The effective electron neutrino mass can be determined by analyzing the end-point region of the ${}^{163}\mathrm{Ho}$ electron capture spectrum, provided a measurement with high-energy resolution and high statistics using calorimetric techniques. Here, the Electron Capture in ${}^{163}\mathrm{Ho}$ Collaboration (ECHo) presents an analysis of the most precise ${}^{163}\mathrm{Ho}$ spectrum currently available, obtained with the ECHo-1k experiment and comprising about 200 million events. A very low background rate of $b_{\text{const}}=9.1(1.3)\times {10}^{-6}$ eV/pixel/day was achieved allowing for a reliable analysis of the end-point region. The derived end-point energy $Q=2862(4)\mathrm{eV}$ is in excellent agreement with the one independently determined via Penning-trap mass spectrometry of $Q=2863.2(6)\mathrm{eV}$ [Ch. Schweiger et al., Nat. Phys. 226, 921 (2024)]. The upper limit of the effective electron neutrino mass is improved by almost a factor of 2 compared to the lowest current value [B. K. Alpert et al., Phys. Rev. Lett. 135, 141801 (2025)], reaching $m_{{\nu }_{\mathrm{e}}}<15\mathrm{eV}/c^2$ (90% credible interval).

Most of the matter in the Universe is in the form of dark matter, which has evaded detection so far. Ultralight axionlike particles (ALPs) are a class of dark matter candidates that produce measurable signatures in the form of oscillating violations of discrete symmetries in nuclei. We report results from a search for an oscillating parity-odd time-reversal-odd nuclear Schiff moment of ${}^{153}\mathrm{Eu}$ ions in a crystal, which leads to constraints on ALP-gluon coupling strength across a wide band spanning eight decades in ALP mass.

Understanding the dissociation of multiply charged molecules is crucial yet challenging due to complex multibody correlations and nonadiabatic dynamics. Conventional ab initio molecular dynamics simulations commonly struggle to capture excited electronic states and intricate electron-nuclear coupling, particularly in distinguishing sequential and nonsequential dissociation pathways. To address these limitations, we present a combined theoretical and experimental study on the dissociation mechanisms of ${\mathrm{CO}}_2^{3+}$. Our approach employs on-the-fly nonadiabatic molecular dynamics simulations, utilizing Dalitz plots and Newton diagrams to differentiate dissociation channels. The simulations reproduce the key dynamical signatures observed via a COLTRIMS reaction microscope, enabling the state-resolved disentanglement of overlapping spectral features. This Letter provides mechanistic insights into the fragmentation dynamics, refining the interpretation of experimental data and offering an in-depth understanding of nonadiabatic molecular dynamics.

We measure strong field ionization of cesium atoms, observing a robust feature near $2U_{\mathrm{p}}$ in the photoelectron spectrum, which we call the intermediate energy structure (IES). Using a Coulomb-corrected strong-field approximation, we show it arises from electrons born with large inward velocities that rapidly undergo forward scattering off the Coulomb potential. The IES is similar to the previously identified low energy structure in that they are both due to forward scattering. However, it is different in that IES requires both nonadiabatic ionization conditions (as defined by the Keldysh parameter) and a more weakly bound initial state. Our joint experimental and theoretical study supports the need for an additional parameter in characterization of strong field ionization, which depends both on nonadiabaticity of the process and the principal quantum number of the target. Together with Reiss and Keldysh parameters, this dimensionless parameter expands the description of strong field ionization across a broad range of atomic targets and incorporates ionization from excited states.

Optically levitated nanoparticles are promising candidates for the generation of macroscopic quantum states of mechanical motion. Protocols to generate such states expose the particle to a succession of different potentials. Limited reproducibility of the alignment of these potentials across experimental realizations introduces additional noise. Here, we experimentally investigate and model how such shot-to-shot noise limits the coherence length of a levitated nanoparticle during a state-expansion protocol using a dark, inverted electrical potential. We identify electric stray fields and mechanical instabilities as major sources of shot-to-shot fluctuations. We discuss the resulting experimental requirements for state-expansion protocols exploiting inverted potentials.

The negatively charged boron vacancy ($V_{\text{B}}^{-}$) in two-dimensional (2D) hexagonal boron nitride (hBN) has emerged as a promising candidate for quantum sensing. The coherence time of $V_{\text{B}}^{-}$ spins which coherent quantum sensing resides in is limited by spin-phonon interactions, while the underlying physical mechanism of the interactions is still not fully understood. Here, we probe the relaxation rates on $V_{\text{B}}^{-}$ centers’ $|0⟩\leftrightarrow |\pm ⟩$ (single-quantum, SQ) and $|+⟩\leftrightarrow |-⟩$ (double-quantum, DQ) over the temperature range from 198 to 393 K. The results show that both relaxation rates increase with increasing temperature, and the increase of the DQ relaxation rate is much stronger than that of the SQ relaxation rate. At high temperature (above 393 K), our theoretical estimations indicate that the DQ relaxation rate exceeds three times the SQ relaxation rate, implying that the contribution of DQ relaxation surpasses that of SQ relaxation in the decoherence channel of spin-phonon interactions. Moreover, the experimental results are consistent with calculations based on the theoretical model of second-order spin-phonon interactions, which can be further simplified to a form that interacts with three effective phonon modes (23.48, 77.39, and 165.75 meV). Our findings contribute to a further understanding and provide guidance for practical sensing applications.

Recent discoveries in kagome materials have unveiled their capacity to harbor exotic quantum states, including intriguing charge density wave (CDW) and superconductivity. Notably, accumulating experimental evidence suggests time-reversal symmetry breaking within the CDW, hinting at the long-pursued loop current order (LCO). Despite extensive research efforts, achieving its model realization and understanding the mechanism through unbiased many-body simulations have remained both elusive and challenging. In this Letter, we develop a microscopic model for LCO on the spinless kagome lattice with nonlocal interactions, utilizing unbiased functional renormalization group calculations to explore ordering tendencies across all two-particle scattering channels. At the Van Hove filling, we identify sublattice interference to suppress onsite CDW order, leaving LCO, charge bond order, and nematic CDW state as the main competitors. Remarkably, a $2\times 2$ LCO emerges as the many-body ground state over a significant parameter space with strong second nearest-neighbor repulsion, stemming from the unique interplay between sublattice characters and lattice geometry. The resulting electronic model with LCO bears similarities to the Haldane model and culminates in a quantum anomalous Hall state. We also discuss potential experimental implications for kagome metals.

We report the emergence of an anomalous Hall response induced by smectic vortex order in a layered superconductor. By tuning the in-plane magnetic field and temperature, we uncover a distinct transport regime in which the longitudinal resistance remains low, whereas the transverse resistance becomes finite and even exceeds it—a definitive hallmark of unconventional vortex dynamics. This behavior arises from Magnus-force-driven motion of smectic dislocation vortices generated via interlayer smectic kink excitations, directed along the applied current within a smectic vortex liquid crystal phase, where partial translational symmetry breaking enables anisotropic and coherent vortex flow. These results establish smectic vortex matter as a new class of quantum vortex phases with hydrodynamic and topological character. Our findings open pathways to controlling topological vortex transport in anisotropic superconductors and suggest that the intrinsic entanglement of smectic vortex arrays may provide a platform for vortex-based quantum information functionalities.

Ferroelectric materials embedded with dielectric inclusions offer a unique platform for exploring novel topological polar textures. Using first-principles-based atomistic simulations, we investigate the polarization behavior of a ${\mathrm{BaTiO}}_3$ matrix containing segregated ${\mathrm{BaZrO}}_3$ nanoregions. We demonstrate that the polar texture in three-dimensionally ordered arrays of dielectric inclusions is governed by their size and spacing, revealing three distinct regimes. At large separations, the nanocomposite exhibits bulklike ${\mathrm{BaTiO}}_3$ phase transitions, while at smaller spacings, interconnected swirling polarization patterns give rise to vortex supercrystal states. We analyze the stabilization mechanisms of these states and show that each regime is characterized by distinct switching behavior. Furthermore, we find that nanocomposites with randomly distributed dielectric inclusions exhibit swirling polarization textures, giving rise to an amorphous network of entangled vortices. Our findings provide new insights into the physics of relaxor ferroelectrics, are consistent with recent experimental observations, and open up new possibilities for designing materials with emergent topological functionalities.

Here, we elucidate the role of collective vibrational dynamics in governing the ionic transport in solids. It is demonstrated that ionic transport is mediated through a synergistic interplay between unstable and stable vibrational modes. Unstable vibrational modes directly initiate the hopping of ions by displacing ions from their equilibrium sites. Stable vibrational modes, in parallel, facilitate ion diffusion indirectly by amplifying the separation of local ionic pairs through coordinated collective rearrangements. The interaction between unstable and stable vibrational modes collectively results in a high ionic diffusivity in solids. The “vibration-ion” interaction is further designed via defect engineering. Our results show that the population of unstable vibrational modes is increased by tailoring the vibrational spectrum using intrinsic ionic vacancies. This concurrently strengthens the direct ionic translation and the coupling between unstable and stable vibrational modes. As a result, the ionic diffusivity of the example system ${\mathrm{Ag}}_2\mathrm{Te}$ increases from $0.84\times {10}^{-5}$ to $1.54\times {10}^{-5}{\mathrm{cm}}^2/\mathrm{s}$ at 500 K when $10\%{\mathrm{Te}}^{2-}$ vacancies are introduced. Our Letter establishes a physical picture to bridge the microscopic vibrational dynamics to macroscopic diffusion properties.

We present a dynamical mean-field study of nonperturbative electronic mechanisms, which may lead to significant enhancements of the electron-phonon coupling in correlated electron systems. Analyzing the effects of electronic correlations on the lowest-order electron-phonon processes, we show that in the proximity of the Mott metal-to-insulator transition of the doped square lattice Hubbard model, where the isothermal charge response becomes particularly large at small momenta, the coupling of electrons to the lattice is strongly increased. This, in turn, induces significant corrections to both the electronic self-energy and phonon-mediated pairing interaction, indicating the possible onset of a strong interplay between lattice and electronic degrees of freedom even for small values of the bare electron-phonon coupling.

Metals at the brink of electronic quantum phase transitions display high-temperature superconductivity, competing orders, and unconventional charge transport, revealing strong departures from conventional Fermi liquid behavior. Investigation of these fascinating intertwined phenomena has been at the center of research across a variety of correlated materials over the past many decades. A ubiquitous experimental observation is the emergence of a universal timescale that governs electrical transport and momentum relaxation. In this Letter, we analyze an equally important theoretical question of how the energy contained in the electronic degrees of freedom near a quantum phase transition relaxes to the environment via their coupling to acoustic phonons. Assuming that the bottleneck for energy dissipation is controlled by the coupling between electronic degrees of freedom and acoustic phonons, we present a universal theory of the temperature dependence of the energy relaxation rate in a marginal Fermi liquid. We find that the energy relaxation rate exhibits a complex set of temperature-dependent crossovers controlled by emergent energy scales in the problem. We place these results in the context of recent measurements of the energy relaxation rate via nonlinear optical spectroscopy in the normal state of hole-doped cuprates.

We theoretically demonstrate the first photonic spin-meron tube lattice in free space using spin-angular momentum vectors. Square-block diffraction creates $C_4$-symmetric beams with $\pi /2$ phase steps. Nonparaxial spin-orbit coupling then forms finite-length meron tubes ($N_{sk}\approx \pm 1/2$), whose length is dependent on diffractive element dimensions. Extending the geometry driven formalism, we show that $C_3$ geometry of triangular block yields spin-skyrmion tubes while effective moiré bilayer results in spin twistronics in free space without the need of strong near-field confinement. Stratton-Chu theory and full-vectorial finite-difference time-domain calculations both support this material-agnostic geometric driven approach as a platform to explore the symmetry-driven free-space topology.

The search for photocathode materials with low mean transverse energies (MTEs) and, hence, low intrinsic emittance is of crucial importance for various fields of particle and solid-state physics. Here, we demonstrate that polycrystalline multialkali ${\mathrm{Na}}_2\mathrm{KSb}(\mathrm{Cs},\mathrm{Sb})$ photocathodes with negative effective electron affinity (NEA) have MTE values at room temperature by a factor of 2 lower than those of monocrystalline $p$-GaAs(Cs,O) photocathodes. These low MTE values are due to the electron refraction on the jump in mass between a small effective mass in ${\mathrm{Na}}_2\mathrm{KSb}$ and free electron mass in vacuum. It is proved that, at the NEA state, up to half of photoelectrons are emitted in a narrow-angle cone with the fractional MTE of $(9\pm 1)\mathrm{meV}$ at room temperature. We also showed that the transition from NEA to positive effective affinity results in the subthermal total MTE of the ${\mathrm{Na}}_2\mathrm{KSb}(\mathrm{Cs},\mathrm{Sb})$ photocathode, along with quantum efficiency of about ${10}^{-2}$. The physical reasons for the manifestation of the refraction effect in multialkali photocathodes are discussed, opening up opportunities for the development of high-brightness and ultracold robust electron sources.

Quantum steering, measurement incompatibility, and instrument incompatibility have recently been recognized as unified manifestations of quantum incompatibility. Building on this perspective, we develop a general framework for constructing optimization-free, nonlinear incompatibility witnesses based on convex functionals, valid in arbitrary dimensions. We prove that these witnesses are nontrivial precisely when the underlying functional is nonaffine on extremal points (e.g., pure states for ensembles). For pure bipartite states, the witnesses yield lower bounds on entanglement measures, thereby outperforming most linear steering inequalities in the pure-state regime. Moreover, the construction extends in full generality to certify measurement and instrument incompatibility, where the witnesses act as genuine incompatibility monotones. We demonstrate the versatility of our approach with two operationally relevant functionals: the Wigner-Yanase skew information and an ${\ell }_2$-type coherence functional.

We show that chaos-assisted tunneling (CAT) imposes an intrinsic limit to the protection of Kerr-cat qubits. In the static effective description, tunneling between the quasidegenerate cat states can be exponentially suppressed, ensuring long lifetimes. However, our Floquet analysis reveals that when the nonlinearities increase, chaotic states mediate tunneling between the cat states, producing large quasienergy splittings. We compute tunneling rates using both full quantum simulations and semiclassical WKB theory, finding quantitative agreement and confirming that the splittings are directly linked to chaos. These results provide the first evidence of CAT in the Kerr-cat qubit and demonstrate that chaos sets a fundamental bound on the coherence of dynamically protected superconducting qubits.

Magic state distillation and injection is a promising strategy toward universal fault tolerant quantum computation, especially in architectures based on the bosonic Gottesman-Kitaev-Preskill (GKP) grid codes where non-Clifford gates remain challenging to implement. Here we address GKP magic state preparation by studying a non-Gaussian unitary mediated by a self-Kerr nonlinearity which realizes a logical gate ${\sqrt{H}}_L$ for square grid GKP codes. This gate does not directly involve an auxiliary qubit and is compatible with finite energy constraints on the code. Fidelity can be further enhanced using the small-Big-small error correction protocol and postselection, making the scheme robust against a single photon loss event. We finally propose a circuit QED implementation to operate the self-Kerr nonlinearity.

We present the first computation of the nonlinear gravitational memory waveform for the scattering of two compact objects in general relativity at leading order in the post-Minkowskian expansion. We use the scattering-amplitude-based representation of the gravitational waveform, which naturally expresses the nonlinear memory as the contribution of soft gravitons emitted by the gravitational waves themselves. We perform the calculation by applying a multipolar decomposition to the waveform and using the reverse unitarity method to obtain explicit exact-in-velocity predictions. We validate the results by calculating the corresponding velocity-expanded post-Newtonian multipoles, finding perfect agreement. Our results complete the knowledge of the gauge-invariant nonanalytic-in-frequency part of the $\mathcal{O}(G^3)$ multipolar waveform, thus providing a useful benchmark for future calculations of this quantity.