Merging bound states in the continuum (BICs) has significant promise for wave manipulation since it can provide an ultrahigh $Q$ factor when compared to the isolated BICs. However, the study of merging topological bound states in the continuum (TBICs) remains largely unexplored. In this Letter, we introduce a straightforward structure for crafting the merged higher order TBICs, i.e., the merged topological corner states in the continuum (MTCICs), via a synthetic way. Two identical topological insulators, supporting topological corner states within the bulk band, are mirror stacked. The eigenstates inherited from a single layer experience energy spectrum shifts without hybridization as interlayer couplings change, leading to the emergence of MTCICs. With acoustic crystals, we experimentally identify and characterize the MTCICs. The results evidently confirm the superior energy confinement capabilities of MTCICs over TBICs and gapped topological corner states (TCSs). Our Letter may deepen the understandings of both topological and BIC physics to inspire the development of devices with ultrahigh $Q$ factor and enhanced robustness.

The molecular triangular lattice system, ${\beta }^{\prime }\text{−}{\mathrm{EtMe}}_3\mathrm{Sb}[\mathrm{Pd}{(\mathrm{dmit})}_2{]}_2$, is considered as a candidate material for the quantum spin liquid state, although ongoing debates arise from recent controversial results. Here, the results of electron spin resonance and muon-spin relaxation measurements on ${\beta }^{\prime }\text{−}{\mathrm{EtMe}}_3\mathrm{Sb}[\mathrm{Pd}{(\mathrm{dmit})}_2{]}_2$ are presented. Both results indicate characteristic behaviors related to quasi-one-dimensional spin dynamics, whereas the direction of anisotropy found in electron spin resonance is in contradiction with previous theories. We succeed in interpreting the experiments by combining density-functional theory calculations and analysis of the effective model taking into account the multiorbital nature of the system. While the quantum-spin-liquid–like origin of ${\beta }^{\prime }\text{−}{\mathrm{EtMe}}_3\mathrm{Sb}[\mathrm{Pd}{(\mathrm{dmit})}_2{]}_2$ was initially attributed to the magnetic frustration of the triangular lattice, it appears that the primary origin is a 1D spin liquid resulting from the dimensional reduction effect.

New unconventional compensated magnets with a $p$-wave spin polarization protected by a composite time-reversal translation symmetry have been proposed in the wake of altermagnets. To facilitate the experimental discovery and applications of these unconventional magnets, we construct an effective analytical model. The effective model is based on a minimal tight-binding model for unconventional $p$-wave magnets that clarifies the relation to other magnets with $p$-wave spin-polarized bands. One of the most prominent advantages of our analytical model is the possibility to employ various analytical approaches while capturing essential features of $p$-wave magnets. We illustrate the effective model by evaluating the tunneling conductance in junctions with $p$-wave magnets, revealing a large magnetoresistance, spin filtering, and anisotropic bulk spin conductivity beyond linear response despite the absence of a net magnetization. These results show that unconventional $p$-wave magnets offer several useful functionalities, broadening the material selection for spintronics devices.

We study ferroelectricity in the classic perovskite ferroelectric ${\mathrm{PbTiO}}_3$ to high pressures with density functional theory (DFT) and experimental diamond-anvil techniques. We use second harmonic generation spectroscopy to detect lack of inversion symmetry. Consistent with early understanding and experiments, we find that ferroelectricity disappears at moderate pressures. However, DFT computations show that the disappearance arises from the overtaking of zone boundary instabilities, and not from the squeezing out of the off-centering ferroelectric displacements with pressure, as previously thought. Moreover, at high pressures the distorted perovskite phases are metastable with respect to a new dense centrosymmetric postperovskite phase with $\mathrm{P}{2}_1/m$ symmetry and 8-coordinated Ti, which becomes stable at about 70 GPa.

Optical simulators for the Ising model have demonstrated great promise for solving challenging problems in physics and beyond. Here, we develop a spatial optical simulator for a variety of classical statistical systems, including the clock, $XY$, Potts, and Heisenberg models, utilizing a digital micromirror device composed of a large number of tiny mirrors. Spins, with desired amplitudes or phases of the statistical models, are precisely encoded by a patch of mirrors with a superpixel approach. Then, by modulating the light field in a sequence of designed patterns, the spin-spin interaction is realized in such a way that the Hamiltonian symmetries are preserved. We successfully simulate statistical systems on a fully connected network, with ferromagnetic or Mattis-type random interactions, and observe the corresponding phase transitions between the paramagnetic and the ferromagnetic or spin-glass phases. Our results largely extend the research scope of spatial optical simulators and their versatile applications.

We investigate the aging properties of phase-separation kinetics following quenches from $T=\infty$ to a finite temperature below $T_c$ of the paradigmatic two-dimensional conserved Ising model with power-law decaying long-range interactions $\sim r^{-(2+\sigma )}$. Physical aging with a power-law decay of the two-time autocorrelation function $C(t,t_w)\sim {(t/t_w)}^{-\lambda /z}$ is observed, displaying a complex dependence of the autocorrelation exponent $\lambda$ on $\sigma$. A value of $\lambda =3.500(26)$ for the corresponding nearest-neighbor model (which is recovered as the $\sigma \to \infty$ limit) is determined. The values of $\lambda$ in the long-range regime ($\sigma <1$) are all compatible with $\lambda \approx 4$. In between, a continuous crossover is visible for $1\lesssim \sigma \lesssim 2$ with nonuniversal, $\sigma$-dependent values of $\lambda$. The performed Metropolis Monte Carlo simulations are primarily enabled by our novel algorithm for long-range interacting systems.

From a quantum information perspective, verifying quantum coherence in a quantum experiment typically requires adjusting measurement settings or changing inputs. A paradigmatic example is that of a double-slit experiment, where observing the interference pattern on the screen in a series of experimental settings where one, the other, and both slits are open unambiguously proves quantum coherence. Here we show that this is not necessary by verifying quantum coherence in a network scenario without the need for inputs. We show that there exist probability distributions for joint outcomes of three parties in a triangular network with independent sources that cannot be replicated using classical resources. Furthermore, we generalize our results to $n$-party networks and show that the discrepancy between correlations in classical and quantum networks increases with the number of parties. To this end, we derive nonlinear inequalities that are satisfied by classical resources (i.e., without coherence) and find quantum states that violate them.

In recent years, energy correlators have emerged as a powerful tool to explore the field theoretic structure of strong interactions at particle colliders. In this Letter we initiate a novel study of the nonperturbative power corrections to the projected $N$-point energy correlators in the limit where the angle between the detectors is small. Using the light-ray operator product expansion as a guiding principle, we derive the power corrections in terms of two nonperturbative quantities describing the fragmentation of quarks and gluons. In analogy with their perturbative leading-power counterpart, we show that power corrections obey a classical scaling behavior that is violated at the quantum level. This crucially results in a dependence on the hard scale $Q$ of the problem that is calculable in perturbation theory. Our analytic predictions are successfully tested against Monte Carlo simulations for both lepton and hadron colliders, marking a significant step forward in the understanding of these observables.

Energy correlators provide a powerful observable to study fragmentation dynamics in QCD. We demonstrate that the leading nonperturbative corrections for projected $N$-point energy correlators are described by the same universal parameter for any $N$, which has already been determined from other event shape fits. Including renormalon-free nonperturbative corrections substantially improves theoretical predictions of energy correlators, notably the transition into the confining region at small angles. Nonperturbative corrections are shown to have a significant impact on ${\alpha }_s$ extractions.

We give for the first time theoretical estimates of unknown rare electron-capture (EC) decay branchings of ${}^{44}\mathrm{Ti}$, ${}^{57}\mathrm{Co}$, and ${}^{139}\mathrm{Ce}$, relevant for searches of (exotic) dark-matter particles. The nuclear-structure calculations have been done exploiting the nuclear shell model with well-established Hamiltonians and an advanced theory of $\beta$ decay. In the absence of experimental measurements of these rare branches, these estimates are of utmost importance for terrestrial searches of dark-matter particles, such as axionic dark matter in the form of axionlike particles, anapole dark matter, and dark photons in nuclear transitions. Predictions are made for EC-decay rates of second-forbidden unique and second-forbidden nonunique EC transitions that can potentially mimic dark-matter-particle detection in dedicated underground experiments designed to observe the absence of the corresponding nuclear electromagnetic transitions.

Via conductance measurements of thousands of single-molecule junctions, we report that the $\pi –\pi$ coupling between neighboring aromatic molecules can be manipulated by laser illumination. We reveal that this optical manipulation originates from the optical plasmonic gradient force generated inside the nanogaps, in which the gapped antenna electrodes act as optical tweezers pushing the neighboring molecules closer together. These findings offer a nondestructive approach to regulate the interaction of the molecules, deepening the understanding of the mechanism of $\pi –\pi$ interaction, and open an avenue to manipulate the relative position of extremely small objects down to the scale of single molecules.

Atom-ion hybrid systems are promising platforms for the quantum simulation of polaron physics in certain quantum materials. Here, we investigate the ionic Fermi polaron, a charged impurity in a polarized Fermi bath, at zero temperature using quantum Monte Carlo techniques. We compute the energy spectrum, residue, effective mass, and structural properties. Significant deviations from field-theory prediction occur in the strong coupling regime due to large density inhomogeneities around the ion. We observe a smooth polaron-molecule transition in contrast with the neutral case. This study provides insights into solid-state systems like Fermi exciton polarons in thin semiconductors and quantum technologies based on atom-ion platforms.

Electronic coherences are key to understanding and controlling photoinduced molecular transformations. We identify a crucial quantum-mechanical feature of electron-nuclear correlation, the projected nuclear quantum momenta, essential to capture the correct coherence behavior. For simulations, we show that, unlike traditional trajectory-based schemes, exact-factorization-based methods approximate these correlation terms and correctly capture electronic coherences in a range of situations, including their spatial dependence, an important aspect that influences subsequent electron dynamics and that is becoming accessible in more experiments.

This study introduces a novel method to investigate in situ light transport within optically thick ensembles of cold atoms, exploiting the internal structure of alkaline-earth metals. A method for creating an optical excitation at the center of a large atomic cloud is demonstrated, and we observe its propagation through multiple scattering events. In conditions where the cloud size is significantly larger than the transport mean free path, a diffusive regime is identified. We measure key parameters, including the diffusion coefficient, transport velocity, and transport time, finding a good agreement with diffusion models. We also demonstrate that the frequency of the photons launched inside the system can be controlled. This approach enables direct time- and space-resolved observation of light diffusion in atomic ensembles, offering a promising avenue for exploring new diffusion regimes.

We predict that ultracold bosonic dipolar gases, confined within a multilayer geometry, may undergo self-assembling processes, leading to the formation of chain gases and solids. These dipolar chains, with dipoles aligned across different layers, emerge at low densities and resemble phases observed in liquid crystals, such as nematic and smectic phases. We calculate the phase diagram using quantum Monte Carlo methods, introducing a newly devised trial wave function designed for describing the chain gas, where dipoles from different layers form chains without in-plane long-range order. We find gas, solid, and chain phases, along with quantum phase transitions between these states. Specifically, we predict the existence of quantum phase transitions from gaseous to self-ordered phases, as the interlayer distance is decreased. Remarkably, in the self-organized phases, the mean interparticle distance can significantly exceed the characteristic length of the interaction potential, yielding solids and chain gases with densities several orders of magnitude lower than those of conventional quantum solids.

Quantum entanglement—correlations of particles that are stronger than any classical analog—is the basis for research on the foundations of quantum mechanics and for practical applications such as quantum networks. Traditionally, entanglement is achieved through local interactions or via entanglement swapping, where entanglement at a distance is generated through previously established entanglement and Bell-state measurements. However, the precise requirements enabling the generation of quantum entanglement without traditional local interactions remain less explored. Here, we demonstrate that independent particles can be entangled without the need for direct interaction, prior established entanglement, or Bell-state measurements, by exploiting the indistinguishability of the origins of photon pairs. Our demonstrations challenge the long-standing belief that the prior generation and measurement of entanglement are necessary prerequisites for generating entanglement between independent particles that do not share a common past. In addition to its foundational interest, we show that this technique might lower the resource requirements in quantum networks, by reducing the complexity of photon sources and the overhead photon numbers.

Harnessing high-dimensional entangled states of light presents a frontier for advancing quantum information technologies, from fundamental tests of quantum mechanics to enhanced computation and communication protocols. In this context, the spatial degree of freedom stands out as particularly suited for on-chip integration. But while traditional demonstrations produce and manipulate path-entangled states sequentially with discrete optical elements, continuously coupled nonlinear waveguide systems offer a promising alternative where photons can be generated and interfere along the entire propagation length, unveiling novel capabilities within a reduced footprint. Here we exploit this concept to implement a compact and reconfigurable source of path-entangled photon pairs based on parametric down-conversion in semiconductor nonlinear waveguide arrays. We use a double-pump configuration to engineer the output quantum state and implement various types of spatial correlations, exploiting a quantum interference effect between the biphoton state generated in each pumped waveguide. This demonstration, at room temperature and telecom wavelength, illustrates the potential of continuously coupled systems as a promising alternative to discrete multicomponent quantum circuits for leveraging the high-dimensional spatial degree of freedom of photons.