In recent years, several architectures have been proposed for implementing two-qubit operations on fluxonium superconducting qubits. A particularly promising approach, which was demonstrated experimentally by Refs. [L. Ding et al. Phys. Rev. X 13, 031035 (2023), S. Singh et al. Phys. Rev. Appl. 25, 024020 (2026)], employs a transmon superconducting qubit as a tunable coupler between the fluxonium qubits. These experiments have shown that the transmon coupler enables fast, high-fidelity two-qubit operations while suppressing unwanted $ZZ$ crosstalk between the fluxonium qubits. In this work, we numerically study the scalability of this architecture. We find that, when trivially scaling this architecture, crosstalk from spectator qubits limits the gate fidelity to below 90%. We show that these spectator errors can be reduced to below ${10}^{-4}$ by reducing the coupling strength and by dynamically tuning transmons that are not used for a two-qubit operation to an off position. We further investigate the resilience of the operation to direct capacitive coupling between the transmon couplers and to microwave crosstalk.

Surface-acoustic-wave (SAW) resonators are a promising platform for constructing hybrid quantum systems, where confined acoustic waves enable strong interactions with various physical systems. Focusing SAW resonators, which reduce mode volume while suppressing diffraction losses, have recently been investigated for applications in such hybrid systems. However, the resonator leads to additional transverse-mode resonances, which cause undesired responses. In this work, we develop focusing SAW resonators using a thin-film lithium niobate on sapphire. A film thinner than the SAW wavelength allows a highly confined acoustic-wave mode to be localized on the substrate surface. By using contoured electrodes following a two-dimensional Gaussian beam shape, we focus the SAW mode to near the diffraction limit and confirm this focusing via optical imaging. Furthermore, by engineering the spatial mode overlap of the interdigital transducer electrodes, we suppress the excitation of higher-order transverse modes.

Controlled disorder in correlated materials provides a new route to emergent stochastic dynamics in neuromorphic hardware. Here we show that focused ion beam irradiation in ${\text{VO}}_2$- and ${\mathrm{V}}_2{\mathrm{O}}_3$-based resistive-switching oscillators induces a transition from regular periodic oscillations to strongly irregular stochastic firing, while simultaneously reducing the required switching energy by orders of magnitude. Under an applied electric field, these materials undergo a volatile insulator-to-metal transition characterized by the formation of percolating metallic filaments within an insulating bulk. Using numerical simulations based on the Mott resistor network, we demonstrate that defect-induced modifications to filament nucleation and stability drive these devices into stochastic oscillatory regimes. These results are validated by experimental measurements on irradiated ${\text{VO}}_2$ and ${\mathrm{V}}_2{\mathrm{O}}_3$ devices.

Energy dissipation in solids under gigahertz (GHz) vibrations is critical to the performance of advanced devices and materials, for example, in nanoresonators used in quantum information systems. Here, we investigate energy loss from forced vibrations due to phonon scattering and thermalization. Our time-resolved models, based on the full phonon scattering matrix, show that intermode temperature differences compete with the effects of underrelaxed nonequilibrium phonons when the period of the forced oscillations is shorter than the phonon scattering rates, leading to the usual unimodal damping behavior as a function of oscillator frequency. In addition, the Akheizer damping mechanism used with the time-dependent phonon dynamics models captures the damping response in closer agreement with fully atomistic models in the ultrasonic to mid-GHz regime than phonon models that rely on the relaxation time approximation. These findings are shown to generalize to multiple single crystals, including silicon, diamond, and nickel.

We demonstrate high-contrast, edge-enhanced proton imaging using a relativistic hollow Laguerre-Gaussian laser (approximately ${10}^{20}\text{W}/{\text{cm}}^2$) incident on nanometer-scale CH foils. In contrast to conventional Gaussian drive, which produces a dotlike proton source, the Laguerre-Gaussian beam generates a ring-shaped proton beam that preferentially enhances peripheral features and enables high-contrast boundary imaging. As a proof of principle, we obtain a clear outline of low-($Z$) soft tissue in a beetle specimen, benefiting from the strong sensitivity of proton energy loss to modest density variations. By comparison, x-ray radiography in the same geometry primarily emphasizes high-($Z$) components (e.g., skeletal structures). Our results establish Laguerre-Gaussian-laser-driven proton radiography as a promising, complementary modality to x-ray imaging, offering improved soft tissue contrast and potential utility for medical diagnostics and radiotherapy guidance.

Here, we present a proof-of-principle high-dimensional quantum key distribution (QKD) protocol utilizing the position and momentum entanglement of photon pairs. The protocol exploits the fact that position and momentum form mutually unbiased bases, linked via a Fourier transform. One photon of the entangled pair is measured by the sender in a randomly chosen basis—either position or momentum—selected passively via a beam splitter. This projective measurement remotely prepares the partner photon in a corresponding spatial mode, which is sent to the receiver, who similarly performs a random measurement in one of the two bases. In this implementation, we achieve a photon information efficiency of 5.07 bits per photon using 90 spatial modes and a maximum bit rate of $0.9\mathrm{Kb}/\mathrm{s}$ with 361 modes. To assess the scalability of this spatial mode encoding scheme, we theoretically show that using a brighter entangled photon source along with next-generation single-photon cameras—featuring improved quantum efficiency, timing, and spatial resolution—this approach could achieve 9 bits per photon at 2000 spatial modes and a bit rate of over $700\mathrm{Mb}/\mathrm{s}$ at 4400 modes while accounting for finite-key effects. These results quantify the opportunities and performance bounds of spatially encoded, entanglement-based QKD and provide a benchmark for future high-dimensional quantum communication systems.

Interfacial electric fields are widely exploited in heterojunction photocatalysts to promote charge separation. However, conventional type-II heterojunctions inevitably suffer from severe loss of redox potential, while Z-/S-scheme architectures retain strong redox capability only at the expense of substantial carrier consumption. Here, we propose a polarization-driven $\Upsilon$-scheme heterojunction that harnesses two oppositely oriented polarization fields to establish an unconventional charge-transfer pathway. Specifically, polarized Janus monolayers ($\mathrm{M}\text{−}{\mathrm{M}}^{\prime }\text{−}\mathrm{C}\text{−}\mathrm{X}\text{−}{\mathrm{X}}^{\prime }$; $\mathrm{M}/{\mathrm{M}}^{\prime }=\mathrm{Sc}$, Y; $\mathrm{X}/{\mathrm{X}}^{\prime }=\mathrm{F}$, Cl, Br, H) are integrated with ferroelectric MXenes (${\mathrm{M}}_2{\mathrm{CO}}_2$; M $=$ Sc, Y), enabling intralayer electron migration toward high-potential regions and hole migration toward low-potential regions. This mechanism preserves intrinsic redox potentials while suppressing interfacial recombination, thereby facilitating near-complete utilization of photogenerated carriers. Consequently, oxidation and reduction reactions are spatially separated at the surface and interface, respectively. Our strategy resolves the long-standing dilemma between maintaining strong redox potentials and maximizing carrier utilization, offering a robust design principle for next-generation high-efficiency photocatalysts.

Silicon dioxide (${\text{SiO}}_2$) is arguably one of the most technologically relevant materials due to its use as a native gate dielectric in silicon-based metal-oxide-semiconductor transistors. In such devices, hydrogen is intentionally introduced during a forming gas anneal to passivate electrically active defects, which would otherwise degrade device performance. While the $\mathrm{Si}─\mathrm{H}$ bonds resulting from this passivation process are highly stable and mostly chemically inert, it has been deduced from experiments and first-principles calculations that radiation-induced holes in the ${\text{SiO}}_2$ valence band mediate the release of ${\mathrm{H}}^{+}$ from such bonds in the oxide. Here, we show through first-principles calculations combined with the theory of multiphonon emission that isolated $\mathrm{Si}─\mathrm{H}$ bonds in ${\text{SiO}}_2$ can be easily broken upon capturing a hole. Our calculations show that capturing holes from the ${\text{SiO}}_2$ valence band leads to an efficient $\mathrm{Si}─\mathrm{H}$ bond dissociation mechanism, with a large effective capture cross section of $\sigma =6\times {10}^{-15}{\text{cm}}^2$. The resulting ${\mathrm{H}}^{+}$ can easily diffuse away, leaving behind a neutral paramagnetic $E^{\prime }$ center, i.e., an ${\mathrm{O}}_3=\text{Si}·$ dangling bond, confirming earlier results reporting ${\mathrm{H}}^{+}$ release and $E^{\prime }$ center creation upon hole injection into the ${\text{SiO}}_2$ valence band.

Nonlinear frequency conversion in the terahertz regime is significant for emerging applications in high-speed communications, imaging, and sensing, yet enhancing light-matter interactions in two-dimensional materials often relies on multilayer stacking or complex resonant architectures. Here, we introduce a transmission-type nonlinear metamaterial based on a single-layer graphene architecture that enables geometry-controlled dual-frequency terahertz third-harmonic generation. By employing a rail-like graphene meta-atom, strong and spatially redistributed local electric-field hot spots are generated through geometry-induced edge confinement and narrow-gap resonances. This enables effective coupling between the enhanced electromagnetic fields and graphene’s intrinsic third-order nonlinearity, allowing dual-frequency nonlinear conversion within a single planar structure without multilayer stacking. Within the adopted fixed-temperature perturbative nonlinear surface-current framework and at an incident pump intensity of $10\mathrm{MW}/{\mathrm{cm}}^2$, the proposed structure predicts third-harmonic generation conversion efficiencies of 4.0% and 4.4% at 1.781 and 2.206 THz, respectively, together with local-field enhancement factors that are one to two orders of magnitude higher than those of bare graphene. This work demonstrates a geometry-driven strategy for controlling terahertz nonlinear responses, showing that nonlinear frequency selectivity can be engineered through geometry-induced local-field redistribution rather than structural complexity. The proposed approach provides a compact strategy for designing single-layer graphene metamaterials with controllable dual-frequency terahertz nonlinear functionality within the adopted theoretical framework.

Continuous-variable quantum secure direct communication (CV-QSDC) utilizes quadrature components of the quantized electromagnetic mode to accomplish direct transmission of secret messages over the channel, offering the advantage of its compatibility with telecommunication facilities. However, phase noises during the running of systems destroy the correlation between the data of two parties and severely limit the effective communication rate. In this paper, we design a phase reference scheme to achieve phase synchronization between the signal light and the local oscillator in the coherent-state CV-QSDC system. To deal with the inaccurate modeling of phase drift in reference pulses, we further propose a phase compensation scheme using model-based deep learning, in which KalmanNet learns the Kalman gain from the data to track the true values of phase drift. In the simulation experiment, the frequency noise acts as the source of inaccuracy, and the results show that the phase compensation scheme based on KalmanNet accomplishes phase estimation effectively and thus improves the communication performance of CV-QSDC.

Defects in solid-state systems constitute a promising platform for the realization of deterministic quantum emitters. Among many candidate materials and emitters, point defects in hexagonal boron nitride (hBN) have recently emerged as particularly promising. In this work, we probe the coherence of an individual B center with a zero-phonon line at 436 nm under pulsed resonant excitation. We observe power-dependent Rabi oscillations up to $5\pi$, demonstrating optical coherent control of the transition. We achieve an excellent single-photon purity of 93% at $\pi$-pulse. Furthermore, we probe the coherence of the two-level system using Ramsey interferometry, revealing an inhomogeneous coherence time of $T_2^{*}=0.64\pm 0.02\mathrm{ns}$. These results establish B centers in hBN as viable candidates for triggered, coherent quantum emitters and represent a significant step toward their integration into quantum photonic platforms.

The diamond nitrogen-vacancy (N-$V$) center ensemble exhibits substantial potential for room-temperature quantum sensing. However, its practical implementation has long been limited by spectral line broadening and a reduced signal-to-noise ratio, which arise from multiaxis orientations of the N-$V$ centers. The (111) crystal plane is considered an optimal growth direction, as it enables near-perfect axial alignment of N-$V$ centers ($>99\%$) and enhances photon collection efficiency. Nonetheless, the perfect alignment was maintained at the sacrifices, including low growth rates and limited nitrogen-to-N-$V$ conversion efficiencies. In this study, we demonstrate a microwave plasma chemical vapor process in which a growth rate of $94.0\mathrm{\mu }\mathrm{m}/\mathrm{h}$ (14-fold enhancement to the highest previous record) was achieved with uniform N-$V$ ensemble distribution, an N-$V$ concentration of 0.54 ppm, and a nitrogen-to-N-$V$ conversion efficiency of 4.1%–4.7%. The resulting volume-normalized dc and ac magnetic field sensitivities reached $2.15\mathrm{nT}\mathrm{\mu }{\mathrm{m}}^{3/2}{\mathrm{Hz}}^{-1/2}$ and $0.30\mathrm{nT}\mathrm{\mu }{\mathrm{m}}^{3/2}{\mathrm{Hz}}^{-1/2}$, respectively.

The time evolution of initially localized wavepackets in the discrete Hatano-Nelson lattice displays a rich dynamical structure shaped by the interplay between dispersion and nonreciprocity. Our analysis reveals a characteristic evolution of the wave-packet center of mass, which undergoes an initial constant acceleration, subsequently decaying acceleration, and ultimately enters a regime of uniform motion, accompanied throughout by exponential amplification of the wave-packet amplitude. To capture this behavior, we develop a continuum approximation that incorporates higher-order dispersive and nonreciprocal effects and provides accurate analytical predictions across all relevant time scales. We then demonstrate the existence of a non-Hermiticity-induced jump—an abrupt spatial shift of the wave-packet center even in the absence of disorder—and derive its underlying analytical foundation. The analytical predictions are in excellent agreement with direct numerical simulations of the Hatano-Nelson chain. Our results elucidate the interplay between dispersion and nonreciprocity in generating unconventional transport phenomena and pave the way for controlling wave dynamics in nonreciprocal and non-Hermitian metamaterials.

Nitrogen-vacancy (NV) centers in diamond have precipitated profound advances in microwave detection, manifesting themselves both in spatial resolution and sensitivity. However, typical methods based on Rabi oscillations are subject to detunings due to thermal and magnetic fluctuations and/or gradients, which introduce systematic errors and render the measurements susceptible to environmental perturbations. Here, we propose and demonstrate a novel approach for determining both the magnitude and direction of microwaves, by exploiting the spectral line broadening effect in the optically detected magnetic resonance of NV centers. This method eliminates the requirement of aligning the MW frequency to the spin transitions and is therefore immune to variations and inhomogeneities of the magnetic field and temperature, providing an optimal tool for fast imaging applications. With this method, we achieved near-field microwave imaging of a microscale “$\mathrm{\Omega }$”-pattern antenna with a resolution of 800 nm. Using multiaxis NVs, a reconstruction of the vector microwave fields is obtained. Our results augment the applicability of diamond-based microwave near-field imaging in applications under complex scenarios, especially where large dynamic range, fast imaging, and highspatial resolution are demanded.

We demonstrate a triple-key optical encryption system that integrates orbital angular momentum (OAM) multiplexing with physical scattering and ultra-sparse sampling. At its core is an adaptive ResNeXt-SPD decoder that achieves 99.28% accuracy in decoding 24-bit OAM superposition states with only 64 pixels—a sampling point density of 0.13%. The system implements a cross-domain security architecture comprising three keys: a physical key (an unclonable scattering medium), a digital key (a sparse sampling pattern), and a computational key (trained network weights). We validate the sparse sampling performance in the full architecture, explore the sampling threshold under constrained networks, and investigate the criticality of each security key. Security analysis confirms that the absence or mismatch of any single key renders the system inoperative. Substituting the physical key drops accuracy to $\mathrm{approximately}50\%$. One pixel shift in the digital key reduces accuracy from 99.28% to $\mathrm{approximately}50\%$. Untrained model weights yield performance equivalent to random guessing. End-to-end image transmission under extreme sparsity maintains high reconstruction quality. This work advances OAM-based secure communication by achieving the lowest sampling-density and multilayer cryptographic protection simultaneously.

We demonstrate a robust, high-visibility nonlocal Franson interferometry for fiber-based quantum networks by copropagating a classical radio-over-fiber clock signal with energy-time entangled photon pairs in the same fiber. Utilizing cross-band allocation (O-band for classical, L-band for quantum signals), the spontaneous Raman scattering noise photons are effectively suppressed. At the same time, their environmental delay fluctuations remain highly correlated for common-mode noise cancellation, achieving a passive synchronization with picoseconds precision. Over 50 km of single-mode fiber, this copropagation enables nonlocal quantum interference with a visibility of $(88.35\pm 3.62)\%$, without relying on external dedicated timing infrastructure. This work provides a practical, scalable synchronization solution for metropolitan-scale entanglement-based quantum networks.

We propose and validate a framework for analog simulation of the Heisenberg spin model using a circuit-quantum-electrodynamics (circuit-QED) platform. To this end, we develop an $f$-deformed boson representation of the $SU(2)$ algebra, which includes the Holstein–Primakoff and Dyson–Maleev transformations as special cases. While this representation is generally non-Hermitian, for spin-$1/2$ systems, we introduce a procedure to circumvent this limitation, showing that the mapping yields the extended Bose-Hubbard (EBH) Hamiltonian. For the experimental realization of this EBH model, we design a scalable circuit-QED architecture based on an engineered Josephson junction array. Numerical simulations confirm that the microwave photon dynamics in this simulator accurately reproduces the original spin dynamics. Our work establishes an experimentally accessible method for investigating complex quantum spin dynamics in a highly controllable bosonic setting.

Nondestructive detection of single-electron motion is crucial for quantum information processing with electrons trapped in Paul traps. The standard approach in Penning traps is to detect the image current induced on the trap electrodes by the electron’s oscillatory motion. However, applying this approach in Paul traps for single electrons is currently hindered by motional frequency fluctuations arising from trap anharmonicities and instabilities in the rf trapping field. In this work, we propose a robust detection scheme exploiting the transient dynamics of parametric driving to overcome these limitations. Distinct from traditional steady-state approaches, our method focuses on the transient regime to break the temporal constraints imposed by steady-state assumptions, thereby enabling fast readout. We show that a controlled ramp of the parametric drive effectively locks the frequency of the electron motion in the transient regime, rendering the signal highly resilient to realistic experimental noise and inherent micromotion. This work paves the way for the experimental realization of nondestructive detection of single-electron motion in Paul traps.

Photons are ideal in many aspects for quantum technologies. However, the absence of direct photon-photon interaction and the problem of wave-packet distortion inherent in nonlinear media-based interactions have long posed a grand challenge in constructing two-qubit logic gates, which are indispensable for universal quantum information processing. Here we report on the theory and design to overcome the challenge, leading to a deterministic, passive, and near-unity-fidelity (exceeding 99%) controlled-$\pi$-phase gate for photonic qubits. The proposed gate comprises only a single two-level emitter and a few cavities and operates under the key concept of time-reversal-symmetric photon transport. It ensures a nonlinear $\pi$ phase shift and circumvents the long-standing difficulty of wave- packet distortion inherent in photonic phase gates using nonlinear media. We develop an analytical solution to reveal the dynamics of two-photon wave-packet transport and to obtain the optimal design. The proposed gate architecture is compatible with the platforms of integrated photonics.