We revisit the decay rate of the electroweak vacuum in the standard model with the full one-loop prefactor. We focus on the gauge degrees of freedom and derive the degeneracy factors appearing in the functional determinant using group theoretical arguments. Our treatment shows that the transverse modes were previously overcounted, so we revise the calculation of that part of the prefactor. The new result modifies the gauge fields’ contribution by 6% and slightly decreases the previously predicted lifetime of the electroweak vacuum, which remains much longer than the age of the Universe. Our discussion of the transverse mode degeneracy applies to any calculation of functional determinants involving gauge fields in four dimensions.

We report measurements of time-dependent $CP$ asymmetries in $B^0\to K_S^0{\pi }^0\gamma$ decays based on a data sample of $(388\pm 6)\times {10}^{6}B\overline{B}$ events collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle II detector. The Belle II experiment operates at the SuperKEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We measure decay-time distributions to determine $CP$ -violating parameters $S$ and $C$. We determine these parameters for two ranges of $K_S^0{\pi }^0$ invariant mass: $m(K_S^0{\pi }^0)\in (0.8,1.0)\mathrm{GeV}/c^2$, which is dominated by $B^0\to K^{*0}(\to K_S^0{\pi }^0)\gamma$ decays, and a complementary region $m(K_S^0{\pi }^0)\in (0.6,0.8)\cup (1.0,1.8)\mathrm{GeV}/c^2$. Our results have improved precision as compared to previous measurements and are consistent with theory predictions.

One of the main goals of studying semileptonic decays in flavor physics is to gain a better understanding of hadronic transitions in the nonperturbative region of Quantum Chromodynamics. This involves measuring Cabibbo-Kobayashi-Maskawa matrix elements, understanding form factors, and comparing them with theoretical predictions. We report a first study of the semileptonic decay $D^0\to K^{-}{\pi }^0{\mu }^{+}{\nu }_{\mu }$ by analyzing an $e^{+}{e}^{-}$ annihilation data sample of $7.93{\mathrm{fb}}^{-1}$ collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The absolute branching fraction of $D^0\to K^{-}{\pi }^0{\mu }^{+}{\nu }_{\mu }$ is measured for the first time, providing necessary input for extracting the $c\to s$ Cabibbo-Kobayashi-Maskawa matrix element through this process. This measurement allows us to test lepton flavor universality, with no indication of violation found. Furthermore, a series of hadronic form factors have been determined and compared with theoretical predictions, which will impose stricter constraints on theoretical models.

We report the first ab initio calculation of the nuclear-structure-dependent radiative correction ${\delta }_{\mathrm{NS}}$ to the ${}^{10}\mathrm{C}\to {}^{10}\mathrm{B}$ superallowed transition, computed with the no-core shell model and chiral effective field theory. We obtain ${\delta }_{\mathrm{NS}}=-0.422(29{)}_{\mathrm{nuc}}(12{)}_{n,\mathrm{el}}$ with a 1.6-times reduction in the total uncertainty when compared to the current literature estimate based on the shell model and Fermi gas picture. This Letter paves the way for a precise determination of $V_{ud}$ from superallowed beta decays within a systematically improvable framework.

Ultracold atoms are crucial for unlocking truly precise and accurate quantum metrology and provide an essential platform for quantum computing, communication, and memories. One of the largest ongoing challenges is the miniaturization of these quantum devices. Here, we show that the typically macroscopic optical lattice architecture at the heart of many ultraprecise quantum technologies can be realized with a single-input laser beam on the same diffractive chip already used to create the ultracold atoms. Moreover, this inherently ultrastable platform enables access to a plethora of new lattice dimensionalities and geometries, ideally suited for the design of high-accuracy, portable quantum devices.

The honeycomb supersolid state is predicted to form in a dipolar Bose-Einstein condensate with a planar confining potential. Our results for its excitation spectrum reveal the gapless bands and the emergence of Dirac points at the Brillouin zone edge, manifesting as points where the second sound and transverse sound bands touch. The honeycomb supersolid has three sound speeds that we connect to its elastic parameters through hydrodynamic theory. From this analysis we find conditions where a shear instability occurs as the honeycomb rigidity disappears. This gives insight into the nonequilibrium dynamics following an interaction quench, where the honeycomb pattern melts and different crystal orders emerge.

The concept of nuclear spin temperature has been a cornerstone of the theory of dynamic nuclear spin polarization by electrons in various semiconductor structures for decades. Still, it is not always applicable to strongly localized electrons due to their long spin correlation times. This motivated the use of the oversimplified central spin model for the description of the nuclear spin dynamics in quantum dots. Here, we present a microscopic theory that bridges the gap between these two approaches by describing the nuclear spin thermodynamics for systems with long electron spin correlation times. Importantly, our theory predicts that efficient nuclear spin cooling by strongly localized electrons requires an external magnetic field by far exceeding the local field of nuclear spin-spin interaction, and that the time of the nuclear spin heating by unpolarized electrons may change by several orders of magnitude depending on the magnetic field.

We investigated photon-helicity–induced magnetization precession in ${\mathrm{Co}}_{1-x}{\mathrm{Pt}}_x$ alloy thin films. In addition to field-like torque, attributable to magnetic field generation owing to the “inverse Faraday effect,” we observed nontrivial and large damping-like torque that has never been discussed for single ferromagnetic layer. The composition dependence of these two torques is effectively elucidated by a model that considers mutual coupling via spin-orbit interaction between magnetization and the electronic orbital angular momentum generated by photon helicity. This Letter significantly enhances our understanding of the physics relevant to the interplay of photon helicity and magnetization in magnetic metals.

Ferromagnetic insulators are receiving ever-increasing research activities driven not only by the unique advantage of low power loss during spin-wave-based information processing but also by the potential to construct next-generation spintronic devices. However, either the exceedingly rare candidates or the low Curie temperature far below room temperature greatly hinder their practical application. Here, through the modulation of a novel three-dimensional (3D) tensile strain, a room-temperature ferromagnetic insulating state with a Curie temperature as high as 594 K is achieved in self-assembled ${\mathrm{LaCoO}}_3:\mathrm{MgO}$ nanocomposite thin films. Atomically resolved electron microscopy quantifications identify the 3D strain state of the thin film, where the $+2.6\%$ out-of-plane and $+2.1\%$ in-plane tensile strains are attributed to the interphase mismatch between the ${\mathrm{LaCoO}}_3$ and MgO building blocks and epitaxial constraint, respectively. Combined with the assessment of electronic states and theoretical analysis, we correlate the strain state with the resulting ferromagnetic insulating property and clarify the underlying mechanisms, by which the emergent strain states break the degeneracy of crystal-field splitting and tailor the on-site Coulomb interactions and spin configuration. These findings underscore the efficacy of a three-dimensional strain strategy in engineering the long-desired high-temperature ferromagnetic insulators via the manipulation of strong spin-lattice coupling, providing a promising approach for the exploitation of exotic functionalities in correlated oxides.

Magnons—carriers of spin information—can be controlled by electric fields in the multiferroic ${\mathrm{BiFeO}}_3$ (BFO), a milestone that brings magnons closer to application in future devices. The origin of magnon-spin currents in BFO, however, is not fully understood due to BFO’s complicated magnetic texture. In this Letter, we present a phenomenological model to elucidate the existence of magnon spin currents in generalized multiferroics by examining the symmetries inherent to their magnetic and polar structures. This model is grounded in experimental data obtained from BFO and its derivatives, which informs the symmetry operations and resultant magnon behavior. By doing so, we address the issue of symmetry-allowed, switchable magnon spin transport in multiferroics, thereby establishing a critical framework for comprehending magnon transport within complex magnetic textures.

Polarized x-rays allow for imaging birefringent or dichroic properties of materials with nanometric resolution. To disentangle these properties from the electronic density, either a polarization analyzer or several measurements with different polarizations (typically two or more) are needed. Here we demonstrate that ptychography can disentangle these from a single polarization measurement by using a multimodal analysis. This new method provides an alternative to obtain polarization-resolved images of a sample when manipulating the incident polarization is not possible or sufficient.

Van der Waals magnets are an emerging material family for investigating light-matter interactions and spin-correlated excitations. Here, we report the discovery of a photo-induced state with a lifetime of 17 ps in the van der Waals antiferromagnet ${\mathrm{NiPS}}_3$, which appears exclusively with resonant pumping at 1.476 eV in the antiferromagnetic state. The long-lived state comes with a negative photoconductivity, a characteristic optical response of population inversion. Our findings demonstrate a promising pathway to potentially achieve long-lived lasing at terahertz frequencies in reduced dimensions.

We present a protocol for detecting multipartite entanglement in itinerant many-body electronic systems using single-particle Green’s functions. To achieve this, we first establish a connection between the quantum Fisher information and single-particle Green’s functions by constructing a set of witness operators built out of single electron creation and destruction operators in a doubled system. This set of witness operators is indexed by a momentum $k$. We compute the quantum Fisher information for these witness operators and show that for thermal ensembles it can be expressed as an autoconvolution of the single-particle spectral function. We then apply our framework to a one-dimensional fermionic system to showcase its effectiveness in detecting entanglement in itinerant electron models. We observe that the detected entanglement level is sensitive to the wave vector associated with witness operator. Our protocol will permit detecting entanglement in many-body systems using scanning tunneling microscopy and angle-resolved photoemission spectroscopy, two spectroscopies that measure the single-particle Green’s function. It offers the prospect of the experimental detection of entanglement through spectroscopies beyond the established route of measuring the dynamical spin response.

We introduce an effective field theory (EFT) for conformal impurity by considering a pair of transversely displaced impurities and integrating out modes with mass inversely proportional to the separation distance. This EFT captures the universal signature of the impurity seen by a heavy local operator. We focus on the case of conformal boundaries and derive universal formulas from this EFT for the boundary structure constants at high energy. We point out that the more familiar thermal EFT for conformal field theory is a special case of this EFT with distinguished conformal boundaries. We also derive, for general conformal impurities, nonpositivity and convexitylike constraints on the Casimir energy which determines the leading EFT coefficient.

Embezzlement of entanglement refers to the counterintuitive possibility of extracting entangled quantum states from a reference state of an auxiliary system (the “embezzler”) via local quantum operations while hardly perturbing the latter. We uncover a deep connection between the operational task of embezzling entanglement and the mathematical classification of von Neumann algebras. Our result implies that relativistic quantum fields are universal embezzlers: any entangled state of any dimension can be embezzled from them with arbitrary precision. This provides an operational characterization of the infinite amount of entanglement present in the vacuum state of relativistic quantum field theories.

We present the concept of time-domain bound states in continuum. We show that a rapid judiciously designed temporal modulation of the refractive index in a spatially homogenous medium gives rise to a bound state in time, embedded in a continuum of wave numbers. Mathematically, these bound states in the continuum are closed form solutions of the Maxwell equations in time and one-dimensional space. Our results show the potential to extend known wave phenomena in space to the temporal domain, providing new avenues for light-matter interactions in time-varying media.

Linear colliders rely on high-quality flat beams to achieve the desired event rate while avoiding potentially deleterious beamstrahlung effects. Here, we show that flat beams in plasma accelerators can be subject to quality degradation due to emittance mixing. This effect occurs when the beam particles’ betatron oscillations in a nonlinearly coupled wakefield become resonant in the horizontal and vertical planes. Emittance mixing can lead to a substantial decrease of the luminosity, the main quantity determining the event rate. In some cases, the use of laser drivers or flat particle beam drivers may decrease the fraction of resonant particles and, hence, mitigate emittance deterioration.

The tetragonal heavy-fermion superconductor ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ ($T_{\mathrm{c}}=0.3\mathrm{K}$) exhibits an exceptionally high critical field of 14 T for $\mathbf{B}\parallel \mathbf{c}$. It undergoes a field-driven first-order phase transition between superconducting states, potentially transitioning from spin-singlet to spin-triplet superconductivity. To further understand these superconducting states and the role of magnetism, we probe spin fluctuations in ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ using neutron scattering. We find dynamic $(\pi ,\pi )$ antiferromagnetic (AFM) spin correlations with an anisotropic quasi-two-dimensional correlation volume. Our data place an upper limit of $0.31{\mu }_{\mathrm{B}}$ on the staggered magnetization of corresponding Néel orders at $T=0.08\mathrm{K}$. Density functional theory calculations, treating Ce $4f$ electrons as core states, show that the AFM wave vector connects significant areas of the Fermi surface. Our findings indicate that the dominant excitations in ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ for $\hslash \omega <1.2\mathrm{meV}$ are magnetic and suggest that superconductivity in ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ is mediated by AFM spin fluctuations associated with a proximate quantum critical point.