We report a single-ion optical clock based on the $4S_{1/2}\to 3D_{5/2}$ transition of the ${}^{40}{\mathrm{Ca}}^{+}$ ion, operated in a liquid nitrogen cryogenic environment, achieving a total systematic uncertainty of $4.4\times {10}^{-19}$. We employ a refined temperature evaluation scheme to reduce the frequency uncertainty due to blackbody radiation, and 3D sideband cooling to minimize the second-order Doppler shift. We have precisely determined the average Zeeman coefficient of the ${}^{40}{\mathrm{Ca}}^{+}$ clock transition to be $14.345(15)\mathrm{Hz}/{\mathrm{mT}}^2$, thereby significantly reducing the quadratic Zeeman shift uncertainty. Moreover, the cryogenic environment enables the lowest reported heating rate due to ambient electric field noise in trapped-ion optical clocks.

We theoretically propose a scheme to enhance the photon indistinguishability of spectrally mismatched single photons via Floquet-engineered optical frequency combs in cavity quantum electrodynamic systems. By periodically modulating two distinct single-photon states under a modulation frequency which is exactly equal to the spectral mismatch of two cavity modes, a pair of single-photon frequency-comb states is prepared energy-conservatively based on full unitary operations. The two states show high indistinguishability with an ideal $g_{\mathrm{HOM}}^{(2)}(0)$ down to zero due to the superposition of intensity-matched single-photon states coherently distributed across the teeth of the combs.

Exceptional points (EPs), namely non-Hermitian spectral singularities, enable unconventional light-matter interactions, leading to intriguing phenomena, such as chiral mode transfer, state flip, and chiral phase accumulation. Yet considerable previous EP effects in topological photonics based on a standard strategy, i.e., evolution encircling EPs, require fine tuning of multiple parameters. To go beyond this approach for designing unconventional topological devices with more convenient tunabilities, it is essential to study how to control open trajectories by tuning fewer or even a single parameter without encircling EPs. This route remains largely unexplored. Here, we demonstrate $2\pi$ optical phase control with open evolution trajectories by tuning a single geometrical parameter of the structure in a terahertz metasurface featuring a pair of EPs in a complex-frequency space, while only $\pi$ phase control can be achieved with open trajectories in the metasurface with a single EP. We find that such full $2\pi$-phase control without encircling EPs is realized due to the open trajectories passing between the two EPs with identical chirality but opposite topological charges. Furthermore, we demonstrate topological spin-selective beam deflection and realize dynamical control of EP positions in the complex-frequency space by tuning the angle of split-ring resonators. Our Letter drives the field of EP topological photonics into a broader regime with open trajectory approaches, opening up perspectives for achieving unconventional photonic devices that are more controllable with exciting applications, such as novel wavefront control and polarization multiplexing.

We introduce a fiber-based method to directly measure turbulent energy dissipation. Combining original measurements of the full-body rotation—tumbling and spinning—of short, Kolmogorov-scale fibers in turbulent channel flow with direct numerical simulations using a point-fiber model, we show that the mean-square angular velocity closely reproduces the mean dissipation rate. The method is accurate both in the nearly homogeneous turbulence of the channel center and in the logarithmic layer, with a mean deviation below 6%, demonstrating that Kolmogorov-scale fibers provide a robust and reliable tool for quantifying dissipation.

The air-water and graphene-water interfaces represent quintessential examples of the liquid-gas and liquid-solid boundaries, respectively. While the sum-frequency generation (SFG) spectra of these interfaces show similarities, a consensus on their signals and interpretations has yet to be reached. Leveraging deep learning, we computed first-principles SFG spectra for both systems, addressing experimental discrepancies. Our findings reveal that similarities in SFG signals do not translate into comparable interfacial microscopic properties. Instead, graphene-water and air-water interfaces exhibit fundamental differences in SFG-active thicknesses, hydrogen-bonding networks, and surface dynamics. These distinctions underscore roughness suppression and electronic interactions present at the solid-liquid interface but absent at the gas-liquid interface.

Transverse electron transport in magnetic materials such as the anomalous Hall and Nernst effects holds promise for spintronic and thermoelectric applications. Efforts to enhance transverse transport have focused on finding quantum materials with large Berry curvature, skew scattering, or side jump. Here, we report a distinct approach based on composite formation. Using both theoretical modeling and experiments, we show that disordered composites of two ferromagnetic materials can exhibit significantly stronger transverse transport than constituent materials. This enhancement originates from meandering electron pathways created by the disordered composites. We identify the condition for this enhancement, which can be broadly satisfied across diverse material systems, offering a universal and tunable strategy to engineer large transverse responses.

The Christoffel symbol is an essential quantity in Einstein’s general theory of relativity. We discover that an electric field can induce a nonlinear magnetization in quantum materials, described by a Christoffel symbol defined in the Hilbert space of quantum states (quantum Christoffel symbol). Quite different from the previous scenarios, this orbital magnetization does not need spin-orbit coupling and inversion symmetry breaking. Through symmetry analysis and first-principles calculations, we identify a number of point groups and 2D material candidates (e.g., ${\mathrm{BiF}}_3$, ${\mathrm{ZnI}}_2$, and ${\mathrm{Ru}}_4{\mathrm{Se}}_5$) that host this quantum Christoffel nonlinear magnetization. More importantly, this nonlinear magnetization allows the quantum Christoffel symbol to be probed by optical techniques such as magneto-optical Kerr spectroscopy or transport measurements such as tunneling magnetoresistance. This quantum Christoffel nonlinear magnetization gives a paradigm of how geometry dictates physics.

It is now known that in addition to electrons, other quasiparticles such as phonons and magnons can also generate a thermal Hall signal. Graphite is a semimetal with extremely mobile charge carriers of both signs and a large lattice thermal conductivity. We present a study of the thermal Hall effect in highly oriented pyrolytic graphite (HOPG) samples with electronic, phononic, and phonon drag contributions to the thermal Hall signal. The measured thermal Hall conductivity (${\kappa }_{xy}$) is 2 orders of magnitude higher than what is expected by electronic carriers according to the electrical Hall conductivity and the Wiedemann-Franz law, yielding a record Hall Lorenz number of $164.9\times {10}^{-8}{\mathrm{V}}^2{\mathrm{K}}^{-2}$ ($\sim 67L_0$)—the largest ever observed in a metal. The temperature dependence of the thermal Hall conductivity significantly differs from its longitudinal counterpart, ruling out a purely phononic origin of the nonelectronic component. Based on the temperature dependence and the amplitudes of the Seebeck and Nernst responses, we demonstrate that ambipolar phonon drag dominates the thermal Hall response of graphite.

The discovery of fractional charge excitations in new platforms offers crucial insights into strongly correlated quantum phases. While a range of fractional quantum anomalous Hall (FQAH) states have recently been observed in two-dimensional twisted moire systems, the theoretically anticipated filling factor $\nu =-1/3$ FQAH state has remained elusive, with debates centering on its nature of charge density wave or a topological Chern insulator. Here, we report the optical detection of a $\nu =-1/3$ FQAH state in twisted ${\mathrm{MoTe}}_2$ bilayers. Using photoluminescence and reflective magnetic circular dichroism techniques, we identify ferromagnetic states at filling factors $\nu =-1$, $-2/3$, and $-1/3$, all tunable by a vertical electric field. The corresponding Curie temperatures are approximately 11, 3.5, and 2.4 K, respectively. The $-1/3$ state emerges over a narrower electric field range and a lower temperature compared to the integer and other fractional states, indicating a fragile nature that may have led to its absence in previous reports. Notably, the photoluminescence spectra at $\nu =-1/3$ disperse as the out-of-plane magnetic field increases, consistent with a nontrivial topological origin. Theoretical calculations based on the exact diagonalization method further support the interpretation of this topologically nontrivial state.

Predicting the stable phase configuration in a liquid-gas system becomes a fundamental challenge when the stratification favored by gravity conflicts with arrangements induced by heat flow, particularly because standard equilibrium thermodynamics is insufficient in such nonequilibrium steady states. We propose a variational principle based on an extended thermodynamics, called global thermodynamics, to address this state selection problem. Our key finding is that gravity and heat flow effects are unified into a single parameter, “effective gravity” ($g_{\mathrm{eff}}$), within this framework. Crucially, the sign of $g_{\mathrm{eff}}$ determines the stable configuration: liquid is at the bottom if $g_{\mathrm{eff}}>0$, and floats above the gas if $g_{\mathrm{eff}}<0$. This provides a quantitative tool for the configuration prediction under competing drives.

Continuous-variable quantum thermodynamics in the Gaussian regime provides a promising framework for investigating the energetic role of quantum correlations, particularly in optical systems. In this Letter, we introduce an entropy-free criterion for entanglement detection in bipartite Gaussian states, rooted in a distinct thermodynamic quantity: ergotropy—the maximum extractable work via unitary operations. By defining the “relative ergotropic gap,” which quantifies the disparity between global and local ergotropy, we derive two independent analytical bounds that distinguish entangled from separable states. These bounds coincide for a broad class of quantum states, making the criterion both necessary and sufficient in such cases. Unlike entropy-based measures, our ergotropic approach captures fundamentally different aspects of quantum correlations and entanglement, particularly in mixed continuous-variable systems. We also extend our analysis beyond the Gaussian regime to certain non-Gaussian states and observe that Gaussian ergotropy continues to reflect thermodynamic signatures in entangled states, albeit with some limitations. These findings establish a direct operational link between entanglement and energy storage, offering an experimentally accessible approach to entanglement detection in continuous-variable optical platforms.

Identifying quantum phase transitions poses a significant challenge in condensed matter physics, as this requires methods that both provide accurate results and scale well with system size. In this work, we demonstrate how relaxation methods can be used to generate the phase diagram for one- and two-dimensional quantum systems. To do so, we formulate a relaxed version of the ground-state problem as a semidefinite program, which we can solve efficiently. Then, by taking the resulting vector of moments for different model parameters, we identify all phase transitions based on their cosine similarity. Furthermore, we show how spontaneous symmetry breaking is naturally captured by bounding the corresponding observable. Using these methods, we reproduce the phase transitions for the one-dimensional transverse field Ising model and the two-dimensional frustrated bilayer Heisenberg model. We also illustrate how the phase diagram of the latter changes when a next-nearest-neighbor interaction is introduced. Overall, our work demonstrates how relaxation methods provide a novel framework for studying and understanding quantum phase transitions.

We study an angular dipole deformation of maximally supersymmetric Yang-Mills (SYM) theory that preserves its classical scale invariance. Two-point functions of suitable single trace operators, restricted to an invariant plane, are determined by scaling dimensions computable via an integrable spin chain. This spin chain is a twisted version of the famous integrable spin chain of SYM theory. It matches expectations from the dual string theory perfectly, presenting a precision test of holography in this new setting, and an important step to understanding general twisted integrable $\mathrm{AdS}/\mathrm{CFT}$.

Ferroelectric instabilities in perovskites are known to be suppressed by a moderate hydrostatic pressure. The prediction of their re-entrance in a much higher pressure regime is well accepted theoretically, but a conclusive experimental confirmation is still missing. Here, we show its occurrence in a classical but comparatively underlooked ferroelectric perovskite ${\mathrm{KNbO}}_3$. We use single crystal x-ray diffraction, infrared and Raman spectroscopy, and second-harmonic generation to explore the phase transition sequence at high pressures up to 63 GPa. We show that polar cation displacements emerge locally but have to combine with tilts of the oxygen octahedra that are also developing under pressure. This results in a macroscopically centrosymmetric phase with an incommensurate modulation that reflects the tight competition between the polar and tilt instabilities. Soft modes associated with the tilts and the modulation, along with persistent order-disorder signatures, are clearly observed, suggesting that local disorder plays an important role in mediating this competition.

For quantum spin systems in equilibrium, the dynamic structure factor (DSF) is among the most feature-packed experimental observables. However, from a theory perspective it is often hard to simulate in an unbiased and accurate way, especially for frustrated and high-dimensional models at intermediate temperature. To address this challenge, we compute the DSF from a dynamic extension of the high-temperature expansion to frequency moments. We focus on nearest-neighbor Heisenberg models with spin lengths $S=1/2$ and 1. We provide comprehensive benchmarks and consider a variety of frustrated two- and three-dimensional antiferromagnets as applications. In particular we shed new light on the anomalous intermediate temperature regime of the $S=1/2$ triangular lattice model and reproduce the DSF measured recently for the $S=1$ pyrochlore material ${\mathrm{NaCaNi}}_2{\mathrm{F}}_7$. An open-source numerical implementation for arbitrary lattice geometries is also provided.

Chains of Rydberg atoms have emerged as a powerful platform for exploring low-dimensional quantum physics. This success originates from the precise control of lattice geometries provided by optical tweezers, which allows access to a wide range of synthetic quantum phases. Experiments on one-dimensional arrays have stimulated tremendous progress in understanding quantum phase transitions into crystalline phases. However, the finite width of tweezers introduces small variations in interatomic distances, leading to quenched disorder in the interactions. In this Letter, we numerically study how such disorder alters the nature of two critical regimes observed in experiments. First, following experimental protocols, we analyze Kibble-Zurek dynamics and find a crossover from the clean Ising transition to the infinite-randomness fixed point as system size and disorder strength increase. Second, we show that the floating phase—an incommensurate Luttinger liquid phase emerging at stronger interactions—is localized by the disorder, yet preserves short-range incommensurate correlations with the same leading wave vector. Our results clearly reveal an additional conceptual challenge in understanding critical phenomena using Rydberg-based quantum simulators.

Engineering and controlling heat and spin transport on the femtosecond timescale in spintronic devices opens up new ways to manipulate magnetization with unprecedented speed. Yet the underlying reversal mechanisms remain poorly understood due to the challenges of probing ultrafast, nonequilibrium spin dynamics. In this Letter, we demonstrate that typical magneto-optical experiments can be leveraged to access the time evolution of the spin accumulation generated within a magnetic multilayer following an ultrafast laser excitation. Furthermore, our analysis shows that the final magnetic state of the free layer in a spin valve is mainly dictated by the ultrafast dynamics of the reference-layer magnetization. Our results disentangle magnetization and spin transport dynamics within a multilayer stack and identify demagnetization and remagnetization-driven spin accumulation as the key mechanism for all-optical switching. These findings establish new design principles for ultrafast spintronic devices based on tailored spin current engineering.