Angle gratings can efficiently extract light trapped in high-order-topological-charge whispering-gallery modes of microring resonators into free-space beams, yet backscattering remains the key factor compromising the purity of the emitted topological charge. In this study, we develop a coupled-mode theory for defect scattering in passive microring cavities. Using a non-Hermitian Hamiltonian framework, we describe the defect-induced asymmetric coupling between clockwise and counterclockwise modes. This defect-induced asymmetry drives the evolution from standing-wave modes to unidirectional traveling-wave modes, ultimately enabling the generation of high-purity vortex light emission. Rotating a single grating tooth defect by $0–2\pi$ in a rotationally symmetric microring periodically modulates intracavity backscattering and mode coupling. When weak backscattering is fully suppressed by destructive interference, the intracavity standing wave decouples and reconstructs into a unidirectional traveling wave, emitting a one-handed vortex beam. Even weak defect-induced backscattering degrades traveling-wave purity. Introducing a second independent grating tooth defect moving along the inner wall enables periodic coherent cancellation, restoring the traveling-wave state with vortex emission purity up to 99%. These theoretical predictions agree well with simulations. Of note, this study reveals the evolution of microcavity eigenvalues and eigenstates with defect position. First, when backscattering is canceled out, the real parts of the eigenvalue spectrum exhibit contact and separation behavior at degenerate frequencies, while the imaginary parts cross linearly, describing the merging of split eigenvalues back to a degenerate state by suppressing of mode coupling. Second, eigenstate phase rigidity remains well above zero, demonstrating that eigenvectors maintain linear independence without coalescing. This distinguishes the coherent cancellation process from non-Hermitian exceptional points. Additionally, the electric-field overlap integral approaches unity, indicating perfect spatial reconstruction of the standing wave into the original unidirectional traveling wave. This study provides a theoretical basis for defect engineering and non-Hermitian photonic devices. In addition, the high-purity vortex will have broad application prospects in on-chip information processing and particle micromanipulation.

The atomic magnetometer exhibits high sensitivity in weak magnetic field detection, with diverse applications in dark matter detection, biomagnetic sensing, wireless communication, etc. However, its performance, especially in environmental robustness and sensitivity, is largely limited by laser characteristics. Here, we realized two potassium Faraday lasers operating at potassium D1 (770 nm) and D2 (767 nm) lines, serving as pump and probe lasers for a potassium atomic magnetometer. Utilizing the Faraday anomalous dispersive effect for frequency selection, the lasers achieve automatic wavelength locking within the atomic Doppler broadening, enabling robust, self-stabilizing operation without tedious adjustments. Furthermore, both lasers exhibit strong immunity to environmental disturbances, such as vibration and temperature variations. By implementing the modulation transfer spectroscopy (MTS) technique, the frequency stability of the pump laser and probe laser reaches approximately $5.1\times {10}^{-13}/\sqrt{\tau }$ and $6.2\times {10}^{-13}/\sqrt{\tau }$, respectively. Notably, the optimized frequency stability is accompanied by better power stability, showing threefold and fivefold improvements over their free-running counterparts, which reaches the ${10}^{-5}$ level at 1 s. The enhancements in laser performance directly improved the magnetometer’s performance, yielding a magnetic noise floor of approximately $100\mathrm{fT}/\sqrt{\mathrm{Hz}}$ at 10 Hz under a bias field of 1000 nT. Therefore, with hands-off operation, environmental robustness and competitive sensitivity, this achievement holds promising prospects for both laboratory and field-deployable applications.

We present a comprehensive study of quantum dot (QD) coupling to various phononic modes in a phononic waveguide (WG), combining multiband $\mathit{k}·\mathit{p}$ and configuration-interaction (CI) QD state simulations with finite-element WG mode modeling. We consider self-assembled Stranski-Krastanov InGaAs/GaAs as well as local droplet-etched GaAs/AlGaAs structures. Using $\mathit{k}·\mathit{p}$-CI calculations, we quantify the strain and piezoelectric responses of InAs and GaAs QDs. By systematically isolating volumetric/shear deformation-potential and piezoelectric channels, we demonstrate how mode symmetries dictate distinct coupling mechanisms. We identify the dominant coupling channels and characterize their observable signatures in the QD response. We predict strong linear energy shifts under volumetric strain and quadratic behavior under shear strain, especially in GaAs QDs. The piezoelectric effect is dominated by polarizability, which also leads to a quadratic response. The simulations show energy modulations up to 0.7 meV for an acoustic wave with 0.1 nm amplitude. The quadratic response to shear strain and piezoelectric field leads to frequency doubling in the QD response to a mechanical wave and to nonharmonic time traces when linear and quadratic effects contribute to a similar degree. The deep understanding of QD-acoustic couplings opens pathways to the optimal design of QD and WG structures, as well as to improved engineering of acousto-optic quantum interfaces.

Magnetic skyrmions are spin textures with nontrivial topology that form two-dimensional hexagonal lattices (SkX) in chiral magnets. Element-specific reciprocal-space characterization of skyrmion lattices with soft x-rays commonly relies on transmission geometries, which require thinning of bulk crystals and can modify their magnetic properties. Here, we show that resonant elastic x-ray scattering in a grazing-incidence geometry (GIREXS) provides a nondestructive and geometrically flexible probe of skyrmion lattices in bulk materials. Using MnSi as a model system, GIREXS resolves the helical, conical, and skyrmion-lattice states through their characteristic magnetic satellite peaks and yields the skyrmion wave vector. By operating just above the critical angle (${\alpha }_{\mathrm{c}}\approx 1.6°$ in MnSi at the Mn $L_3$ edge), the method achieves a probing depth of approximately $3\mathrm{nm}$, tunable up to approximately $20\mathrm{nm}$ via the incidence angle, while maintaining full reciprocal-space access to the in-plane magnetic correlations. The grazing-incidence approach circumvents the structural Bragg-peak constraints that limit conventional reflection resonant elastic x-ray scattering (REXS) at fixed soft-x-ray energies. Our measurements establish GIREXS as a practical method for studying magnetic superstructures in bulk crystals, providing direct reciprocal-space access to magnetic satellite reflections and a basis for future depth-controlled, element-selective investigations of complex spin textures.

Efficient loading of single atoms into tightly confined traps is crucial for advancing quantum information processing and exploring atom-photon interactions. However, directly loading atoms from a magneto-optical trap (MOT) into static traps in cavity-based systems and hybrid atom-photon interfaces remains a challenge. Here, we demonstrate atom loading in a tightly confined optical tweezer $0.6\mathrm{mm}$ away from MOT by an optical conveyor belt. By employing real-time feedback control of the atom number in the overlapping region between the conveyor belt and the tweezer, we achieve a single-atom loading probability of 77.6%. Our technique establishes a feedback-controlled loading protocol for deterministic single-atom loading in various experimental settings and provides a foundation for diverse applications based on hybrid photonic-atom structures.

Broadband and low-loss superconducting switches can facilitate large-scale quantum information processors and cryogenic detectors by dynamically reconfiguring the connectivity of their circuits. The time-dependent connectivity is enabled by the nonlinearity of lossless Josephson-junctions, which are often wired into superconducting loops to be controlled by magnetic flux. However, this approach needs a power-consuming constant flux bias and dynamic flux actuation, both of which are hard to isolate from other switches or flux-sensitive elements, limiting their integration density. Here, we design and characterize a microwave switch that implements a persistent current bias and direct-current actuation to reduce static power consumption, actuation energy, and potential crosstalk to other devices. We show that persistent current associated with tens of flux quanta is stable and long-lived, reducing the need for on-the-fly tuning. We further demonstrate that our switch has desirable performance for superconducting-circuit-based quantum information processing, including an off mode with more than 20 dB isolation comparable to commercial ferrite isolators, power handling larger than 100 pW sufficient for resonator readout tones and amplifier pumps, and modulation bandwidth broader than 600 MHz useful for multiplexing schemes.

In spaceborne gravitational-wave detectors, the test mass is treated as an ideal rigid end mirror for interferometric-displacement readout. In reality, however, as a thermoelastic body, it deforms under radiative heating from the surrounding electrode housing, shifting the effective laser-reflection point and coupling into displacement noise. In this work, we develop a coupled model of radiative heating, thermoelastic deformation, and laser sensing and derive an analytical expression relating housing temperature fluctuations to displacement noise. Applying TianQin parameters, the result shows that a displacement noise allocation of $0.1\mathrm{pm}/\sqrt{\mathrm{Hz}}$ requires electrode-housing temperature fluctuations below $43\mathrm{\mu }\mathrm{K}/\sqrt{\mathrm{Hz}}$ at $0.1\mathrm{mHz}$ and $430\mathrm{\mu }\mathrm{K}/\sqrt{\mathrm{Hz}}$ at $1\mathrm{mHz}$.

Optimal measurements for quantum multiparameter estimation are complicated by the uncertainty principle. Generally, there is a trade-off between the precision with which different parameters can be simultaneously estimated. The task of determining the minimum achievable estimation error is a central task of multiparameter quantum metrology. For estimating parameters encoded in pure quantum states, the ultimate limit is known but is given by the solution of a nontrivial minimization problem. We present an alternative expression for the achievable bound for two-parameter estimation with pure states that is considerably simpler. We also determine the optimal measurements, completing the problem of two-parameter estimation with pure-state probes. To demonstrate the utility of our result, we determine the precision limit for estimating displacements using grid states.

We present a thorough study of the surface impedance $Z_s$ in the mixed state of sputtered Nb-Ti coatings on insulating substrates, with the aim to assess and quantify the mechanisms governing vortex motion. Measurements are performed by means of a dual mode dielectric-loaded resonator allowing the simultaneous determination of $Z_s$ at 16.5 and 26.7 GHz, which enable to derive the various relevant vortex dynamics parameters. A static magnetic field ${\mathrm{\mu }}_{0}H\le 1.25\mathrm{T}$ is applied normally to the sample surface, in the $T=5\mathrm{K}-T_c$ temperature range. The measured pinning frequency is $\approx 4.5\mathrm{GHz}$ at 5 K and 1 T, with a pronounced decrease with field. A scaling analysis of the pinning constant $k_p(H,T)$ dependence shows that pinning is dominated by point pins. Thermal creep is negligibly small at the lowest $T$, possibly becoming finite only near $T_c$. Flux flow resistivity is found to be consistent with the time-dependent Ginzburg-Landau predictions for a moderately dirty superconductor.

Acoustic tweezers based on standing surface acoustic waves (SAWs) enable contactless manipulation of microscale and nanoscale particles through acoustic radiation forces (ARFs) and acoustic streaming-induced drag forces. However, the effects of Fresnel interference on particle manipulation in the near field of SAW devices are often overlooked. Here, we employ a pair of straight-electrode interdigital transducers (IDTs) to generate standing SAWs in the Fresnel interference-affected near field for particle patterning. We observe lateral variations in SAW intensity along the electrode length, showing multiple periodically distributed SAW beams with relatively higher intensities. The number of these beams gradually increases with the IDT aperture size. Such intensity variations influence the ARFs acting on microparticles and nanoparticles, the resulting vortex streaming fields, and the streaming-induced drag forces, thereby affecting particle distributions. In particular, we observe size-dependent particle patterning in the near field with Fresnel interference. Polystyrene particles with diameters of 500 nm, $6\mathrm{\mu }\mathrm{m}$, and $20\mathrm{\mu }\mathrm{m}$ exhibit distinct behaviors: 500 nm particles are accumulated by streaming vortices due to dominant streaming drag effects; $20\mathrm{\mu }\mathrm{m}$ particles, primarily governed by ARFs, are trapped along pressure nodal lines while avoiding regions of high-intensity SAW beams; $6\mathrm{\mu }\mathrm{m}$ particles, influenced by both ARF and streaming effects, form discrete chains along pressure nodal lines while being attracted to regions with strong streaming vortices.

Line-of-sight point-to-point links are typically rank-limited when they are driven and observed only through conventional uniform-aperture far-field ports: with finite apertures and no scatterers, the dominant contribution is the Friis mode, whose received power scales as $1/r^2$. We introduce Multimodal Direct-Ray Transmission (MDRT), a mode-synthesis and link-budget framework derived from an asymptotic expansion of the free-space Green’s function that retains radiative near-field terms. The expansion identifies deterministic coaxial current distributions whose field amplitudes scale as $1/r^{m+1}$ (power $\propto 1/r^{2(m+1)}$), with $m=0$ recovering the classical Friis term and $m=1$ producing first-order secondary channels with power $\propto 1/r^4$. MDRT does not create degrees of freedom beyond the full dyadic Green-function channel; rather, it provides closed-form current weights, scaling laws, and generalized Friis-like formulas for accessing weak but existing higher-order singular channels. Because the relevant weights reduce to uniform, linear-gradient, and monopulse profiles, the leading MDRT channels can be realized as a small number of passive or hybrid modal antenna ports, reducing the rf-chain and calibration burden relative to fully digital element-level multiple input multiple output and singular value decomposition (SVD) implementations. We extend the analysis to the dyadic Green’s function and express the first higher-order link budget in terms of a dimensionless first-order tensor directivity, interpretable as the squared angular slope of the normalized far-field vector at a boresight null. Numerical operator SVD confirms that the predicted current distributions approximate the dominant higher-order singular modes in the Fresnel or transition region. Finite-signal-to-noise ratio (SNR) capacity tables quantify when these modes are above the water-filling threshold for realistic frequencies, apertures, ranges, and receiver SNRs. Finally, a two-mode prototype demonstrates modal separation and the measured $1/r^2$ versus $1/r^4$ decay. The method requires accurate boresight alignment and is most relevant near the far-field boundary of large electrical apertures.

We present a fiber-ring resonator that realizes an ultranarrowband, high-extinction, low-loss, tunable optical filter. It consists of a pair of commercial variable ratio directional couplers that allow precise adjustment of the filter bandwidth and its on-resonance transmission. This design also grants access to multiple modes of operation, such as a simultaneous band-stop and band-pass filter. Our characterization reveals a bandwidth of less than 2 MHz, together with an extinction exceeding 20 dB. The tunability of the filter properties establishes our device as a versatile platform for selective frequency filtering with sub-natural atomic linewidth resolution.

The variable-range hopping (VRH) model has been widely applied to describe low-temperature electrical transport in disordered systems. However, it relies on oversimplified approximations that restrict its applicability to rigid integer dimensions and narrow thermal windows, often resulting in problematic fitting behaviors and unphysical parameter extraction. In this work, we formulate an integral variable-range hopping (IVRH) model that replaces the traditional empirical temperature power laws with a physics-inspired integral formulation. The model builds upon the standard hopping rate $\omega (R)$ as a function of hopping distance $R$ and incorporates the density of accessible electronic states through a dimension-dependent hopping volume function $V(R)$, which naturally reflects the underlying system geometry. The IVRH formulation inherently captures both the low-temperature Mott VRH behavior and the high-temperature Arrhenius activation limit, enabling a seamless description of the crossover regime without manual temperature-window partitioning. We systematically apply the IVRH model to two-dimensional (2D), three-dimensional (3D), and multilayered systems. Monte Carlo simulations validate the model’s predictions and yield consistent, universal values for the geometric parameters, exhibiting substantially reduced variances compared with the standard VRH fits. Furthermore, the IVRH model outperforms traditional Mott-based power laws in trans-dimensional hafnium nitride (HfN) thin films and provides physically sound interpretations of carrier-density and gate-voltage-modulated localization physics in monolayer ${\mathrm{WS}}_2$ devices. Ultimately, the IVRH model offers a stable, precise, and unified framework for interpreting hopping transport in disordered, low-dimensional, and layered materials, providing deeper insights into the geometric scaling factors that govern charge transport.

We theoretically investigate the design of a highly efficient tunable selective emitter for thermophotovoltaic (TPV) applications that integrates two subsystems into a single device. The first subsystem consists of a one-dimensional highly doped silicon (HDSi) trapezoidal grating that acts as a broadband absorber, while the second subsystem is a multilayer structure (MS) composed of a stack of three photonic crystals (PCs) serving as a spectral filter. A simple, efficient, and fast numerical model is developed by transforming the grating into an equivalent multilayer stack using the effective medium approximation and the staircase approximation. To design the PC stack, and in contrast to previous works, we optimize the first photonic crystal and deduce the characteristics of the second and third PCs using appropriate scaling factors. The radiative properties of the full system are then calculated using the transfer matrix method. A parametric analysis is performed to optimize the emitter design for spectral matching with three commonly used TPV cells: GaSb, InGaAs, and InGaAsSb. It is found that using the same grating parameters and scaling factors for the MS, combined with tuning of the band gap wavelength, allows an excellent spectral match with all three TPV cells. The efficiency of the proposed selective emitter is evaluated using three standard formulations reported in the literature to enable direct comparison with prior work. The results show that the combined final system enables highly selective narrow band emission with efficient suppression of sub-band gap photons over a broad spectral range, up to $8\mathrm{\mu }\mathrm{m}$, achieving high emitter efficiencies of 97.9% for the GaSb cell, exceeding 99% for InGaAs and InGaAsSb cells, and 77% at 1200 K for the three considered photovoltaic cells. Finally, the effect of high temperature on the spectral emission of the structure is investigated, considering the temperature dependence of the HDSi permittivity, and it is demonstrated that the structure exhibits good thermal stability at elevated temperatures.