The color glass condensate (CGC) effective theory and the collinear factorization at high twist (HT) are two well-known frameworks describing perturbative QCD multiple scatterings in nuclear media. It has long been recognized that these two formalisms have their own domain of validity in different kinematic regions. Taking direct photon production in proton-nucleus collisions as an example, we clarify for the first time the relation between CGC and HT at the level of a physical observable. We show that the CGC formalism beyond shock-wave approximation, and with the Landau-Pomeranchuk-Migdal interference effect is consistent with the HT formalism in the transition region where they overlap. Such a unified picture paves the way for mapping out the phase diagram of parton density in nuclear medium from dilute to dense region.

A topological quantum number, the Witten index, characterizes supersymmetric models by probing for zero energy modes and the possibility of supersymmetry breaking. We propose an averaging method to infer the Witten index in quantum analog simulators. Motivated by recent work on Rydberg atoms trapped in optical tweezer arrays, we consider a related supersymmetric XXZ spin model. We show how to infer the Witten index from open-system averaging and numerically demonstrate its topological robustness in this model. Our Letter defines a route for quantum analog simulators to directly identify many-body topological physics.

We study the collective decay of an initially inverted ensemble of two-level emitters in two distinct scenarios: when coupled to a squeezed photonic reservoir and when interacting with a one-dimensional waveguide. Using a quantum-state diffusion approach to unravel the emission process, we investigate entanglement and classical correlations along individual quantum trajectories over time. This numerical analysis shows that despite an initial buildup of entanglement and a significant amount of entanglement due to either spin squeezing or dark states at late times, the essential features of the superradiant burst are well described by averages over fully factorizable states. We explain this observation in terms of an almost complete factorization of all 2-local observables, which we identify as a generic property of superradiant decay. Based on this insight, we provide a purely classical theory for the burst in squeezed superradiance, which is both intuitive and exact for a large number of emitters. Moreover, we find that our numerical approach also performs well in the presence of subradiant states, which dominate the slow residual decay of nonuniform ensembles at late times.

Thickness dependence is a unique trait for the friction of two-dimensional materials, where thinner samples are typically found to exhibit higher friction than thicker ones. In this Letter, we show that friction on two-dimensional ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ nanosheets transferred on silicon substrates with predominantly upward polarization can behave in a manner completely opposite to the conventional trend, showing enhanced friction with increasing thicknesses. Assisted by Kelvin Probe Force Microscopy measurements and first-principles calculations, this unusual behavior is attributed to the work-function regulated friction mechanism. Specifically, as the sample thickness increases, the work function decreases for the ferroelectric material, which results in a more pronounced electron transfer effect and thereby stronger interactions across the intimate contact interface. This work sheds light on the physical origins of friction for ferroelectric materials and suggests an effective strategy to actively regulate friction via work-function engineering.

We investigate resistive anomalies in metals near a ferromagnetic phase transition, emphasizing the role of long-range critical fluctuations. Our analysis shows that electron diffusion near the critical temperature $T_c$ enhances the singular behavior of resistivity via a classical memory effect, exceeding the prediction of Fisher and Langer [Phys. Rev. Lett. 20, 665 (1968)]. Close to $T_c$, the resistivity develops a cusp or anticusp controlled by the critical exponent of the order parameter. We also express a concomitant non-Drude behavior of the optical conductivity in terms of critical exponents. These results provide deeper insight into the origin of resistive anomalies and their connection to criticality in metallic systems.

We identify a previously unrecognized class of two-dimensional (2D) collinear magnetic phase that extends beyond the established categories of ferromagnets, antiferromagnets, and altermagnets. These type IV 2D collinear magnets exhibit spin-degenerate bands in the nonrelativistic limit, yet support time-reversal symmetry-breaking responses, such as the anomalous Hall effect (AHE), despite having zero net magnetization. Based on spin layer group analysis, we derive the symmetry criteria for this phase and perform first-principles calculations to screen viable candidate materials from 2D databases. Using monolayer ${\mathrm{Hf}}_2\mathrm{S}$ as a prototype, we demonstrate that in the absence of spin-orbit coupling, the bands are spin degenerate, while its inclusion induces an AHE driven by spin-polarized and even spin-neutral currents, accompanied by a symmetry-protected, truly full-space persistent spin texture. These findings expand the classification of magnetic phases and broaden avenues for realizing unconventional spintronic functionalities in two dimensions.

We have investigated the terahertz (THz) nonlinear response of the multigap superconductor ${\mathrm{MgB}}_2$, using THz two-dimensional coherent spectroscopy (THz 2DCS). With broadband THz drive fields, we identified a nonlinear response at twice the lower superconducting gap energy $2{\mathrm{\Delta }}_{\pi }$ at the lowest temperatures. Using narrow-band THz driving pulses, we observed first (FH) and third harmonic responses. The FH intensity shows a monotonic increase with decreasing temperature when properly normalized by the driving field strength. This is distinct from the single-gap superconductor NbN, where the FH signal exhibited a resonant enhancement at temperatures when twice the gap energy $2\mathrm{\Delta }$ was resonant with the driving photon energy, which was interpreted to originate from the superconducting amplitude mode. Our results in ${\mathrm{MgB}}_2$ are consistent with a well-defined amplitude mode only at the lowest temperatures and indicate strong damping as temperature increases. This likely indicates the importance of interband coupling in ${\mathrm{MgB}}_2$ and its influence on the nature of the amplitude mode and its damping.

We report an unusual T-shaped Fe-based multistoichiometry stereoscopic composite catalyst with multifunctional active sites, fabricated via a one-step graphene-controlled all-solid-state synthesis. This tailored catalyst can improve all three catalysis processes of ${\mathrm{H}}_2{\mathrm{O}}_2$ adsorption, peroxide bond activation, and ${\mathrm{HO}}^{•}$ desorption, resulting in a novel catalytic framework where the two-dimensional (2D) ${\text{Fe}}_2{\mathrm{O}}_3$ nanosheets optimize ${\mathrm{H}}_2{\mathrm{O}}_2$ adsorption, and the 2D FeOCl nanosheets vertically grown on the ${\text{Fe}}_2{\mathrm{O}}_3$ surface can facilitate both the generation and desorption of ${\mathrm{HO}}^{•}$.

We show, for any finite $n\ge 2$, that there exist quantum correlations obtained from performing $n$ dichotomic quantum measurements in a bipartite Bell scenario, which cannot be reproduced by mixtures of measurement devices with at most ($n-1$) incompatible measurements across different partitions in any no-signaling theory. That is, it requires for any no-signaling theory an unbounded number of measurements to reproduce the predictions of quantum theory. We prove our results by showing that there exist linear Bell inequalities that have to be obeyed by any no-signaling theory involving only ($n-1$)-wise incompatible measurements and show explicitly how these can be violated in quantum theory. Finally, we discuss the relation of our work to previous works ruling out alternatives to quantum theory with some kind of bounded degree of freedom and consider the experimental verifiability of our results.

In H. Xu et al. [Phys. Rev. Lett. 110, 064102 (2013)], a numerical method is introduced—an extension of the conformal-map method of Robnik [J. Phys. A 17, 1049 (1984)] for nonrelativistic quantum billiards—for the quantization of relativistic neutrino billiards consisting of a massless noninteracting spin-$1/2$ particle confined to a two-dimensional domain. We demonstrate in this Letter that this method does not provide solutions of the associated Weyl (Dirac) equation, nor does it fulfill the boundary conditions imposed on the spinor eigenfunctions to ensure confinement of the particle to the domain of the billiard. We review in detail the wave equation, boundary conditions, and quantization of neutrino billiards and derivation of relevant equations to make the proof comprehensible for the general reader. Our results are corroborated with numerical ones for nonrelativistic and relativistic quantum billiards whose shapes depend on a parameter, which allows the study of the properties of their eigenstates as the classical dynamics experiences a transition from regular to chaotic dynamics.

Estimating ground state energies of many-body Hamiltonians is a central task in many areas of quantum physics. In this Letter, we give quantum algorithms which, given any $k$-body Hamiltonian $H$, compute an estimate for the ground state energy and prepare a quantum state achieving said energy, respectively. Specifically, for any $ϵ>0$, our algorithms return, with high probability, an estimate of the ground state energy of $H$ within additive error $ϵM$, or a quantum state with the corresponding energy. Here, $M$ is the total strength of all interaction terms, which in general is extensive in the system size. Our approach makes no assumptions about the geometry or spatial locality of interaction terms of the input Hamiltonian and thus handles even long-range or all-to-all interactions, such as in quantum chemistry, where lattice-based techniques break down. In this fully general setting, the run-time of our algorithms scales as $2^{cn/2}$ for $c<1$, yielding the first quantum algorithms for low-energy estimation breaking a standard square root Grover speedup for unstructured search. The core of our approach is remarkably simple, and relies on showing that an extensive fraction of the interactions can be neglected with a controlled error. What this ultimately implies is that even arbitrary $k$-local Hamiltonians have structure in their low energy space, in the form of an exponential-dimensional low energy subspace.

Self-testing protocols enable the certification of quantum systems in a device-independent manner, i.e., without knowledge of the inner workings of the quantum devices under test. Here, we demonstrate this high standard for characterization routines with superconducting circuits, a prime platform for building large-scale quantum computing systems. We first develop the missing theory allowing for the self-testing of Pauli measurements. We then self-test Bell pair generation and measurements at the same time, performing a complete self-test in a system composed of two entangled superconducting circuits operated at a separation of 30 m. In an experiment based on 17 million trials, we measure an average CHSH (Clauser-Horne-Shimony-Holt) $S$ value of 2.236. Without relying on additional assumptions on the experimental setup, we certify an average Bell state fidelity of at least 58.9% and an average measurement fidelity of at least 89.5% in a device-independent manner, both with 99% confidence. This enables applications in the field of distributed quantum computing and communication with superconducting circuits, such as delegated quantum computing.

The quasinormal mode spectrum of black holes is unstable against small modifications of the radial potential describing massless perturbations. We study how these small modifications affect the convergence of the quasinormal mode expansion and the mode excitation by computing the mode amplitudes from first principles, without relying on any fitting procedure. We show that the decomposition of the prompt ringdown waveform is not unique: small modifications in the radial potential produce new quasinormal mode “basis sets” that can improve the convergence of the quasinormal mode expansion, even capturing the late-time tail. We also study avoided crossings and exceptional points of the Kerr and Kerr–de Sitter spectrum. We show that while the mode amplitude can be resonantly excited, modes that exhibit avoided crossing destructively interfere with each other, so that the prompt ringdown waveform remains stable.

We investigate cosmic censorship in anti–de Sitter space in holographic models in which the ground state is described by a good singularity. These include supersymmetric truncations of string/M theory, for which a positive-energy theorem holds. At the boundary, our solutions describe a boost-invariant fluid in which the temperature decreases monotonically with time. On the gravity side, they correspond to black-brane spacetimes with a receding horizon. In classical gravity, curvature invariants at the horizon grow without bound. In the full theory this regime may or may not be reached. In some cases it is avoided by a phase transition to a regular geometry. In others it is reached but the boundary hydrodynamic evolution can be continued, provided the equation of state at parametrically small energies is known. Both cases require the inclusion of finite-$N$ or finite-coupling effects.

We derive the full system of canonical differential equations for all planar two-loop massless six-particle master integrals and determine analytically the boundary conditions. This fully specifies the solutions, which may be written as Chen iterated integrals. We argue that this is sufficient information for evaluating any scattering amplitude in four dimensions up to the finite part. We support this claim by reducing, for the most complicated integral topologies, integrals with typical Yang-Mills numerators. We use the analytic solutions to the differential equations, together with dihedral symmetry, to provide the full solution space relevant for two-loop six-particle computations. This includes the relevant function alphabet, as well as the independent set of iterated integrals up to weight four. We also provide the answer for all master integrals in terms of iterated integrals that can be readily evaluated numerically. As a proof of concept, we provide a numerical implementation that evaluates the integrals in part of the Euclidean region and validate this against numerical evaluation of the Feynman integrals. Our result removes the bottleneck of the Feynman integral evaluation, paving the way for future analytic evaluations of six-particle scattering amplitudes.

Dynamic interference is an elusive strong-field effect where photoelectrons from intense laser pulses interfere in time, forming rich kinetic energy patterns. Here, we present the first experimental demonstration of isolated dynamic interference using a novel two-color scheme: chirped laser-assisted dynamic interference. Isolation was achieved with a crossed-polarization setup combining an extreme ultraviolet harmonic field and an infrared pulse with tailored spectrotemporal properties. Beyond prior works, our approach enables precise control over interfering trajectories, yielding holographic interference patterns and advancing our understanding of strong-field phenomena.

We report theoretical momentum distributions of electrons ejected from the C and O $K$ shells of fixed-in-space CO molecules by Compton scattering of 20 keV photons for different magnitudes and orientations of the photon momentum transfer with respect to the molecular axis. We observe distinct diffraction patterns in our computed momentum distributions, which are governed by the interference of the direct Compton electrons and those which are scattered on the parent and neighboring nuclei. The observed phenomenon is similar to that employed in diffraction imaging using high-energy photoelectrons. It persists after integration over different magnitudes and the orientation of the photon momentum transfer in the molecular frame of reference. A corresponding coincidence experiment confirms our theoretical predictions.