Spinel-type magnetite ${\mathrm{Fe}}_3{\mathrm{O}}_4$ is predicted to be a half-metal material with negative spin polarization. However, magnetic tunnel junctions (MTJs) using an ${\mathrm{Fe}}_3{\mathrm{O}}_4$ electrode exhibit a small tunnel magnetoresistance (TMR) effect, the sign of which has not been established experimentally. The development of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ as an excellent TMR material requires a better understanding of the characteristics of the interface and the phase transition of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ called the Verwey transition. We fabricate MTJs using epitaxial ${\mathrm{Fe}}_3{\mathrm{O}}_4$-based stacks on $\mathrm{Mg}\mathrm{O}(001)$ substrates and find a large inverse TMR ratio of −55.8% at 80 K, which corresponds to 126% by the optimistic definition of the TMR ratio. The temperature dependence of the TMR ratio is significantly affected by the Verwey transition. Moreover, we investigate the dependence of TMR on oxygen partial pressure during ${\mathrm{Fe}}_3{\mathrm{O}}_4$ deposition. It is found that the magneto-transport properties of the MTJs show different behaviors depending on the oxygen partial pressure because the Verwey transition is sensitive to the oxygen concentration. Furthermore, the electronic and magnetic properties at the interfacial regions are investigated by x-ray magnetic spectroscopy and first-principles calculation. These findings greatly support the use of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ in spintronic devices and should lead to further developments in oxide spintronics.

Being a general wave phenomenon, bound states in the continuum (BICs) appear in acoustic, hydrodynamic, and photonic systems of various dimensionalities. Here, we report the first experimental observation of an accidental electromagnetic BIC in a one-dimensional periodic chain of coaxial ceramic disks. We show that the accidental BIC manifests itself as a narrow peak in the transmission spectra of the chain placed between two loop antennas. We demonstrate a linear growth of the radiative quality factor of the BICs with the number of disks that is well described with the developed tight-binding model. We estimate the number of disks when the radiation losses become negligible in comparison to material absorption and, therefore, the chain can be considered as practically infinite. The presented analysis is supported by near-field measurements of the BIC profile. The obtained results provide useful guidelines for practical implementations of structures with BICs opening up horizons for the development of radio-frequency and optical metadevices.

Bismuth chalcohalides of ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{X}_2$ (X = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$) are solvothermally synthesized and systematically characterized as a light absorber for photovoltaics. Rietveld refinements reveal that ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{X}_2$ compounds adopt the same hexagonal structure with space group P3 and a chemical composition of $({\mathrm{Bi}}^{3+}{)}_{12}({\mathrm{Bi}}_2^{4+}{)}_{0.5}({\mathrm{S}}^{2-}{)}_{18}(X^{-}{)}_2$, where a triangular tunnel is constructed from [${\mathrm{Bi}}_4{\mathrm{S}}_6$]-ribbon spokes in the c-axial direction, $X^{-}$ is located in the tunnel sites, and Bi(II) dimers of (${\mathrm{Bi}}_2^{4+}$) are located at the hexagonal center. The photoelectric behavior is investigated using ultraviolet-to-visible-to-near-infrared (UV-vis-NIR) absorption spectroscopy, ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, Mott-Schottky plots, and conductivity measurements. The ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{X}_2$ compounds are indirect n-type semiconductors with narrow band gaps of 0.76, 0.80, and 0.81 eV for ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{\mathrm{Cl}}_2$, ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{\mathrm{Br}}_2$, and ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{\mathrm{I}}_2$, respectively, and exhibit strong light absorbance over a wide wavelength range from UV to NIR. A facile physical vapor deposition approach is developed for the fabrication of a homogeneous ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{X}_2$ thin film to study the photovoltaic performances. Solar cells with the architecture fluorine-doped tin oxide/${\mathrm{Ti}\mathrm{O}}_2$/${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{X}_2$/(${\mathrm{I}}_3^{-}/{\mathrm{I}}^{-}$ redox couple)/$\mathrm{Pt}$ demonstrate power conversion efficiencies of 0.91, 1.12, and 0.75% for ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{\mathrm{Cl}}_2$, ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{\mathrm{Br}}_2$, and ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{\mathrm{I}}_2$, respectively. The highest cell performance of ${\mathrm{Bi}}_{13}{\mathrm{S}}_{18}{\mathrm{Br}}_2$ can be attributed to its higher light-absorption ability.

Transformation optics, which is generically applicable to other classical waves such as acoustic and elastic waves, provides an emerging design paradigm to manipulate waves. However, some lenses and optical-transformation devices require a singular refractive index; meeting this requirement is a significant challenge. A method called transmutation can relax some types of index singularity into finite anisotropy around the singularity. Here, we show that such lenses with a singularity for flexural waves can be obtained by approaching a near-zero thickness of the plate precisely at the location of the singularity. As examples, we demonstrate a series of Eaton lenses theoretically and experimentally by projecting the refractive index in space onto the thickness in plates and by working in a broad frequency range in which impedance mismatch is negligible. This framework offers an insight into feasible methods that can be used to develop singular devices such as cloaking devices on thin flexible curved plates and can be further extended to a general methodology for shaping elastic waves. We hope that this elastic platform can also be a test bed to indirectly study unprecedented phenomena enabled by gravitational and quantum fields in terms of analog models.

Asymmetrically sandwiched thin magnetic layers with perpendicular anisotropy and Dzyaloshinskii-Moriya interaction (DMI) is the prospective material science platform for spin-orbitronic technologies that rely on the motion of chiral magnetic textures, like skyrmions or chiral domain walls (DWs). The dynamic performance of a DW-based racetrack is defined by the strength of the DMI and the DW damping. The determination of the latter parameter is typically done based on technically challenging DW motion experiments. Here, we propose a method to access both the DMI constant and DW damping from static experiments by monitoring the tilt of magnetic DWs in nanostripes. We experimentally demonstrate that in perpendicularly magnetized ${\mathrm{//Cr}\mathrm{O}}_x\mathrm{/Co/Pt}$ stacks, DWs can be trapped on edge roughness in a metastable tilted state as a result of the DW dynamics driven by an external magnetic field. The measured tilt can be correlated to the DMI strength and DW damping in a self-consistent way in the frame of a theoretical formalism based on the collective coordinate approach.

Isomeric fission products, such as ${}^{134m}\mathrm{Te}$ ($T_{1/2}=164$ ns) and ${}^{136m}\mathrm{Xe}$ ($T_{1/2}=2.95\mu \mathrm{s}$), are proposed as a signature of special nuclear materials in active interrogation applications. To test this conjecture, monoenergetic 9, 11, and 13 MeV photons from the $\mathrm{HI}\gamma \mathrm{S}$ facility are used to induce fission of ${}^{235}\mathrm{U}$, ${}^{238}\mathrm{U}$, and ${}^{239}\mathrm{Pu}$ targets. The de-excitation $\gamma$ rays of the isomers are measured using time-gated spectroscopy with high-purity germanium detectors. The ${}^{134m}\mathrm{Te}$ and ${}^{136m}\mathrm{Xe}$ isomers are detected and identified by the energy and decay half-life of their characteristic $\gamma$-ray transitions. The ratio of yields for these two signature $\gamma$ rays, corresponding to ${}^{134m}\mathrm{Te}/{(}^{136m}\mathrm{Xe}{+}^{136}\mathrm{I})$, is found to be strongly correlated with the identity of the fissioning nuclei. These results show that fission-product isomers may be used in active interrogation to detect and identify special nuclear materials, even providing information on the isotopic enrichment. The feasibility of an active interrogation scenario using a bremsstrahlung beam is discussed.

The flourishing of attosecond science (1 as = ${10}^{-18}$ s) has created a need to control exquisitely the delay between two ultrashort light pulses, where one of them is intense and in the visible spectral range, while the other is weak and in the extreme-ultraviolet spectral range. Here we introduce a robust technique, named LIZARD (Laser-dressed IoniZation for the Adjustment of the pump-pRobe Delay), allowing active stabilization of this pump-probe delay. The important feature of the method is the use of an error signal calculated from a two-photon photoelectron signal obtained by photoionizing a gas target in an electron spectrometer with the two superimposed beams. The modulation of sidebands in phase quadrature allows us to perform an in situ measurement of the pump-probe phase and to compensate for fluctuations with a uniform noise sensitivity over a large range of delay. Despite an interferometer length of several meters, we achieve a long-term stability of 28 as rms over hours. This method could be applied to the stabilization of other types of two-color interferometer, provided that the required phase-shifted photoionization signals can be obtained.

How can a target’s differential image of multiple components at a certain degree of freedom (DOF) of light (e.g., wavelength, polarization, and position) be obtained? Previous schemes often need two steps, i.e., first collecting each component of the target simultaneously with multiple detectors or sequentially with a single detector, then performing the difference operation in the digital postprocessing. Based on the principle of computational ghost imaging (GI), we here take advantage of the natural complementarity in space to design an illumination mode, which is no longer the spatiotemporal fluctuation of photon number (light intensity) but the photons with different components under the same DOF. By applying this engineered illumination to computational GI, termed ghost difference imaging (GDI), we can achieve differential imaging of multiple components of a certain DOF in a single-round acquisition using only one single-pixel detector with no extra digital-subtraction operations but higher SNR. Both multiwavelength-difference GDI and position-difference GDI are well demonstrated in simulations and experiments. Further, the GDI scheme reduces the number of sampling times for differential imaging while also increasing photons’ utilization. Our work, therefore, provides an insight for GI modality, along with a straightforward and low-cost update of the light path, which is suitable for all computational GI systems using the digital micromirror device.

Randomness is a fundamental feature of quantum mechanics, which is an invaluable resource for both classical and quantum technologies. Practical quantum random-number generators (QRNGs) usually need to trust their devices, but their security can be jeopardized in the case of imperfections or malicious external actions. In this work, we present a robust implementation of a semi-device-independent QRNG that guarantees both security and fast generation rates. The system works in a prepare-and-measure scenario, where measurement and source are uncharacterized, but a bound on the energy of the prepared states is assumed. Our implementation exploits heterodyne detection, which offers increased generation rate and improved long-term stability compared to alternative measurement strategies. In particular, due to the tomographic properties of heterodyne measurement, we can compensate for fast phase fluctuations via postprocessing, avoiding complex active phase-stabilization systems. As a result, our scheme combines high security and speed with a simple setup featuring only commercial-off-the-shelf components, making it an attractive solution in many practical scenarios.

Cloud cavitation causes nontrivial energy concentration and acoustic shielding in liquid and its control is a long-standing challenge due to complex dynamics of bubble clouds. We present a framework to study closed-loop control of cavitation through acoustic feedback. While previous approaches have used empirical thresholding, we employ model-based state estimation of coherent bubble dynamics based on theory and high-performance computing. Using a pulsed ultrasound setup, we demonstrate set-point control of the pulse-repetition frequency (PRF) to modulate acoustic cavitation near a solid target over $O(100)$ s. We identify a quasiequilibrium correlation between the PRF and the bubble dynamics and an optimal PRF to minimize acoustic shielding of the target. This framework can be readily scaled up by enhanced acoustic sensing and computational power.

A scheme for a high-yield photonuclear pulsed neutron source is proposed by use of a relativistic femtosecond laser interacting with a microstructure target combined with a high-$Z$ converter. By using three-dimensional particle-in-cell and Monte Carlo simulations, we find that bright $\gamma$ rays are emitted by bremsstrahlung radiation when energetic dense electron bunches pulled out from the microstructure target pass through the converter. A large number of neutrons are thus induced via photonuclear reactions. With a laser of intensity of approximately $3.4\times {10}^{21}{\mathrm{W/cm}}^2$ and energy of approximately $6.2$ J, a neutron pulse of yield as high as $1.9\times {10}^8{\mathrm{J}}^{-1}$ and duration of approximately $45$ ps can be obtained. This scheme could be realized in laboratories with current multipetawatt laser facilities.

Nitrogen-vacancy (N-V) centers, optically active atomic defects in diamond, have been widely applied to emerging quantum sensing, imaging, and network efforts, showing unprecedented field sensitivity and nanoscale spatial resolution. Many of these advantages derive from their excellent quantum-coherence, single-spin addressability, and remarkable functionality over a broad temperature range, enabling opportunities to outperform their classical counterparts. To date, N-V measurements of spin fluctuations have mainly focused on systems with in-plane magnetization, but applications to material systems with a spontaneous out-of-plane magnetization remain largely unexplored despite their technological importance. Here, we report N-V sensing of intrinsic spin fluctuations of magnetic insulator ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ thin films with perpendicular magnetic anisotropy. The measured field dependence of N-V relaxation rates is well correlated to the variation of magnon density and band structure of the magnetic samples, which are challenging to access by the conventional magnetometry methods. Our results highlight the significant opportunities offered by N-V centers in diagnosing the noise environment of functional magnetic elements, providing valuable information to develop next-generation, high-density, and scalable spintronic devices.

Vector beams are inhomogeneously polarized optical fields with nonseparable quantumlike correlations between their polarization and spatial components, and they hold tremendous promise for classical and quantum communication across various channels, e.g., the atmosphere, underwater, and in optical fiber. Here, we show that by exploiting their quantumlike features by virtue of the nonseparability of the field, the decay of both the polarization and spatial components can be studied in tandem. In particular, we invoke the principle of channel-state duality to show that the degree of nonseparability of any vector mode is purely determined by that of a maximally nonseparable one, which we confirm using orbital angular momentum (OAM) as an example for topological charges of $\ell =1$ and $\ell =10$ in a turbulent atmosphere. A consequence is that the well-known cylindrical vector vortex beams are sufficient to predict the behavior of all vector OAM states through the channel. Our method reveals interesting features about the performance of various modes through the channel: the decay in vector quality decreases with an increasing OAM value, even though the spread is higher for larger OAM modes. Our approach offers a fast and easy probe of noisy channels, while at the same time revealing the power of quantum tools applied to classical light.

Solid-state atomlike systems have great promise for linear optic quantum computing and quantum communication but are burdened by phonon sidebands and broadening due to surface charges. Nevertheless, coupling to a small-mode-volume cavity would allow high rates of extraction from even highly dephased emitters. We consider the nitrogen-vacancy center in diamond, a system understood to have a poor quantum optics interface with highly distinguishable photons, and design a silicon nitride cavity that allows 99% efficient extraction of photons at 200 K with an indistinguishability of $>$ 50%, improvable by external filtering. We analyze our design using Lumerical fdtd simulations and treat optical emission using a cavity-QED master equation valid at and beyond strong coupling and that includes both zero-phonon line broadening and sideband emission. The simulated design is compact ($<10\mu \mathrm{m}$) and, owing to its planar geometry, can be fabricated using standard silicon processes. Our work therefore points toward scalable fabrication of noncryogenic atomlike efficient sources of indistinguishable photons.

The efficiency of state-of-the-art $\mathrm{Cd}\mathrm{Te}$ solar cells remains limited by the relatively low open-circuit voltage ($V_{OC}$). Improving the front interface is key towards realizing a higher $V_{OC}$ after achieving the necessary bulk carrier density and lifetime. Recent efforts in identifying buffer layers beyond $\mathrm{Cd}\mathrm{S}$ have focused on ${\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}$, which offers tunability of the band offsets, but often suffers from high interfacial defect densities. ${\mathrm{Ga}}_2{\mathrm{O}}_3$-based buffer layers demonstrate tremendous improvements in interfacial defect passivation in crystalline silicon and dye-sensitized solar cells, leading to record high $V_{OC}$, yet remain largely unexplored in $\mathrm{Cd}\mathrm{Te}$-based devices. Here, we perform hybrid density-functional-theory calculations to investigate pure ${\mathrm{Ga}}_2{\mathrm{O}}_3$ and ${\mathrm{In}\mathrm{Ga}\mathrm{O}}_3$ alloys as a window layer in $\mathrm{Cd}\mathrm{Te}$ photovoltaics. We report calculated band offsets for several pairs of solid-solid interfaces comprising transparent conducting oxide (TCO) and $\mathrm{Cd}\mathrm{Te}$ heterojunctions. The results support a large conduction band offset spike of 0.67 eV for the $\mathrm{Cd}\mathrm{Te}/{\mathrm{Ga}}_2{\mathrm{O}}_3$ (100) interface, while the offset is reduced to 0.18 eV for the ${\mathrm{In}\mathrm{Ga}\mathrm{O}}_3$ alloy and matches closely with the preferred optimum value of 0.2 eV. Device-level modeling tests of $\mathrm{Cd}\mathrm{Te}$ solar cells integrating our results indicate that the highest efficiency is achieved with ${\mathrm{In}\mathrm{Ga}\mathrm{O}}_3$ acting both as a buffer layer and TCO. Our results suggest that alloys of ${\mathrm{In}}_2{\mathrm{O}}_3$ and ${\mathrm{Ga}}_2{\mathrm{O}}_3$ may be attractive alternatives to ${\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}$ for tailoring optimal conduction-band offsets of the buffer and TCO layers in high-efficiency $\mathrm{Cd}\mathrm{Te}$ thin-film solar cells.

Quantum amplitude estimation (QAE) can achieve a quadratic speedup for applications classically solved by Monte Carlo simulation. A key requirement to realize this advantage is efficient state preparation. If state preparation is too expensive, it can diminish the quantum advantage. Preparing arbitrary quantum states has exponential complexity with respect to the number of qubits, and thus, is not applicable. Currently known efficient techniques require problems based on log-concave probability distributions, involve learning an unknown distribution from empirical data, or fully rely on quantum arithmetic. In this paper, we introduce an approach to simplify state preparation, together with a circuit optimization technique, both of which can help reduce the circuit complexity for QAE state preparation significantly. We demonstrate the introduced techniques for a numerical integration example on real quantum hardware, as well as for option pricing under the Heston model, i.e., based on a stochastic volatility process, using simulation.

Quantum error mitigation (QEM) is vital for noisy intermediate-scale quantum (NISQ) devices. While most conventional QEM schemes assume discrete gate-based circuits with noise appearing either before or after each gate, the assumptions are inappropriate for describing realistic noise that may have strong gate dependence and complicated nonlocal effects, and general computing models such as analog quantum simulators. To address these challenges, we first extend the scenario, where each computation process, being either digital or analog, is described by a continuous time evolution. For noise from imperfections of the engineered Hamiltonian or additional noise operators, we show it can be effectively suppressed by a stochastic QEM method. Since our method assumes only accurate single qubit controls, it is applicable to all digital quantum computers and various analog simulators. Meanwhile, errors in the mitigation procedure can be suppressed by leveraging the Richardson extrapolation method. As we numerically test our method with various Hamiltonians under energy relaxation and dephasing noise and digital quantum circuits with additional two-qubit crosstalk, we show an improvement of simulation accuracy by 2 orders. We assess the resource cost of our scheme and conclude the feasibility of accurate quantum computing with NISQ devices.

Electrochemically efficient electrode materials are required for clean energy storage in $\mathrm{Li}$ ion batteries. We predict two-dimensional hexagonal metal nitrides, borides, and phosphides (${\mathrm{Sc}}_2\mathrm{B}$, ${\mathrm{Sc}}_2\mathrm{N}$, ${\mathrm{Y}}_2\mathrm{B}$, ${\mathrm{Y}}_2\mathrm{N}$, and ${\mathrm{Y}}_2\mathrm{P}$) and evaluate the feasibility of experimental realization. The materials combine excellent metallicity, as required for electrodes, with $\mathrm{Li}$ binding energies providing high storage capacity and a low average open-circuit voltage. In contrast to two-dimensional silicene, borophene, and ${\mathrm{Sn}\mathrm{S}}_2$, we observe negligible structural distortions during $\mathrm{Li}$ adsorption and extraction, which results in high reversibility and a long cycle life. Superionic $\mathrm{Li}$ diffusion enables fast charge or discharge of next-generation $\mathrm{Li}$ ion batteries.