The interplay between causal mechanisms and emerging collective behaviors is a central aspect of understanding, controlling, and predicting complex networked systems. In our work, we investigate the relationship between higher-order mechanisms and higher-order behavioral observables in two representative models with group interactions: a simplicial Ising model and a social contagion model. In both systems, we find that group (higher-order) interactions show emergent synergistic (higher-order) behavior. The emergent synergy appears only at the group level and depends in a complex, nonlinear way on the trade-off between the strengths of the low- and higher-order mechanisms and is invisible to low-order behavioral observables. Our work sets the basis for systematically investigating the relation between causal mechanisms and behavioral patterns in complex networked systems with group interactions, offering a robust methodological framework to tackle this challenging task.

Compact objects observed in gravitational-wave astronomy so far always come in pairs and never individually. Identifying the two components of a binary system is a delicate operation that is often taken for granted. The labeling procedure (i.e., which is object “1” and which is object “2”) effectively acts as systematics, or, equivalently, an unspecified prior, in gravitational-wave data inference. The common approach is to label the objects solely by their masses, on a sample-by-sample basis. We show that object identification can instead be tackled using the posterior distribution as a whole. We frame the problem in terms of constrained clustering—a flavor of semisupervised machine learning—and find that unfolding the labeling systematics can significantly impact, and arguably improve, our interpretation of the data. In particular, the precision of black-hole spin measurements improves by up to 50%, multimodalities and tails tend to disappear, posteriors become closer to Gaussian distributions, and the identification of the nature of the object (i.e., black hole vs neutron star) is facilitated. We estimate that about 10% of the LIGO/Virgo posterior samples are affected by this relabeling, i.e., they might have been attributed to the other compact object in the observed binaries.

We simulated Coulomb explosion dynamics due to fast ionization induced by high-intensity x-rays in six proteins that share similar atomic content and shape. We followed and projected the trajectory of the fragments onto a virtual detector, providing a unique explosion footprint. After collecting 500 explosion footprints for each protein, we utilized principal component analysis and $t$-distributed stochastic neighbor embedding to classify these. Results show that the classification algorithms were able to separate proteins on the basis of explosion footprints from structurally similar proteins into distinct groups. The explosion footprints, therefore, provide a unique identifier for each protein. We envision that method could be used concurrently with single-particle coherent imaging experiments to provide additional information on shape, mass, or conformation.

The coherent interaction between free electrons and optical fields can produce free-electron compression and push the temporal resolution of ultrafast electron microscopy to the attosecond regime. However, a large electron-light interaction is required to attain a strong compression, generally necessitating short light and electron pulses combined with optical scattering at nanostructures. Here, we theoretically investigate an alternative configuration based on stimulated Compton scattering, whereby two counterpropagating Gaussian light beams induce energy jumps in a collinear electron beam by multiples of their photon-energy difference. Strong recoil effects are produced by extending the electron-light interaction over millimetric distances, enabling a dramatic increase in temporal compression and substantially reshaping the electron spectra for affordable laser powers. Beyond its fundamental interest, our Letter introduces a practical scheme to achieve a large temporal compression of continuous electron beams without involving optical scattering by material structures.

In approximate ground states obtained from imaginary-time evolution, the spectrum of the state—its decomposition into exact energy eigenstates—falls off exponentially with the energy. Here we consider the energy spectra of approximate matrix product ground states, such as those obtained with the density matrix renormalization group. Despite the high accuracy of these states, contributions to the spectra are roughly constant out to surprisingly high energy, with an increase in the bond dimension reducing the amplitude but not the extent of these high-energy tails. The unusual spectra appear to be a general feature of compressed wavefunctions, independent of boundary or dimensionality, and are also observed in neural network wavefunctions. The unusual spectra can have a strong effect on sampling-based methods, yielding large fluctuations. The energy variance, which can be used to extrapolate observables to eliminate truncation error, is subject to these large fluctuations when sampled. Nevertheless, we devise a sampling-based variance approach which gives excellent and efficient extrapolations.

We investigate the locomotion of thin, living T. Tubifex worms, which display active polymerlike behavior, within quasi-2D arrays of cylindrical pillars, examining varying spatial arrangements and densities. These active worms spread in crowded environments, with a dynamics dependent on both the concentration and arrangement of obstacles. In contrast to passive polymers, our results reveal that in disordered configurations, increasing the pillar density enhances the long-time diffusion of our active polymerlike worms, while we observe the opposite trend in ordered pillar arrays. We found that in disordered media, living worms reptate through available curvilinear tubes, whereas they become trapped within pores of ordered media. Intriguingly, we show that reducing the worm’s activity significantly boosts its spread, enabling passive sorting of worms by activity level. Our experimental observations are corroborated through simulations of the tangentially driven polymer model with matched persistence length predicting the same trends.

This Letter reports the first complete observation of magnetized collisionless shock precursors formed through the compression of Biermann-battery magnetic fields in laser produced plasmas. At OMEGA, lasers produce a supersonic CH plasma flow which is magnetized with Biermann-battery magnetic fields. The plasma flow collides with an unmagnetized hydrogen gas jet plasma to create a magnetized shock precursor. The situation where the flowing plasma carries the magnetic field is similar to the Venusian bow shock. Imaging $2\omega$ Thomson scattering confirms that the interaction is collisionless and shows density and temperature jumps. Proton radiographs have regions of strong deflections and FLASH magnetohydrodynamic (MHD) simulations show the presence of Biermann fields in the Thomson scattering region. Electrons are accelerated to energies of up to 100 keV in a power-law spectrum. OSIRIS particle-in-cell (PIC) simulations, initialized with measured parameters, show the formation of a magnetized shock precursor and corroborate the experimental observables.

In the Alphatrap experiment, the $g$ factor of boronlike ${}^{118}{\mathrm{Sn}}^{45+}$ has been measured with a 0.5 ppb uncertainty. This is the first high-precision measurement of the $g$ factor of a heavy boronlike ion. The measured value of 0.6 447 038 265(4) is consistent with the presented ab initio state-of-the-art theory calculations, which predict a value of 0.64 470 29(8). So far, the only boronlike ion of which the $g$ factor was measured with high precision has been ${}^{40}{\mathrm{Ar}}^{13+}$. The measurement presented here therefore tests quantum electrodynamics as well as many-electron interactions at much higher $Z$. Furthermore, we discuss the potential for an independent determination of the fine-structure constant $\alpha$, which can be achieved with a specific difference of $g$ factors, combining the presented results with the recent electron $g$-factor measurement of hydrogenlike tin.

Ion-molecule reactions proceed with highly rotational-state-specific rate coefficients and are amenable to stereodynamical control at low temperatures. We introduce a scheme to control cold ion-molecule chemistry with microwaves based on the coherent transfer of molecular rotational-state populations. We use a merged-beam approach to reach collision energies in the range from $\sim 0$ to $k_{\mathrm{B}}\times 10\mathrm{K}$ for the reaction between ${\mathrm{He}}^{+}$ and rotationally cold CO molecules ($T_{\mathrm{rot}}\approx 3\mathrm{K}$) and manipulate the rotational-state population of CO using microwave pulses. We achieve reaction inhibition by up to $\sim 40\%$ with microwave pulses resonant with pure-rotational transitions in CO, unambiguously demonstrating a nonthermal mechanism for microwave-assisted chemistry.

A striking example of frustration in physics is Hofstadter’s butterfly, a fractal structure that emerges from the competition between a crystal’s lattice periodicity and the magnetic length of an applied field. Current methods for predicting the topological invariants associated with Hofstadter’s butterfly are challenging or impossible to apply to a range of materials, including those that are disordered or lack a bulk spectral gap. Here, we demonstrate a framework for predicting a material’s local Chern markers using its position-space description and validate it against experimental observations of quantum transport in artificial graphene in a semiconductor heterostructure, inherently accounting for fabrication disorder strong enough to close the bulk spectral gap. By resolving local changes in the system’s topology, we reveal the topological origins of antidot-localized states that appear in artificial graphene in the presence of a magnetic field. Moreover, we show the breadth of this framework by simulating how Hofstadter’s butterfly emerges from an initially unpatterned 2D electron gas as the system’s potential strength is increased and predict that artificial graphene becomes a topological insulator at the critical magnetic field. Overall, we anticipate that a position-space approach to determine a material’s Chern invariant without requiring prior knowledge of its occupied states or bulk spectral gaps will enable a broad array of fundamental inquiries and provide a novel route to material discovery, especially in metallic, aperiodic, and disordered systems.

The anomalous Hall effect (AHE) has emerged as a key indicator of time-reversal symmetry breaking (TRSB) and topological features in electronic band structures. Absent of a magnetic field, the AHE requires spontaneous TRSB but has proven hard to probe due to averaging over domains. The anomalous component of the Hall effect is thus frequently derived from extrapolating the magnetic field dependence of the Hall response. We show that discerning whether the AHE is an intrinsic property of the field-free system becomes intricate in the presence of strong magnetic fluctuations. As a study case, we use the Weyl semimetal PrAlGe, where TRSB can be toggled via a ferromagnetic transition, providing a transparent view of the AHE’s topological origin. Through a combination of thermodynamic, transport, and muon spin relaxation measurements, we contrast the behavior below the ferromagnetic transition temperature to that of strong magnetic fluctuations above. Our results on PrAlGe provide general insights into the interpretation of anomalous Hall signals in systems where TRSB is debated, such as families of kagome metals or certain transition metal dichalcogenides.

Here, a novel photonic spin Hall effect is demonstrated based on the spatially varying Pancharatnam-Berry (PB) phases, aroused naturally in an $X$-cut ${\mathrm{LiTaO}}_3$ crystal via the Pockels effect. Applied with an electric field, the principal axes of crystal will rotate around the $x$-axis with the rotation angle varying linearly with the $y$ component of the applied field. By depositing an asymmetric electrode pair on the crystal to induce inhomogeneously distributed electric fields, spatially varying rotations of the principal axes of crystal are generated, resulting in spatially varying PB phases. These spatially varying PB phases are redistributable by the applied voltage, different from those unchangeable PB phases aroused by the spatially varying orientations of anisotropic structure units such as patterned liquid crystals and metasurfaces. The redistributable PB phases can cause tunable separations of spin photons in the momentum space. The separation speed is measured as $\sim 0.16\mathrm{GHz}$. These findings deepen the understanding of the geometric phase and pave the way for high-speed control of spin photons.

Non-Hermitian topological phases, which exhibit unique features such as skin effect and exceptional points originated from nontrivial band topologies in complex plane, have attracted enormous attention in condensed-matter physics and metamaterials. Here, we report the realization of an exceptional line semimetal in a three-dimensional non-Hermitian phononic crystal. A pair of exceptional rings with opposite topologies are connected by the drumhead bulk states in the first Brillouin zone. The exceptional rings not only possess wave-function topology and thus result in the drumhead surface states, but also host spectral topology and thereby give rise to the geometry-dependent skin effect in three dimensions. Our experimental results evidence the complete non-Hermitian bulk-boundary correspondence of the three-dimensional exceptional line semimetal and may pave the way for designing non-Hermitian acoustic devices.

We search for dark matter (DM) with a mass $[3,12]\mathrm{GeV}/c^2$ using an exposure of $3.51\mathrm{tonne}\hspace{0.17em}\mathrm{year}$ with the XENONnT experiment. We consider spin-independent DM-nucleon interactions mediated by a heavy or light mediator, spin-dependent DM-neutron interactions, momentum-dependent DM scattering, and mirror DM. Using a lowered energy threshold compared to the previous weakly interacting massive particle search, a blind analysis of [0.5, 5.0] keV nuclear recoil events reveals no significant signal excess over the background. XENONnT excludes spin-independent DM-nucleon cross sections $>2.5\times {10}^{-45}{\mathrm{cm}}^2$ at 90% confidence level for $6\mathrm{GeV}/c^2$ DM. In the considered mass range, the DM sensitivity approaches the “neutrino fog,” the limitation where neutrinos produce a signal that is indistinguishable from that of light DM-xenon nucleus scattering.

The intrinsic chirality of natural materials is known to be weak, prompting extensive efforts to enhance chiral light-matter interactions on the metasurface platform. Chiral metasurfaces are typically created by manipulating the geometry of nanostructures, such as three-dimensional helical structures and slanted structures. However, these approaches are generally challenging to implement experimentally in optical frequency ranges. Here, we present the achievement of significant chirality on planar lithium niobate metasurfaces. We theoretically demonstrate that the birefringence of lithium niobate enables a strong coupling between two nearly degenerate resonant modes when rotating the optical axis. Despite the achiral geometric morphology of the lithium niobate structure, we show that these mixed modes exhibit chirality and can produce nearly full circular dichroism signals. Moreover, we experimentally validate our theoretical proposal using our advanced process technique for lithium niobate nanostructures and the measured circular dichroism signal reaches $-0.53$. These findings offer new possibilities for chiral metaphotonics.

Recently, it was discovered that the proton structure at high energies exhibits maximal entanglement. This leads to a simple relation between the proton’s parton distributions and the entropy of hadrons produced in high-energy inelastic interactions, which has been experimentally confirmed. In this Letter, we extend this approach to the production of jets. Here, the maximal entanglement predicts a relation between the jet fragmentation function and the entropy of hadrons produced in jet fragmentation. We test this relation using the ATLAS Collaboration data on jet production at the Large Hadron Collider, and find a good agreement between the prediction based on maximal entanglement within the jet and the data. This study represents the first use of a quantum entanglement framework in an experimental study of the hadronization process, offering a new perspective on the transition from perturbative to nonperturbative QCD. Our results open the door to a more comprehensive understanding of the quantum nature of hadronization.

We report the recent derivation of the backbone exponent for 2D percolation. In contrast to previously known exactly solved percolation exponents, the backbone exponent is a transcendental number, which is a root of an elementary equation. We also report an exact formula for the probability that there are two disjoint paths of the same color crossing an annulus. The backbone exponent captures the leading asymptotic, while the other roots of the elementary equation capture the asymptotic of the remaining terms. This suggests that the backbone exponent is part of a conformal field theory (CFT) whose bulk spectrum contains this set of roots. Our approach is based on the coupling between Schramm-Loewner evolution curves and Liouville quantum gravity (LQG), and the integrability of Liouville CFT that governs the LQG surfaces.

We revisit the bootstrap percolation model, leveraging recent mathematical advances linking it with its local counterpart. This new perspective resolves, for the first time, historic discrepancies between Monte Carlo simulations and theoretical results: previously, those predictions disagreed even in the first-order asymptotics of the model. In contrast, our framework achieves excellent agreement between numerics and theory, which now match up to the third-order expansion, as the infection probability approaches zero. Our algorithm allows us to generate novel predictions for the model.

The probability per unit area for a radioactive ${}^{88}\mathrm{Zr}$ nucleus (83.4 d half life) to absorb neutrons across resonance energies—its neutron-capture resonance integral—is the largest ever reported [Shusterman et al.,Phys. Rev. C 103, 024614 (2021).] and implies that the neutron-capture cross section is orders of magnitude larger than previously thought at energies relevant to nuclear test diagnostics and nucleosynthesis applications such as the $\nu r$ process [Xiong et al.,Phys. Rev. Lett. 132, 192701 (2024).]. However, these applications require the shape of this cross section across a range of energies, not just this integral quantity. We measured the ${}^{88}\mathrm{Zr}$ neutron total cross section from 0.0253 to 500 eV. Because the same resonances or other nuclear structure responsible for the neutron-capture cross section are reflected in the total cross section, we used these data to extract the former from the latter as a function of energy. Our data reveal a resonance at 0.171 eV and result in a thermal neutron-capture cross section of $771000\pm 31000\mathrm{b}$, in good agreement with the recently published value. In contrast, the neutron-capture resonance integral extracted from our data is $15210\pm 670\mathrm{b}$ and is roughly a factor of 200 smaller than the recently reported value. We discuss the impact of this difference on applications.

Multiband superconductivity arises when multiple electronic bands contribute to the formation of the superconducting state, allowing distinct pairing interactions and gap structures. Here, we present field- and temperature-dependent data on the vortex lattice structure in $2H\text{−}{\text{NbSe}}_2$ as a contribution to the ongoing debate as to whether the defining feature of the superconductivity is the anisotropy or the multiband nature. The field-dependent data clearly show that there are two distinct superconducting bands, and the contribution of one of them to the vortex lattice signal is completely suppressed for magnetic fields above $\sim 0.8\mathrm{T}$, well below $B_{\mathrm{c}2}$. By combining the temperature and field scans, we can deduce that there is a moderate degree of interband coupling. From the observed temperature dependences, we find that at low field and zero temperature, the two gaps in temperature units are $13.1\pm 0.2$ and $6.5\pm 0.3\mathrm{K}$ (${\mathrm{\Delta }}_0=1.88$ and 0.94 $k_{\mathrm{B}}{T}_{\mathrm{c}}$); the band with the larger gap gives just under two-thirds of the superfluid density. The penetration depth extrapolated to zero field and zero temperature is $160\pm 2\mathrm{nm}$.