physical units and used as a controlled constitutive baseline. The critical sheet current is constrained by the final penetration geometry, while the criterion field and creep exponent are constrained by the turnover and relaxation times. The calibration reveals an intrinsic degeneracy: the turnover time depends primarily on the product of the criterion field and saturation parameter, equivalently on the saturated sheet resistivity, so these quantities cannot be identified independently. After parameterizing this degeneracy, the model captures a guarded-current turnover near 22~ms, a relaxation constant of 41.2~ms compared with the measured 37.5 and 43.7~ms, and a late maximum approximately 0.92~mm from the film edge. The amplitude remains discrepant: the calculated transient maximum is $1.90J_{c0}$ and the peak-to-225-ms ratio is 2.13, compared with the reported 1.20. This excess persists under changes in the creep exponent, the degenerate parameter direction, the Kim field dependence, and mesh resolution. Matching the measured ratio through the criterion field would require a value about three orders of magnitude below the conventional scale, while spatial exclusion sufficient to match it would remove the edge peak itself. We also decompose the electric field into irrotational and solenoidal parts and quantify the boundary layer where spectral and finite-difference forms of Faraday's law disagree. The results establish a reproducible non-local power-law baseline and identify limitations of the bounded, constant-exponent constitutive family rather than of non-local thin-film electrodynamics.
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Soft Condensed Matter
Reversing strain deformations probe mechanisms for enhanced segmental mobility of polymer glasses
Kelly Hebert and M.D. Ediger
Optical probe reorientation measurements were performed to monitor changes in segmental dynamics resulting from the nonlinear deformation of a
polymer glass. Segmental dynamics were monitored in a poly(methyl methacrylate) glass near Tg before and after a series of reversing deformations in which the sample was extended at constant strain rate and then allowed to retract back to zero stress at constant strain rate. Evidence of a rejuvenation mechanism, as quantified by a departure of the segmental dynamics from the quiescent aging dynamics after the reversing deformation, is observed for deformations which reach 60% of the yield strain or greater. By this measure, a saturation of the rejuvenation mechanism is not observed until at least five times the yield strain. For comparison, purely mechanical measurements of rejuvenation, based upon the reduction of the yield stress in a subsequent deformation, were also performed. These purely mechanical experiments show broad qualitative agreement with the probe reorientation experiments, but quantitatively differ in the pre-yield regime. The results are discussed in the context of recent theoretical approaches and simulations which provide a molecular-level description of
polymer glass deformation.
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Superconductivity
Perspectives on Magnetic/Superconductor Hybrid Systems: Long-range Electromagnetic Phenomena Induced by Proximity Effect and Interfacial Spin-orbit Coupling
S. V. Mironov, A. S. Mel'nikov and A. I. Buzdin
In this Perspective we review recent achievements in physics and applications of hybrid
superconductor-ferromagnet structures. In particular, we focus on the manifestations of the electromagnetic phenomena in these systems originating from the response of the induced superconducting correlations modified by the exchange field and additional effects coming from the interface Rashba-type
spin-orbit coupling. The review includes the long-range electromagnetic proximity effect and related modification of
magnetic textures, spontaneous currents, properties of
vortex matter and its interaction with
magnetic ordering,
spin-galvanic, photogalvanic and nonreciprocal transport phenomena in exemplary hybrid systems. We also present our views on the future development of this field including both the theoretical challenges and promising opportunities for fundamental experiments.
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Materials Science
Interplay of nonrelativistic and relativistic spin splittings in altermagnets
Daegeun Jo, Peter M. Oppeneer and Mohsen Yarmohammadi
Despite their compensated
magnetic moments, altermagnets (AMs) exhibit nonrelativistic
spin splitting (NRSS) that offers routes to spintronic functionality without relying on relativistic
spin-orbit coupling. However, how NRSS influences relativistic phenomena remains largely unexplored. Here we show that NRSS plays a crucial role in reshaping the Rashba effect in AMs with broken inversion
symmetry. Using a tight-binding model, we demonstrate that Rashba
spin splitting, whose magnitude is typically limited by the strength of
spin-orbit coupling, is governed by NRSS energy scales. The resulting Rashba bands combined with NRSS generate anomalously large charge-to-
spin conversion with a Néel-vector-tunable
spin polarization. First-principles calculations for the noncentrosymmetric AM GdAlSi corroborate the emergence of these effects in a real system. Our results reveal the interplay between nonrelativistic and relativistic effects in AMs and identify them as fertile platforms for
spin-orbitronic applications.
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Quantum Gases
Photon-mediated thermodynamics and density fluctuations in an ensemble of laser-cooled Cesium atoms
Arnab Ghosh, Inderpreet Kaur, Hemant Yadav et al. (+5 more)
We present an experimental study of detuning-dependent properties of a
laser-cooled cesium cloud in a magneto-optical trap. Fluorescence images are used to extract the cloud size, shot-to-shot width fluctuations, optical depth, density profiles, and spatial density fluctuation spectra as the trapping-
laser detuning is varied. Near resonance, the cloud exhibits larger spatial extent, increased width fluctuations, higher optical depth, and enhanced density-fluctuation power, while larger detunings produce a more reproducible and spatially confined cloud. The measured density profiles are analysed phenomenologically using a generalized Lane-Emden model with a polytropic equation of state, yielding detuning-dependent effective fit parameters in a weak-interaction regime. Power-spectrum and autocorrelation analyses reveal reproducible scale-dependent density correlations. The results provide a quantitative characterization of detuning-dependent radiative and collective effects in a cesium MOT and establish a basis for future measurements that can more directly test nonequilibrium transport and
photon-mediated interaction models.
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All authors Arnab Ghosh, Inderpreet Kaur, Hemant Yadav, Shiva Kant Dwivedi, R Shanmukesh, Mithun Thudiyangal, Matthew J. Davis, Bodhaditya Santra
Mesoscale and Nanoscale Physics
$\mathcal{PT}$ and anti-$\mathcal{PT}$ phase transitions in a trimerized Su–Schrieffer–Heeger chain with nonreciprocal Rashba spin-orbit coupling
Milad Jangjan, Linhu Li, Longwen Zhou et al. (+1 more)
We theoretically investigate a one-dimensional trimerized Su–Schrieffer–Heeger chain with three sublattices per unit
cell subjected to a nonreciprocal Rashba
spin-orbit coupling. Invoking a
spin-flip
symmetry, the non-Hermitian
Hamiltonian decomposes into two independent
spin sectors, enabling a
spin-resolved analysis of non-Hermitian skin effects and system
symmetries. We identify a rich phase diagram consisting of four bulk phases and two edge-state phases. The bulk phases include fully $\mathcal{PT}$-unbroken (real-spectrum) and fully anti-$\mathcal{PT}$-unbroken (imaginary-spectrum) regimes, as well as two mixed phases where one band remains on the real or imaginary axis while the other two form complex-conjugate pairs. The two edge-state phases correspond to topological edge modes with either $\mathcal{PT}$-unbroken (real) or anti-$\mathcal{PT}$-unbroken (imaginary) energies. Using non-Bloch band theory and Cardano's method, we derive closed-form expressions for phase boundaries and establish the bulk-edge correspondence for each
spin sector. Calculations of Berry phase and directional inverse participation ratios confirm our analytical predictions. Our results provide a minimal platform for realizing
spin-resolved non-Hermitian
topology and edge-selective
symmetry preservation, in which the bulk and edge states belong to distinct
symmetry classes.
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All authors Milad Jangjan, Linhu Li, Longwen Zhou, Mir Vahid Hosseini
Materials Science
Revealing the Role of Confined Molecular H$_2$ in the Passivation of Defective Silicon Using First-Principles Simulations
Hania Azzam, Tobias Binninger, Benedikt Fischer et al. (+2 more)
The passivation of silicon dangling bonds by hydrogen is a crucial requirement for silicon-based optoelectronic technology, especially for
solar cells. Recent experiments on intense light soaking of silicon heterojunction
solar cells unveiled interesting dynamical aspects of hydrogen passivation that are linked to Si-H bond breaking and repassivation. These processes take place predominantly in porous regions near the amorphous/crystalline interface, where hydrogen can exist in molecular form. This work addresses the question of whether molecular H$_2$ directly participates in Si-H depassivation and repassivation. Using density functional theory, we calculate and compare formation energies of point defects, multivacancy cavities and the Si(100) surface to identify relevant passivated and depassivated states. Furthermore, we employ nudged elastic band calculations to determine the activation barriers of the corresponding pathways. We find that sufficient local free volume enables a direct double-H pathway for depassivation through the formation of confined molecular H$_2$. Despite involving the breaking of two Si-H bonds, the double-H process can be energetically and kinetically competitive with the single-H process and can exhibit a reverse repassivation barrier as low as $0.15\,$eV under p-type conditions. These findings provide a plausible atomistic explanation for passivation recovery during light soaking and illuminated annealing in porous regions near amorphous/crystalline silicon interfaces.
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All authors Hania Azzam, Tobias Binninger, Benedikt Fischer, Uwe Rau, Michael Eikerling
Materials Science · Cross-listed from physics.chem-ph
Real-time ESR tracking for sub-micron 3D magnetic mapping with VB- quantum sensors in hexagonal boron nitride
Jefferson A. O. Galindo, Edwin D. C. Sanchez, Cecília L. A. V. Campos et al. (+6 more)
The discovery of
spin-dependent luminescent properties of negatively charged boron-vacancy centers ($V^-_B$) in hexagonal boron nitride (hBN) enabled a new platform for
quantum sensing with van der Waals materials. Particularly, the possibility of performing optically detected
magnetic resonance (ODMR) for determining the electron
spin resonance (ESR) frequencies of hBN color centers became a strong tool for
quantum sensing of
magnetic fields with submicrometric resolution. However, due to low ODMR contrast, current techniques proposed for mapping DC
magnetic fields require hours of integration to obtain a
magnetic image of a micron-sized region. In this work, we report the implementation of a frequency-tracking approach for real-time monitoring of ESR frequencies of localized $V^-_B$ centers in hBN. With this technique,
magnetic field monitoring was used to map the field pattern generated by a micron-sized conical
magnetic tip in only a few minutes. By controlling the
magnetic sample's position relative to the
quantum sensor, three-dimensional
magnetic mapping of the field was achieved with diffraction-limited resolution and shot-noise-limited sensitivity of 54 $\mu$T$/\sqrt{\text{Hz}}$.
Magnetic field gradients of 3.6 $\pm$ 0.2 $\mu$T/nm were measured with our system, in which a maximum detected field rate of 6 mT/s was achieved. The results of this study establish
spin resonance frequency-tracking as a viable technique and fast method for minute-scale
magnetic imaging, reducing acquisition times by at least one order of magnitude if compared to conventional techniques.
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All authors Jefferson A. O. Galindo, Edwin D. C. Sanchez, Cecília L. A. V. Campos, Allison R. Pessoa, Hugo A. D. Correia, José D. M. de Lima, Klaus Krambrock, Leonardo de S. Menezes, Anderson M. Amaral
Mesoscale and Nanoscale Physics
Quantum critical behavior in chains of hindered dipolar planar rotors
Wenxue Zhang, Muhammad Shaeer Moeed, Estevao De Oliveira et al. (+2 more)
We study the ground-state properties of linear chains of dipolar planar rotors hindered by a six-fold on-site potential, a model motivated by water molecules confined in the hexagonal cavities of beryl. Using density
matrix renormalization group (DMRG) calculations, we locate the
quantum phase transition between the disordered and ferroelectrically ordered phases using the von Neumann
entanglement entropy and the Binder ratio of the polarization. A sweep of the six-fold pinning strength shows that increasing hindrance shifts the critical dipolar coupling gc to smaller values. These results suggest that
crystal-field hindrance can promote, rather than suppress, dipolar ordering. This work has implications for ferroelectricity and
quantum-device tuning in confined molecular rotors
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All authors Wenxue Zhang, Muhammad Shaeer Moeed, Estevao De Oliveira, Hui Li, Pierre-Nicholas Roy
Materials Science
Carrier Capture at Defects from Finite-Temperature Lattice Dynamics
Menglin Huang, Shanshan Wang and Shiyou Chen
Defect-assisted carrier capture is commonly described within nonradiative multiphonon (NMP) theory using normal modes of the
equilibrium defect structure. This description becomes inadequate when finite-temperature
lattice fluctuations explore configurations that cannot be represented by a fixed normal-mode basis. Here, we present a trajectory-based method for calculating carrier capture rate from first principles, which allows
lattice relaxation and electron–
lattice coupling
matrix element to be reconstructed directly from correlation functions of finite-temperature
lattice dynamics. For hole capture at C$_\mathrm{N}$ in GaN within harmonic regime, the method reproduces static NMP results including mode mixing and agrees with experiment. For oxygen vacancy in SiO$_2$, by contrast, the thermally sampled potential energy surface is substantially softer than the zero-temperature normal-mode harmonic expansion, strongly modifying the
lattice relaxation and electron–
lattice coupling, and producing pronounced changes in both the capture coefficient and its temperature dependence. These results establish the finite-temperature configurational ensemble, rather than
phonon occupations alone, as an essential ingredient of defect-assisted carrier capture.
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Quantum Gases
Self-limiting electrostriction of a single ion in an ultracold polar gas: From mesoscopic ions to crystalline molecular rings
Ruiren Shi, Saajid Chowdhury, Leon Karpa et al. (+1 more)
We investigate the self-assembly of polar molecules around a single ion immersed in an ultracold, dilute two-dimensional molecular gas. The ion aligns and attracts the molecules through charge-dipole interactions, producing a strong electrostrictive accumulation around the
impurity, while intermolecular repulsion limits further densification and favors spatially extended configurations. By combining global optimization with
diffusion Monte Carlo, we calculate the evaporation energy as a function of the number of molecules bound to the ion. In contrast to conventional charged and van der Waals clusters, the evaporation energy exhibits a plateau-like dependence on cluster size, reflecting the sequential formation of concentric molecular rings. These structures are governed by the
topology of the ion's electric field and by the competition between attractive ion-molecule interactions, repulsive intra-ring interactions, and attractive correlations between neighboring rings, rather than by conventional coordination or icosahedral packing. In the weak-interaction regime, the resulting structures form extended mesoscopic molecular ions, whereas stronger interactions produce increasingly rigid,
crystal-like molecular rings. We further analyze their stability against thermal perturbations and the time-dependent ion trap and find that a broad range of clusters remain stable under experimentally relevant conditions. The intermolecular repulsion and dipolar geometry also suppress close-range ion-molecule encounters, suggesting an intrinsic shielding mechanism. Our results establish ion-bound polar-molecule clusters as a distinct class of mesoscopic molecular ions and open a route to studying charged
impurities in
quantum baths with anisotropic interactions.
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All authors Ruiren Shi, Saajid Chowdhury, Leon Karpa, Jesús Pérez-Ríos
Soft Condensed Matter
The friction-era VOS amplitude of a $\mathbb{Z}_2$ string network from nematic disclination data
Dimitrios Efstratiou, Evangelos Achilleas Paraskevas and Leandros Perivolaropoulos
A tangle of line defects coarsens as the mean spacing $L$ between neighbouring lines grows. In a viscous medium the motion is overdamped, and the velocity-dependent one-scale (VOS) model predicts a late-time attractor $L^{2}=\mathcal{A}\,\ell_d\,t$, with $\ell_d=T/\Gamma$ the ratio of line tension to drag and $\mathcal{A}$ a dimensionless amplitude. The growth law $L\propto t^{1/2}$ holds for every value of the three model parameters—the momentum parameter $k\le1$, the sink coefficient $\tilde{c}$, and the
curvature ratio $\lambda\equiv R/L$—since all three enter only through $\mathcal{A}=\kappa(\kappa+\tilde{c})$, $\kappa\equiv k/\lambda$. Thus, the exponent constrains none of them, and the amplitude is the only quantity a density history can deliver. We measure it from the disclination data of Chuang, Turok and Yurke on a nematic
liquid crystal, whose companion measurement of loop collapse fixes $\ell_d$ on the same samples, canceling the 5CB material constants. Treating the unmatched per-quench $\ell_d$ as a nuisance parameter with a Gaussian prior and marginalizing it analytically, we obtain $\mathcal{A}=10.0^{+1.3}_{-1.1}$ from the three quenches in the $234~\mu$m
cell; the fourth, the only one in the thinner $158~\mu$m
cell, gives $\mathcal{A}=3.0^{+0.8}_{-0.6}$ and is fitted separately. Converting either into $\tilde{c}$ requires $\lambda$, which these data do not determine, so the result is a curve, $\tilde{c}(\lambda)=\mathcal{A}\lambda/k-k/\lambda$, not a number. At $\lambda=1$ with $k\le1$ they give $\tilde{c}\ge9.0$ and $\tilde{c}\ge2.0$, against $\tilde{c}=0.23$–$0.57$ from relativistic $U(1)$ simulations, values reached only at $\lambda\simeq0.33$–$0.35$ and $0.62$–$0.68$. We know of no VOS calibration for a cosmological $\mathbb{Z}_2$ network, so we cannot attribute the excess to
topology, and we list what a repeat experiment must measure.
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Materials Science
An LLM agent for end-to-end computational materials discovery
Chen Yuntong, Huang Ju, Liu Yu et al. (+6 more)
The coordination of multi-scale tasks is an effective strategy for computational materials discovery, yet the repeated application of diverse
algorithms and tools renders it challenging. We report MAESTRO, a large
language model (LLM)
agent system capable of executing the entire screening pipeline for metal-organic frameworks (MOFs). It processes a large body of MOF literature, links relevant publications to their
crystal structures, and curates the results into a computation-ready database, which is then screened through a strategy of progressively increasing computational cost. The promising candidates identified for separation under wet flue gas conditions all originate from unrelated studies. By connecting the heterogeneous stages of computational materials discovery, the LLM-based
agents of MAESTRO can operate across application domains and uncover high-performance materials that conventional screening approaches would be unlikely to consider.
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All authors Chen Yuntong, Huang Ju, Liu Yu, Zhao Dan, Sun Mingqi, Ju Chentian, Liu Yanbing, Huang Lijiang, Zhao Guobin
Strongly Correlated Electrons · Cross-listed from hep-th
Maximal Total Quantum Dimension at Bounded Rank in WZW Modular Tensor Categories
Ce Shen
We determine the maximal
torus topological
entanglement entropy (TEE) at bounded
torus ground-state degeneracy within simply connected untwisted Wess–Zumino–Witten theories. For a fixed modular tensor category $\mathcal C$, maximization over normalized
torus ground states gives $\max_\psi\Gamma_{T^2}(\psi)=2\log{\mathcal D(\mathcal C)}$, attained in particular by the
vacuum-flux state. The remaining problem is therefore to maximize total $\mathcal D$ at bounded categorical rank. For a simple WZW category $\mathcal C(\mathfrak g,k)$, write $r(\mathfrak g,k)$ and $\mathcal D(\mathfrak g,k)$ for its categorical rank and total
quantum dimension, and define $F_{\WZW}(R)=\sup_{r(\mathfrak g,k)\leq R}2\log\mathcal D(\mathfrak g,k)$. We prove the sharp asymptotic law $\lim_{R\to\infty}\frac{F_{\WZW}(R)}{(\log_2R)^2} =\frac{7\zeta(3)}{4\pi^2}.$ The balanced
symplectic sequence $Sp(2n)_n$ attains the coefficient. The constant arises from the odd
Fourier modes of the type-$C$ root product at equal rank and level. A sharp
entropy–spectral inequality, rank-level duality, and fixed-rank estimates give the global upper bound. A separate corollary extends the same leading law to semisimple WZW categories,equivalently finite Deligne products of simple factors. The unrestricted TQFT envelope remains open; the
theorem is sharp within the stated WZW class and supplies a constructive lower bound for the general problem.
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Quantum Gases · Cross-listed from physics.atom-ph
A Protocol for Shielding-Enhanced Loading of Single Polar Molecules into Optical Tweezers
Reuben R. W. Wang, Christian H. Nunez, Conner Williams et al. (+4 more)
We propose the high-fidelity preparation of single bosonic molecules in optical tweezers starting from small tweezer-trapped molecular ensembles. Our scheme combines a static electric field and a microwave field to generate strong, tunable, anisotropic interactions that shield the molecules against two-body collisional loss. We show that this shielding eliminates all long-range bound states, preventing three-body recombination. This elimination persists for all microwave ellipticities, including the experimentally practical limit of linear polarization. Application of an additional electric field gradient can be used to induce controlled spilling of strongly interacting molecules out of the trap until one remains. With realistic experimental parameters, we estimate that single tweezer-trapped NaCs molecules can be isolated from a pair with fidelities exceeding 99%, and $> 95\%$ per site across an array. These results establish collisional shielding with electric fields as an effective tool for preparing highly-filled tweezer arrays of polar molecules.
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All authors Reuben R. W. Wang, Christian H. Nunez, Conner Williams, Amanda Younes, Li Du, H. R. Sadeghpour, Kang-Kuen Ni
Strongly Correlated Electrons
Torus Berry Data Determine All-Genus Abelian Topological Orders
Daniel Galviz
We show that for Abelian Chern-Simons topological orders,
torus Berry
matrices determine the all-genus extended TQFT. We identify the topological part of the projective Berry holonomy under metric deformations with the mapping-class-group representation of the Abelian Chern-Simons TQFT and prove that the normalized
torus data reconstruct its finite quadratic module (G,q). Recent work showed that (G,q) classifies the extended theory up to symmetric monoidal natural isomorphism, and that the associated Abelian defect extension is determined by the pointed modular category C(G,q) arising from the same finite quadratic-module data. Therefore genus-one Berry data determine not only the all-genus bulk theory but also its associated defect structures without choosing a K-
matrix presentation. We also prove that, for normalized character row errors $\delta$<21.96%, nearest-row decoding recovers the Abelian fusion
algebra independently of the number of anyons. The result applies to Abelian fractional
quantum Hall and
spin-
liquid phases described by even-
lattice Chern-Simons theories.
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Statistical Mechanics
The Memory Hidden in Response Fluctuations: Trajectory-Level Fluctuation-Response Theory and Inequalities for Non-Markovian Jump Dynamics
Jiming Zheng and Zhiyue Lu
Modern experiments often record nonequilibrium dynamics as sequences of discrete events whose rates depend on the realized past. We develop a fluctuation-response theory for such non-Markovian jump processes directly on the observed event record.
Memory can destroy a closed master equation for the state probabilities. Each transition count nevertheless obeys an exact
stochastic equation. After the history-dependent mean event tendency is subtracted, the remaining random increment is a martingale increment–the part of the event that cannot be predicted from the past. Martingale increments associated with different transitions and different times are orthogonal. These increments form a complete orthogonal basis for the random deviation of any observable measured from the record, such as a current, occupation time, or event count. The coefficient of a given increment is the event-consequence kernel. It measures how that event changes the predicted final observable, relative to continuing without the event, for the particular history already realized. Multiplying this kernel by the event intensity gives the history-conditioned response to perturbing the corresponding transition rate. Thus, the intensity-normalized response is exactly the expansion coefficient of that event in the observable fluctuation. This identification yields exact finite-time and finite-frequency fluctuation-response relations. Averaging over histories leaves a nonnegative response-heterogeneity gap. The gap measures how strongly the consequence of the same event varies across histories and tests whether a proposed
memory coordinate is response-sufficient. Finite-history versions can be estimated from spontaneous trajectories. Bounding the logarithmic rate sensitivity further gives response-kinetic uncertainty relations controlled by dynamical activity.
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Quantum Gases
Competing triangular and stripe supersolid orders in a dipolar quantum gas
Karthik Chandrashekara, Christian Gölzhäuser, Lily Platt et al. (+6 more)
Supersolids are exotic
quantum states in which long-range phase coherence coexists, and may interplay, with emergent spatial orders. A particularly rich phase diagram featuring several competing spatial orders is predicted for dipolar supersolids with two-dimensional
crystals, yet the experimental observation of this structural variety has remained limited. Here we experimentally form competing triangular and stripe density-modulated states in a
quantum gas of highly
magnetic atoms confined in a surfboard-shaped trap by tuning contact interaction strength and dipole orientation. We define a structural order parameter and study its statistical behavior. Thereby, we identify both the triangular and stripe phases and the transition between them, the associated critical behavior being marked by enhanced non-Gaussian fluctuations. Furthermore, we observe each spatial structure in both the phase-coherent supersolid regime and the phase-incoherent insulating one, near and far from the unmodulated-to-modulated transition, respectively. Our results establish a versatile platform in which multiple phases of the two-dimensional-supersolid phase diagram, and more generally, intertwined
symmetry-breaking phenomena, can be investigated.
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All authors Karthik Chandrashekara, Christian Gölzhäuser, Lily Platt, Jianshun Gao, Julian Kusch, Lennart Hoenen, Manon Ballu, Wyatt Kirkby, Lauriane Chomaz
Superconductivity
Strange Metal Hall Effect in Underdoped BaFe$_2$(As$_{1-x}$P$_x$)$_2$
Augusto Ghiotto, Darian Hall, Yuanqi Lyu et al. (+7 more)
The unusual transport properties of strange metals point to the breakdown of the quasiparticle picture, the understanding of which remains one of the most vexing problems in physics. Here, we report investigations of the electrical
Hall effect of the strange metal
superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$. We show that a doping-independent contribution to the
Hall effect exists within a fan shaped region above a putative
quantum critical point. This `strange metal
Hall' contribution echoes many of the properties of the antiferromangetic
Hall response, but attains universal properties that distinguish it from the effects of
Fermi surface reconstruction. This is consistent with an underlying origin connected to the presence of critical fluctuations, tying it to observations of $T$-linear resistivity and the appearance of unconventional superconductivity.
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All authors Augusto Ghiotto, Darian Hall, Yuanqi Lyu, Kohtaro Yamakawa, Sophie Rodehutskors, Corina Dunn, Philip J. W. Moll, John Singleton, Nikola Maksimovic, James G. Analytis
Mesoscale and Nanoscale Physics · Cross-listed from physics.app-ph
Spin-torque microwave detectors of positive rectangular pulse signals
V. Prokopenko, O. Shtanko, I. Sotnyk et al. (+1 more)
We analyze the performance of a
spin-torque microwave detector (STMD) driven by positive rectangular current pulses $I(t)$ of various amplitudes $I_0$, durations $\tau$, and repetition periods $T$ and reveal two distinct regimes of STMD operation. In the first (linear) regime, the time-averaged voltage across the detector, $U_{\rm dc}$, changes linearly with the pulse amplitude $I_0$ and depends on the ratio $\tau/T$: $U_{\rm dc} \sim I_0 (\tau/T)$. This regime is observed for a wide range of pulse amplitudes $I_0$ in the case of in-plane (IP) magnetization dynamics and for rather small pulse amplitudes $I_0 \le I_{\rm th}$ in an STMD with out-of-plane (OOP) magnetization dynamics. The other (nonlinear) regime is characterized by voltage jumps and drops and is observed only in a structure with OOP magnetization dynamics for input pulses with short repetition periods and large amplitudes $I_0 \ge I_{\rm th}$. We believe that the linear regime of STMD operation can be used to unambiguously detect input pulse parameters, which could be important for the development and optimization of spintronic devices capable of detecting and processing non-harmonic (e.g., digital) microwave signals.
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All authors V. Prokopenko, O. Shtanko, I. Sotnyk, O. Prokopenko
Quantum Gases
Imaging the vacuum fluctuations of a quantum field
Yansheng Zhang, Feiyang Wang, Yi Jiang et al. (+5 more)
Heisenberg uncertainties lead to inevitable fluctuations in the measurement outcomes for
quantum-mechanical observables. For
quantum fields, these uncertainties result in random spatial structures in snapshots of a field, even when the field is in its ground (
vacuum) state. Such `
vacuum fluctuations' are at the heart of a wide range of phenomena, from spontaneous decay processes to the Casimir force and Hawking radiation. Their existence is a key manifestation of the quantumness of the physical world, but usually it is only their consequences that are directly observed. Here, we directly observe spatial
vacuum fluctuations of a bosonic
quantum field. Our experiments are based on a homogeneous planar atomic Bose–Einstein condensate. The condensate comprises two coherently coupled interacting components (
spin states), and the
quantum field describes its
spin degrees of freedom. In the regime where the interactions dominate over the coherent coupling, our system emulates a (massive relativistic) sine-Gordon field. Images of the field reveal simultaneous fluctuations on different length scales, with scale-dependent amplitudes consistent with theoretical predictions for a
vacuum state. Observing such fluctuations in the sine-Gordon limit opens many possibilities for laboratory simulations of relativistic fields in regimes that are presently not theoretically tractable.
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All authors Yansheng Zhang, Feiyang Wang, Yi Jiang, Alexander C. Jenkins, Paul H. C. Wong, Christoph Eigen, Gehrig Carlse, Zoran Hadzibabic
Mesoscale and Nanoscale Physics
Signatures of a light-induced exciton condensate exhibiting BEC-BCS crossover
Khanh Duy Nguyen, Gabriele Berruto, Yunhe Bai et al. (+7 more)
Exciton condensates provide a platform to study quasiparticle pairing, Bose-Einstein condensation-Bardeen-Cooper-Schrieffer (BEC-BCS) crossover, and excitonic topological phenomena. Achieving a nonequilibrium
exciton condensate allows the ultimate tunability of these emergent phenomena. Yet, evidence of a light-induced, nonequilibrium
exciton condensate and its BEC-BCS crossover remains elusive. Here, we use time- and angle-resolved photoemission spectroscopy to demonstrate signatures of a non-
equilibrium exciton condensate and its BEC-BCS crossover in monolayer MnBi2Te4. Following optical excitation, a distinctive hole-like dispersion representing
excitons emerges and persists for >20 ps. Strikingly, energy-domain sharpening in the valence band occurs 2 ps after time zero and exhibits a sharp onset at a threshold pump fluence of 0.84 mJ/cm2. The delayed and strongly nonlinear response is difficult to reconcile with transient field effects or conventional carrier-induced band shifts but is consistent with a model of
exciton condensation governed by a Berezinskii-Kosterlitz-Thouless transition. The estimated threshold
exciton density agrees quantitatively with the Nelson-Kosterlitz critical density. At higher fluences, the
exciton feature develops a camel-back-shaped dispersion, consistent with the BEC-BCS crossover in the condensate framework. Our work establishes ultrathin MnBi2Te4 as a model system for studying nonequilibrium
exciton condensates with a connection to superconductivity and
exciton-driven topological phases.
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All authors Khanh Duy Nguyen, Gabriele Berruto, Yunhe Bai, Thomas Marchese, Woojoo Lee, Haoran Lin, Jiangang Yang, Chong Liu, Y. Shirley Meng, Shuolong Yang
Quantum Gases · Cross-listed from quant-ph
Programmable cavity QED with a fiber-integrated atomic array
Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca et al. (+3 more)
Strong atom-
photon interactions in optical cavities are a key resource for
quantum information processing,
quantum networking, and the exploration of
quantum optical effects. Optical tweezer arrays offer scalable, site-resolved control of neutral atoms, but their integration with high-cooperativity cavity QED systems remains challenging. Here we combine a twelve-site $^{87}$Rb optical tweezer array with a high-cooperativity fiber Fabry-Pérot microcavity. The array is positioned within the cavity mode and individual sites are controlled with subwavelength precision, enabling continuous tuning of the single-atom coupling strength via deterministic displacement through the standing-wave field. For up to five atoms coupled to the cavity, we measure collectively enhanced
vacuum Rabi splitting and implement cavity-based non-destructive readout of the number of coupled atoms. These results establish a scalable architecture for cavity-mediated
entanglement generation and many-body cavity QED with single-atom control, and they lay the foundation for fiber-integrated
quantum network nodes.
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All authors Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca, Marvin Holten, Damien Bloch, Julian Léonard
Quantum Gases · Cross-listed from quant-ph
Quantum-mechanical wave functions in singular potentials: linear and nonlinear states
Hidetsugu Sakaguchi and Boris A. Malomed
It is known that the attractive singular inverse-square potential gives rise to the critical
quantum collapse in the framework of the three-dimensional (3D) linear Schroedinger equation. This article summarizes theoretical results which demonstrate suppression of the collapse, caused by this singular potential, and the creation of the otherwise missing ground state (GS) in a 3D gas of bosonic particles, carrying an electric dipole moment, which are pulled to the central electric charge, with repulsive contact interactions between the particles. In the mean-field approximation, the repulsive interactions are represented by the cubic term in the respective Gross-Pitaevskii (GP) equation. In addition to the GS, excited states with angular momentum are briefly considered too. Another topic considered in the article is 1D and 2D bound states in the linear Schroedinger and GP equations with the repulsive potential, which demonstrates a singularity at r –> infinity. A very recent result is that such a potential, growing faster than the negative harmonic-oscillator potential, produces a full spectrum of counter-intuitive normalizable (localized) bound states. The article puts forward perspectives for further studies of linear and nonlinear bound states existing under the action of the potentials with the singularity at r –> 0 or r –> infinity.
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Statistical Mechanics · Cross-listed from nlin.CD
Flip rate prediction in the double pendulum
Peleg Haham and Barak Kol
The intermediate-energy double pendulum is a prototypical chaotic system. Despite its irregular motion, it exhibits recurrent flips - events in which one of the arms passes over the top. We develop a statistical prediction for the mean flip rate in terms of phase space flux. Applying this flux-based approach to the equal-mass, equal arm ("egalitarian") double pendulum, we find excellent agreement between the statistical prediction and numerical simulations: ensemble-averaged flip rates agree at about the 1% level, while even the statistics of individual chaotic trajectories agree at the few-percent level, quantifying the validity of the ergodic approximation. This agreement holds for flips of either arm and over a broad range of energies. This flux-based approach is closely related to that used for the egalitarian three-body system. A central role is played by the saddle orbits: periodic orbits that tend to the stable saddle eigenmode as the energy approaches the saddle energy from above and approximately follow the ridge of the potential at higher energies. These orbits provide a natural dividing surface for defining flips while avoiding recrossings. Indeed, the resulting distribution of crossing times exhibits a distinct gap. We also present two alternative simplified dividing surfaces, one of which is based on an accurate analytic approximation to the saddle orbits.
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Strongly Correlated Electrons
Nonlinear Drude weight of the one-dimensional Hubbard model
Tetsuya Iwasaki and Hosho Katsura
We investigate nonlinear Drude weights (NLDWs) in the one-dimensional repulsive Hubbard model at zero temperature by combining exact Bethe-ansatz calculations with low-energy effective field theory. At quarter filling, we first derive the strong-coupling expansion of the NLDWs and confirm it numerically over a wide range of interaction strength. We then compare the numerical results with the prediction of the Tomonaga-Luttinger
liquid (TLL) description including irrelevant perturbations. While band-
curvature corrections yield finite contributions to higher-order NLDWs, the Umklapp interaction predicts divergent NLDWs when the order $n$ of the Drude weight exceeds a threshold determined by the TLL parameter. In contrast, finite-size scaling of the exact Bethe-ansatz results indicates that all calculated NLDWs remain finite in the thermodynamic limit, revealing a discrepancy between the exact results and the predictions of the low-energy effective field theory. At half filling, we analyze the finite-size scaling of the NLDWs across the Mott metal-
insulator transition. We derive their asymptotic behavior in the insulating phase and propose a hyperscaling ansatz for NLDWs near the critical point, which is verified numerically. Our results clarify the interaction dependence and critical scaling of nonlinear transport coefficients in the one-dimensional Hubbard model and highlight limitations of the conventional low-energy effective description for higher-order transport.
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Statistical Mechanics
Learning Potts Models and $Z_3$ Toric Codes: Higher and Ordinary Nishimori Criticality
Rushikesh A. Patil, Malte Pütz, Rohit Mukherjee et al. (+3 more)
Motivated by a previous Ising study, we identify a ${\it higher}$ Nishimori line in the learning phase diagram of the $2D$ $q$-state Potts model $(2 < q\leq 4)$ under bond-energy measurements. This ${\it higher}$ Nishimori line meets the critical temperature line of the Potts model, in a ${\it higher}$ Nishimori critical point – a tricritical point at finite inference strength that separates a paramagnetic, a
ferromagnetic and a '
spin-glass' phase. With analytical tools, we discuss the general structure of the rich phase diagram, which contains two unstable and three stable fixed points, and obtain a number of exact results for universal quantities, including the decay exponent of the Edwards-Anderson correlator, using a Gaussian measurement protocol which allows for exact calculations. Using extensive numerical tools, we confirm these statements for a generic, discrete $q$-state measurement protocol and determine precise numerical estimates for the location of higher and ordinary Nishimori critical points as well as RG flows between the various fixed points. We also discuss the Casimir effective central charges of the critical points in the learning phase diagram, and their monotonic ${\it decrease}$ along measurement-induced RG flows, as established non-perturbatively by the c-effective
theorem and its extensions, and contrast it to the monotonic increase along the corresponding RG flows in the random-bond Potts model. Finally, we discuss a general argument based on ${\it Elitzur's \; theorem}$ that establishes stability of the ordinary Nishimori critical points in their respective learning phase diagrams. Equivalently, our results describe a monitored deformed $\mathbb{Z}_q$ toric code where the tricritical ${\it higher}$ Nishimori point is an 'information' critical point that separates stable
quantum, classical, and no
memory phases.
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All authors Rushikesh A. Patil, Malte Pütz, Rohit Mukherjee, Guo-Yi Zhu, Simon Trebst, Andreas W. W. Ludwig