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.

The imaging of slits with various sizes is considered to evaluate the reliability of using them to estimate the optical resolution in classical microscopy. For this purpose, the images are calculated using an ab initio approach that includes the key aspects of microscopy: partial coherence of wide-angle illumination and diffraction of light described by the Maxwell equations. It is shown that, under standard operating conditions, slits with sizes comparable to or smaller than the wavelength produce images whose resolution can be greatly exaggerated if evaluated using the spatial scale or the incoherent model, potentially leading to superresolution claims. Furthermore, the visibility of slits depends not only on their width and separation but, to a large extent, on their number as well. The issues of resolution evaluation are discussed by representing the images using the complex correlation function for the equivalent currents and analyzing its properties, including its relation to the incoherent model. In general, images of wavelength-scale slits, bars, or discs do not directly yield resolution values that can be compared with the Rayleigh or Abbe criteria. Consequently, obtaining high resolution for images of such objects under different microscopy regimes but using simple estimation methods should not be used to claim superresolution.

We introduce a simulation-free approach to fidelity estimation in chaotic circuits implemented on universal quantum processors, based on the order statistics of measured output probabilities. The approach requires only the most frequently observed measurement outcomes and builds on analytical results for the order statistics of Haar-random quantum states derived here. Modeling noise via an effective depolarizing channel, we construct maximum-likelihood estimators that infer circuit fidelity from a small number of top-ranked outcomes, without requiring classical amplitude calculations. The method is benchmarked on publicly available data from Google’s 12-qubit Sycamore experiment and supported by numerical simulations, providing a framework for fidelity estimation in intermediate-scale quantum devices.

Te-doped GaSb single crystals have great application potential in infrared detectors owing to their high mobilities. Therefore, improving the room-temperature mobility is crucial to suppressing device dark current and enhancing detector response speed. However, most of the previous studies focus only on the impurity compensation effect of Te doping while ignoring its critical regulation on carrier transport mechanisms. In this study, ${\mathrm{GaSb}}_{1-x}{\mathrm{Te}}_x$ single crystals ($0\le x\le 3.48\%$) were grown via the flux method. The crystal with $x=137\mathrm{ppm}$ achieves an exceptional room-temperature electron mobility of $4273{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$, exceeding previously reported values. Systematic transport measurements reveal two successive doping-driven transitions: a carrier-type conversion from $p$-type to $n$-type at $x=137\mathrm{ppm}$, followed by a transition from nondegenerate semiconducting behavior to degenerate metalliclike behavior at $x=0.29\%$. The evolution of carrier characteristics and mobility stems from the complex interplay between impurity compensation, ionized impurity scattering, and phonon scattering mechanisms. Electrical transport and spectroscopic analyses demonstrate that Te doping induces a shift of the Fermi level into the conduction band. Furthermore, the distinct Shubnikov-de Haas oscillations directly confirm the establishment of degenerate behavior. These results clarify the dual role of Te in impurity compensation and band structure modulation, while providing key insights for designing high-quality infrared detectors via precise doping.

Triangular-lattice quantum magnets with strong spin-orbital coupling constitute a fertile playground for realizing unconventional magnetic ground states. Here, we report the synthesis, crystal structure, and magnetic properties of a new family, ${\mathrm{Ba}}_3{\mathrm{REBiPbB}}_4{\mathrm{O}}_{13}$ ($\mathrm{RE}=\mathrm{Pr}$, Nd, Gd–Yb), where perfect triangular-lattice layers of ${\mathrm{RE}}^{3+}$ ions are well separated ($>13Å$) along the $c$ axis in an AAA-type stacking, resulting in an exceptionally low magnetic ion density. No evidence of long-range magnetic ordering is detected down to 0.4 K for $\mathrm{RE}=\mathrm{Gd}$ and Yb members and to 1.8 K for the others, despite dominant antiferromagnetic interactions. Quasi-adiabatic demagnetization measurements show that the Gd compound reaches a minimum temperature of 69 mK, while the Yb counterpart cools down to 26 mK from 2 K under an initial field of 9 T, among the lowest temperatures reported for similar conditions. Notably, the Gd compound exhibits two distinct temperature minima in the cooling profile and a broad peak in specific heat at approximately $0.19\mathrm{K}$, indicative of a cooperative magnetic ground state without long-range ordering. In contrast, the Yb member likely remains paramagnetic down to its lowest cooling temperature, 26 mK. The diversity of RE ions in triangular-lattice ${\mathrm{Ba}}_3{\mathrm{REBiPbB}}_4{\mathrm{O}}_{13}$ provides a low-magnetic-ion-density platform for exploring spin-orbit-driven exotic quantum magnetism, as well as potential applications in sub-Kelvin magnetic cooling.

In donor qubit arrays, each electron is not confined to a specific donor: long-range Coulomb interactions enable changes in gate biases near one donor to modify the charge configurations of others. This nonlocal crosstalk arises not only from electrostatic effects but also from interactions that are strong across the donor array. Here we investigate the strong interaction-induced charge redistribution as a function of gate voltages in $2\times 2$ phosphorus donor arrays in silicon. We construct a multiorbital Hubbard model of the donor array, parametrized by density functional theory, atomic tight-binding, and effective-mass theory, and we solve this Hubbard model with the density matrix renormalization group. We find that an effective two-orbital subspace provides an accurate description at experimentally relevant donor separations, enabling tractable many-body calculations. An interaction-induced charge redistribution is discovered that is not detectable in total-charge stability diagrams and cannot be captured by noninteracting models. We show that these features are protected by same-symmetry correlation energies. The findings have deep implications for operating donor-array-based quantum technology hardware.

Mapping quantum approximate optimization algorithm (QAOA) circuits with nontrivial connectivity in fixed-layout quantum platforms, such as superconducting quantum processing units (QPUs), requires a transpilation process to match the circuit to the hardware layout. This step is critical for reducing error rates on noisy QPUs. Two approaches that improve the resources required for such transpilation are the SWAP network and parity twine chains (PTC), which reduce the two-qubit gate count and circuit depth needed to represent fully connected circuits. In this work, we introduce a simulated annealing-based method that further reduces the encoding overhead of PTC and SWAP networks for QAOA circuits with nonfully connected two-qubit interactions. The method is benchmarked against various transpilers, including the Qiskit SAT mapper, demonstrating that beyond specific connectivity thresholds it achieves significant reductions in both two-qubit gate count and circuit depth. For example, for a 120-qubit QAOA instance with 25% connectivity, our method achieves an 87% reduction in depth and a 29% reduction in two-qubit gates compared with the Qiskit transpiler. Finally, the practical impact of PTC encoding is validated by benchmarking QAOA on the ibm_fez and ibm_kingston devices, showing improved performance for systems of up to 20 qubits.

In the context of spaceborne gravitational-wave detection, residual gas-damping noise induced by thermal molecular motion represents the primary limitation on the sensitivity of a gravitational reference sensor (GRS) operating within the mHz band. This study reconstructed and unified the microscopic physical image that characterizes the various gas-damping effects in high-vacuum free-molecular flows for high-precision GRS. This facilitates the execution of a comprehensive analytical modeling of the total gas-damping effects on the test mass (TM) within the sensitive probe geometry. An improved Monte Carlo numerical simulation method was also developed by tracking molecular scattering processes on the TM and quantifying the momentum transfer from molecular fluctuations. The normal and tangential damping force noise acting on the TM was systematically validated by this method. The results demonstrate exceptional agreement with proposed theoretical models, exhibiting minimal relative deviations of 8.7% and 0.14%, respectively. Furthermore, the study revealed a crucial conclusion that the tangential gas-damping noise acting on the TM is independent of electrode gaps in all directions. This accurate model of residual gas-damping noise was subsequently applied to the TianQin mission. A full frequency band residual gas-damping noise power spectral density (PSD) in scientific mode was demonstrated. Assuming a conservative sealed-housing configuration (i.e., no effective venting to an external reservoir), it is recommended that the electrode gap along the sensitive axis be maintained at a minimum of 5 mm to ensure compliance with the TianQin residual acceleration noise requirement. This finding is determined by the excellent agreement between the PSD and theoretical model prediction within the observation band. The incorporation of potential venting features has been identified as a means of reducing proximity-enhanced damping, thereby relaxing this constraint.

Radio-frequency (rf) reflectometry provides a useful method for sensitive and fast detection of dynamic processes in quantum systems. We use this method to detect excitation of the quantized (Rydberg) states of the vertical motion in a system of surface-bound electrons on liquid helium. The Rydberg transition is detected as a change in the rf reflection from a resonant circuit coupled to microwave-excited electrons. It is found that the observed reflection response drastically differs from an expected state-dependent dispersive shift of the resonant frequency. To elucidate the origin of the observed response, the result is compared with an independent reflection measurement on the same electron system modulated by an electrostatic potential and with a numerical simulation using the Green’s function method. The findings suggest that the observed response to the Rydberg resonance must be attributed to the in-plane motion of the photoexcited many-electron system rather than to the Rydberg transitions of independent electrons. Our work demonstrates that rf reflectometry could be a useful tool to study dynamic processes, such as quantum ac transport and collective excitations, in this system.

High-fidelity two-qubit gates are essential for scalable quantum computing. We present a scheme based on superconducting transmon qubits and a control pulse delivery protocol that enables arbitrary controlled-phase gates modulated solely by an independent arbitrary waveform generator pulse. We combined a tunable coupler design with bipolar flux-pulsing to demonstrate a controlled-phase gate, achieving a peak fidelity of 99.5%. Our gates inherit the advantages of both approaches: minimal residual $ZZ$ coupling, built-in echo-like low-frequency noise protection, and time-scale control pulse reproducibility, while remaining easy to calibrate. We optimize the system’s energy levels to mitigate leakage to the coupler and suppress residual interactions. Numerical simulations of the scheme as three qutrits indicate that an error below $1\times {10}^{-3}$ is achievable. We confirm the scalability potential of the proposed scheme on high-fidelity four-qubit and eight-qubit quantum processors.