Superconductivity
Distribution of Majorana modes in the extended-range Kitaev chain
Pedro B. Widniczck and Gerardo Martínez
The topological properties of the Kitaev chain model with extended-range interactions are investigated, focusing on cases where the topological winding number is preserved. We assume that the pairing and hopping terms decay algebraically in space with exponents $\alpha$ and $\beta$, respectively. We show that in the truncated-range scenario, there are as many distinct topological phases as the number of coupled neighboring sites. In addition, an explicit analytical formulation is provided to evaluate the topological invariant and the phase transitions that emerge in these systems. Besides the analytical description, we introduce a new physical insight into the topological excitations of the ground-state by measuring the spatial distribution of the edge modes with the Majorana average position. Taking the next-nearest neighbor Kitaev chains as a probe, various numerical calculations of Majorana edge states were performed in finite-size clusters to determine the sensitivity of the topological zero energy modes to the parameters of interest. The occupation of edge-to-edge non-local
fermion states is computed and defined as an effective parity. Such an effective parity exhibits new interesting features beyond the energetic exchange from the ground-state
fermion parity switches, which are related to the distribution of the respective edge modes. Our calculations show a direct correlation between the ground-state
fermion parity and the edge occupation numbers, which are translated into localization and delocalization of the Majorana average position.
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Statistical Mechanics · Cross-listed from nlin.AO
Collective drift and pinning in active rotator networks with Kuramoto coupling and mixed-sign feedback disorder
Arpan Dey
Active rotator models provide a minimal phase description of excitable and oscillatory systems and have long been used to study mutual entrainment, synchronization, and collective transitions. In this paper, we investigate fully connected active rotator networks with Kuramoto coupling, where a common positive intrinsic drive competes with local feedback amplitudes drawn from a zero-mean Gaussian distribution. We characterize the dynamics using the mean absolute late-time drift, the polar and nematic order parameters, and the fractions of positive and negative drifting oscillators. The model with an even mixed-sign feedback ensemble has an exact discrete
symmetry under a simultaneous phase shift by $\pi$ and reversal of the feedback amplitudes. This exposes two physically distinct low-drift states: at weak coupling and strong disorder, local pinning produces an approximately antipodal, nematically ordered population, whereas at strong coupling the system can form a polar, coherently pinned state. A self-consistent stationary mean-field theory determines the existence edge of a nonzero coherent branch, provides quantitative predictions for the polar and nematic order, and shows that the coherent branch followed here is fully pinned. Sustained negative drift is impossible in a stationary mean field; the negative-drift population observed is instead localized to an intermediate-coupling regime characterized by a non-stationary mean field. Finally, finite-size extrapolations show persistent coupling-induced drift recovery and are compatible with vanishing strong-coupling drift at large disorder in the thermodynamic limit. These results show that even with a homogeneous intrinsic drive, mixed-sign local feedback can generate distinct regimes of drift, pinning, and collective phase organization.
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Strongly Correlated Electrons
Exactly solvable non-planar $\mathbb{Z}_{2}$ dimer liquids on checkerboard and ruby lattices
Julia Wildeboer, Zohar Nussinov, Thomas Iadecola et al. (+1 more)
We generalize an influential framework for exactly solvable
quantum dimer models with dual Ising gauge theory descriptions realizing the $\mathbb{Z}_{2}$ topological phase from trivalent to tetravalent parent
lattices. The resulting
quantum dimer models live on crossed-medial
lattices and possess the remarkable feature of having crossed plaquettes, leading to transition graphs with generically intersecting loops. This non-planar structure runs counter to established templates for analytically tractable dimer
liquids. As the simplest realization of the construction, we introduce an exactly solvable
quantum dimer model on the checkerboard
lattice that allows an exact mapping to the toric code, thus providing a particularly direct connection between the latter and Anderson's short range resonating valence bond paradigm. We further show that a corresponding crossed ruby
lattice construction, dual to an Ising gauge theory on the kagome
lattice, naturally falls within the same framework. More generally, the construction gives rise to a broad class of exactly solvable crossed-medial
quantum dimer models and admits natural iteration, generating cascades of solvable $\mathbb{Z}_{2}$ topological dimer
liquids beyond the standard planar setting. We furthermore extend Kasteleyn methods to the relevant non-planar graphs, enabling controlled wave-function deformations away from the commuting-projector points while retaining efficient evaluation of correlation functions.
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All authors Julia Wildeboer, Zohar Nussinov, Thomas Iadecola, Alexander Seidel
Mesoscale and Nanoscale Physics
Fabry-Perot Interference, g-factor Anisotropy, and Gate-Tunable Quantum dot in Chiral Tellurium Nanowires
Suresh Ghimire, Mohammad Hafijur Rahaman, Nathan Tanner Sawyers et al. (+8 more)
Chiral materials with strong
spin-orbit coupling offer a unique platform for exploring the interplay between
topology, chirality, and
quantum transport yet the
quantum coherent regime in elemental tellurium nanostructures remains largely unexplored. Here we demonstrate phase-coherent quasi-ballistic transport, anisotropic Zeeman spectroscopy, and gate-tunable
quantum dot formation in hydrothermally grown t-tellurium nanowires. Single nanowire field-effect transistors exhibit p-type transport with hole mobilities rising from approx. 80 cm2 V-1 s-1 at 210 K to approx. 190 cm2 V-1 s-1 at 1 K, consistent with a crossover from
phonon-limited to Coulomb scattering dominated regimes near 50 K. Notably, devices segregate into two distinct regimes based on their room temperature two-terminal resistance : low-resistance devices (< 30 kOhm) exhibit Fabry-Perot interference, whereas high resistance devices (> 30 kOhm) display Coulomb-blockade behavior revealing a two-terminal resistance-driven transition between quasi-ballistic and strongly localized transport regimes. Zeeman spectroscopy in in-plane and out-of-plane
magnetic fields yields highly anisotropic Lande g-factors (an in-plane gparallel = 1.18 and an out-of-plane gperp = 18.41) and directly resolves a
spin-orbit energy gap DeltaSO = 0.864 meV from an avoided crossing. These results establish
chiral tellurium nanowires as a versatile platform for gate-defined
spin qubits exploiting large, tunable g-factors and for hybrid tellurium-
superconductor architectures targeting Majorana zero modes in an elemental vdW system.
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All authors Suresh Ghimire, Mohammad Hafijur Rahaman, Nathan Tanner Sawyers, Madan Mohan Bhandari, Gokul Acharya, Syed Zulfiqar Hussain Shah, Iris Nandhakumar, Pawan Kumar, Zainul Aabdin Khan, Hugh O. H. Churchill, Dharmraj Kotekar-Patil
Superconductivity
Quantum-geometric origin of superfluid weight in quasicrystals with critical states
Kazuma Saito, Ryo Okugawa, Yusuke Kato et al. (+1 more)
A distinctive feature of many quasiperiodic systems is the presence of critical states that are neither extended nor exponentially localized. We investigate the
geometric effect on the superfluid weight in quasiperiodic systems with critical states at zero temperature. We employ both real-space and momentum-space approaches to superfluid weight in quasicrystals, which allows us to separate the conventional and
quantum geometric contributions. We find that the superfluid weight is dominated by the
geometric contribution in quasiperiodic systems with critical states. This finding reveals a fundamental interplay between superconductivity and critical states in quasicrystals.
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All authors Kazuma Saito, Ryo Okugawa, Yusuke Kato, Takami Tohyama
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Absence of poor local minima in matrix product states
Hao-Kai Zhang, Chenghong Zhu, Shuo Liu et al. (+2 more)
Quantum circuits suffer from severe trainability issues: even shallow
circuits are swamped with poor local minima. Yet
matrix product states (MPS), which can be prepared by sequential
circuits, are remarkably trainable in practice – as demonstrated by decades of successful density
matrix renormalization group calculations. In this work, we resolve this apparent paradox by proving that the energy landscapes of MPS are free from poor local minima, under the same setting where brickwork
circuits are not. The key insight is that the gauge freedom of MPS creates an effective local overparametrization that causes local minima to concentrate near the global minimum, analogous to overparametrized classical neural networks. We rigorously prove that the local minimum distribution is invariant under moves of the orthogonality center of MPS representations. Numerical experiments further confirm that the optimization of sequential
circuits converges to near-optimal solutions even for random
Hamiltonians, in stark contrast to brickwork
circuits. Our findings establish a theoretical understanding of the trainability of MPS, providing a valuable guide for designing variational
quantum circuits and
algorithms with better trainability in the future.
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All authors Hao-Kai Zhang, Chenghong Zhu, Shuo Liu, Shi-Xin Zhang, Tao Xiang
Statistical Mechanics · Cross-listed from hep-th
Bootstrap Cone of the Multicritical Deconfined Quantum Critical Point
Zhijin Li and Tinhong Shen
The deconfined
quantum critical point (DQCP) provides a prominent example of the unconventional phase transitions beyond the Landau-Ginzburg-Wilson paradigm and its nature has been controversial for decades. The DQCP has been extensively studied and the results lead to two opposite scenarios with pseudo-criticality or multicriticality. The pseudo-criticality is a prevailing scenario of DQCP which interprets the approximately scale invariant numerical results with the walking behavior near complex fixed points. In contrast, the multicriticality scenario
conjectures the DQCP is a
unitary fixed point with a relevant $SO(5)$ singlet scalar. In this work we provide substantial evidence for the multicriticality scenario using conformal bootstrap. We start with the observation that the large scale
Quantum Monte Carlo (QMC) results nearly saturate the bootstrap bounds. After imposing suitable sparseness condition the bootstrap bound forms a sharp cone in the three-dimensional parameter space. The bootstrap cone is close to the QMC data. We use the navigator
algorithm to locate the apex of the cone and extract the extremal solutions. We find striking consistencies between the bootstrap solutions and the fuzzy sphere data of DQCP, including the coefficients in the operator product expansions (OPEs) and the higher spectrum! The bootstrap cone unifies the QMC and the fuzzy sphere data into a
unitary conformal field theory with a relevant $SO(5)$ singlet scalar, thus strongly supporting the multicriticality scenario of DQCP. The agreement between the conformal bootstrap, QMC and fuzzy sphere results is a surprise towards solving DQCP and decoding the profound phase diagram of the two-dimensional
quantum magnets.
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Statistical Mechanics · Cross-listed from hep-lat
Tame the Umklapp Processes in Real-Time Lattice Simulation for Hydrodynamics: An Ising Field Theory Study
Xiaojun Yao
We calculate the real-time symmetric correlation function of the stress-energy tensor for a near-integrable Ising field theory consisting of three stable scalar particles via
lattice Hamiltonian simulation. Using classical exact diagonalization and the
matrix product state tensor network methods, we find that in the scaling region of the
lattice theory, Umklapp processes that break continuum momentum conservation are suppressed and the sound modes of relativistic hydrodynamics emerge at long wavelength and late time in non-
equilibrium dynamics. The extracted ratio of bulk viscosity to
entropy density is $\zeta/s=3.06\pm 0.68$ and the speed of sound is $c_s/c=0.76 \pm 0.02$ at the temperature $T\approx 7.14$ in units of the lowest stable particle's mass. Our study demonstrates the utility of real-time
lattice Hamiltonian simulation for describing hydrodynamization and calculating transport coefficients nonperturbatively.
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Materials Science
Anatomy of fast current-induced skyrmion motion in synthetic antiferromagnets
W. C. Chen, H. X. Yang and X. F. Zhang
The high mobility of current-driven skyrmions in synthetic antiferromagnets (SAFs) is widely explained by the macroscopic suppression of the skyrmion
Hall effect through gyrotropic force compensation. This established view, however, overlooks a concurrent and significant reduction in the Gilbert damping parameter {\alpha}, a key factor in the Thiele equation governing skyrmion velocity. Here, we show that this damping attenuation originates from a reconfigured
magnon-electron scattering landscape. Using a microscopic s-d model, we demonstrate that the strong
antiferromagnetic interlayer Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange coupling in SAFs increases the magnonic gap of skyrmion collective modes, thereby suppressing the thermal
magnon population and, consequently, the
magnon-electron scattering rate that dominates damping in metallic ferromagnets. Our work establishes a dual-mechanism framework to fully explain the superior kinetics of SAF skyrmions: the macroscopic topological effect rectifies the motion direction, while the microscopic dissipation mechanism reduces the drag. This synergy enables high-speed and efficient motion, providing a fundamental elucidation of the enhanced mobility reported in recent studies such as the work by Pham et al. [Science 384, 307-312 (2024)].
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Strongly Correlated Electrons
Topological Triplons in the Pinwheel Valence Bond Solid on the Kagome Lattice
Laura Calonge-Martínez, Peng Rao, Frédéric Mila et al. (+1 more)
We investigate the triplon excitations of the pinwheel valence-bond-solid phase on the deformed kagome
lattice compound Rb2Cu3SnF12. Using bond-operator mean-field theory, we compute the triplon band structure, dynamical structure factor, Berry
curvatures and the associated thermal
Hall response. We show that the presence of Dzyaloshinskii-Moriya interactions and an external
magnetic field are key for endowing triplon bands with nontrivial Chern numbers. We find good qualitative agreement of the low-energy dynamical structure factor with
neutron-scattering experiments. An applied
magnetic field can isolate the lowest triplon Chern band leading to a tunable thermal
Hall conductivity for accessible temperature and field regimes. Our results establish the deformed kagome pinwheel valence-bond solid as a promising platform for topological triplon physics and for observing the associated thermal
Hall effect.
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All authors Laura Calonge-Martínez, Peng Rao, Frédéric Mila, Johannes Knolle
Mesoscale and Nanoscale Physics
Persistent currents, whirlpools, and local Chern markers in twisted TMD Chern insulators
Francesco Cioni, Lorenzo Cavicchi, Nazzareno Africani et al. (+4 more)
Recent materials advances have made it possible to fabricate twisted transition metal dichalcogenide homobilayers. These systems have been shown to host integer and fractional Chern insulating states. Because of spontaneous time reversal
symmetry breaking, their ground state harbors intriguing
spin-polarized currents with whirlpools on the moiré length scale that can be measured by scanning probe methods. We first provide a quantitative analysis of these persistent currents and then show that the maximum of the amplitude of the current density in the bulk of the sample is an accurate tracker of topological order. We conclude by calculating how the quantization of the
Hall conductance is affected by finite-size effects.
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All authors Francesco Cioni, Lorenzo Cavicchi, Nazzareno Africani, Giacomo Mazza, Fabio Taddei, Amir Yacoby, Marco Polini
Superconductivity
Proximity-induced orbital antiferromagnetism in Ising superconductors
G. A. Bobkov, V. A. Bobkov, T. Karabassov et al. (+2 more)
We predict a fundamentally new superconducting state in
superconductor/antiferromagnet
heterostructures with Ising
spin–orbit coupling: proximity-induced orbital antiferromagnetism. In this state, the order parameter acquires a periodic phase modulation locked to the
magnetic lattice, generating atomic-scale loop currents with opposite orbital moments on neighboring unit
cells. Its emergence requires at least three nonequivalent
magnetic sublattices per unit
cell and finite
spin–orbit coupling. Using NbSe$_2$/MnPS$_3$ as a concrete example, we combine first-principles and Bogoliubov–de Gennes calculations to demonstrate that the proximity-induced exchange field leads to robust phase modulation. Unlike FFLO and helical states, the phase gradient is atomic-scale, the state is current-carrying, and it remains uniquely stable over the full parameter range. The state manifests as characteristic finite-energy dips in the local density of states, accessible by STM.
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All authors G. A. Bobkov, V. A. Bobkov, T. Karabassov, I. V. Bobkova, A. A. Golubov
Strongly Correlated Electrons · Cross-listed from hep-lat
Certified spectral functions from lattice Monte Carlo data
Sophie Mutzel and Antoine Tilloy
The Monte Carlo method, applied to
lattice quantum field theory, gives access to Euclidean correlation functions with well-understood error bars. Recovering the observables one cares about, such as the spectral density, requires solving an ill-posed inverse problem, usually tackled with heuristics that lose rigorous control of the error. Instead of trying to find the “best” spectral density $\rho(\omega)$, we ask how small or large linear functionals $\int_{\mathbb{R}^+} G(\omega) \rho(\omega) \mathrm{d} \omega$ of it can be, given the Monte Carlo data and the reflection positivity of the
lattice action. This is a convex but infinite-dimensional problem. We show how its dual can be rigorously relaxed into a hierarchy of finite semidefinite programs, solvable with standard solvers and enjoying strong convergence guarantees. The resulting bounds are rigorous even when the relaxation is not tight, and converge quickly to the regime where the error is entirely dominated by Monte Carlo statistics. The method also flags implausible Monte Carlo data, for instance underestimated error bars, through an infeasibility certificate. We demonstrate it on
lattice $\phi^4$ theory in two dimensions.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG
Perturbative Contrastive Physical Learning
Kyungeun Kim, Amanuel Anteneh, Israel Klich et al. (+2 more)
Responses to perturbations are key to understanding physical systems. The ability to contrast such responses by comparing how a system reacts under slightly different conditions provides a mechanism for learning. Here, we introduce Perturbative Contrastive Physical Learning (PCPL), a general framework in which learning emerges from measurable contrasts between physical states produced by controlled changes to inputs, boundary conditions, parameters, or interpreter functions. PCPL unifies and extends prior approaches:
Equilibrium Propagation is rooted in contrasts between free and nudged
equilibria in energy-based systems, while Frequency Propagation corresponds to contrasts extracted from sinusoidally driven, frequency-demodulated responses. We show that contrast-driven updates can reflect either local sensitivities or global inverse-problem structure, yet do not require centralized gradient computation. Instead, effective learning geometry emerges implicitly from the system's own physical response, allowing learning behavior to arise without an external processor or explicit backpropagation. We demonstrate PCPL in two platforms: (i) spring networks that update bond stiffness using measured displacements and forces, and (ii) continuous-variable photonic
circuits trained via x quadrature measurements and finite-difference estimates of the Jacobian. Both platforms successfully learn classification tasks. We further show that a continuous-variable photonic
circuit can be trained to implement analog multiplication, illustrating a step toward more autonomous physical learning systems.
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All authors Kyungeun Kim, Amanuel Anteneh, Israel Klich, Olivier Pfister, J. M. Schwarz
Mesoscale and Nanoscale Physics
Radiowave-induced Resistance Oscillations
E. Bell, A.Zhakenuly, C. Hnatovsky et al. (+5 more)
Microwave-induced resistance oscillations (MIROs) occur when a 2D electron gas is subjected to radiation of frequency $\omega = 2 \pi f$ and varying
magnetic field $B$. MIROs are periodic in $1/B$, with the period determined by the radiation frequency $\omega$, and their amplitude scales with the radiation power. Stepping from single-
photon transitions between Landau levels, MIROs are found on the low-field side of the cyclotron resonance, $\omega_c \lesssim \omega$, where $\omega_c$ is the cyclotron frequency. Here, we report on another class of magneto resistance oscillations, which are induced by high-intensity radiation in the
radio frequency range and occur at $\omega_c \gg \omega$. These oscillations are independent of frequency $\omega$, can be either $1/B$ or $1/B^2$-periodic, and their period is controlled by the radiation electric field. We further show that using a displacement model in the limit of short-range (“sharp”) disorder we can extract the radiation field and the width of the cyclotron resonance.
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All authors E. Bell, A.Zhakenuly, C. Hnatovsky, K. W. Baldwin, L. N. Pfeiffer, K. W. West, S. Studenikin, M. A. Zudov
Disordered Systems and Neural Networks · Cross-listed from cs.LG
Learning Dynamics Reveal a Hierarchy of Weight-Induced Layerwise Gram Metrics
Claudio Nordio
We study feed-forward ReLU networks with fixed readout and quadratic loss, and rewrite gradient descent as a collective dynamics of activation fields and conjugate fields on the training set. Working to first order in the learning rate inside a fixed activation chamber, we derive explicitly the one-, two- and three-hidden-layer cases, and then give the arbitrary-depth recursion. For one hidden layer the activation dynamics closes directly and the residual update is governed by the product of an input Gram
matrix and a co-activation/backpropagation Gram
matrix. For two hidden layers a conjugate field is required, but no nontrivial pullback Gram metric has yet appeared. For three hidden layers the first weight-induced pullback Gram metric enters the conjugate-field dynamics. At arbitrary depth, activation variations propagate forward through a recursive response operator \(\cU_\ell^{\alpha\beta}\), while conjugate-field variations propagate backward through an effective transport operator \(\cM_\ell^{\alpha\beta}\). Their contractions reconstruct a layerwise residual kernel \[ K_{\alpha\beta}^{(L)}=\sum_{\ell=1}^{L}Q_{\alpha\beta}^{(\ell-1)}S_{\alpha\beta}^{(\ell)}. \] The resulting description exposes a duality between push-forward and pullback transport across every layer cut, and identifies the first Gram metrics as the lowest nontrivial terms in a broader hierarchy of activation-conditioned transport operators. We deliberately stop at the level of collective fields, conjugate fields, residual kernels and cut-wise transport metrics, leaving the later tensorial
geometric formulation outside the scope of this paper.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Sambe Approach to Floquet-Lindblad Open Quantum Systems
Andriani Keliri and Marco Schirò
We study driven and open
quantum systems described by a time-periodic Lindblad master equation. In closed systems, the stroboscopic dynamics can always be described by an effective time-independent Floquet
Hamiltonian; this idea is the basis of Floquet engineering. However, in the presence of dissipation, the existence of an effective time-independent Floquet Lindbladian is not guaranteed due to the non-
unitary nature of the
evolution. Using Floquet theory, we construct a well-defined time-independent Floquet Lindbladian in an extended Sambe-Liouville space, transforming the initial time-dependent problem to a static and non-Hermitian
eigenvalue problem. For harmonic driving, we introduce a
matrix continued fraction method to nonperturbatively resum multiphoton processes and construct an effective Floquet Lindbladian acting only on the physical Liouville space. Compared to other high-frequency expansions, this method has the advantage of providing the whole infinite series expansion at once. Using a resolvent formalism, we show how to obtain a spectral Floquet representation of correlation functions of an open
quantum system. As an application, we consider a dissipating two-level system in a linearly polarized field and calculate its resonance fluorescence spectrum. Furthermore, we consider a parametrically driven
quantum dot with pump and loss for which we calculate its spectral function and current-voltage characteristics.
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Mesoscale and Nanoscale Physics
Frequency-resolved decoherence spectroscopy of a semiconductor charge qubit coupled to a high-impedance resonator
Ekaterina Al-Tavil, Wonjin Jang, David J. van Woerkom et al. (+10 more)
Superconducting resonators coupled to
semiconductor quantum dots provide a powerful platform to investigate light-matter interaction and decoherence mechanisms in solid-state
quantum systems. Here we study a hybrid
circuit quantum electrodynamics architecture consisting of a GaAs double-
quantum-dot charge
qubit capacitively coupled to a high-impedance, frequency-tunable SQUID-array resonator. By tuning the
qubit transition frequency over the range $\omega_\mathrm{q}/2\pi \sim 3$-$6$ GHz, we perform frequency-resolved decoherence spectroscopy of the charge
qubit across a broad energy window. Time-resolved measurements enable us to disentangle relaxation and pure dephasing processes and to identify distinct decoherence regimes as a function of
qubit frequency. We find that at lower frequencies ($\leq 4.5$ GHz) dephasing dominates the
qubit linewidth, whereas at higher frequencies energy relaxation becomes the leading contribution. The measured frequency dependence of the relaxation rate exhibits a cubic scaling, consistent with charge-
qubit decay dominated by coupling to a piezoelectric
phonon bath and providing frequency-resolved access to the corresponding
phonon-induced spectral density. Our results show that hybrid
semiconductor–superconducting
circuits can serve as sensitive spectroscopic tools to probe microscopic decoherence mechanisms relevant for a wide range of hybrid
quantum devices.
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All authors Ekaterina Al-Tavil, Wonjin Jang, David J. van Woerkom, Ville Maisi, Stefano Bosco, Jan A. Krzywda, Jeroen Danon, Christian Reichl, Werner Wegscheider, Thomas Ihn, Klaus Ensslin, Andreas Wallraff, Pasquale Scarlino
Quantum Gases · Cross-listed from physics.atom-ph
Long-term laser frequency stabilization with an FPGA-controlled scanning cavity
R. Forti, R. Panza, A. Muzi Falconi et al. (+5 more)
We present an FPGA-based implementation of a scanning transfer cavity lock (STCL) for
laser frequency stabilization, allowing for the simultaneous stabilization of multiple
laser sources with respect to a single reference
laser by means of a continuously scanned Fabry-Perot cavity. By exploiting the FPGA architecture to simultaneously perform cavity scanning, peak detection, and feedback actuation, we minimize latency and allow independent control loops for several
lasers within a single device, offering direct scalability. The system performance is analyzed through heterodyne measurements from short ($<1\,$s) to long ($\sim20\,$hours) timescales. The end-to-end locking performance is validated through atomic spectroscopy of ytterbium atoms in a magneto-optical trap, demonstrating sub-MHz absolute frequency stability over several hours for the stability transfer across $\sim 150\,$nm in the visible-wavelength range. Importantly, we demonstrate a novel fast-scanning approach based on acousto-optic modulator (AOM) frequency modulation, enabled by the low detection latency of our FPGA implementation. This increases significantly the effective locking bandwidth and reduces the intrinsic noise of the system with respect to standard piezo-actuated scanning of the cavity length, allowing to reach sub-$100\,$kHz long-term stability and offering perspectives for
laser-line narrowing. Owing to its modularity, low cost and ease of implementation within the open-source PyRPL firmware package for the STEMlab Red Pitaya platform, our architecture offers a compact and flexible alternative to existing STCL and locked-cavity implementations, providing a practical approach to the operation of a state-of-the-art cold-atom experiment without relying on any atomic references for
laser stabilization.
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All authors R. Forti, R. Panza, A. Muzi Falconi, S. Sbernardori, A. Vardé, M. Marinelli, A. Carini, F. Scazza
Quantum Gases
Analog quantum simulation of chiral magnetic dynamics using optical superlattices
Sabhyata Gupta and Luis Santos
We propose an analog
quantum simulation of
chiral magnetic dynamics using ultracold atoms in an optical superlattice. The massive Schwinger model in the zero gauge coupling limit maps onto the Rice-Mele model, with the
fermion mass and topological angle encoded in the superlattice parameters. We study the real-time dynamics of the vector current following two quench protocols that drive continuous chirality injection and chirality relaxation. Simulations with realistic superlattice parameters and experimental noise demonstrates clear mass dependence of the current dynamics in both protocols, robust against experimental imperfections. The vector current may be directly measurable via single-bond-resolved detection, establishing cold atom superlattices as a viable platform for probing non-
equilibrium chiral phenomena.
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Statistical Mechanics · Cross-listed from cs.LG
When Do Local Score Models Extrapolate Across Size? A Diagnostic Theory and Benchmark
Wenjie Xi
Scientific generative modeling often requires size transfer, where models trained on small systems are evaluated on larger ones. While translation-invariant architectures enable this evaluation, we show that architectural locality alone does not guarantee stable size extrapolation. Instead, stable extrapolation is governed by the quasi-locality of the Gaussian-smoothed score. Through Tweedie's formula, far-away perturbations can influence local score components via posterior covariance, meaning a local model succeeds only if its receptive field covers the smoothed score's response range. We formalize this mechanism, proving a size-uniform comparison
theorem for local marginals under reverse
diffusion. We also introduce Finite-Depth Local Flow (FDLF), a white-box diagnostic
benchmark with exact scores, densities, and controllable response ranges. Empirically, we validate the interplay between spatial mixing, smoothed-score quasi-locality, and model receptive fields. Under spatial mixing, the smoothed score remains quasi-local relative to the receptive field, enabling stable extrapolation. Conversely, when spatial mixing weakens, the score's locality rapidly degrades, causing size transfer to fail.
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Materials Science
Bi-S network origin of cation-disorder stability and dispersive band edges in AgBiS2
Han-Pu Liang, Songyuan Geng, Heng Kang et al. (+9 more)
Cation-disordered AgBiS2 is a promising lead-free optoelectronic material, but both its ordered structure and the microscopic origin of its favorable electronic properties remain debated. Theory has proposed a mixed-coordination tendency with tetrahedral AgS4 and octahedral BiS6 units, whereas experiments mainly report octahedrally coordinated ordered and cation-disordered phases, together with local cation off-centering. Here, we combine a machine-learning interatomic potential with a deep-learning
Hamiltonian to resolve the coupled structural and electronic
evolution of AgBiS2 at large length scales. We identify the three-dimensional Bi-S network as the central structural motif governing both disorder stability and band-edge electronic states. At weak disorder, Ag/Bi exchange competes with the off-centering tendency of the Ag sublattice, producing strongly distorted local environments and convoluted diffraction signatures that hinder the identification of the ordered phase. With increasing disorder, BiS6-like units connect into a continuous Bi-S network, which stabilizes the rocksalt-like disordered phase. Despite strong cation disorder, AgBiS2 retains clear
semiconductor-like band dispersion and develops a direct band gap. The connected Bi:p-S:p states supported by the Bi-S network preserve a dispersive conduction-band edge and a small electron effective mass. In contrast, mobile Ag disrupts the long-range periodicity of Ag-S bonding, leading to strongly localized valence states. These results clarify the structural controversy in ordered AgBiS2 and establish a unified physical picture of disorder stability and optoelectronic response in nonisovalent
semiconductor alloys.
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All authors Han-Pu Liang, Songyuan Geng, Heng Kang, Chen Qiu, Xiao-Ping Yao, Qing'an Li, Bozhao Zhang, Lechuan Sun, Yuxuan Chen, Shan Zhang, Su-Huai Wei, Peng-Fei Guan
Soft Condensed Matter
Elastoinertial effects govern dynamic response of soft hair beds
Jonas Smucker, Naiesa Freeman, Eric Caballero et al. (+2 more)
Fluid-immersed hair beds are ubiquitous in biology-from the endothelial glycocalyx and primary cilia to intestinal microvilli-where they serve as mechanosensors that transduce dynamic flow signals into biochemical regulatory responses. Despite the inherently dynamic nature of physiological flows, the dynamic mechanical properties of fluid-immersed hair beds under time-varying conditions remain poorly characterized. Here we investigate the transient rheological response of elastic hair beds to large-amplitude oscillatory shear flows at low to intermediate Reynolds number. While the hairs and fluid themselves obey linear constitutive laws, their coupled interaction produces a dynamic nonlinear response that depends sensitively on driving frequency and amplitude. We identify a crossover from a stress-lagging regime to a stress-leading regime, which is governed by an interplay between fluid viscosity, fluid inertia, and hair elasticity. A simplified rigid-beam model qualitatively captures the crossover behavior. Characterizing the dynamic flow response of soft hair beds has direct biological implications, since the lag time sensitively determines the stability of mechanosensory signaling in the feedback loops underlying essential biological processes such as vasodilation, ciliary remodeling, and tubular reabsorption. Our results establish a framework for understanding how the physical properties of biological hair beds optimize dynamic information transmission during mechanotransduction.
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All authors Jonas Smucker, Naiesa Freeman, Eric Caballero, Philip J. Morrison, José Alvarado
Materials Science
Crystallography of periodic nanotextures in a strained Mott insulator
Benjamin Z. Gregory, Yorick A. Birkhölzer, Noah Schnitzer et al. (+9 more)
Here we investigate stripes of alternating structural phases spontaneously forming in epitaxially strained $Ca_2RuO_4$ thin films below the metal-
insulator transition. Using large-volume X-ray reciprocal-space mapping, we show that satellite-pattern intensities across 24
symmetry-inequivalent Bragg reflections collapse onto a single parameter-free curve. The collapse identifies a coherent martensitic laminate of few-nm-wide domains separated by ${012}$ interfaces, with displacements along $\left\langle01\bar{2}\right\rangle$. Satellite-extinction analysis demonstrates that both coexisting phases retain the bulk orthorhombic space group despite the pseudocubic $LaAlO_3$ substrate, biaxial epitaxial strain, and intrinsic strain at the interfaces. Classical invariant-plane-strain crystallography thus governs the nanoscale domain geometry of a Mott
insulator with intertwined
magnetic, electronic, and
lattice order.
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All authors Benjamin Z. Gregory, Yorick A. Birkhölzer, Noah Schnitzer, Ziming Shao, Jeff Hodgson, Suchismita Sarker, Jacob P. Ruff, Berit H. Goodge, David A. Muller, Kyle M. Shen, Darrell G. Schlom, Andrej Singer
Statistical Mechanics
Geometric Dissipation Constraints in Stochastic Reaction Dynamics: A Variational Observable for Hidden Kinetic Structure in Energy Landscapes
Shlomo Segal
We propose a
geometric framework for characterizing hidden kinetic constraints in
stochastic reaction dynamics. While free-energy barriers and
entropy production provide global descriptors of thermodynamic behavior, they are largely insensitive to local
geometric structure in configuration space that governs pathway selection. Starting from overdamped Langevin dynamics formulated as a gradient flow in Wasserstein space, we derive a variational functional whose leading-order asymptotic structure defines a local dissipation-geometry coupling observable. This quantity combines force-drift
alignment with phase-space contraction induced by the divergence of the drift field, yielding a scalar field that reflects second-order
geometric features of the underlying energy landscape. We demonstrate that this observable distinguishes kinetically distinct reaction channels that are degenerate under conventional free-energy analysis, as shown through numerical experiments on
benchmark systems including the Muller-Brown potential, corrugated periodic landscapes, and the conformational transitions of Alanine Dipeptide. These experiments demonstrate robust separation of pathways and are consistent with a quadratic scaling behavior in the high-frequency homogenization regime. Our results suggest that
stochastic reaction dynamics contain an additional
geometric layer of kinetic control in molecular motion not captured by standard thermodynamic or reaction-coordinate descriptions.
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Materials Science
Ab initio parametrization of distributed polarizable force fields
Felix Post, Jean-Philip Filling, Toulik Maitra et al. (+3 more)
Polarizable force fields offer superior transferability and accuracy compared to classical force fields, enabling access to electronic response properties such as refractive index and electronic density of states. Here, we demonstrate two key improvements that significantly enhance their accuracy: (1) assigning atomic polarizability to individual atoms rather than atom types, and (2) employing atomic polarizability tensors instead of scalar values. These modifications extend the applicability of polarizable force fields to cations, anions, and excited states, while also providing more accurate descriptions of neutral molecules. We propose a first-principles-based parameterization procedure for atomic polarizability tensors and scalars, validated on a set of small organic molecules with conjugated building blocks. To overcome the computational cost of ab initio calculations, we train a message-passing graph neural network to predict polarizability parameters, enabling efficient and scalable parameterization. Crucially, this approach imposes no additional computational cost during simulations and provides a clear diagnostic criterion for identifying cases where polarizable force field models fail to accurately describe molecular polarizability.
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All authors Felix Post, Jean-Philip Filling, Toulik Maitra, Falk May, Michael Wand, Denis Andrienko
Quantum Gases
Mapping the parameter space of double microwave shielding
Hubert J. Jóźwiak, Ian Stevenson, Sebastian Will et al. (+1 more)
Double microwave shielding employs $\sigma^{+}$- and $\pi$-polarized microwave fields, tuned close to the lowest rotational transition, to engineer a long-range repulsive barrier between polar molecules. By preventing molecules from reaching the short range, this technique suppresses detrimental two-body losses and recently enabled the realization of molecular Bose-Einstein condensates and self-bound droplets. Yet, the optimal operating regimes of the shielding mechanism remain largely unexplored. Here, by leveraging the underlying universality of the scattering problem, we systematically map the four-dimensional microwave parameter space-spanned by the detunings and intensities of the two fields-to identify configurations that maximize both shielding efficiency and interaction tunability. We define optimal operating regimes as configurations that are strictly free of field-linked bound states while sufficiently suppressing two-body losses to exceed typical lifetimes of ultracold samples. In these regimes, we evaluate the elastic-to-inelastic collision ratios required for efficient evaporative cooling and explore the accessible tuning range of the effective dipolar interactions. Finally, to identify the best platforms for future
quantum simulation experiments, we conduct a global survey of candidate molecular species under realistic field constraints. We identify heavy, strongly dipolar molecules as the most promising candidates, demonstrating that they can achieve extreme loss suppression-reaching two-body loss rates as low as $10^{-18}$ cm$^{3}$/s-alongside robust interaction tunability using only moderate field strengths.
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All authors Hubert J. Jóźwiak, Ian Stevenson, Sebastian Will, Tijs Karman
Strongly Correlated Electrons
Uniaxial-Stress-Induced Magnetic Transitions in the Triangular-Lattice Antiferromagnet PdCrO2
Nina Stilkerich, Tobias Ritschel, Hilary M. L. Noad et al. (+10 more)
Uniaxial stress is a promising method to tune
magnetic frustration, allowing its effects to be studied in a precise way. In this work, uniaxial stress is applied to the triangular-
lattice antiferromagnet PdCrO2. The Cr-Cr
magnetic interaction is very sensitive to interatomic separation, so laboratory-achievable stress can induce substantial changes in
magnetic structure. Results from three types of measurement are presented: X-ray diffraction, the stress-strain relationship, and
neutron diffraction. The combined data show that the elastic
moduli of PdCrO2 are strongly affected by stress-induced changes in
magnetic structure. A new, first-order stress-induced
magnetic transition is observed, at which the
lattice constant shrinks by 0.21%. The
lattice stiffens dramatically across this transition: the Young's modulus increases by about 80 GPa, and the Poisson ratio falls from about 1 to about 0.4. This stiffening indicates that the
magnetic order "locks," that is, becomes insensitive to
lattice strain. This locking might occur because the new stress-induced
magnetic order nests the
Fermi surface of the Pd sheets. Other frustrated magnets, including candidate
spin liquids, may show similarly strong coupling between
magnetic and elastic degrees of freedom.
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All authors Nina Stilkerich, Tobias Ritschel, Hilary M. L. Noad, Richard Waite, Dmitry Khalyavin, Kousuke Ishida, Pascal Manuel, Fabio Orlandi, Seunghyun Khim, Elena Gati, Andrew P. Mackenzie, Jochen Geck, Clifford W. Hicks
Strongly Correlated Electrons
Evolution of terahertz third harmonic response across rare-earth nickelate phase-diagram
Gulloo Lal Prajapati, Igor Ilyakov, Alexey Ponomaryov et al. (+8 more)
High harmonic generation (HHG) is a sensitive probe for investigating electronic structures and dynamics of materials and a source for attosecond pulses. In particular, HHG with terahertz (THz) light can enable probing of nonlinear responses in correlated materials arising from low-energy many-body interactions. However, THz HHG studies have so far largely focused on topological materials and
superconductors, leaving out other potential material systems which could also become efficient THz HHG sources. Here, we report THz third harmonic generation (THG) in rare-earth nickelates – a prototype material for exploring the Mott
insulator-metal transition and related technological applications. We find that the THG amplitude is highly sensitive to the strengths of electronic and
magnetic phases of nickelates. In films with sharp phase-transitions, the local maximum and minimum in the temperature-dependent THG amplitude coincide with
insulator-metal and
magnetic transition temperatures, respectively. While in films with weaker transitions, these features shift toward lower temperatures or even monotonous THG enhancement is observed down to low temperatures. We developed a generalized theory for THz harmonic generation in negative charge-transfer
insulators and outlined strategies to enhance the THz nonlinearities further. Our study broadens the scope of THz HHG studies and related applications to strongly correlated materials.
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All authors Gulloo Lal Prajapati, Igor Ilyakov, Alexey Ponomaryov, Atiqa Arshad, Sanjeev Kumar, Jayaprakash Sahoo, Dhanvir Singh Rana, Abdelrahman Azab, Friedemann Queisser, Ralf Schützhold, Jan-Christoph Deinert
Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
Revealing Wavelength- and Size-Dependent CO2 Reduction Selectivity via Operando Scanning Photo-Electrochemical Microscopy
Fatemeh Kiani, Milad Sabzehparvar, Priscila Vensaus et al. (+6 more)
Controlling product selectivity in plasmonic catalysis, particularly in CO2 reduction (CO2R), remains a central unsolved challenge with direct implications for light-driven fuel and chemical synthesis. Here, we deploy quantitative operando scanning photoelectrochemical microscopy (photo-SECM) to provide a direct demonstration that tuning
photon energy switches CO2R selectivity through an electronically driven pathway. On plasmonic Au/p-GaN photocathodes, interband excitation (460-560 nm) drives selective CO production while intraband excitation (640-800 nm) favors H2
evolution. By maintaining constant absorbed power across wavelengths and confirming linear power dependence, we isolate the role of hot-carrier energy from photonic and photothermal contributions. Density functional theory calculations reveal that higher-energy interband excitation progressively increases the overlap between hot-electron-accessible states and the CO-producing intermediate, selectively promoting CO over formate, in excellent agreement with experiment. We further show that selectivity is geometrically gated by hot-carrier transport: sub-100 nm nanostructures sustain CO2R activity, while ~300 nm nanodisks suffer transport losses that suppress it, consistent with ab initio hot-carrier transport calculations. Together, these results establish
photon energy, carrier transport, and nanostructure geometry as coupled design parameters for plasmonic CO2R selectivity, resolve a longstanding debate on the origin of plasmon-driven selectivity effects, and position photo-SECM as a broadly applicable operando platform for photo(electro)catalysis.
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All authors Fatemeh Kiani, Milad Sabzehparvar, Priscila Vensaus, Elif Nur Dayi, Olga D'Anania, Tarique Anwar, Nuria Lopez, Ravishankar Sundararaman, Giulia Tagliabue