Crystal stacking offers a powerful yet underexplored route to engineer symmetry in layered superconductors. Here we report superconductivity in rhombohedral-stacked ${\mathrm{NbSe}}_2$ ($3R\text{−}{\mathrm{NbSe}}_2$), a noncentrosymmetric polytype in which global inversion symmetry is removed by stacking alone. Using comprehensive structural, transport, magnetic, and thermodynamic measurements, we establish superconductivity as a bulk property of the $3R$ phase and find that the in-plane upper critical field exceeds the Pauli paramagnetic limit, indicating the persistence of strong Ising-type spin-orbit coupling. Unlike the thickness-dependent superconductivity in centrosymmetric $2H\text{−}{\mathrm{NbSe}}_2$, the superconducting transition temperature in $3R\text{−}{\mathrm{NbSe}}_2$ shows little dependence on the layer number but exhibits an unusually strong sensitivity to disorder. We further observe strongly enhanced nonlinear optical and electrical responses near the superconducting transition, consistent with stacking-induced inversion-symmetry breaking. Our results identify $3R\text{−}{\mathrm{NbSe}}_2$ as a single-phase platform in which stacking engineering reshapes superconductivity and enables nonlinear transport phenomena in layered materials.

Reduced oxide surfaces often undergo complex reconstructions in which atomic rearrangements and reduction-induced electronic redistribution are strongly coupled, obscuring the electronic principles that govern their stability. Here, we address this problem on the prototypical rutile ${\mathrm{TiO}}_2(110)$ surface by combining machine-learning-accelerated global structure search, first-principles calculations, simulated scanning tunneling microscopy, and data-driven electronic-structure analysis. We identify previously unreported ${\text{Ti}}_3{\mathrm{O}}_2\text{−}(2\times 1)$ and ${\text{Ti}}_3{\mathrm{O}}_4\text{−}(2\times 1)$ reconstructions, with ${\text{Ti}}_3{\mathrm{O}}_2\text{−}(2\times 1)$ being more stable than the previously proposed ${\mathrm{Ti}}_3{\mathrm{O}}_2\text{−}(1\times 2)$ model by up to 0.67 eV per minimal reconstruction unit and reproducing the experimentally observed rosettelike STM motifs. Analysis of 80 ${\mathrm{Ti}}_3{\mathrm{O}}_2$ reconstruction configurations reveals that their thermodynamic stability is governed by the integrated hybridization between occupied Ti $3d$ states associated with ${\mathrm{Ti}}^{3+}$ small polarons and $\mathrm{O}2p$ states of the reconstructed oxide lattice. This polaronic lattice state hybridization distinguishes low-energy reconstructions from the broader configurational ensemble and explains the stabilization of the newly found ground-state structure. The ${\mathrm{Ti}}^{3+}$-derived states are also present near the Fermi level, which facilitates electron transfer to adsorbates, allowing the reconstructed surface to combine thermodynamic stability with chemical activity. These results establish polaronic lattice state hybridization as a microscopic mechanism for stabilizing reduced ${\mathrm{TiO}}_2$ surface reconstructions and suggest a broader electronic principle governing reconstruction of defect-rich reducible oxide surfaces.

Ballistic transport is traditionally regarded as a limiting regime for scattering-free energy transfer. Here, we predict a superballistic radiative heat transport regime that surpasses this limit in dilute chains of plasmonic nanoparticles confined within cavities. This anomalous regime exhibits superlinear scaling of the effective thermal conductivity ($\kappa \sim L^{1.5}$) and originates from the amplification of long-range interactions mediated by cavity-guided modes. Our results establish a framework for ultrafast photonic heat transport and open pathways for thermal management, information processing, and energy transfer in quantum and nanoscale systems.

Research on altermagnetism has thus far primarily focused on spin-polarized bulk electronic states in magnetic materials. In this work, we advance the field by introducing the concept of surface altermagnetism (SAM), wherein altermagnetic spin polarization emerges at the surfaces of collinear antiferromagnets (AFMs) or altermagnets (AMs). To lay the theoretical groundwork for this phenomenon, we construct a thorough symmetry-based framework that systematically connects bulk spin groups to surface spin groups for both types of systems. Through symmetry analysis, we identify all symmetry-breaking surfaces capable of supporting SAM, identifying 35 for $PT$-symmetric AFMs and 61 distinct cases for bulk AMs. Moreover, we show that 203 collinear spin space groups—including 100 without and 103 with the $[C_2\parallel P]$ operation—permit the appearance of SAM on the surface of $\mathit{t}T$-symmetric AFMs via the breaking of fractional translational symmetries. The proposed framework is verified using tight-binding models and first-principles calculations, with practical material implementations shown in representative compounds like NaMnP, LiMnAs, and CrSb. Our results establish SAM as a robust, symmetry-protected magnetic state, extending altermagnetic phenomena to material surfaces and paving the way for advanced, field-free spin manipulation in next-generation spintronic technologies.

We demonstrate strong coupling between propagating spin-wave modes and microwave photons in superconducting resonator-magnetic thin film hybrid circuits. By fabricating the resonator directly on yttrium iron garnet thin films grown on rare-earth-free ${\mathrm{Y}}_3{\mathrm{Sc}}_2{\mathrm{Ga}}_3{\mathrm{O}}_{12}$ substrates, we achieve strong coupling of both Damon-Eshbach and backward-volume spin-wave modes to the resonator, with coupling strengths exceeding both the magnon and photon damping rates. Furthermore, we observe nonreciprocal spin-wave radiation of the hybrid magnonic mode in the Damon-Eshbach configuration, highlighting the potential for incorporating intrinsic spin-wave nonreciprocity into hybrid magnonic systems. These results open new avenues for integrating spin-wave magnonics with cavity magnonics and for harnessing spin waves for potential applications in quantum information science.

We propose a general expression for the domain-wall width in generic multisublattice Heisenberg magnets with collinear order and uniaxial anisotropy, applicable to ferro-, antiferro-, and ferrimagnetic orders. The result follows from an exact connection between the domain-wall profile and the long-wavelength spin-wave dispersion, yielding a unified framework for describing magnetic textures across distinct ordering types. The predictions show excellent quantitative agreement with large-scale atomistic spin dynamics simulations over a broad range of exchange and anisotropy values and multisublattice spin structures, including three-dimensional rock-salt-type magnets and two-dimensional honeycomb and kagome ferromagnets. Moreover, we establish a general microscopic foundation for the temperature dependence of the domain-wall width. Our approach offers a powerful tool for understanding domain-wall profiles in complex spin systems.

Thin polymer films are archetypal nonequilibrium systems in which chain conformations are frozen by rapid preparation. The resulting molecular recoiling stress drives the system toward equilibrium and relaxes with time and temperature. We show that the activation energy governing this relaxation depends on the magnitude of the stress, revealing that polymers farther from equilibrium must overcome higher barriers, while stress release enables relaxation through progressively easier pathways. This stress-dependent evolution of activation barriers reflects a balance between energetic and entropic contributions and departs from the behavior typically observed for segmental mobility. Our experimental trends are quantitatively captured by the collective small displacements framework, consistent with recent observations of analogous relaxation behavior in adsorption-desorption, surface crystallization, and dipole reorientation. Our findings establish a direct link between nonequilibrium induced stress and molecular mobility, uncovering a general mechanism by which molecules reorganize toward equilibrium through localized, correlated motions.

Scaling up superconducting quantum computers requires denser control wiring, introducing microwave crosstalk along the entire cryogenic signal path rather than only near the chip. Here, we introduce a framework that combines microwave transmission-line theory with a quantum Hamiltonian description to quantify the wiring-induced microwave crosstalk and the resulting gate infidelity for an all-microwave universal gate set. Using this approach, we determine the equal-level far-end crosstalk (ELFEXT) required to operate fixed-frequency transmons at arbitrary target fidelities and find that achieving 99.99% fidelity requires ELFEXT levels of approximately $-43\mathrm{dB}$ for the $R_X$ gate and $-73\mathrm{dB}$ for the cross-resonance gate. Finally, we use these results to bound the number of physical qubits on a chip.

Multipartite entanglement is a fundamental resource for quantum information processing. Various degrees of freedom of light, such as time, frequency, and space, have been widely exploited to create large-scale entangled quantum sources, enhancing information transmission capacity. Here, we demonstrate the generation of honeycomb-structured entanglement among 13 spatially separated beams with a reconfigurable pump field of a hexagonal structure, featuring the simultaneous multiplexing of 18 four-wave mixing processes within a single atomic ensemble. Such a reconfigurable spatially structured pump is constructed by loading a reprogrammable hologram onto a spatial light modulator. Additionally, we analyze 8190 possible steering bipartitions and examine the robustness of the quantum properties inherent in the system. Furthermore, by reconfiguring the pump fields with square, hexagonal, and eightfold quasicrystal structures, we can generate square-, hexagonal-, and octagonal-structured output fields. This enables the output mode number to be extended from 9 and 19 up to 21. These results provide a promising route to realizing spatially programmable multipartite entanglement, enabling reconfigurable multiuser quantum communication networks, and suggesting potential avenues toward exploring topological phenomena in continuous-variable quantum systems.

We show that the standard approach to characterize collective entanglement via genuine multiparty entanglement (GME) leads to an area law in ground and thermal Gibbs states of local Hamiltonians. To capture the truly collective part one needs to go beyond this short-range contribution tied to interfaces between subregions. Genuine network multiparty entanglement (GNME) achieves a systematic resolution of this goal by analyzing whether a $k$-party state can be prepared by a quantum network consisting of ($k-1$)-partite resources. We develop tools to certify and quantify GNME, and benchmark them for GHZ, W and Dicke states. We then study the 1d transverse field Ising model, where we find a sharp peak of GNME near the critical phase transition, and rapid suppression elsewhere. Finite temperature leads to a faster death of GNME compared to GME. Furthermore, certain 2d quantum spin liquids do not have GNME in microscopic subregions, while possessing strong GME. This approach will allow us to chart truly collective entanglement in quantum matter both in and out of equilibrium.

Recent progress in open many-body quantum systems has highlighted the importance of the Markov length, the characteristic scale over which conditional correlations decay. It has been proposed that nonequilibrium phases of matter can be defined as equivalence classes of states connected by short-time evolution while maintaining a finite Markov length, a notion called local reversibility. A natural question is whether well-known classical models of nonequilibrium criticality fit within this framework. Here we investigate the Domany-Kinzel model—which exhibits an active phase and an absorbing phase separated by a $(1+1)\mathrm{D}$ directed-percolation transition—from this information-theoretic perspective. Using tensor network simulations, we provide evidence for local reversibility within the active phase. Notably, the Markov length diverges upon approaching the critical point. The power-law decay of conditional correlations sharply quantifies the non-Gibbs nature of the directed-percolation critical point and also introduces a new critical exponent whose value we estimate using our simulations. Further, we analytically study the case of $(1+1)\mathrm{D}$ compact directed percolation, where the Markov length diverges throughout the phase diagram due to spontaneous breaking of domain-wall parity symmetry from strong to weak. Nevertheless, the conditional mutual information continues to faithfully detect the corresponding phase transition.

Weak measurements have been predicted to dramatically alter universal properties of quantum critical wave functions, though experimental validation remains an open problem. Here we devise a practical scheme for realizing measurement-altered criticality in a chain of Rydberg atoms tuned to Ising and tricritical Ising phase transitions. In particular, we show that projectively measuring a periodic subset of atoms alters quantum critical correlations in distinct ways that one can control via the choice of measured sites and the measurement outcomes. While our protocol relies on postselection, the measurement outcomes yielding the most dramatic consequences occur with surprisingly large probabilities: $O(10\%)$ with chains featuring $O(100)$ sites. Characterizing the proposed postmeasurement states requires only an adjustment in the post-process averaging of outcomes used to characterize unmeasured critical states, resulting in minimal additional experimental overhead for demonstrating measurement-altered criticality.

Quantum key distribution (QKD) enables information-theoretic secure communication, yet its ultimate tolerance to noise and achievable transmission distance remain fundamentally constrained. We establish the maximum quantum bit error rate (QBER) compatible with secure QKD and derive corresponding upper bounds on communication distance. Our results follow from a fundamental capacity threshold for qubit Pauli channels and apply to protocols based on two or more mutually unbiased bases, using either single-photon or weak coherent sources. By connecting information-theoretic limits to realistic physical noise models, we obtain universal bounds on achievable distances in fiber and free-space links, including diffraction-limited constraints relevant to deep-space quantum communications. These findings clarify the ultimate noise robustness of QKD and delineate the fundamental boundaries of secure quantum communication.

Quantum networks enable a variety of quantum information processing tasks, where multiuser quantum communication is one of the important objectives. Quantum cryptographic conferencing (QCC) serves as an essential solution to establish secure keys to realize secure multiuser communications. However, existing QCC implementations have been fundamentally limited by the low probability of multiuser coincidence detection to measure or construct the Greenberger-Horne-Zeilinger (GHZ) entangled state. In this Letter, we report the experimental realization of QCC eliminating the need for coincidence detection, where the GHZ state is constructed by correlating detection events occurring within the coherence time, thereby greatly enhancing the success probability of GHZ-state measurement. Meanwhile, to establish and maintain high-visibility GHZ measurement among three independent users, we developed a three-party phase compensation scheme combined with precise temporal and polarization alignment within a time-bin-phase encoding framework. Furthermore, we designed an efficient pairing strategy to simplify subsequent data processing and enhance processing efficiency. Based on these techniques, we successfully performed QCC experiments over total loss of 66.3 dB, with the channel loss of 51.24 dB, achieving secure key rates of $5.4\mathrm{bit}/\mathrm{s}$, whereas previous QCC experiments have been limited to 100 km. The results establish a new regime of scalable, multiuser quantum communication and paving the way for metropolitan quantum networks.

Even 50 years after the discovery of a positron annihilation line from the inner Galaxy, no class of astrophysical sources has emerged as a definitive explanation for both the emission morphology and flux. Positrons produced by dark matter annihilation or decay have been proposed, but the mass of any such candidate is constrained by continuum $\gamma$-ray emission at energies $>511\mathrm{keV}$. Earlier analyses have claimed that this emission requires that the positrons have kinetic energies less than a few MeV at injection, disfavoring both much of the dark matter parameter space and many potential compact astrophysical source classes such as pulsars. However, these constraints were not based on a full forward model of the absolute flux of the $\gamma$-ray line and continuum data, and did not marginalize over uncertainties about the relative angular distributions of the line and continuum. Here we describe an improved analysis that overcomes these limitations, and show that constraints on the injection energy are much weaker than previously claimed; even under conservative assumptions the data are consistent with initial energies up to $\sim 110\mathrm{MeV}$ from INTEGRAL/SPI data alone, and up to $\sim 55\mathrm{MeV}$ when including COMPTEL and EGRET data, subject to cross-normalization between them and INTEGRAL.

We propose a new mechanism for the formation of seeds of supermassive black holes at early cosmic epochs. Our scenario explores density fluctuations that are enhanced relative to $\mathrm{\Lambda }\mathrm{CDM}$ expectations, but with amplitudes that are not large enough to form primordial black holes, and that can still lead to collapsed dark matter halos at very early times. For halos forming prior to $1+z\approx 200$, the cosmic microwave background (CMB) is energetic enough to suppress the formation of molecular hydrogen, hence preventing cooling and fragmentation, as a consequence of which baryons falling into the potential well of the halo may undergo “direct collapse” into a black hole. We show, using a few illustrative models, how this mechanism may account for the abundance of high-redshift black holes inferred from observations by the James Webb Space Telescope while remaining consistent with limits from CMB spectral distortions. Limits on the primordial power spectrum are also derived by requiring that the universe not reionize too early.

We compute the gravitational interaction of two coalescing compact objects at sixth post-Newtonian order in the static limit, employing the diagrammatic approach within the effective field theory framework of general relativity. The calculation requires the evaluation of six-loop Feynman diagrams that are mapped onto two-point integrals with a gauge-theory-like structure, which are computed here for the first time. The resulting seventh-order contribution in Newton’s constant is finite in three space dimensions. This result provides the most technically demanding missing ingredient for the determination of the conservative dynamics of the gravitational two-body system at sixth post-Newtonian order.