We investigate the low-Reynolds-number propulsion of a slender elastic filament with a dipolar magnetic head actuated by an oscillating magnetic field in a viscous fluid by studying its strokes and net forward motion. To capture these dynamics, we employ an elastohydrodynamic (EH) framework that couples Euler-Bernoulli beam mechanics with resistive force theory. Unlike prescribed-kinematics models, filament shapes here emerge self-consistently from the actuation and the force and torque boundary conditions (BCs). We demonstrate that viscous boundary contributions are crucial for quantitative agreement and show that the swimming dynamics are governed by the EH length and a magneto-viscous-elastic stroke amplitude introduced here. The swimming speed is nonmonotonic with increasing ratio of the swimmer length to the EH length and is shown to reach a maximum when the swimmer length is on the order of the EH length. We further discuss the analytical limit in which the tail BCs can be described as free, and the limitations that arise when viscous contributions to the BCs are ignored.

We present a theoretical approach for computing and analyzing two-dimensional spectroscopy of bosonic collective excitations in disordered many-body systems. Specifically, we employ the Keldysh formalism to derive, within a nonperturbative treatment of disorder effects, the third-order nonlinear response and obtain two-dimensional spectroscopy maps. In the weak nonlinear regime of our formalism, we demonstrate the ability of the echo peak to distinguish between elastic and inelastic scattering processes, in perfect agreement with the intuition developed in isolated two-level systems. Furthermore, we discuss unique many-body effects on the echo peak signature arising from interaction-induced quantum fluctuations. In particular, we show that these quantum fluctuations induce a finite nonrephasable broadening and examine how the echo peak is influenced by the attractive or repulsive nature of the collective excitations.

Fock-space fragmentation, as it is currently investigated, primarily originates from specific kinematic constraints or emergent conservation laws in many-body systems with translation invariance. It leads to nonergodic dynamics and possible breakdown of the eigenstate thermalization hypothesis. Here, we demonstrate that also in disordered systems, such as the XXZ model with random on-site fields, fragmentation appears as a natural concept offering fresh perspectives, for example, on many-body localization. Specifically, for a given quenched initial state, we identify a potential-energy shell in Fock space, defined by its energy and energy uncertainty, which represents the energetically accessible part of the many-body configuration space. For example, the drastic sample-to-sample fluctuations observed in the weak disorder regime, $W<W_{\text{frag}}$, represent fluctuations of the mass of the shell. Upon increasing disorder, the potential-energy shell becomes increasingly fragmented. Its finite-size evolution exhibits a turnaround flow; extrapolating this flow to the disorder at which the turnaround vanishes provides a heuristic estimate of the strong-fragmentation scale $W_{\text{frag}}$. We conjecture that the fragmentation identified here provides a geometric mechanism contributing to the finite-time slowing down of relaxation observed in studies of disordered interacting systems.

The circular Unruh effect is the excitation of a detector moving along a planar circular trajectory within an electromagnetic vacuum. We demonstrate that the magnetic dipole transitions in an atom, acting as the detector, dominate the electric dipole transitions. Our analysis of both free-space and cavity schemes shows that the sensitivity to the circular Unruh effect can be maximized by balancing the minimization of mode volume against the resulting decrease in mode density. Moreover, we propose a measurement scheme that uses the atom's multilevel structure to suppress the spontaneous emission rate, thereby enabling the experimental detection of the circular Unruh effect.

We introduce a framework for remotely tunable dynamical metamaterials based on interacting nodes embedded in an elastic matrix, effectively forming meta-atoms governed by a programmable nonlinear landscape. Using secondary acoustic radiation forces between microbubble arrays, we predict and experimentally realize an acoustically actuated linear unit cell exhibiting geometric reconfiguration, discontinuous switching, and memory. Building on these results, we introduce a general numerical model for the system that predicts diverse behaviors in larger lattices, including a remote stiffness softening up to 60% and auxeticity up to $\nu =-0.22$. The theory applies to other modes of actuation (e.g., optical or magnetic) and reveals universal behavior in these systems arising purely from the interplay of local $r^{-n}$ forces and elastic interactions in the lattice.

A recent proposal suggested that neutron orbital angular momentum (OAM) states could be detected via spin-polarized absorption in polarized ${}^3\mathrm{He}$, with predicted cross-section variations linked to the neutron’s OAM. We experimentally tested this hypothesis using spin-polarized neutron beams with OAM $=-2$ to 2, generated by fork-dislocation phase gratings and transmitted through a polarized ${}^3\mathrm{He}$ cell. Within statistical precision, no OAM-dependent change in the absorption cross section was observed. This null result places stringent constraints on polarized ${}^3\mathrm{He}$-based OAM detection schemes. The absence of an effect in the given regime is traced to the proposal’s disregard of the spatial character of neutron OAM: Unlike spin, OAM arises from the transverse phase structure of the wavefunction and couples only through spatial gradients and overlap. The transverse extent of neutron OAM modes expands rapidly, producing a doughnut-shaped intensity profile with negligible overlap with on-axis ${}^3\mathrm{He}$ nuclei, while off-axis capture samples only a locally uniform phase and reduces the interaction to the known spin dependence. These results establish the limits of absorptive nuclear methods for probing neutron OAM and emphasize the necessity of spatially resolved interactions in any viable detection scheme.

Understanding equilibration and universality after sudden quantum quenches remains a central challenge in isolated many-body systems. Persistent oscillations and anomalous scaling reported in lattice models appear to challenge the standard picture based on integrability and quantum-to-classical correspondence. Focusing on the quantum $O\left(n\right)$ model in the large-$n$ limit, we show that these apparent anomalies originate from lattice effects and an underlying integrable structure. In particular, we map the postquench dynamics onto an integrable Neumann system and we derive an exact action-angle description valid in the thermodynamic limit. This framework explains both the convergence of long-time averages to the generalized Gibbs ensemble and the emergence of persistent oscillations associated with an isolated mode at the upper edge of the phonon spectrum. We further show that the expected thermal universality class is recovered in the appropriate scaling regime, while the oscillations disappear in the quantum-field-theory limit.

Membrane remodeling into vesicles is essential for processes such as receptor transport and viral budding. In many cases, this remodeling is driven by the assembly of multivalent protein lattices that stochastically grow while coupled to bending the membrane. Here, we ask how membrane mechanics can bias the structural pathways sampled during lattice growth. Using a continuum membrane model coupled to growing human immunodeficiency virus Gag lattice intermediates, we show that radially symmetric lattice growth is energetically favored over eccentric growth because it induces membrane bending at lower cost per protein. For rigid lattices, the penalty for asymmetric growth is controlled primarily by the shape of the lattice perimeter rather than by the density of protein-membrane links, with all membrane deformations retaining strong radial symmetry. Reevaluating the energy relative to the circumscribing radius of the lattice thus collapses all growth pathways to a similar curve. When the lattice is flexible, asymmetric growth introduces another cost, as these intermediates also generate weaker curvature. Analytical spherical-cap estimates support the trends in our numerical energy minimization calculations, and our results remain robust across a range of tested modeling assumptions including membrane spontaneous curvature. Although kinetic barriers along growth pathways are not assessed, our results show that membrane bending can strongly select for symmetric assembly pathways, providing a mechanical bias against irregular lattice growth during membrane remodeling.

Triple-layer cuprate superconductor ${\mathrm{HgBa}}_2{\mathrm{Ca}}_2{\mathrm{Cu}}_3{\mathrm{O}}_8$ (Hg1223) keeps the record of the highest superconducting (SC) critical temperature $T_{\mathrm{c}}\sim 134\mathrm{K}$ among all the existing materials at ambient pressure. $T_{\mathrm{c}}$ further increases under pressure up to $T_{\mathrm{c}}\sim 160\mathrm{K}$, thereby holding the key to the realistic and comprehensive understanding of the cuprate superconductors, which is one of the grand challenges in physics. However, the microscopic mechanism of high $T_{\mathrm{c}}$ of Hg1223 remains to be elucidated. Here, we perform first-principles calculations of Hg1223 both at ambient and applied pressures by solving ab initio Hamiltonians with an accurate variational solver supplemented by a neural network. The pressure dependence of the calculated $d$-wave SC order parameter and estimated $T_{\mathrm{c}}$ shows a structure supporting a $T_{\mathrm{c}}$ peak around 30 GPa in quantitative agreement with the reported experimental indications. The origin of the strong SC amplitude of Hg1223 at ambient pressure compared to other cuprates is identified as strong local Coulomb repulsion $U$ attributed to poorer screening of the Coulomb interaction in multilayer compounds. The origin of the further increase in $T_{\mathrm{c}}$ under pressure is ascribed to a unique interplay of three elements, namely, increased electron hopping $t$, decreased $U$, and more importantly, strongly reduced nonlocal Coulomb repulsion $V$ with increasing pressure. The origin of Cooper pairing is identified as the emergent local attraction counterintuitively arising from the strong bare local repulsion $U$ for Hg1223. It explains why Hg1223 shows the highest $T_{\mathrm{c}}$ among other cuprates, while the pairing mechanism is common in other cuprates as well. The emergent attraction is interpreted from “attraction from reduced repulsion,” originating from the release of the fluctuating doubly occupied sites characterized from the “false vacuum” in the Mott insulator to the double-occupation-free $d$-wave SC states caused by the carrier doping. This instantaneous and local attraction is in marked contrast with the case of the conventional BCS SC mediated by bosonic glues. The local attraction is consistent with the electron fractionalization supported in experimental analyses. The coexistence of SC and antiferromagnetic orders is also demonstrated as a characteristic feature of the multilayer system with self-doping in the underdoped region. The quantitative and microscopic understanding of the high $T_{\mathrm{c}}$ in Hg1223 provides a new perspective on the origin of the cuprate superconductivity and offers a new route explicitly using this channel of the emergent attraction for future superconductivity research aiming at designing and optimizing SC materials.

Space-charge compensation is routinely used to mitigate emittance growth in linear accelerator beam transport lines. Severe space-charge effects and incomplete compensation within low-energy beam transport sections universally induce beam divergence and emittance degradation, constituting a key bottleneck for low-energy, high-intensity beams. This work investigates the evolution of residual-gas-generated secondary-ion clouds under applied electric fields and their impact on primary beam emittance growth. By implementing barrier electrodes to confine the secondary-ion cloud, we achieve substantial reductions in both the emittance and beam radius of an ${\mathrm{H}}^{-}$ beam while preserving full beam intensity. The proposed ion cloud trap scheme also has important implications for neutral beam injection in magnetic confinement fusion and high-current ion implanters, providing insights into low-energy charged particle transport across diverse ion-beam platforms.

Motivated by the prospect of chiral-mode control in compact photonic systems, we analyze discrete coupled single-mode resonators. Using the minimal three-resonator model, we show that an infinitesimal complex on-site perturbation near a Hermitian diabolic point (DP) induces chiral-mode selection, governed by what we term an asymptotic exceptional point (AEP). Here, an AEP denotes a Hermitian DP equipped with a non-Hermitian perturbation that induces an asymptotically defective effective Hamiltonian. The eigenvectors coalesce in the asymptotic limit toward the DP, although the Hamiltonian at the point itself remains diagonalizable. Operationally, this AEP response realizes chirality switching from an achiral state to a chiral state. The associated eigenvalue response exhibits the anomalous fractional-power scaling $\mathrm{\Delta }\lambda \propto {\varepsilon }^{3/2}$, distinct from the square-root response of an ordinary exceptional point (EP). We further show that, in a broader two-parameter perturbation space, ordinary EPs lie on exceptional-line branches that meet at the AEP. A finite-bias control sweep crosses these branches at an EP pair, enabling chirality reversal between opposite chiral states. The central message is therefore that the AEP organizes two related routes for chirality switching: direct switching from an achiral state to a chiral state via the AEP and switching between opposite chiral states via an EP2 pair in the vicinity of the AEP. Within a finite-resolution averaging model, these two operating points exhibit different practical performance characteristics, and under sufficiently high control resolution, the AEP operating point can become more favorable than the EP-pair operating point, suggesting a route toward compact and low-energy chiral photonic devices.

Fixation probabilities are essential for characterizing stochastic evolutionary dynamics, but analytical results remain limited mainly to systems with two competing types. We develop a perturbative framework to compute fixation probabilities in multiallele Moran processes under weak selection. Exploiting the general structure of the backward Fokker-Planck operator in this regime, we show that fixation probabilities admit a systematic expansion around their neutral solution. We first introduce the framework for $M$ competing alleles with multivariate polynomial fitness functions. We then apply it to three biologically motivated examples: a constant-fitness model, which we solve for an arbitrary number of alleles; a three-allele coordination game in which allele fitness increases with its frequency in the population; and a three-allele model of clonal interference between mutualistic alleles. These results extend the analytical understanding of fixation probabilities beyond pairwise interactions, establishing a framework for investigating multistrategy stochastic evolutionary dynamics.

An active research line within the broader field of network science is the one concerning link prediction. Close in scope to network reconstruction, link prediction targets specific connections with the aim of uncovering the missing ones, as well as predicting those most likely to emerge in the future, from the available information. In this paper, we consider two families of methods, i.e., those rooted in statistical physics and those based upon machine learning: the members of the first family identify missing links as the most probable nonobserved ones, the probability coefficients being determined by solving maximum-entropy benchmarks over the accessible network structure; the members of the second family, instead, associate the presence of single edges with explanatory node-specific variables. Running likelihood-based models such as the configuration model, or one of its many fitness-based variants, in parallel with the gradient boosting decision tree algorithm reveals that the accuracy of the former is comparable to the accuracy of the latter. Such a result confirms that white-box algorithms are viable competitors to the currently available black-box ones, being more interpretable and computationally faster.

Externally seeded free-electron lasers (FELs) provide radiation with full longitudinal and transverse coherence in the extreme ultraviolet and soft x-ray spectral ranges, inaccessible to conventional laser sources. Until now, externally seeded operation has been limited to the extreme ultraviolet and soft x-ray regime, while shorter wavelengths have been accessed primarily through stochastic self-amplified spontaneous emission processes (or derivatives thereof, one based on self-seeding) or through nonlinear harmonic generation at strongly reduced pulse energy. At the FERMI FEL facility, we have demonstrated stable operation in high-gain harmonic generation (HGHG) covering the nitrogen K-edge, most of the water-window spectral range, and approaching the oxygen K-edge by combining short-wavelength ultraviolet seeding (200 nm), increased electron beam energy, and preservation of an ultralow relative slice energy spread at the ${10}^{-5}$ level. The emitted radiation at such short wavelengths still exhibits the typical narrow bandwidth and wavelength stability of the HGHG scheme enabling, for example, time-resolved x-ray absorption spectroscopy measurements. Longitudinally coherent emission at 1 nm is obtained as the third harmonic of the fundamental FEL emission. Despite the lower intensity typical of nonlinear harmonic emission, these results demonstrate that external seeded FELs can be extended to nanometer wavelengths, establishing deterministic, fully coherent soft x-ray generation and surpassing the previous wavelength operation limits. This advance opens new opportunities for coherent control and nonlinear x-ray experiments that require both high photon energy and longitudinal coherence, and demonstrates a promising pathway toward further extension of externally seeded FELs to shorter wavelengths.

Quorum sensing (QS) is known in biology as a form of intercellular communication mediated by signaling molecules called autoinducers. The QS protocol governs the transition from individual to collective cell behavior once a critical population density is reached. Using numerical simulations, we investigate how defects influence the QS transition and the structural organization of the resulting colonies. Our model system consists of a mixture of slow (“cold”) and fast (“hot”) diffusing colloidal particles that obey the QS protocol, together with defect particles characterized by a constant diffusivity. A striking reentrant solidification of QS particles, characterized by long-range order, is induced by hot defects, whereas cold defects give rise to amorphous structures with only short-range order. These findings deepen our understanding of the QS interaction and provide a mechanism to control the degree of organization in QS systems, with potential applications in robotics, social sciences, and medicine—for instance, in overcoming antimicrobial resistance.

We present a single-orbital tight-binding model for the low-energy electronic states of the chiral one-dimensional hybrid organic-inorganic lead halide perovskite $(R/S\text{−}\mathrm{PEA}){\mathrm{PbI}}_3$. The model is constructed from a single effective orbital on each of the four symmetry-related sites in the primitive unit cell and incorporates layer, in-plane sublattice, and spin degrees of freedom. With separate parameter sets for the conduction and valence bands, the effective Hamiltonian reproduces the overall band dispersions obtained from density-functional-theory calculations and quantitatively captures the spin splittings near the band edges. It also captures the leading spin-polarization patterns of the Bloch states, showing that the band-edge spin splitting and spin polarization are encoded in a small number of symmetry-adapted spin-dependent hopping terms. We further analyze the accidental degeneracies of the effective Hamiltonian using screw eigenvalues and antiunitary operators. This analysis separates accidental degeneracies originating from the restricted term content of the effective Hamiltonian from degeneracies enforced by nonsymmorphic screw symmetries and time-reversal symmetry. The present model provides a symmetry-transparent starting point for understanding the band-edge electronic structure of chiral lead halide perovskites and for analyzing optical, spin, and transport responses in this class of materials.

We demonstrate that $k$-Markov sequences of unitary gates provide low-cost handles to manipulate the rate and structure of information spreading compared to traditional random, 0-Markov, circuits. For swap gates and brickwork circuits, we use graph cover time to demonstrate how $k$-Markov processes can be used to control operator transport. With swap gates and the set of Clifford gates that can change operator weight, we show how $k$-Markov sequences can be used to manipulate scrambling time and generate novel structures of spatial-temporal correlations across a qubit network. We show that $k$-Markov circuits constructed from pswap gates at fixed angle are equivalent to standard brickwork circuits with pswap angle drawn from nonuniform distributions generated by the $k$-Markov process. In those circuits, the time evolution of the average Hamming weight and the space-time correlation structure that remains after one-point quantities equilibrate again vary significantly from the 0-Markov case, depending on the transition probabilities of the process. More broadly, these results identify finite temporal memory as a control handle distinct from a circuit's degree of quantum chaos. For gate sets that fall short of volume-law scrambling, the equilibrium reached by one-point diagnostics is fixed by the gates alone, while the choice of $k$-Markov rule controls the approach to equilibrium and the structure of persistent, late-time correlations.

Thermal phonons in crystals are typically described in Fourier space, leaving open how disordered thermal vibrations are organized in real space-time. Recent work on two-dimensional crystals identified thermally excited vortical phonons—vorticity waves composed of traveling vortices with varying shapes and alternating-sign vorticity. Whether and how the dynamics of thermal vibrations can be organized by topological defects of vortex cores and saddles remain unclear. Here, using direct experiments on dusty plasma crystals and molecular-dynamics simulations of Yukawa crystals, we show that topological defects in the instantaneous velocity field organize thermally excited vortical phonons. In the Eulerian frame, slow-mode vorticity fluctuations are locally Gaussian yet develop coherent, intermittent, multiscale clusters of large vorticity-wave amplitude in space-time. In the Lagrangian frame, vortex cores display persistent superdiffusivelike transport together with concurrent evolution of core vorticity. Their kinetics obey robust topological rules, including charge-conserving pair creation and annihilation, exponential lifetime statistics, charge-dependent short-range correlations, and saddle-mediated splitting and merging of corotating vortices. These results move the description of thermal lattice vibrations beyond spectra alone and establish topological defects as organizing centers of thermally driven multiscale wave dynamics.

We show that low-frequency magnonic noise provides statistical fingerprints of nonlinear scattering-network configurations in a yttrium iron garnet waveguide. By tuning the magnetic field, we control whether three-magnon splitting and confluence are kinematically allowed and change the active scattering pathways. When three-magnon processes are allowed, the noise exhibits abrupt anomalies and distinct fluctuation classes, including random-telegraph and $1/f$-type spectra; otherwise, it approaches a near-white-noise form and evolves smoothly. Simulations support multistep magnon redistribution through competing nonlinear scattering pathways. Fluctuation statistics thus provide an experimental probe of dynamical-state selection in nonlinear magnon scattering networks.