Conventional multiple vortex beams carrying different orbital-angular-momentum (OAM) modes propagating in different directions suffer from beam divergences along with the increasing transmission distance, which greatly limits their practical applications. This article presents a diffraction-resisting dual high-order Bessel-beam (DHOBB) generator based on an anisotropic holographic impedance metasurface (AHIM) operating at 30 and 30.5 GHz. By virtue of leaky-wave theory and the optical holographic principle, surface waves excited by a monopole antenna welded on the back of the metasurface can be modulated into nondiffractive DHOBBs. Different geometric parameters of the subwavelength meta-atoms can be mapped by the interference patterns between the reference surface waves and the desired beams. Furthermore, this designed single-layer anisotropic metasurface can be equivalent to the functionalities of spiral-phase-plate, refractive-hyperbolic, and axicon lenses synthetically utilized in the popular air-fed metasurface to generate HOBBs. Compared with the most popular air-fed metasurface, this design results in predominant performances of ultralow profile, easy fabrication, and integration with other electronic components and avoids alignment errors. Both simulated and measured results demonstrate that nondiffractive DHOBBs carrying different OAM modes can be generated by this designed AHIM. Nondiffractive DHOBBs with different Bessel orders with distinctive properties may open a window for wireless communications with multiarea coverage and multitarget radar detection.

In this work, we briefly overview various options for Josephson junctions, which should be scalable down to nanometer range for utilization in nanoscale digital superconducting technology. Such junctions should possess high values of critical current, $I_c$, and normal state resistance, $R_N$. Another requirement is the high reproducibility of the junction parameters across a wafer in a fabrication process. We argue that superconductor-normal metal-superconductor ($SN$-$N$-$NS$) Josephson junction of “variable thickness bridge” geometry is a promising choice to meet these requirements. Theoretical analysis of the $SN$-$N$-$NS$ junction is performed in the case where the distance between the $S$ electrodes is comparable to the coherence length of the $N$ material. The restriction on the junction geometrical parameters providing the existence of superconductivity in the $S$ electrodes is derived for the current flowing through the junction of an order of $I_c$. The junction heating, as well as available mechanisms for the heat removal, is analyzed. The obtained results show that a $SN$-$N$-$NS$ junction with a high (submillivolt) value of $I_c{R}_N$ product can be fabricated from a broadly utilized combination of materials like Nb/Cu using well-established technological processes. The junction area can be scaled down to that of semiconductor transistors fabricated in the frame of a 40-nm process.

Transition-edge sensors (TESs) are the selected technology for future spaceborne x-ray observatories, such as Athena, Lynx, and HUBS. These missions demand thousands of pixels to be operated simultaneously with high energy-resolving power. To reach these demanding requirements, every aspect of the TES design has to be optimized. Here we present the experimental results of tests on different devices where the coupling between the x-ray absorber and the TES is varied. In particular, we look at the effects of the diameter of the coupling stems and the distance between the stems and the TES bilayer. Based on measurements of the ac complex impedance and noise, we observe a reduction in the excess noise as the spacing between the absorber stem and the bilayer is decreased. We identify the origin of this excess noise to be internal thermal fluctuation noise between the absorber stem and the bilayer. In addition, we see an impact of the coupling on the superconducting transition in the appearance of kinks. Our observations show that these unwanted structures in the transition shape can be avoided with careful design of the coupling geometry. The stem diameter appears to have a significant effect on the smoothness of the TES transition. This observation is still poorly understood, but is of great importance for both ac and dc biased TESs.

The excellent optoelectronic and transport properties of halide perovskites have led to the rapid development of perovskite-based optoelectronic devices. A fundamental understanding of charge-carrier dynamics, as well as the implementation of physical models able to accurately describe their behaviour, is essential for further improvements in the field. Here, combining advanced modeling and characterization, a method for analyzing the short time dynamics of time-resolved fluorescence imaging (TRFLIM) decays is demonstrated. A theoretical scaling law for the time derivative of transient photoluminescence decays as a function of excitation power is extracted. This scaling law, computed from classical drift-diffusion equations, defines an innovative and simple way to extract quantitative values for several transport parameters, including the external radiative-recombination coefficient. The model is notably applied on a set of images acquired with a temporal shift of 250 ps to map the top-surface recombination velocity of a triple-cation mixed-halide perovskite thin film at the microscale. The development of high-time-resolution imaging techniques coupled with a scaling method for analyzing short time dynamics provides a solid platform for the investigation of local heterogeneities in semiconductor materials and the accurate determination of the main parameters governing their carrier transport.

Inference is the task of drawing conclusions about unobserved variables given observations of related variables. Applications range from identifying diseases from symptoms to classifying economic regimes from price movements. Unfortunately, performing exact inference is intractable in general. One alternative is variational inference, where a candidate probability distribution is optimized to approximate the posterior distribution over unobserved variables. For good approximations, a flexible and highly expressive candidate distribution is desirable. In this work, we use quantum Born machines as variational distributions over discrete variables. We apply the framework of operator variational inference to achieve this goal. In particular, we adopt two specific realizations: one with an adversarial objective and one based on the kernelized Stein discrepancy. We demonstrate the approach numerically using examples of Bayesian networks, and implement an experiment on an IBM quantum computer. Our techniques enable efficient variational inference with distributions beyond those that are efficiently representable on a classical computer.

We report the realization of fully compensated synthetic antiferromagnets (SAFs) in $\mathrm{Pt}/\mathrm{Co}/\mathrm{Ru}/{\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x$ multilayers with perpendicular magnetic anisotropy, pronounced anomalous Hall resistances and magneto-optical responses. In particular, the properties of SAFs are systematically investigated through optimizing the thicknesses of the $\mathrm{Co}$ layer, the $\mathrm{Ru}$ spacer, and the concentration (x) of the ferrimagnet (FIM) ${\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x$ layers. The incorporation of the FIM ${\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x$ films into SAFs accelerates the search for a magnetic multilayer with fully compensated magnetism and exhibiting pronounced anomalous Hall resistance and magneto-optical signals. These advantages enable spin-orbit-torque switching and magneto-optical Kerr effect imaging experiments on the fully compensated SAFs to be readily investigated. Through incorporating FIMs into SAFs, we believe that the present material system could provide a promising platform not only for adequately addressing the fully compensated spin dynamics of SAFs at room temperature, but also for developing intriguing SAF-based spin-orbitronic devices.

We use balanced optical low-coherence interferometry to measure the ultralow light power back-reflected and/or back-scattered by optical interfaces. Indeed, backscattered light from optical surfaces can be a critical source of noise in interferometric gravitational-wave detectors, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), Virgo, or the Laser Interferometer Space Antenna (LISA), and therefore, it is required to characterize, with high sensitivity, the scattering properties of elementary components involved in their optical design. The use of a broadband light source makes an easy identification of the scattering interface possible, while the implementation of balanced interferometric detection allows very low light levels to be detected, thanks to the simultaneous use of coherent gain and source intensity noise suppression. Experimental results are reported, first on bare glass optical windows (N-BK7 and S-LAH66) and then on a silver-coated mirror, that demonstrate the ability of this setup to quantify specular- or diffuse-reflectance coefficients as low as ${10}^{-11}$.

It is demonstrated that a system of two interfacing hyperbolic metamaterials may be used for direct subwavelength imaging in the visible range. The proposed configuration consists of two anisotropic photonic crystals: a multilayered metal-dielectric structure and an adjoined wired structure. The results of analytical calculations and numerical modeling show that the light emitted by a dipole placed on the top of the multilayered structure propagates within a narrow cone along the direction $\mathbf{n}$, where $\mathrm{Re}\epsilon (\omega ,\mathbf{n})=0$. Owing to impedance matching and negative refraction at the interface, a bright image with a maximum transverse size of approximately $50$ nm is focused in the wired structure at the wavelength $\lambda =670$ nm.

Emergent behaviors in antiferroelectric thin films due to a coupling between surface electrochemistry and intrinsic polar instabilities are explored within the framework of the modified 2-4-6 Landau-Ginzburg-Devonshire (LGD) thermodynamic approach. By using phenomenological parameters of the LGD potential for a bulk antiferroelectric and a Stephenson-Highland (SH) approach, we study the role of surface ions with a charge density proportional to the relative partial oxygen pressure on the dipole states and their reversal mechanisms in antiferroelectric thin films. The combined LGDSH approach allows the boundaries of antiferroelectric, ferroelectriclike antiferroionic, and electretlike paraelectric states as a function of temperature, oxygen pressure, surface-ion formation energy and concentration, and film thickness to be delineated. This approach also allows the characterization of the polar and antipolar orderings dependence on the voltage applied to the antiferroelectric film, as well as the analysis of their static and dynamic hysteresis loops. The applications of the antiferroelectric films covered with a surface-ion layer for energy and information storage are explored and discussed.

The stability of high-end piezoacoustic drop-on-demand (DOD) inkjet printing is sometimes compromised by the entrainment of an air bubble inside the ink channel. Here, bubble pinch-off from an oscillating meniscus is studied in an optically transparent DOD printhead as a function of the driving waveform. We show that bubble pinch-off follows from low-amplitude high-frequency meniscus oscillations on top of the global high-amplitude low-frequency meniscus motion that drives droplet formation. In a certain window of control parameters, phase inversion between the low- and high-frequency components leads to the enclosure of an air cavity and bubble pinch-off. Although phenomenologically similar, bubble pinch-off is not a result of capillary-wave interaction such as observed in drop impact on a liquid pool. Instead, we reveal geometrical-flow focusing as the mechanism through which, at first, an outward jet is formed on the retracted concave meniscus. The subsequent high-frequency velocity oscillation acts on the now toroidal-shaped meniscus and it accelerates the toroidal ring outward, resulting in the formation of an air cavity that can pinch off. Through incompressible boundary-integral simulations, we reveal that bubble pinch-off requires an unbalance between the capillary and inertial time scales and that it does not require acoustics. The critical control parameters for pinch-off are the pulse timing and amplitude. To cure the bubble entrainment problem, the threshold for bubble pinch-off can be increased by suppressing the high-frequency driving through appropriate waveform design. The present work therefore aids the improvement of the stability of inkjet printers through a physical understanding of meniscus instabilities.

Microwave delivery to samples in a cryogenic environment can pose experimental challenges such as restricting optical access, space constraints, and heat generation. Moreover, existing solutions that overcome various experimental restrictions do not necessarily provide a large homogeneous oscillating magnetic field over macroscopic length scales, which is required for control of spin ensembles or fast gate operations in scaled-up quantum computing implementations. Here, we show fast and coherent control of a negatively charged nitrogen-vacancy spin ensemble by taking advantage of the high permittivity of a ${\mathrm{K}\mathrm{Ta}\mathrm{O}}_3$ dielectric resonator at cryogenic temperatures. We achieve Rabi frequencies of up to 48 MHz, with a total power-to-field conversion factor $C_{\mathrm{P}}=9.66\mathrm{mT}/\sqrt{\mathrm{W}}$ (approximately $191{\mathrm{MHz}}_{\mathrm{Rabi}}/\sqrt{\mathrm{W}}$). We use the nitrogen-vacancy-center spin ensemble to probe the quality factor, the coherent enhancement, and the spatial distribution of the magnetic field inside the diamond sample. The key advantages of the dielectric resonator utilized in this work are ease of assembly, in situ tunability, a high magnetic field conversion efficiency, a low-volume footprint, and optical transparency. This makes ${\mathrm{K}\mathrm{Ta}\mathrm{O}}_3$ dielectric resonators a promising platform for the delivery of microwave fields for the control of spins in various materials at cryogenic temperatures.

A continual change in resistance plays an important role in simulating the biological synapses and an abrupt switching mode helps to store information with fast speed and low-power operation. The manipulation of dual-mode switching and comprehension of switching mechanisms, which are the key to developing multifunctional resistance random access memory devices, has made little progress due to the complexity of the influencing factors. We observe that both gradual and abrupt reset behaviors exist in the $\mathrm{Ta}/{\mathrm{Ta}}_2{\mathrm{O}}_5/\mathrm{In}\text{−}\mathrm{Sn}\text{−}\mathrm{O}$ (ITO) structure, and the utilization of various compliance currents ($I_{\mathrm{CC}}$) can control the reset processes of the device. The difference in switching behavior is a result of the different compositions of the conductive filaments (CFs). $\mathrm{Ta}$ and oxygen-vacancy dual filaments contribute to resistive switching at low $I_{\mathrm{CC}}$, whereas the change in valence states of ${\mathrm{Ta}\mathrm{O}}_x$ dominates the formation and rupture of CFs at high $I_{\mathrm{CC}}$. The introduction of a thin ${\mathrm{Mo}\mathrm{S}}_2$ intermediate layer also leads to a transition between abrupt- and gradual-switching modes. The $\mathrm{Ta}/{\mathrm{Mo}\mathrm{S}}_2/{\mathrm{Ta}}_2{\mathrm{O}}_5/\mathrm{ITO}$ device exhibits digital switching behavior with ultralow power consumption. Moreover, the $\mathrm{Ta}/{\mathrm{Ta}}_2{\mathrm{O}}_5/{\mathrm{Mo}\mathrm{S}}_2/\mathrm{ITO}$ device with an analog reset process can be applied to realize synaptic functions.

High-performance artificial synaptic devices are key building blocks for developing efficient neuromorphic computing systems. However, the nonlinear and asymmetric weight update of existing devices has restricted their practical applications. Herein, floating gate nonvolatile memory (FG NVM) devices based on two-dimensional (2D) ${\mathrm{Hf}\mathrm{S}}_2$/$h$-BN/FG-graphene heterostructures have been designed and investigated as multifunctional NVM and artificial optoelectronic synapses. Benefiting from the FG architecture, the ${\mathrm{Hf}\mathrm{S}}_2$-based NVM device exhibits competitive performances, such as a high on:off ratio ($>{10}^5$), large memory window (approximately 100 V), excellent charge retention ability ($>{10}^4\mathrm{s}$), and robust durability ($>{10}^3$ cycles). Notably, the artificial optoelectronic synapses based on ${\mathrm{Hf}\mathrm{S}}_2$ FG NVM show an impressive large conductance margin and good linearity, owing to the ultrahigh photoresponsivity and photogain of ${\mathrm{Hf}\mathrm{S}}_2$. The energy consumption of per spike in our artificial synapse is as low as 0.2 pJ. Therefore, a high recognition accuracy up to 91.5% of the artificial neural network on the basis of our ${\mathrm{Hf}\mathrm{S}}_2$-based optoelectronic synapse at the system level has been achieved, which is superior to other reported 2D artificial optoelectronic synapses. This work paves the way forward for all 2D material-based memory for developing efficient optogenetics-inspired neuromorphic computing in brain-inspired intelligent systems.

${\mathrm{Hf}\mathrm{O}}_2$-based films have attracted much attention due to their robust ferroelectric properties at the nanometer scale and their great potential for data storage. The interface between the substrate and the ${\mathrm{Hf}\mathrm{O}}_2$-based film has a significant effect on its ferroelectric behavior. A seed layer between the films and substrates, such as a ${\mathrm{Zr}\mathrm{O}}_2$ seed layer, is proved to be an effective way to realize the beneficial interface effect. However, the interfacial tuning mechanism for the ferroelectric properties of ${\mathrm{Hf}\mathrm{O}}_2$-based thin films brought by the substrate or seed layer remains unclear so far. By performing first-principles calculations, the phase stability and crystalline orientation of ${\mathrm{Hf}\mathrm{O}}_2$ thin films on ${\mathrm{Zr}\mathrm{O}}_2$ seed layers are systematically studied. Results indicate that the ${\mathrm{Zr}\mathrm{O}}_2$ seed layer, especially the [111]-oriented one, substantially stabilizes the orthorhombic ferroelectric phase and the high-symmetry tetragonal phase of the ${\mathrm{Hf}\mathrm{O}}_2$ thin film compared with the most stable monoclinic phase. Furthermore, the polarization magnitude of the ${\mathrm{Hf}\mathrm{O}}_2$ film on the ${\mathrm{Zr}\mathrm{O}}_2$ seed layer is in good agreement with experiment. The [100]-oriented ${\mathrm{Zr}\mathrm{O}}_2$ seed layer also has a great effect on the stability of the orthorhombic ferroelectric phase of the ${\mathrm{Hf}\mathrm{O}}_2$ thin film. These results are meaningful for the understanding of the interfacial effects of the ferroelectricity of ${\mathrm{Hf}\mathrm{O}}_2$-based thin films and the development of ferroelectric devices.

Achieving strong repulsive Casimir forces through engineered coatings can pave the way for micro- and nanoelectromechanical applications where adhesive forces currently cause reliability issues. Here, we exploit Lifshitz theory to identify the requirements for repulsive Casimir forces in gyrotropic media for two limiting cases (ultrastrong gyroelectric and nongyroelectric). We show that the origin of repulsive force in media with strong gyrotropy such as Weyl semimetals arises from the giant interconversion of polarization of vacuum fluctuations.