The rapid progress in antiferromagnetic and altermagnetic spintronics has led to increased interest in magnetic materials with vanishing net magnetization but strong spin-dependent transport properties. As thin films of such materials become central to device concepts, precise magnetic characterization is essential, to quantify intrinsic moments and interpret transport signatures such as the anomalous Hall effect. In this work, we show that commercial $\mathrm{Mg}\mathrm{O}$ substrates, commonly used in epitaxial growth, often produce substantial parasitic magnetic signals that can match or exceed the response of weakly magnetic films. We identify two major components: a low-field ferromagnetic-like contribution originating from the epi-ready surface, and a temperature-dependent paramagnetic background associated with dilute bulk impurities. These artifacts vary between samples and cannot be corrected using standard linear background subtraction or a measured reference substrate. To address this, we develop and put forward a compensation scheme that combines two complementary, nondestructive measurement protocols. We demonstrate up to 97% efficacy without requiring prior measurements of the bare substrate. The proposed framework enables reliable extraction of intrinsic magnetic signals and provides a general strategy for high-fidelity magnetometry in weakly magnetic thin-film systems, including emerging classes of materials such as topological phases and two-dimensional magnets. We also report the diamagnetic susceptibility of crystalline $\mathrm{Mg}\mathrm{O}$, ${\chi }_{\mathrm{Mg}\mathrm{O}}=-4.0\times {10}^{-7}$ emu/g/Oe.

Quantum transduction is essential for connecting quantum technologies across varied frequencies. Achieving a positive quantum capacity of a traditional quantum transduction channel is a long-pursued goal in the field. However, to overcome the high threshold remains a major challenge, owing to practical limitations. Recently, an entanglement-assisted transducer was proposed based on a cavity-optic system [Opt. Quantum 2, 475 (2024)], where a modified bosonic loss channel was obtained, and the transduction efficiency could be enhanced by properly tuning the squeezing parameters. In this paper, we further identify three types of quantum channel enabled by this design, offering additional options for implementing the proposed transduction schemes. Compared with transducers without entanglement assistance, the scheme also shows a great enhancement in the conversion bandwidth for achieving high quantum capacity, further increasing its value in practical applications.

Hong-Ou-Mandel (HOM) interference is an intrinsic quantum phenomenon that goes beyond the possibilities of classical physics, and enables various applications in quantum metrology. While the timing resolution of HOM-based sensors is generally investigated, the ultimate quantum sensitivity in the estimation of transverse deflection or displacement between paired photons interfering at a balanced beam splitter has been explored relatively little. Here we present an experimental demonstration of a spatial HOM interferometry for measuring the transverse deflection of an optical beam by using transverse momentum sampling measurements. This feasible scheme suffices to achieve great precision with comparatively little technological effort, which circumvents the stringent requirement in direct imaging resolution at the diffraction limit. We can adaptively determine optimum working points using a Fisher information analysis, and demonstrate an optimized spatial HOM interferometry according to practical applications. These results may significantly facilitate the use of quantum interference for high-precision spatial sensing, and may pave the way to more complex quantum imaging techniques such as nanoscopic microscopy.

The generation and dynamic control of optical skyrmions enable topological structured light. However, existing approaches require complex experimental setups or sophisticated fabrication technology, limiting their scalability. Here, we introduce a method to generate and manipulate optical skyrmions without nanofabrication or precise alignment, leveraging spin-orbit interaction in a uniaxial crystal. By focusing a fundamental Gaussian beam along the optical axis of the crystal, the skyrmion texture will be generated in the output field. Furthermore, we demonstrate controlled transformation between different topological states by modulating the incident polarization. This approach provides a direct route for manipulating compact topological light and paves the way for applications based on optical skyrmions.

The development of hafnia-based ferroelectric memory necessitates careful balancing of retention time and switching endurance—both critically dependent on operating voltage. While lower voltages naturally reduce power consumption and increase endurance, they induce partial polarization switching (polydomain states), whose retention properties remain poorly understood. This challenge is compounded by the industry’s requirement for 10-year retention, which cannot be directly measured. Here we establish a physics-based framework predicting polarization loss in polydomain ${\mathrm{Hf}}_{0.5}{\mathrm{Zr}}_{0.5}{\mathrm{O}}_2$ capacitors under low-voltage operation. Time-resolved $I$-$V$ analysis reveals opposing imprint effects in domains with upward (P$\uparrow$) and downward (P$\downarrow$) polarization, manifested as peak splitting in switching currents. This behavior drives retention degradation through two distinct mechanisms: progressive domain inaccessibility as shifting coercive fields surpass read-voltage thresholds, and polarization backswitching during read operations due to imprint-induced asymmetric switching. The proposed model predicts retention loss across arbitrary read voltages by correlating the time-dependent coercive-voltage evolution in the P$\uparrow$ domain and P$\downarrow$ domain populations that constitute the domain configuration established during the write operation. The framework demonstrates that read voltage dominates retention stability, providing essential design rules for memory optimization. These findings bridge fundamental domain dynamics with practical device engineering, advancing scalable ferroelectric memory development.

Nitrogen-vacancy ($\mathrm{N}$-$V$) centers in diamond exhibit long spin-coherence times, optical initialization, and optical-spin readout under ambient conditions, making them excellent quantum sensors. However, the conventional scheme for charge-state initialization based on off-resonant green excitation results in significant state-preparation errors, typically around $30\mathrm{\%}$. One method for improving charge-state initialization fidelity is to use multicolor excitation, which has been demonstrated to achieve a near-unity preparation fidelity for bulk $\mathrm{N}$-$V$ centers by using a few milliseconds of near-infrared (NIR) (5-mW) and green ($10$-$\text{μ}\mathrm{W}$) excitation. The translation of such schemes to $\mathrm{N}$-$V$ centers near the diamond surface with higher-efficiency optical pumping would enable new applications in nanoscale sensing. Here, we demonstrate a protocol for efficient charge initialization of shallow $\mathrm{N}$-$V$ centers between 5 nm and 15 nm from the diamond surface. By carefully studying the charge dynamics of shallow $\mathrm{N}$-$V$ centers, we identify a region of parameter space that allows for near-unity (95%) charge initialization within $300\text{μ}\mathrm{s}$ of NIR (905-nm, 1-mW) and green (520-nm, $10$-$\text{μ}\mathrm{W}$) excitation. The time to 90% charge initialization can be as fast as $10\text{μ}\mathrm{s}$ for 4 mW of NIR and $39\text{μ}\mathrm{W}$ of green illumination. This fast, efficient charge initialization protocol will especially benefit nanoscale sensing applications in which state-preparation errors currently prohibit scaling, such as measuring higher-order multipoint correlators.

Parameter-shift rules (PSRs) are useful methods for computing arbitrary-order derivatives of the cost function in parameterized quantum circuits. The basic idea of PSRs is to evaluate the cost function at different parameter shifts, then use specific coefficients to combine them linearly to obtain the exact derivatives. In this work, we propose an extended PRS (EPSR), which generalizes a broad range of existing PSRs and has the following two advantages. First, EPSR offers an infinite number of possible parameter shifts, allowing the selection of the optimal parameter shifts to minimize the final derivative variance and thereby obtaining the more accurate derivative estimates with limited quantum resources. Second, EPSR extends the scope of the PSRs in the sense that EPSR can handle arbitrary Hermitian operator $H$ in gate $U(x)=\exp (iHx)$ in the parameterized quantum circuits, while existing PSRs are valid only for simple Hermitian generators $H$ such as simple Pauli words. Additionally, we show that the widely used “general PSR”, introduced by Wierichs et al. (2022), is a special case of our EPSR, and we prove that it yields globally optimal shifts for minimizing the derivative variance under the weighted-shot scheme. Finally, through numerical simulations, we demonstrate the effectiveness of EPSR and show that the usage of the optimal parameter shifts indeed leads to more accurate derivative estimates.

We demonstrate a compact 780-nm rubidium optical clock, comprising an optical-frequency standard and an optical-frequency comb, with a total optical volume of 11.6 liters. Unlike the 778-nm rubidium atomic clocks based on two-photon transitions, the laser frequency in our system was stabilized to the hyperfine transition of ${}^{87}\mathrm{Rb}$ $5^2{\mathrm{S}}_{1/2}$ (F = 2) → $5^2{\mathrm{P}}_{3/2}$ (F′ = 3) using modulation transfer spectroscopy. This approach effectively eliminates Doppler background and provides higher signal-to-noise ratio and sensitivity. After correcting for systematic perturbations, the absolute frequency was measured to be 384 228 115 200.7(2.7) kHz. A nearly 300-MHz microwave signal, whose phase exactly tracked that of the optical-frequency standard, was generated via the optical-frequency comb, yielding a frequency instability of 1.91 × ${10}^{-13}$ at 1 s and 5.29 × ${10}^{-14}$ at 1000 s in the electronic domain. The reproducibility was measured to be 3.66 × ${10}^{-12}$ by comparing results from four independent daily measurements, each conducted following a complete system shutdown and restart. This is among the most precise frequency stabilization results for the first-excited-state transition of alkali metal atoms to date, and represents an optical clock based on this transition. This work offers a promising approach for the development of portable optical clocks.

The generation of pure spin current, as well as that of pure charge current, is critical for future quantum information processing. Here, we propose a four-probe device based on monolayer $\mathrm{Mo}\mathrm{S}$${}_2$ and investigate both linear and circular photogalvanic effects by employing the nonequilibrium Green’s function combined with density functional theory. Under linearly polarized light, when the polarization direction aligns with one of the transport directions, a pure spin photocurrent is generated along the zigzag direction, while a pure charge photocurrent is produced simultaneously along the armchair direction. This effect is independent of the incident angle for light incident from a plane perpendicular to the monolayer $\mathrm{Mo}\mathrm{S}$${}_2$. In contrast, simultaneous generation of pure spin and pure charge photocurrents cannot be realized under circularly polarized light. Symmetry analysis of the bulk-spin photovoltaic effect indicates that concurrent generation of pure charge and pure spin currents requires broken inversion symmetry combined with mirror symmetry along a specific direction. This mechanism extends to a wide range of two-dimensional materials, offering opportunities for photogalvanic effects in next-generation electronic and spintronic devices.

Ultrafast excitation of nonequilibrium carriers under intense pulses offers unique opportunities for controlling the optical properties of semiconductor materials. In this work, we propose a scheme for ultrafast generation of surface plasmon-polaritons (SPPs) via a transient metagrating formed under two interfering optical pump pulses in a thin film of the semiconductor $\mathrm{Ga}\mathrm{As}$. The grating is formed due to modulation of the refractive index associated with the nonequilibrium carrier generation. The temporal grating structure formed enables the generation of SPP waves at the $\mathrm{Ga}\mathrm{As}$/$\mathrm{Ag}$ interface via weak probe pulse excitation. We propose a theoretical model describing nonequilibrium carriers formation and diffusion and their contribution to permittivity modulation via Drude and band-filling mechanisms. We predict that by tuning the parameters of the pump and probe, one can reach the critical coupling regime and achieve efficient generation of SPPs on timescales of 0.1–1 ps.

Quantum physics-informed neural networks (QPINNs) integrate quantum computing and machine learning to impose physical biases on the output of a quantum neural network, aiming to either solve or discover differential equations. The approach has recently been implemented in both the gate model and continuous-variable quantum computing architecture, where it has been demonstrated capable of solving ordinary differential equations. Here, we aim to extend the method to effectively address a wider range of equations, such as the Poisson equation and the heat equation. To achieve this goal, we introduce an architecture specifically designed to compute second-order (and higher-order) derivatives without relying on nested automatic differentiation methods. This approach mitigates the unwanted side effects associated with nested gradients in simulations, paving the way for more efficient and accurate implementations. By leveraging such an approach, the quantum circuit addresses partial differential equations—a challenge not yet tackled using this approach on continuous-variable quantum computers. As a proof of concept, we solve a one-dimensional instance of the heat equation, demonstrating its effectiveness in handling partial differential equations in both ideal and a noisy regime. We report our experiment on photonic hardware to address a realistic noise scenario for our simulations. Such a framework paves the way for further developments in continuous-variable quantum computing and underscores its potential contributions to advancing quantum machine learning.

Quantum holography exploits quantum correlation in entangled photon pairs to enhance holography. An inherent principle of holography is that each partial hologram can enhance the reconstruction of the entire object, a property that has not yet been explored in the quantum realm. The current fabrication technology for single-photon detectors is limited, making it extremely challenging to manufacture large-area detectors. Since resolution is directly related to the system aperture, achieving a resolution equivalent to that of a large-area detector under the constraint of a limited detection area is a key challenge for realizing high-resolution quantum holography. Here we demonstrate that the spatial correlations of entangled photons can extract crucial additional information from photon wave packets beyond the boundaries of the experimentally recorded region, where the photons have no direct interaction with the object. We validate the approach experimentally and benchmark it against the approach using only the detection area, achieving the advancements with an increase of up to 15 dB in signal-to-noise ratio and up to approximately tenfold improvement in structural similarity. We show the versatility of the approach by demonstrating significantly improved performance across various objects, including quantum holography of complex biological specimens. This work can advance the nascent field of quantum holography and accelerate its application in life sciences and biological systems.

Spintronics has emerged as a promising field for next-generation devices, offering functionalities beyond complementary metal-oxide semiconductor (CMOS). A critical challenge in spintronics is to develop systems that can efficiently generate spin currents and enable their long-distance transport. Here, we demonstrate a graphene (Gr) / heavy-metal (HM) heterostructure system that combines strong charge-spin interconversion efficiency, induced by the spin Hall effect, with a long spin diffusion length. By employing an industry-friendly magnetron-sputtering technique, we deposit HM layers onto few-layer Gr while minimizing structural damage. The proximity effect from the HM enhances the spin Hall angle of Gr while limiting the reduction in its spin diffusion length. Additionally, the spin Hall angle can be tuned via an applied gate voltage, offering high controllability of the system. Importantly, these properties are observed across heterostructures composed of different HMs, indicating the generality of this approach. Our findings establish Gr/HM heterostructures as a scalable and versatile platform for spin current generation, paving the way for advanced spintronic devices with high efficiency, long spin propagation, and straightforward fabrication processes.

Coupling microwave cavity modes with spin qubit transitions is crucial for enabling efficient qubit readout and control, long-distance qubit coupling, quantum memory implementation, and entanglement generation. We experimentally observe the coupling of different spin qubit transitions in silicon carbide ($\mathrm{Si}\mathrm{C}$) material to a three-dimensional microwave (MW) resonator mode around 12.6 GHz at a temperature of 10 mK. Tuning the spin resonances across the cavity resonance via magnetic field sweeps, we perform microwave cavity transmission measurements. We observe spin transitions of different spin defects that are detuned from each other by around 60–70 MHz. By optically exciting the $\mathrm{Si}\mathrm{C}$ sample placed in the MW cavity with an 810-nm laser, we observe the coupling of an additional spin resonance to the MW cavity, also detuned by around 60–70 MHz from the center resonance. We perform complementary confocal optical spectroscopy as a function of temperature from 4 to 200 K, using a part of the same sample used for the cavity measurements. Combining the confocal spectroscopy results and a detailed analysis of the MW-resonator-based experiments, we attribute the observed spin resonances to two different paramagnetic defects, the negatively charged silicon-vacancy spins located at the $V_1$ and $V_2$ lattice sites. The $V_1$ and $V_2$ lines in $\mathrm{Si}\mathrm{C}$ are interesting qubit transitions since they are known to be robust to decoherence. Consequently, the demonstration of the joint coupling of these spin qubits to a MW cavity mode could lead to interesting new modalities: The microwave cavity could act as an information bus and mediate long-range coupling between the spins, with potential applications in quantum computing and quantum communication, which is an especially attractive proposition in a complementary metal-oxide semiconductor–compatible material such as $\mathrm{Si}\mathrm{C}$.

The recent emergence of bound states in the continuum (BICs) has established a powerful paradigm for achieving high-quality-factor resonances in metasurfaces. Here, we propose a silicon nitride metasurface structure capable of supporting polarization-sensitive quasi-BICs, to generate structural colors with a wide gamut, high saturation, and tunable brightness. By designing a periodic array of nanodisks with in-plane symmetry breaking, we successfully excite magnetic dipole quasi-BICs with polarization-sensitive properties. Owing to its high-quality factor, this resonance exhibits a narrow-linewidth reflection peak across the visible spectrum, thereby significantly enhancing color purity. We employ a synergistic approach that combines deep learning with reinforcement learning to efficiently predict the optimal structural parameters, resulting in coverage that approaches the simulated sRGB color gamut. Experimental results further demonstrate that the brightness of the structural colors can be dynamically tuned by controlling the polarization state of incident light. Based on this mechanism, we design and fabricate two categories of chromatic patterns with orthogonally arranged air holes, which exhibit clear polarization-dependent responses under both orthogonal linear polarizations and white-light illumination. Our work offers insights into the application of high-performance structural colors in color printing, dynamic information encryption, and optical anticounterfeiting.

Band crossings in electronic band structures play an important role in determining the electronic, topological, and transport properties in solid-state systems, making them central to both condensed matter physics and materials science. The emergence of noisy intermediate-scale quantum (NISQ) processors has sparked great interest in developing quantum algorithms to compute band-structure properties of materials. While significant research has been reported on computing ground-state and excited-state energy bands in the presence of noise that breaks the degeneracy, identifying the symmetry at crossing points using quantum computers is still an open question. In this work, we propose a method for identifying the symmetry of bands around crossings and anticrossings in the band structure of bilayer graphene with two distinct configurations on a NISQ device. The method uses eigenstates at neighboring $\mathbf{k}$ points on either side of the touching point to recover the local symmetry by implementing a character-checking quantum circuit that uses ancilla qubit measurements for a probabilistic test, with a complexity scaling linearly with the system size. We then evaluate the performance of our method under a depolarizing noise model, using symmetry operations with four distinct matrix representations and four characters to assess its robustness. Finally, we demonstrate the reliability of our method by correctly identifying the correct band crossings of $AA$-stacked bilayer graphene around the $K$ point, using the character-checking circuit implemented on the noisy IBM quantum processor ibm_marrakesh.