Spatial photonic Ising machines (SPIMs) exploit free-space Fourier propagation to perform parallel optical computation of spin-spin couplings, providing a promising platform for large-scale combinatorial optimization. However, their fidelity is limited by intrinsic optical aberrations and nonuniform incident-field amplitudes, which distort the mapping between the modulating plane and the corresponding Fourier plane, thereby degrading energy resolution and annealing reliability. In this work, we propose an in situ differentiable complex-field calibration framework. Based on paired random phase patterns and Fourier-plane captured intensity distributions, the implicit system error can be numerically backpropagated to an exact complex-amplitude distribution on a pixel sampling grid. In single-spin-flip tests, the typical relative deviation between the measured energy and the theoretical value is reduced to 1.31%. Under general SPIM annealing settings, the coefficient of determination between the experimental and theoretical Hamiltonian reaches 0.9998. This work provides a plug-and-play in situ calibration route toward ultrahigh Hamiltonian-evaluation fidelity in more complicated SPIMs.

Floquet engineering of cavity magnon-polaritons by periodically modulating the magnon frequency has recently attracted much interest as a way to manipulate the energy spectrum of magnon-photon hybrid systems. However, modulating the frequency of magnons by a time-varying bias magnetic field can be challenging. We demonstrate cavity magnon-polariton Floquet engineering by modulating the microwave cavity frequency, allowing large modulation depth and bandwidth. We apply commensurate two-frequency Floquet modulations with the higher frequency at twice and three times the lower frequency and demonstrate that the resulting spectrum depends on the relative amplitude and phase of the two drive tones. In comparison with single-frequency Floquet modulations, the spectrum has qualitatively different features; in particular, new anticrossings appear between previously uncoupled sidebands. Our platform offers an alternative way to manipulate Floquet quasienergy levels in hybrid systems.

High-precision, portable, and deployable frequency standards are required for modern navigation and communication technologies. Optical frequency standards are attractive for their improved stability over their microwave counterparts; however, increased complexities have anchored them in the laboratory. Sacrificing the sensitivity of the most stable optical clocks has led to the recent development of deployable and portable optical frequency standards, leveraging hot atomic or molecular vapor. The short-term limit for a majority of previous reports on two-photon rubidium standards is either the shot-noise or intermodulation limit hindering the 1 s fractional frequency stability to around $1\times {10}^{-13}$. The answer for the shot-noise limit is to increase optical power and collected fluorescence, while the intermodulation limit solution requires improvements in laser linewidth, stimulated Brillouin scattering (SBS) lasers are known to reduce frequency noise, suppressing noise of the pump laser. We investigate an optical frequency standard based on the two-photon transition in ${}^{87}\mathrm{Rb}$ probed with a narrow photonic integrated circuit SBS laser with a quality factor over 130 million and instantaneous linewidth $<10\mathrm{Hz}$. The use of a narrow clock laser coupled with operating at higher optical intensities yielded clock instabilities of $2\times {10}^{-14}$ at 1 s, currently the best reported short-term stability for a two-photon rubidium optical frequency standard.

Mechanically isolated defect centers in hexagonal boron nitride are promising coherent quantum emitters, yet spectral instabilities persist, and their spin-related nature remains unclear. Here we investigate a single mechanically isolated quantum emitter in $h\mathrm{BN}$ integrated onto a coplanar waveguide. The emitter exhibits exceptionally bright photoluminescence excitation signals with saturation count rates exceeding $10\mathrm{Mc}/\mathrm{s}$. High-resolution spectroscopy reveals two closely spaced zero-phonon-line transitions originating from the same defect complex. Time-resolved spectroscopy shows that these transitions exhibit markedly different spectral diffusion dynamics, consistent with distinct donor-acceptor-pair-like recombination pathways with different sensitivities to local electrostatic fluctuations. Off-resonant blue illumination redistributes emission between the two transitions and increases the emission duty cycle without significantly modifying the dominant spectral diffusion rates at low temperature, indicating repumping from long-lived shelving states. Magnetic-field-dependent photoluminescence, optically detected magnetic resonance, and pump-probe measurements reveal millisecond-scale relaxation dynamics and magnetic-field-dependent fluorescence contrast, demonstrating spin-dependent population dynamics in the metastable shelving state. These results clarify how charge-driven spectral fluctuations and spin-dependent shelving jointly shape the optical cycling dynamics.

Photoacoustic imaging (PAI) enables high optical contrast at ultrasonic imaging depths; however, real-time volumetric imaging remains challenging due to the complexity of two-dimensional arrays or the slow mechanical scanning of one-dimensional arrays. In this study, we propose a strategy for scan-free four-dimensional imaging that combines photoacoustic signals with ultrasonic timecoding (PAUTC). For targets possessing both optical absorption and acoustic impedance contrast, we utilize a 1D array to acquire volumetric images in a single data acquisition. By synchronizing pulsed optical excitation with orthogonal ultrasound emissions, elevational spatial information is encoded into temporal delays of scattered ultrasound and subsequently combined with the photoacoustic signals. This encoding strategy enables single-shot 3D reconstruction, without the need for 1D array scanning or complex 2D array detection. We theoretically demonstrate that the spatial resolution of the PAUTC method is mainly determined by the effective bandwidth of the 1D array and provide an analytic expression for the resolution. The performance of the PAUTC method is validated through simulations and experiments. PAUTC restores elevational clarity and achieves volumetric imaging of complex 3D structures with optical and acoustic impedance contrast properties, whereas conventional photoacoustic tomography fails due to the lack of elevational resolution missing in a 1D array. Phantom experiments validate the effectiveness of PAUTC in reconstructing complex 3D structures. Furthermore, real-time 4D imaging is demonstrated by quantitatively tracking a moving microbead at a frame rate of 10 Hz. With the efficient continuous volumetric imaging capability, PAUTC might hold promise for applications in hemodynamic monitoring, fluid dynamics characterization, tracking exogenous dual-contrast agents, guiding interventional metallic needles, and superresolution imaging.

Fusion measurements are a key primitive for linear-optical quantum computing and quantum networks. Type-I and type-II fusion gates are widely used to combine small entangled resource states into larger photonic states, but without ancillary resources their success probability is limited to $1/2$. Existing $3/4$-efficient type-I schemes rely on entangled Bell-pair ancillary states, whose preparation is itself probabilistic and resource-intensive. Here, we propose a boosted type-I fusion gate using only four ancillary single photons and standard linear-optical primitives. For multiqubit GHZ and graph states, the gate succeeds directly with probability $5/8$, while a distillation protocol converts partially entangled outcomes into additional successful events, raising the total success probability to $11/16$ after one stage and asymptotically to $3/4$. We quantify the practical advantage of this scheme by estimating the photonic resources required for generating representative large entangled photonic states and show that the proposed gate significantly reduces the required overhead compared with existing schemes. These results expand the set of resource-efficient linear-optical primitives and enable a substantial reduction in the resource requirements for scalable photonic quantum computing and quantum communication.

This paper presents a technology for fabricating microstructures based on carbon nanowalls (CNWs) integrated on silicon nitride (${\text{SiN}}_{\mathrm{x}}$) waveguides. The step-by-step fabrication process is described, including chemical mechanical planarization, deposition of molybdenum contacts, selective etching of the upper ${\mathrm{SiO}}_{\mathrm{x}}$ buffer layer relative to ${\text{SiN}}_{\mathrm{x}}$, and plasma-enhanced chemical vapor deposition of CNWs. The photothermoelectric response of the structures was studied in the C-band, near the $1.55\mathrm{\mu }\mathrm{m}$ wavelength. The results demonstrate that the primary mechanism of the response to the laser emission is the Seebeck effect, providing a maximum sensitivity of $0.037\mathrm{V}/\mathrm{W}$ without thermal degradation of the CNWs. Furthermore, the amplitude-frequency response of the structures corresponds to that of a fourth-order Butterworth filter with a cutoff frequency of 13.4 kHz. The utilization of the Joule-heating-assisted enhancement allows for a 21.4-fold increase in the output signal amplitude, but it also reduces the bandwidth. These findings highlight the prospects for CNWs in integrated photonics for near-infrared emission detection.

We propose a time- and wavelength-multiplexed remote atom-atom entanglement generation protocol based on cavity-assisted photon scattering (CAPS). This is designed to achieve a high rate and high fidelity with robustness to operational imperfections, parameter fluctuations, and auxiliary time costs, such as percent-level photon impurity, timing and cavity parameter jitter, and atom shuttling time costs. We benchmark this protocol using comprehensive analytical and numerical modeling of the atom-cavity dynamics, including state-dependent pulse-delay effects, photon temporal impurity, atom-cavity system parameter fluctuations, and crosstalk among atoms through a shared cavity mode. With realistic atom-cavity system performance, we predict $2\times {10}^5{\mathrm{s}}^{-1}$ successful atom-atom Bell pair generation even without in-cavity qubit reset, substantially enhanced from two-photon-interference-based protocols, at a predicted heralded fidelity of 0.999. We further show that the predicted rate scales further by the use of wavelength multiplexing while maintaining the fidelity.

Distributed quantum computing offers a scalable route to quantum information processing by entangling spatially separated processors. Although gate teleportation enables universal computation across distributed nodes, it requires repeated consumption of high-fidelity Bell pairs, ancillary qubits, and real-time feedforward, which imposes significant overhead and reduces fidelity. However, many variational quantum algorithms do not demand full universality; rather, they rely on sufficient expressibility to explore solution spaces effectively. Building on this, we propose a distributed variational quantum computing protocol based on deterministic entanglement tuning. In contrast to probabilistic filtering, our approach deterministically modulates preshared entanglement using only local operations and classical communication. We validate the protocol through a proof-of-principle experiment by estimating ground-state energies of the $\text{He}\text{−}{\mathrm{H}}^{+}$ molecule and the Schwinger model, showing that diverse entanglement levels can be engineered to match problem-specific requirements. Our results suggest a practical alternative for near-term distributed quantum applications.

Mode interactions in crystalline microresonators play a significant role in determining the behavior and characterization of optical resonances, particularly in the presence of multiple wavelengths or polarization-dependent effects. In this study, we investigate the behavior and error signal response of oppositely polarized modes near mode crossings in a ${\text{MgF}}_2$ whispering-gallery-mode resonator, in the look for nonlinearities that can be used as performance enhancers. Our analysis reveals a pronounced enhancement in the sensitivity of the transverse-electric mode when the crossing modes are closely coupled, compared to when they are further apart. This effect is attributed to the modified energy exchange dynamics and polarization conversion occurring at the crossing point. By characterizing these interactions, we provide new insights into mode hybridization and the underlying physical mechanisms governing mode splitting and detuning in crystalline microresonators. These findings have implications for precision sensing applications and the optimization of resonator-based optical systems.

We report a distributed-feedback behavior in electron-driven dielectric gratings, arising from intrinsic forward-backward wave interactions, relevant to low-threshold coherent emission. Coupled-mode analysis reveals a quasi-stable region in the groove-depth dependence of the distributed-feedback coupling, consistently beginning at a fundamental organ-pipelike resonance. When driven by an electron beam, the guided power exhibits a corresponding resonance landscape, with a peak at the fundamental organ-pipelike resonance followed by regrowth in the quasi-stable region, highlighting a strong correlation between the intrinsic distributed-feedback behavior and electron-surface mode interaction. Based on this framework, we numerically demonstrate a silicon-grating chip-scale distributed-feedback Cherenkov free-electron laser operating in the terahertz (THz) regime and employing a micrometer-scale grating with an optimized groove depth. Small-signal and coupled-mode analyses for the optimized structure predict a milliampere-level oscillation threshold in good agreement with particle-in-cell simulations, while time-domain simulations confirm Bragg-resonant field buildup at 0.328 THz via electron microbunching with sustained guided-field growth along the grating. These results establish a general design principle for low-threshold terahertz sources based on distributed-feedback surface-mode resonances.

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.

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.

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.

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.