By analyzing experimental data on semi-inclusive deep inelastic scattering off longitudinally polarized targets, we extract the transverse momentum dependence of the quark helicity distribution, i.e., the difference between the three-dimensional motion of quarks with polarization parallel or antiparallel to the longitudinal polarization of the parent hadron. We perform the analysis at next-to-leading and next-to-next-to-leading perturbative accuracy. The quality of the fit is very good for both cases, reaching a ${\chi }^2$ per number of data points equal to 1.11 and 1.09, respectively. Although the limited number of data points leads to significant uncertainties, the data are consistent with an interpretation in which the helicity distribution is narrower in transverse momentum than the unpolarized distribution.

We report on the first global analysis of transverse-momentum dependent helicity distributions of the proton. The analysis is performed at next-to-leading order with the evolution factor at next-to-next-to-leading-logarithmic accuracy. Nonzero signals are determined for up and down quarks, and their $k_T$-integrated polarization is consistent with analyses in collinear factorization, while the distributions of other flavors are loosely constrained by existing data. With increasing transverse momentum, quarks at large $x$ become less polarized while those at small $x$ become more polarized.

Photonic microring resonators are used in a variety of chip-integrated sensing applications where they allow one to measure transmission intensity changes upon external signals with a sensitivity that scales linearly with the $Q$ factor. In this work, we suggest exploiting the nonlinear self-phase-modulation effect to increase the overall sensitivity by an additional gain factor appearing when the operational point of the nonlinear resonator is chosen just at the crossover from the monostable to the bistable regime. We present the theoretical idea together with a first proof of concept experiment displaying a gain factor of 22 on a chip-integrated silicon-nitride resonator.

Recent studies of ${\mathrm{La}}_3{\text{Ni}}_2{\mathrm{O}}_7$ have identified a bilayer (2222) structure and an unexpected alternating monolayer-trilayer (1313) structure, both of which feature signatures of superconductivity near 80 K under high pressures. Using angle-resolved photoemission spectroscopy, we measure the electronic structure of 1313 samples. In contrast to the previously studied 2222 structure, we find that the 1313 structure hosts a flat band with a markedly different binding energy, as well as an additional electron pocket and band splittings. By comparison to local-density approximation calculations, we find renormalizations of the $\mathrm{Ni}\text{−}{d}_{z^2}$ and $\mathrm{Ni}\text{−}{d}_{x^2-y^2}$ derived bands to be about 5 to 7 and about 4, respectively, suggesting strong correlation effects. These results reveal important differences in the electronic structure brought about by the distinct structural motifs with the same stoichiometry. Such differences may be relevant to the putative high temperature superconductivity.

Disordering of solids often leads to amorphization, but polymorph transitions, facilitated by favorable atomic rearrangements, may temporarily help to maintain long-range periodicity in the solid state. In far-from-equilibrium situations, such as atomic collision cascades, these rearrangements may not necessarily follow a thermodynamically gainful path, but may be kinetically limited. In this Letter, we focus on such crystallization instead of amorphization in collision cascades in gallium oxide (${\text{Ga}}_2{\mathrm{O}}_3$). We determine the disorder threshold for irreversible $\beta \to \gamma$ polymorph transition and explained why it results in elevating energy to that of the $\gamma$ polymorph, which exhibits the highest polymorph energy in the system below the amorphous state. Specifically, we demonstrate that upon reaching the disorder transition threshold, the Ga sublattice kinetically favors transitioning to the $\gamma$-like configuration, requiring significantly less migration for Ga atoms to reach the lattice sites during postcascade processes. As such, our data provide a consistent explanation of this remarkable phenomenon and can serve as a toolbox for predictive multipolymorph fabrication.

We study quasiparticle interference (QPI) in the Kitaev quantum spin liquid (QSL) for electrons tunneling into the QSL. The local tunneling conductance around a spin vacancy or localized vison reveals unique features associated with fractionalized Majorana fermions, chargons, and visons. In certain parameter regimes, the single-spinon density of states and momentum dispersion can both be directly extracted from the tunneling conductance. Our results suggest that QPI is a promising tool for identifying the Kitaev QSL and its fractionalized excitations.

The algorithmic preparation of ultrastable glasses (UG) has considerably expanded our understanding of the glassy state. In this work, we report on a new protocol for UG preparation in a model colloidal glass that iteratively modifies particle diameters to reduce local virial stress fluctuations, effectively homogenizing the local mechanical environment of individual particles. We apply the algorithm to an additive Lennard-Jones mixture and show that, compared to the states obtained via thermal annealing, virial homogenized glasses are characterized by a considerable increase in both kinetic stability and the number of locally favored structures, and melt during heating ramps via an accumulation of localized events. Our results show that microscopic mechanical homogeneity, a widely applicable concept, can give rise to ultrastability.

Adding swimming bacteria to a liquid causes its effective shear viscosity to decrease, eventually reaching a regime of zero viscosity. We examined whether this property leads to viscous fingerlike displacement fronts like those observed when a less viscous fluid displaces a more viscous liquid. Our study revealed that this system exhibits more complex dynamic characteristics than the classical Saffman-Taylor instability. We discovered that this instability occurs when the bacterial volume fraction exceeds a critical value and the imposed shear rate is below critical value, for which the viscosity of the suspension is zero.

We investigate decays of hypothetical unstable new physics particles into metastable species such as muons, pions, or kaons in the early Universe, when temperatures are in the MeV range, and study how they affect cosmic neutrinos. We demonstrate that the nontrivial dynamics of metastables in the plasma alters the impact of the new physics particles on the neutrino population, including the effective number of neutrino degrees of freedom, $N_{\mathrm{eff}}$, modifies neutrino spectral distortions, and may induce asymmetries in neutrino and antineutrino energy distributions. These modifications have important implications for observables such as big bang nucleosynthesis and the cosmic microwave background, especially in light of upcoming cosmic microwave background observations aiming to reach percent-level precision on $N_{\mathrm{eff}}$. We illustrate our findings with a few examples of new physics particles and provide a computational tool available for further exploration.

The nonlinear interaction of a microresonator pumped by a laser has revealed complex dynamics, including soliton formation and chaos. Initial studies of coupled-resonator systems reveal even more complicated dynamics that can lead to deterministic mode locking and efficient comb generation. Here, we perform theoretical analysis and experiments that provide insight into the dynamical behavior of coupled-resonator systems operating in the normal group-velocity-dispersion regime. Our stability analysis and simulations reveal that the strong mode-coupling regime, which gives rise to spectrally broad comb states, can lead to an instability mechanism in the auxiliary resonator that destabilizes the comb state and prevents mode locking. We find that this instability can be suppressed by introducing loss in the auxiliary resonator. We investigate the stability of both single- and multipulse solutions and verify our theoretical predictions by performing experiments in a silicon-nitride platform. Our results provide an understanding for accessing broad, efficient, relatively flat high-power mode-locked combs for numerous applications in spectroscopy, time-frequency metrology, and data communications.

We report the results of a QCD axion dark matter search with discovery ability for Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) axions using an axion haloscope. Sub-Kelvin noise temperatures are reached with an ultralow noise Josephson parametric amplifier cooled by a dilution refrigerator. This work excludes (with a 90% confidence level) DFSZ axions with masses between 3.27 to $3.34\mathrm{\mu }\mathrm{eV}$, assuming a standard halo model with a local energy density of $0.45\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}{\mathrm{cm}}^3$ made up 100% of axions.

Ultralight dark matter induces time-dependent perturbations in the spacetime metric, enabling its gravitational direct detection. In this Letter, we propose using astrometry to detect dark matter. After reviewing the calculation of the metric in the presence of scalar dark matter, we study the influence of the perturbations on the apparent motion of astrophysical bodies. We apply our results to angular position measurements of quasars, whose vast distances from Earth present an opportunity to discover subcomponent dark matter with a mass as low as ${10}^{-33}\mathrm{eV}$. We explore the prospects of very long baseline interferometry and optical astrometric survey measurements for detecting ultralight relics, finding that for the smallest masses, current astrometric surveys can detect dark matter moving locally with a velocity of ${10}^{-3}$ with energy density as low as $3\times {10}^{-11}\mathrm{GeV}/{\mathrm{cm}}^3$.

We investigate semiclassical dynamics of a coupled atom-photon interacting system described by a dimer of anisotropic Dicke model in the presence of photon loss, exhibiting a rich variety of nonlinear dynamics. Based on symmetries and dynamical classification, we characterize and chart out various dynamical phases in a phase diagram. A key feature of this system is the multistability of different dynamical states, particularly the coexistence of various superradiant phases as well as limit cycles. Remarkably, this dimer system manifests self-trapping phenomena, resulting in a photon population imbalance between the cavities. Such a self-trapped state arises from a saddle-node bifurcation, which can be understood from an equivalent Landau-Ginzburg description. Additionally, we identify a unique class of oscillatory dynamics, “self-trapped limit cycle,” hosting self-trapping of photons. The absence of stable dynamical phases leads to the onset of chaos, which is diagnosed using the saturation value of the decorrelator dynamics. Moreover, the self-trapped states can coexist with chaotic attractor, which may have intriguing consequences in quantum dynamics. Finally, we discuss the experimental relevance of our findings, which can be tested in cavity and circuit quantum electrodynamics setups.

We report on the experimental demonstration of cross-polarization backward stimulated Brillouin scattering (BSBS) in lithium niobate on insulator (LNOI) waveguides. Performing polarization-sensitive pump and probe measurements, we captured both intra- and intermodal scattering between counterpropagating fundamental optical modes. Remarkably, cross-polarization scattering achieved SBS gains that exceeded $G_B=80{\mathrm{m}}^{-1}{\mathrm{W}}^{-1}$. This substantial gain not only broadens the utility of polarization in SBS but also paves the way for high-performance devices, including ultranarrowband lasers, robust broadband nonreciprocal devices, RF filters, and microwave-to-optical converters.

Cooperative optical effects are enabled and controlled by interactions between molecular dipoles, meaning that their mutual orientation is of paramount importance to, for example, superabsorbing light-harvesting antennas. Here we show how to move beyond the possibilities of simple geometric tailoring, demonstrating how a metallic sphere placed within a ring of parallel dipoles engineers an effective Hamiltonian that generates “guide-sliding” states within the ring system. This allows steady-state superabsorption in noisy room temperature environments, outperforming previous designs while being significantly simpler to implement. As exemplified by this showcase, our approach represents a powerful design paradigm for tailoring cooperative light-matter effects in molecular structures that extends beyond superabsorbing systems to a huge array of quantum energy transport systems.