We present a comprehensive theory of electromagnetic modes in spherical cavities, resolving questions about the nature of angular quantization. The standard result that angular indices ($\ell ,m$) must be integers is shown to be a consequence of domain constraints—regularity at both poles and single valuedness in the azimuthal coordinate—rather than a requirement imposed by Maxwell’s equations themselves. We demonstrate that, for the sectoral case $\nu =m$, the function ${\sin }^m\theta$ exactly solves the angular eigenvalue equation for any real $m>0$, giving rise to a continuous dispersion curve. We demonstrate why nonsectoral modes (tesseral and zonal) appear only at isolated integer points on the full sphere and show how boundary modifications such as cones and wedges convert these isolated points into continuous families of modes. Complete field solutions, wave impedances, and energy integrability conditions are derived. At the limiting point $(\nu ,m)=(0,0)$, the electromagnetic field vanishes identically while the underlying Debye potential remains nontrivial—a distinction with implications for mode counting that connects to longstanding questions in gauge theory and cavity quantization. Full-wave simulations validate the theoretical predictions with sub-percent accuracy. These results raise the possibility of structural analogs in wave equations on curved spacetimes, where conical deficits or horizon excisions similarly modify the angular domain.

In our previous work, we have theoretically shown that the temporal interface in a wire medium may result in an unambiguous encoding of the spatial frequencies of the initial wave package propagating along the wires into temporal frequencies of a created pulse propagating obliquely to them. This effect of encoding information on subwavelength spatial field distributions into frequency spectra of propagating waves opens a new door for far-field subwavelength imaging. Earlier, we suggested achieving the needed temporal interface with microplasma discharges. In the present paper, we show analytically and numerically that the same effect may be offered in a simpler and more practical way—by switching PIN diodes loading the wires. Since the temporal interface in this case occurs between two media with strong spatial dispersion, besides the wave packet responsible for the imaging a parasitic one is generated. However, the frequency range of this second wave packet is so different that it cannot spoil the image retrieval.

Perovskite solar cells (PSCs) have rapidly advanced over the past decade, reaching certified efficiencies above 27%, and are now regarded as promising candidates for next-generation photovoltaics. Among the emerging device architectures, quasi-interdigitated back-contact PSCs (QIBC PSCs) eliminate the transparent conductive oxide (TCO) layer and collect charges through patterned rear electrodes, enabling reduced parasitic absorption, improved photocurrent generation, and compatibility with flexible and tandem devices. Despite these advantages, optical losses—particularly front-surface reflection—remain a significant challenge, making antireflective coatings (ARCs) essential for further efficiency enhancement. Different ARCs’ geometries offer a pathway to broadband, omnidirectional light coupling beyond the limits of conventional planar coatings. In this work, we employ numerical simulations to systematically investigate the effect of ARC geometries in QIBC PSCs. We compare planar, double-layer, ball, pyramidal, and dome-like structures in terms of absorption-reflection-transmission spectra, generation rate distribution, and current-voltage characteristics. Our results show that dome-like ARCs provide superior optical and photovoltaic performance, increasing the power conversion efficiency (PCE) from 20.66% (no ARC) to 24.38%, while the addition of a back-side mirror further enhances efficiency to 24.72%. These findings highlight geometry-driven ARCs as a powerful strategy for advancing QIBC PSCs toward their theoretical efficiency limits.

Superconducting quantum interference devices (SQUIDs) are state-of-the-art in ultrasensitive magnetometry; however, conventional SQUIDs are fundamentally limited by the inherently nonlinear, periodic nature of their transfer function. Although flux-locked loop configurations can mitigate this issue, they introduce electronic complexity and bandwidth constraints that hinder scalability in quantum circuits. In this work, we present an experimental demonstration of the bi-SQUIPT, a flux transducer that modulates the density of states in a proximitized superconducting weak link. The device employs a dual-loop architecture with differential readout, which enables cancellation of nonlinearities typical of individual elements, achieving a voltage swing of approximately $120\mathrm{\mu }\mathrm{V}$. Measurements yield a spurious-free dynamic range of up to 60 dB, consistent with theoretical predictions and comparable to that of SQUID arrays, while maintaining femtowatt power dissipation. The results further highlight a remarkable operational stability up to 600 mK, positioning the bi-SQUIPT as an enabling technology for high-density cryogenic quantum electronics.

Photonic quantum computing is a strong contender in the race to fault tolerance. Recent proposals using qubits encoded in frequency modes promise a large reduction in hardware footprint and have garnered much attention. In this encoding, linear optics, i.e., beam splitters and phase shifters, is necessarily not energy conserving and is costly to implement. In this work, we present designs of frequency-mode beam splitters based on modulated arrays of coupled resonators. We develop a methodology to construct their effective transfer matrices based on the SLH formalism for quantum input-output networks. Our methodology is flexible and highly composable, allowing us to define $N$ mode beam splitters either natively based on arrays of $N$-resonators of arbitrary connectivity or as networks of interconnected $l$ mode beam splitters with $l<N$. We apply our methodology to analyze a two-resonator device, a frequency-domain phase shifter, and a Mach-Zehnder interferometer obtained from composing these devices, a four-resonator device, and derive a no-go theorem forbidding the native implementation of a subclass of $N$ mode frequency-domain beam splitters with arrays of $N$-resonators.

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.