We propose a multiphoton interference protocol that characterizes the pairwise overlaps of the internal modes of single photons more efficiently than pairwise Hong-Ou-Mandel characterization experiments. We experimentally implement this protocol to characterize three photons. We show that our implementation of the characterization protocol outperforms the pairwise Hong-Ou-Mandel characterization, even if the Hong-Ou-Mandel characterization would have been performed in a noiseless, perfect experiment. We demonstrate this via the Fisher information matrix. Surprisingly, this advantage persists at arbitrary nonzero transmission, demonstrating the viability of this protocol for real-world characterization of single photons.

With the achievement of thermonuclear ignition, there is interest to increase the performance of inertial-confinement-fusion (ICF) systems to reach high fusion yields and high-energy gain for energy-production purposes. One approach to achieve this is magnetic-direct-drive (MDD) ICF, where magnetic fields are used to compress ICF targets to thermonuclear conditions. To study the scaling of MDD ICF to high yields, we performed experiments on the 20-MA, 100-ns Z machine to study the invariant behavior of the magneto-Rayleigh-Taylor instability when changing the magnetic-field drive. Similarity-scaled aluminum cylindrical shells with preseeded axial perturbations were imploded at two different maximum currents: 14.7 and 19.2 MA. Consistent with dynamical similarity within experimental uncertainties, the magneto-Rayleigh-Taylor growth history measured via x-ray radiography exhibits agreement at the 16% level or better for late-time growth factors of 10x to 50x. However, the early instability development is not dynamically similar due to Ohmic-heating effects, which are not conserved by the proposed scaling prescriptions. This Letter exemplifies the application of similarity scaling to rigorously investigate the scaling of MDD ICF to high yields.

Symmetry-protected ideal flat bands in one-dimensional Hermitian lattices are populated by compact localized states—a special class of localization with wave functions confined within a small region. In this Letter, we demonstrate that the non-Hermitian skin effect can appear in a flat band. Unlike conventional non-Hermitian skin effects for dispersive bands that are protected by nontrivial point-gap topology, the flat-band skin effect (FBSE) emerges even though the flat band remains a point on the complex-energy plane with trivial spectral topology. The FBSE is intriguingly associated with the nontrivial spectral topology of the dispersive bands enclosing the flat band, so it only emerges within a finite range of non-Hermitian parameters and can counterintuitively disappear at large non-Hermiticity. We experimentally observe the FBSE and its parameter dependence in a non-Hermitian mechanical lattice. Our theoretical analyses further reveal that the gap between the flat and the dispersive bands can close at higher-order exceptional points under both periodic and open boundary conditions. The flat-band wave functions are discontinuous in quantum distance across these exceptional points, a property only found in singular flat bands in Hermitian systems. Our Letter reveals flat-band phenomena unique to non-Hermitian systems and highlights new possibilities in quantum geometry and localization control.

The topological magnetoelectric effect (TME) in three-dimensional topological insulators (TIs), described by $\mathrm{\Delta }P=(e^2/2h)N_{\text{Ch}}^{(2)}\mathrm{\Delta }B$, serves as a condensed-matter realization of the four-dimensional quantum Hall effect (4D QHE). In dual-gate axion insulator devices, the TME-induced polarization yields a current $I_{\mathrm{TME}}\propto (C_{\text{total}}/C_{\mathrm{S}})Q_{4\mathrm{D}-\mathrm{QHE}}$, where the signal is suppressed by the capacitance ratio $C_{\text{total}}/C_{\mathrm{S}}$. Here we propose an active compensation scheme that introduces a tunable negative capacitance $C_{\mathrm{comp}}\approx -C_{\mathrm{gate}}$ into the gate line, effectively canceling the gate dielectric capacitance and driving $C_{\text{total}}/C_{\mathrm{S}}\to 1$. We validate the method using a quantum anomalous Hall (QAH) device, which shares the same surface-state physics as the axion insulator but permits direct charge measurement via a single gate, recovering over 95% of the quantized charge signal from an initially half-attenuated state. This compensation method provides a robust means of resolving minute TME signals, offering a pathway toward direct measurements of the 4D QHE.

We report mean-field critical behavior in ${\mathrm{Eu}}_2{\text{MnSi}}_2{\mathrm{O}}_7$, a melilite-type ferrimagnet with spin-only ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Mn}}^{2+}$ moments and negligible orbital contributions. Magnetization measurements combined with neutron powder diffraction reveal critical exponents close to the mean-field values, indicating that long-range dipolar interactions govern the asymptotic critical behavior in this insulating ferrimagnet. The refined magnetic structure, described by the magnetic space group $P{2}_1{2}_1^{\prime }{2}^{\prime }$, exhibits a tilted ferrimagnetic configuration driven by the Dzyaloshinskii-Moriya interaction, reflecting the noncentrosymmetric nature of the lattice. These results extend the applicability of mean-field theory to complex insulating magnets and establish ${\mathrm{Eu}}_2{\text{MnSi}}_2{\mathrm{O}}_7$ as a platform for exploring ferrimagnetism and long-range interactions. To our knowledge, this is the first insulating ferrimagnet in which dipolar interactions drive mean-field criticality.

Two ultranarrow absorption peaks around 1.5 eV, which are widely believed to originate from a transition from a spin-orbital entangled triplet to a singlet state, in the two-dimensional van der Waals crystal ${\mathrm{NiPS}}_3$, have attracted considerable attention because of their pronounced spin-dependent character. An interesting question is whether ultrahigh magnetic fields modify an interaction-driven hybridization between those two peaks. In this Letter we perform systematic magneto-optical measurements of ${\mathrm{NiPS}}_3$ in pulsed magnetic fields of up to 178 T and observe a pronounced mutual repulsion between the two sharp exciton peaks accompanied by a redistribution of oscillator strength, while the band edge shows no detectable field-induced shift within our experimental resolution. We construct a minimal two-level interaction model and compare it semiquantitatively with the experimental data. Our results reveal a magnetic-field-tunable exciton-exciton coupling as the dominant high-field response of ${\mathrm{NiPS}}_3$, and clarify this material as a new experimental platform for exploring strongly correlated exciton physics in magnetic van der Waals insulators.

In a finite-time continuous phase transition, topological defects emerge as the system undergoes spontaneous symmetry breaking. The Kibble-Zurek mechanism predicts how the defect density scales with the quench rate. During such processes, dissipation also arises as the system fails to adiabatically follow the control protocol near the critical point. Quantifying and minimizing this dissipation is fundamentally relevant to nonequilibrium thermodynamics and practically important for energy-efficient computing and devices. However, experimentally measuring dissipation, and optimizing control protocols to reduce it, remains almost completely unexplored. In addition, it is an open question to what extent dissipation is correlated with the formation of defects. Here, we directly measure the dissipation generated during the voltage-driven Fréedericksz transition of a liquid crystal with a sensitivity equivalent to a $\sim 10$ nanokelvin temperature rise. We observe Kibble-Zurek scaling of dissipation and its breakdown, both in quantitative agreement with existing theoretical works. We further implement a fully automated in situ optimization approach that discovers more optimal driving protocols, reducing dissipation by a factor of 3 relative to a simple linear protocol.

Time-translation symmetry strongly constrains physical dynamics, yet systematic characterization for continuous-variable systems lags behind its discrete-variable counterpart. We close this gap by providing a rigorous classification of Gaussian quantum operations that are covariant under time translations, termed Gaussian covariant operations. We show that several key results known for discrete-variable covariant operations break down in the Gaussian optical setting: discrepancies arise in physical and thermodynamic implementation, in the extensivity of asymmetry, and in catalytic advantages. Our results provide comprehensive mathematical and operational toolkits for Gaussian covariant operations, including a peculiar pair of asymmetry measures that are completely nonextensive. Our findings also reveal surprising consequences of the interplay among symmetry, Gaussianity, and thermodynamic constraints, suggesting that real-world scenarios with multiple constraints have a rich structure not accessible from examining individual constraints separately.

In cavity quantum electrodynamics (QED), photons leaving the cavity can be irreversibly lost or reused as a power source. This dichotomy is reflected in two different thermodynamic bookkeeping methods of the light field, both corresponding to valid thermodynamic frameworks. In this Letter, we formulate a rigorous semiclassical limit of cavity QED and show that the resulting thermodynamic description may qualitatively differ from that of the fully quantized model. We find that violations of the thermodynamic uncertainty relations are recovered in the semiclassical limit only by one of the two thermodynamic frameworks: the one which treats part of the photon flux as a power source. We illustrate our findings in a three-level system coupled to a driven cavity.

We explore the lowest mass limit that can be placed on the halo mass function in cold dark matter (CDM) using 28 strong gravitational lenses. For this purpose, we study an extreme model in which the halo mass function and mass-concentration relation follow CDM, with a sharp cutoff at some mass scale, $m_{\mathrm{low}}$. Lensing provides a unique window into this quantity as it does not depend on the presence of baryons in dark matter halos and allows for the detection of low mass halos at cosmological distances, both in the lens galaxies and along the line of sight. Our model incorporates the effects of tidal stripping of subhalos, leading to the presence of many subhalos below a given model cutoff scale. We place an upper limit on the low-mass cutoff of the halo mass function of $m_{\mathrm{low}}<{10}^{8.3}{\mathit{M}}_{\odot }$ at 10∶1 odds using a prior for the normalization of the subhalo mass function from the semianalytic model galacticus and $m_{\mathrm{low}}<{10}^{8.2}{\mathit{M}}_{\odot }$ at 10∶1 odds using a prior from $N$-body simulations. These limits are comparable to, or stronger than, existing constraints based on Milky Way satellite galaxies. Based on these results, we forecast more than an order of magnitude improvement with a sample of 200 quadruply imaged quasar lenses. This number represents a small subset of the thousands that are anticipated to be discovered by Rubin, Euclid, and Roman. Furthermore, with this larger sample of lenses we expect to directly constrain the normalization of the subhalo mass function, thereby eliminating a major source of uncertainty in our current measurements.

I present a new indirect search for dark matter (DM) using hydrogen-$\alpha$ ($\mathrm{H}\alpha$) recombination emission. DM annihilation or decay products can ionize neutral gas; subsequent recombination cascades generate $\mathrm{H}\alpha$ photons through the $3\to 2$ transition. In quiet gas-rich dwarf galaxies, the $n=2$ population is negligible, so $\mathrm{H}\alpha$ is effectively unabsorbed and traces the DM-energy injection site. Using the nondetection of extended $\mathrm{H}\alpha$ emission in the Leo T dwarf galaxy with Multi Unit Spectroscopic Explorer observations, I derive the first $\mathrm{H}\alpha$-based limits on DM annihilation and decay, reaching leading sensitivity for parts of the eV–GeV mass range. Existing and upcoming telescopes can further extend this reach, establishing $\mathrm{H}\alpha$ imaging as a powerful DM search strategy.

This Letter reports on the first evidence of inclusive Higgs-boson production at high transverse momentum in the $b\overline{b}$ final state, reconstructed in a single large-radius jet. The results are based on proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider at a center-of-mass energies of 13 and 13.6 TeV, corresponding to a total integrated luminosity of $301{\mathrm{fb}}^{-1}$. The study profits from the large background suppression provided by the use of a new transformer-based algorithm for jet identification and the sharper mass and transverse momentum, $p_{\mathrm{T}}$, resolution from a dedicated regression model. The yield relative to the standard model prediction for Higgs bosons produced at $p_{\mathrm{T}}$ larger than 450 GeV is measured to be $1.53\pm 0.2{7)}_{-0.27}^{+0.33}\pm 0.17$, where the first uncertainty is statistical, the second is experimental systematic, and the third accounts for theory systematic, corresponding to an observed (expected) significance of $3.8\sigma (2.5\sigma )$ relative to the background-only hypothesis. Results are also obtained in three Higgs boson $p_{\mathrm{T}}$ intervals and found to be compatible with standard model predictions, where the first uncertainty is statistical, the second is experimental systematic, and the third accounts for theory systematic.

The onset of nuclear effects in light-ion collisions is studied by measuring the ratio of $D^0$ meson production between NeNe and OO collisions at a center-of-mass energy per nucleon pair of 5.36 TeV recorded by the LHCb detector. The $D^0$ meson yields are measured differentially in transverse momentum ($p_{\mathrm{T}}$) for $0.5<p_{\mathrm{T}}<20\mathrm{GeV}$ in the rapidity ($y$) region $2.0<y<4.5$, and are normalized to the total number of recorded inelastic nucleus-nucleus collisions in each data sample. The resulting production ratio shows evidence of variation as a function of $p_{\mathrm{T}}$, which is inconsistent with predictions based on nuclear modification of nucleon structure alone. This measurement is consistent with the onset of quark-gluon plasma production with increasing nucleus size in high-energy nuclear collisions.

We use heavy-nucleus effective field theory to compute radiative corrections to two-neutrino double-$\beta$ decay ($2\nu \beta \beta$). Our main result is the first derivation of a universal radiative-correction factor for double-weak decays—the analog of the Sirlin function in single-$\beta$ decay—independent of nuclear matrix elements and excitation energies. This “double-weak Sirlin function” depends on the individual electron energies as well as their relative angle and differs significantly from the approximation obtained by summing two single-$\beta$ decay Sirlin functions. In addition, we calculate the nuclear-structure-dependent component of the radiative corrections and find that they can still be neglected at current experimental sensitivities. On the other hand, the double-weak Sirlin function induces distortions of the electron energies and angular spectra that are comparable in size to the leading nuclear-structure correction parametrized by the ratio of nuclear matrix elements, ${\xi }_{31}$. Our results indicate that extractions of nuclear-structure information and tests of the standard model from high-precision $2\nu \beta \beta$ measurements must include double-weak radiative corrections, implying that recent extractions of ${\xi }_{31}$ should be revisited.

We report a strong size dependence in the electronic heat capacity of silicon nanoclusters, tracing its origin to the distinctive electronic structure of surface atoms. By combining ab initio calculations with machine-learned local density of states and exploiting the extensivity of heat capacity, we develop a computational framework that resolves individual atomic contributions to the electronic heat capacity of silicon nanoparticles ranging from 1 to 100 nm. Deviating significantly from bulk behavior, atomic heat capacity increases by up to an order of magnitude for the undercoordinated surface atoms. Our analysis reveals that a surface layer approximately 3–4 Å thick—independent of structural order and cluster size—exhibits a distinct electronic density of states and dominates the electronic heat capacity as the cluster size decreases. The nonlinear temperature dependence is mainly governed by this surface layer. This work bridges the atomic-scale electronic structure with nanoscale thermal phenomena, resolving the microscopic mechanism behind a key thermodynamic property in silicon nanostructures. The future extension to the vibrational contribution and to other materials and surface states remains an open challenge for a comprehensive description of atom-scale thermal properties in nanostructures.

Electrical control of magnetism represents a fundamental route toward next-generation spintronic functionalities. In this Letter, we introduce a universal current-induced spin phenomenon in bilayer systems, termed the layer Edelstein effect (LEE), which serves as the natural counterpart of the layer Hall effect in real space. It is defined by the emergence of layer-resolved spin magnetizations with opposite components on the top and bottom layers, driven by an in-plane charge current and controllable by an external electric field. We establish the general existence of the LEE using a minimal bilayer $\mathit{k}·\mathit{p}$ theory. By combining symmetry analysis with a general bilayer stacking framework, we derive a model-independent symmetry criterion demonstrating that the LEE is generically allowed in a broad class of nonmagnetic bilayer stacking systems. We further show that the LEE admits two universal manifestations: explicit layer-opposite spin magnetization components mandated directly by symmetry, and components become activated upon symmetry reduction by external electric fields. First-principles calculations on stacked bilayer MoSSe, ${\mathrm{MoTe}}_2$, and ${\mathrm{WTe}}_2$ confirm the predicted effect and illustrate their experimental feasibility. Our Letter establishes the LEE as a generic symmetry-governed response of bilayer systems, providing a unified conceptual framework for electrically generating and manipulating layer-resolved spin polarization.