We present a superconducting qubit, which consists of two strongly coupled modes: one for data storage and one for coupling, allowing faster, higher-fidelity entangling gates and readout. The use of a dedicated coupling mode allows nonlinear couplings of several hundred MHz between the data mode and other elements, with minimal linear coupling to the data mode. Including decoherence, simulations show that this architecture enables microwave-only cz gates with an infidelity of $8.7\times {10}^{-5}$ in 17 ns and always-on $ZZ$ interaction less than 0.4 kHz. Numerical simulations also show readout with state assignment error of $1\times {10}^{-3}$ in 38 ns (assuming quantum efficiency $\eta =0.5$). Our readout scheme naturally reduces Purcell decay to negligible levels without a Purcell filter and provides a mechanism to suppress shot noise dephasing times to the 10 ms level when not performing readout. Single-qubit gate infidelities are below $1\times {10}^{-5}$ including decoherence. These beyond experimental state-of-the-art gate and readout fidelities rely only on capacitive coupling between arm qubits, making the arm qubit a promising scalable building block for fault-tolerant quantum computers.

Exciplex-based organic light-emitting diodes (EX-OLEDs) include interfacial- and bulk-heterojunction devices, and the external quantum efficiency (EQE) of the bulk device is typically higher than that of the interfacial one when fabricated with the same donor and acceptor materials. Although photoluminescence (PL) and transient PL were used to find that this higher EQE is attributed to the enlarged electron-hole recombination zone, its further reasons are still vague. Here, organic magnetic field $(B)$ effects (OMFEs), including magneto-electroluminescence (MEL), magneto-conductance (MC), and magneto-efficiency ($\mathrm{M}\eta$), are used to find new reasons for the improved EQE. Specifically, low-field effects ($|B|\le 10\mathrm{mT}$) of both MEL and $\mathrm{M}\eta$ traces from the interfacial and bulk devices, respectively, show the $B$-mediated intersystem crossing (ISC) and reverse ISC (RISC) features. Furthermore, although both low-field effects of their MC traces exhibit the $B$-mediated ISC feature, the ISC magnitude of the bulk device is lower than that of the interfacial one under the same injection currents. That is, the low-field effects of their OMFE traces reflect that the RISC process from triplet to singlet EX states (${\text{EX}}_3\to {\text{EX}}_1$) in the bulk device is stronger than that in the interfacial one since these low-field effects are determined by the superposition of the $B$-mediated ISC and RISC processes. Moreover, all high-field effects ($10<|B|\le 300\mathrm{mT}$) of their OMFE traces show the $B$-mediated triplet-charge annihilation (TCA) between ${\text{EX}}_3$ and free charges (${\text{EX}}_3+q\to {\text{S}}_0+q^{\prime }$), but the TCA magnitudes of the bulk device are lower than those of the interfacial one under the same injection currents, indicating a weaker TCA process in the bulk device than that in the interfacial one. This is because the enlarged electron-hole recombination zone increases the quantity of the intermolecular contacts between donor and acceptor materials, causing a higher recombination efficiency in the bulk device than that in the interfacial one. The improved recombination efficiency will increase the quantity of ${\text{EX}}_3$ and reduce that of free charges, which results in the enhanced RISC and weakened TCA, respectively. The weakened TCA still increases the quantity of ${\text{EX}}_3$ and then further enhances RISC, leading to the elevated singlet/triplet ratio and the improved device EQE. Therefore, this work not only uses OMFEs to reveal novel physical mechanisms of the higher EQE from the bulk device than that from the interfacial one, but also paves the way for further developing high-efficiency bulk-heterojunction EX-OLEDs.

We present a nonperturbative tensor-network approach to the excitation spectra of superconducting circuits based on Josephson-junction arrays. These arrays provide the large lumped inductances required for qubit designs, yet their intrinsically many-body nature is typically reduced to effective single-mode descriptions. Perturbative treatments attempt to include the collective array modes neglected in these approximations, but a fully nonperturbative analysis is challenging due to the many-body structure and the collective character of these modes. We overcome this difficulty using the DMRG-X algorithm, which extends tensor-network methods to excited states. Our key advance is a construction of trial states from the linearized mode structure, enabling direct computation of excitations, even in degenerate manifolds, which was previously inaccessible. Our results reveal significant deviations from, and allow us to improve upon, previous perturbative treatments in the regime of low array junction impedance.

As superconducting quantum processors continue to scale, high-performance quantum control becomes increasingly critical. In densely integrated architectures, unwanted interactions between nearby qubits give rise to crosstalk errors that limit operational performance. In particular, direct exchange-type ($\mathit{XY}$) interactions are typically minimized by designing large frequency detunings between neighboring qubits at the hardware level. However, frequency crowding in large-scale systems ultimately restricts the achievable frequency separation. While such $\mathit{XY}$ coupling facilitates entangling gate operations, its residual presence poses a key challenge during single-qubit controls. Here, we propose a scalable pulse-level control framework, incorporating frequency modulation and dynamical decoupling to suppress $\mathit{XY}$ crosstalk errors. This framework operates independently of coupling strengths, reducing calibration overhead and naturally supporting multiqubit connectivity. Numerical simulations show orders-of-magnitude reductions in infidelity for both idle and single-qubit gates in a two-qubit system. We further illustrate scalability in a five-qubit layout, where crosstalk between a central qubit and four neighbors is simultaneously suppressed. Our crosstalk suppression framework provides a practical route toward high-fidelity operation in dense superconducting architectures.

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.