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.

Dynamic scattering and imaging with coherent, ultrafast, extreme-ultraviolet (EUV) light sources can resolve charge, phonon, and spin processes on their intrinsic length and time scales. However, while lensless computational imaging approaches have been highly successful in static EUV imaging, the data and computational requirements for phase reconstruction are obstacles to quickly acquiring a large series of frames to reconstruct fast time-dependent sample dynamics. In this paper, we demonstrate a noniterative, computational technique for reconstructing dynamic 1D images of the average unit cell in a time-varying periodic sample. The technique can be applied even to a preexisting time series of diffraction data without the Nyquist sampling requirement common to computational imaging and works by analyzing the changing intensities of the far field diffracted orders. Starting from a system of equations relating small changes in far field diffraction to phase and amplitude perturbations at the sample plane, it is shown that under certain conditions, changes to the $n$th diffracted order map exclusively onto the $n$th Fourier component of the perturbation via a closed-form relation. We show through rigorous coupled-wave analysis simulations that our method can provide a good approximation even outside the scalar diffraction theory framework in which it is derived. Finally, we experimentally demonstrate this reconstruction method by exciting 1D nickel nanowires on a diamond substrate using an infrared laser pump pulse and measuring their relaxation using a time-delayed EUV probe pulse to visualize nanoscale phonon dynamics.

Photonic quantum gates are fundamental building blocks for a wide range of optical quantum information processing tasks. We propose an efficient linear-optical scheme for implementing a postselected three-qubit fan-out gate (also known as a controlled-not-not gate) using only two ancillary single photons and linear optical elements. The scheme can be generalized to an $n$-qubit fan-out gate, requiring $(n-1)$ ancillary single photons and $(3n-3)$ polarizing beam splitters (PBSs), with a success probability of ${(\frac{1}{4})}^{n-1}$. Compared with the standard gate decomposition approach, which requires $(2n-2)$ ancillary single photons, $(5n-5)$ PBSs, and yields a success probability of ${(\frac{1}{8})}^{n-1}$. Our scheme significantly reduces the resource overhead and improves the success probability. We further evaluate the gate performance and demonstrate improved robustness compared with gate decomposition-based methods.

Quantification in fluorescence correlation spectroscopy relies on diffusion models where the confocal volume is approximated usually by a three-dimensional Gaussian (3DG) function. Although this assumption is essential for estimating the fluorophore diffusion parameters (such as the number of molecules, their brightness, and their diffusion coefficient), it is rarely verified experimentally due to the difficulty of performing it in three dimensions. In this work, we propose a method based on the concomitant analysis of fluorescence fluctuation time traces using both autocorrelation and time-integrated cumulants. This approach enables us to confirm the shape of the focal volume. We also show that this confocal volume is not necessarily a 3DG. For some experimental parameters (objective filling factor and confocal pinhole diameter), we demonstrate that it can be more accurately approximated by a two-dimensional Gaussian function in the lateral direction and a Lorentzian function in the axial direction (2DG-L). We report the analytical expressions of both autocorrelation and time-integrated cumulants for free Brownian motion through a 2DG-L volume. By analyzing fluorescence fluctuation time traces with our method, we can unambiguously retrieve the true shape of the observation volume and, consequently, all molecular diffusion parameters. We apply our method to both Monte Carlo simulations and experimental data acquired using a confocal microscope. We find that the number of molecules in the observation volume is overestimated and that their brightness is underestimated by more than 30% if the adequate observation volume is not used. We therefore believe that the proposed method has the potential to significantly improve the quantitative analysis of fluorescence fluctuations.

In trapped-ion chains, multipartite Greenberger-Horne-Zeilinger (GHZ) states can be prepared natively with the help of a single bichromatic laser pulse. However, higher-order terms in the expansion in the Lamb-Dicke parameter $\eta$ limit the GHZ state preparation infidelity for rectangular and bell-like pulses to the order of ${\eta }^4$. For tens of ions, the infidelity caused by out-of-Lamb-Dicke effects can reach several percents. We propose an amplitude and phase-modulated pulse shape, an “echoed lemniscate pulse,” which cancels this contribution into error in the leading order. For the proposed pulse, the infidelity scales as ${\eta }^6$. The improved scaling is achieved because of a special phase trajectory of a collective motional mode following the figure-eight curve (lemniscate). We demonstrate that the lemniscate pulse allows achieving lower infidelity than bell-like pulses, which can be as low as ${10}^{-4}$ for 20-ion chains.

Nanomechanical resonators have demonstrated significant potential in sensing technologies due to their exceptional responsiveness to external stimuli. However, in most cases, dynamics of the device for various applications have been studied under high- vacuum conditions to suppress viscous damping and enhance signal fidelity. Furthermore, sensing methodologies have predominantly focused on tracking shifts in fundamental resonance frequency induced by analytical interaction or environmental changes. In this work, we studied the multimodal behavior of cantilever-based resonators under ambient atmospheric conditions, revealing that there exists a critical mode number at which the resonator exhibits maximum $Q$-factor. This optimum mode is shown to be a function of geometric configuration (length), speed of sound in air, and fundamental resonance frequency of the resonator. Furthermore, in our comprehensive assessment of the first three flexural eigenmodes of the resonator, with an emphasis on temperature-dependent variation in $Q$-factor and frequency, we show that the critical mode exhibits the best noise equivalent temperature difference of 4 mK with moderate vibrational amplitude. These findings are further corroborated by rigorous theoretical modeling and numerical simulations, offering insights into multimodal response characteristics of resonators under thermally influenced atmospheric environments.

We present a potential improvement over the standard method developed to determine antineutrino directionality in inverse-beta-decay detectors. The previously developed method for quantifying directionality in monolithic and segmented detectors may be ambiguous in methodology. In this paper, we present a directionality algorithm and include error analysis. We have developed an algorithm based on a measure of “distance” between two matrices. We report findings for our research in reactor-antineutrino directionality, and emphasize that the algorithm has broad applications whenever one desires computationally efficient two-dimensional pattern matching. We treat data from lithium-6-doped detector segments in the form of a matrix. The validation of our algorithm boils down to comparing a Monte Carlo-generated “empirical” dataset to a simulated dataset. The empirical dataset is generated for a particular orientation of the neutrino beam. We identify an optimal segmentation scale in the low-count regime. We also discuss the shortcomings of the conventional method and how this knowledge can be applied to segmented detectors, hybrid designs, and generalized validation, agnostic to the physics of detector design.

Subpicotesla level magnetometry has been demonstrated using negatively charged nitrogen-vacancy ($\mathrm{N}\text{−}V$) centers in diamond by increasing the number of spins simultaneously used for sensing in an $\mathrm{N}\text{−}V$ ensemble. However, such scale-up often introduces spatial inhomogeneities in detuning and control field amplitudes, which degrade sensitivity. Although several techniques have been utilized to overcome these challenges, including pulsed dynamical decoupling or shaped pulses, these are not generally compatible with the current state-of-the-art techniques for GHz-range ac magnetometry with $\mathrm{N}\text{−}V$ ensembles, which are typically based on Rabi oscillations. In this work, we experimentally demonstrate GHz-range ac magnetometry using a large ensemble of $\mathrm{N}\text{−}V$ centers under spatially inhomogeneous drive fields by employing concatenated continuous dynamical decoupling, which is designed for robustness against such imperfections. We compare its performance with the conventional direct Rabi method and show that the robust dressed states in our method extend significantly the measuring range to weaker signals in GHz-range ac magnetometry.