Topological lattices have recently generated a great deal of interest based on the unique mechanical properties rooted in their topological polarization, including the ability to support localized modes at certain floppy edges. The study of these systems has been predominantly restricted to the realm of in-plane mechanics, to which many topological effects are germane. In this study, we stretch this paradigm by exploring the possibility to export certain topological attributes to the flexural wave behavior of thin lattice sheets. To couple the topological modes to the out-of-plane response, we assemble a bilayer lattice by stacking a thick topological kagome layer onto a thin twisted kagome lattice. The band diagram reveals the existence of modes whose out-of-plane character is controlled by the edge modes of the topological layer, a behavior elucidated via simulations and confirmed via laser vibrometer experiments on a bilayer prototype specimen. These results open an alternative direction for topological mechanics whereby flexural waves are controlled by the in-plane topology, leading to potential applications for flexural wave devices with engineered polarized response.

We report the controllable buckling of free-standing thin-film semiconductor metamaterials using a thin-walled structure spanning $\mathrm{Au}$ grid supports. The buckling is developed by compressing the $\mathrm{Au}$ grids, increasing the internal air pressure during the bonding of $\mathrm{Au}$ pads on the semiconductor to the grids, resulting in upward deformation. The stiffness of the free-standing semiconductor beam is controlled by the grid line spacing, as verified for a wide range of out-of-plane deformations, ranging from nearly flat to microns for grid line spacings from 20 to 150 µm, respectively. We also observe telephone-cord and domelike buckling as the grid line spacings and layer thicknesses are varied. Finite element analysis quantitatively predicts the shape and magnitude of the film deflection. We propose strategies to apply the distorted free-standing metamaterials for thermal energy harvesting, optical reflectors, and pressure sensors.

Switching induced by spin-orbit torque (SOT) is being vigorously explored, as it allows the control of magnetization using an in-plane current, which enables a three-terminal magnetic-tunnel-junction geometry with isolated read and write paths. This significantly improves the device endurance and the read stability, and allows reliable subnanosecond switching. Tungsten in the $\beta$ phase, $\beta$-$\mathrm{W}$, has the largest reported antidamping SOT charge-to-spin conversion ratio $({\theta }_{\mathrm{AD}}\approx -60\mathrm{\%})$ for heavy metals. However, $\beta$-$\mathrm{W}$ has a limitation when one is aiming for reliable technology integration: the $\beta$ phase is limited to a thickness of a few nanometers and enters the $\alpha$ phase above 4 nm in our samples when industry-relevant deposition tools are used. Here, we report our approach to extending the range of $\beta$-$\mathrm{W}$, while simultaneously improving the SOT efficiency by introducing $\mathrm{N}$ and $\mathrm{O}$ doping of $\mathrm{W}$. Resistivity and XRD measurements confirm the extension of the $\beta$ phase from 4 nm to more than 10 nm, and transport characterization shows an effective SOT efficiency larger than $-44.4\mathrm{\%}$ (reaching approximately $-60\mathrm{\%}$ for the bulk contribution). In addition, we demonstrate the possibility of controlling and enhancing the perpendicular magnetic anisotropy of a storage layer ($\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$). Further, we integrate the optimized $\mathrm{W}(\mathrm{O},\mathrm{N})$ into SOT magnetic random-access memory (SOT-MRAM) devices and project that, for the same thickness of SOT material, the switching current decreases by 25% in optimized $\mathrm{W}(\mathrm{O},\mathrm{N})$ compared with our standard $\mathrm{W}$. Our results open the path to using and further optimizing $\mathrm{W}$ for integration of SOT-MRAM technology.

The ongoing rapid progress towards quantum technologies relies on new hybrid platforms optimized for specific quantum computation and communication tasks, and researchers are striving to achieve such platforms. We study theoretically a spin qubit exchange-coupled to an anisotropic ferromagnet that hosts magnons with a controllable degree of intrinsic squeezing. We find this system to physically realize the quantum Rabi model from the isotropic to the Jaynes-Cummings limit with coupling strengths that can reach the deep-strong regime. We demonstrate that the composite nature of the squeezed magnon enables concurrent excitation of three spin qubits coupled to the same magnet. Thus, three-qubit Greenberger-Horne-Zeilinger and related states needed for implementing Shor’s quantum error-correction code can be robustly generated. Our analysis highlights some unique advantages offered by this hybrid platform, and we hope that it will motivate corresponding experimental efforts.

We analyze the magnetic mode structure of axially magnetized finite-length nanoscopic cylinders in a regime where the exchange interaction dominates, along with simulations of the mode frequencies of the ferrimagnet yttrium iron garnet. For the bulk modes, we find that the frequencies can be represented by an expression given by Herring and Kittel by using wavevector components obtained by fitting the mode patterns emerging from these simulations. In addition to the axial, radial, and azimuthal modes that are present in an infinite cylinder, we find localized “cap modes” that are “trapped” at the top and bottom cylinder faces by the inhomogeneous dipole field emerging from the ends. Semiquantitative explanations are given for some of the modes, in terms of a one-dimensional Schrodinger equation, which is valid in the exchange-dominant case. The assignment of the azimuthal-mode number is carefully discussed, and the frequency splitting of a few pairs of nearly degenerate modes is determined through the beat pattern emerging from them.

Deep learning is having a tremendous impact in many areas of computer science and engineering. Motivated by this success, deep neural networks are attracting increasing attention in many other disciplines, including the physical sciences. In this work, we show that artificial neural networks can be successfully used in the theoretical modeling and analysis of a variety of radiative-heat-transfer phenomena and devices. By using a set of custom-designed numerical methods able to efficiently generate the required training data sets, we demonstrate this approach in the context of three very different problems, namely (i) near-field radiative heat transfer between multilayer systems that form hyperbolic metamaterials, (ii) passive radiate cooling in photonic crystal slab structures, and (iii) thermal emission of subwavelength objects. Despite their fundamental differences in nature, in all three cases we show that simple neural-network architectures trained with data sets of moderate size can be used as fast and accurate surrogates for doing numerical simulations, as well as engines for solving inverse design and optimization in the context of radiative heat transfer. Overall, our work shows that deep learning and artificial neural networks provide a valuable and versatile toolkit for advancing the field of thermal radiation.

Active-scattering-cancellation techniques provide a means of achieving electromagnetic cloaking without dealing with passivity-based design and performance limitations. However, a major drawback is that the cloak must be adjusted to accommodate a specific set of illumination conditions. Until recently, configuration has been performed with these conditions known a priori. Although adequate for initial validation, this presents a major obstacle to the development of a practical device that must contend with an unknown and dynamic electromagnetic environment. As a solution, this paper presents the development of an estimation algorithm that uses field measurements, sampled within the vicinity of the object to be cloaked, to deduce incident-wave properties. This information can then be used to adaptively reconfigure the cloak without any prior knowledge of its surroundings. In addition, the use of iterative solvers is avoided in estimator development, sidestepping convergence issues that afflict previous designs while reducing run time. After presenting the development process and operation principles, performance evaluation is conducted by using the algorithm to estimate the incident angle, signal magnitude, and phase offset of an incident wave impinging on either a circular or polygonal quasi-two-dimensional conductive target. Input data sets are initially provided via full-field simulation models and later supplanted by real-world field measurements.

The conversion and interaction between quantum signals at the single-photon level are essential for scalable quantum photonic information technology. Using a fully optimized periodically poled lithium niobate microring, we demonstrate ultraefficient sum-frequency generation on a chip. The external quantum efficiency reaches $(65\pm 3)\mathrm{\%}$ with only $(104\pm 4)$-$\mu \mathrm{W}$ pump power. At peak conversion, $3\times {10}^{-5}$-noise photon is created during the cavity lifetime, which meets the requirement of quantum applications using single-photon pulses. Using a pump and signal in single-photon coherent states, we directly measure the conversion probability produced by a single pump photon to be ${10}^{-5}$, which is a significant improvement from the state of the art, and the photon-photon coupling strength to be 9.1 MHz. Our results mark steady progress toward quantum nonlinear optics at the ultimate single-photon limit, with potential applications in highly integrated photonics and quantum optical computing.

Geometric phases accompanying adiabatic quantum evolutions can be used to construct robust quantum control for quantum information processing due to their noise-resilient feature. A significant development along this line is to construct geometric gates using nonadiabatic quantum evolutions to reduce errors due to decoherence. However, it has been shown that nonadiabatic geometric gates are not necessarily more robust than dynamical ones, in contrast to an intuitive expectation. Here we experimentally investigate this issue for the case of nonadiabatic holonomic quantum computation (NHQC) and show that conventional NHQC schemes cannot guarantee the expected robustness due to a cross-coupling to the states outside the computational space. We implement a different set of constraints for gate construction in order to suppress such cross-coupling to achieve an enhanced robustness. Using a superconducting quantum circuit, we demonstrate high-fidelity holonomic gates whose infidelity against quasistatic transverse errors can be suppressed up to the fourth order, instead of the second order in conventional NHQC and dynamical gates. In addition, we explicitly measure the accumulated dynamical phase due to the abovementioned cross-coupling and verify that it is indeed much reduced in our NHQC scheme. We further demonstrate a protocol for constructing two-qubit NHQC gates also with an enhanced robustness.

Although the origin of sub-band-gap electroluminescence has been extensively studied for organic light-emitting diodes (OLEDs) with a planar heterojunction of rubrene-fullerene (${\mathrm{C}}_{60}$), the dynamic behaviors of exciplexes formed at the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface are still vague. Herein, employing magnetoconductance (MC) and magnetoelectroluminescence (MEL) detection techniques, we find an unreported reverse intersystem crossing (RISC, ${\mathrm{EX}}^3$ → ${\mathrm{EX}}^1$) from triplet to singlet exciplexes dominated at the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface. Besides this RISC evolution channel, the triplet exciplexes also participate in another two processes: one is the scattering channel of triplet-charge annihilation (TCASC, ${\mathrm{EX}}^3$ + $\overleftarrow{e}$ → $S_0$+ ↓e) with excessive charge carriers, which is disadvantageous for RISC to occur, and the other is Dexter-energy transfer to produce a triplet exciton (${\mathrm{EX}}^3$ → $T_1$) in rubrene followed by triplet-triplet annihilation (TTA, $T_1$+ $T_1$ → $S_1$+ $S_0$ → hν↑ + 2$S_0$). This TTA is the physical origin of sub-band-gap EL because TTA needs no respective injection of electrons and holes into the LUMO and HOMO energy levels and requires no direct recombination of LUMO electrons with HOMO holes in rubrene. Moreover, both the bias-current dependences of MC and MEL traces reveal that the RISC process is more obvious in relatively balanced devices due to weak TCASC processes, and they show a monotonic decrease and nonmonotonic variation in unbalanced and relatively balanced $\mathrm{rubrene}/{\mathrm{C}}_{60}$-based OLEDs, respectively, because of the combined effects of the applied electrical field and the TCASC process. Theoretically, a stronger RISC process should be observed in devices by inserting a thin bathocuproine (BCP) interlayer to modify the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface due to the increased separation distance between electron and hole in exciplex states, but the opposite experimental results are obtained because of strong TCASC channels simultaneously occurred with the insertion of a BCP interlayer. The RISC process decreases monotonically upon lowering the operational temperature due to its endothermic property. This work deepens our comprehensive understanding of the dynamic behaviors of exciplexes and the physical origin of sub-gap EL features in $\mathrm{rubrene}/{\mathrm{C}}_{60}$-based OLEDs.

The emissivity and absorptivity of nonreciprocal thermal emitters are not constrained by the well-known Kirchhoff law of thermal radiation, which usually serves as the theoretical basis to characterize thermal properties. When thermal emitters are nondiffracting, which is the case in previous studies of nonreciprocal thermal emitters, the angular distribution of emissivity and absorptivity is mirror symmetric with respect to the normal direction, and the nonreciprocal effect is confined to a relatively narrow angular range. In this work, we consider nonreciprocal thermal emitters that can simultaneously couple to multiple diffraction channels. We show that the symmetry relation between absorptivity and emissivity can be broken in such multichannel emitters. The angular range in which the nonreciprocal effect is strong can also be significantly broadened. Such multichannel emitters can operate as one-way energy splitters. Our work significantly broadens the flexibility of thermal-radiation control in nonreciprocal thermal-emitter design.

In spintronics, one of the long-standing questions is why the $\mathrm{Mg}\mathrm{O}$-based magnetic tunnel junction (MTJ) is almost the only option for achieving a large tunneling magnetoresistance (TMR) ratio at room temperature, although this is not as large as the theoretical prediction. This study focuses on the development of an almost strain-free MTJ using metastable bcc ${\mathrm{Co}}_x{\mathrm{Mn}}_{100\text{−}x}$ ($\mathrm{Co}\text{−}\mathrm{Mn}$) ferromagnetic films. We investigate the degree of crystallization in MTJs consisting of $\mathrm{Co}\text{−}\mathrm{Mn}/\mathrm{Mg}\mathrm{O}/\mathrm{Co}\text{−}\mathrm{Mn}$ in relation to their TMR ratios. Cross-section high resolution transmission electron microscopy reveals that almost consistent lattice constants of these layers for 66 ≤ x ≤ 83 with large TMR ratios of 229% at room temperature, confirming the soft nature of the $\mathrm{Co}\text{−}\mathrm{Mn}$ layer with some dislocations at the $\mathrm{Mg}\mathrm{O}/{\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}$ interfaces. Ab initio calculations confirm the crystalline deformation stability across a broad compositional range in $\mathrm{Co}\text{−}\mathrm{Mn}$, proving the advantage of a strain-free interface for much larger TMR ratios.

We present the design and characterization of a three-Josephson-junction superconducting loop circuit with three large shunt capacitors. Used as a qubit, the circuit shows long energy-relaxation times, of the order of $40\mu \mathrm{s}$ and a spin-echo dephasing time of $9.4\mu \mathrm{s}$. The circuit has high anharmonicity, of $2\pi \times 3.69\mathrm{GHz}$. We extract the multilevel relaxation and dephasing rates of the circuit used as a qutrit and discuss the possible sources for the decoherence. The high anharmonicity allows for fast qubit control with nanosecond-range gate durations and a measured average gate fidelity of 99.92%, characterized by randomized benchmarking. These results demonstrate interesting potential use for fast nanosecond-time-scale two-qubit gates and multilevel quantum logic.

The establishment of chiral coupling in thin magnetic films with inhomogeneous anisotropy has led to the development of artificial systems of fundamental and technological interest. The chiral coupling itself is enabled by the Dzyaloshinskii-Moriya interaction (DMI) enforced by the patterned noncollinear magnetization. Here, we create a domain wall track with out-of-plane magnetization coupled on each side to a narrow parallel strip with in-plane magnetization. With this we show that the chiral torques emerging from the DMI at the boundary between the regions of noncollinear magnetization in a single magnetic layer can be used to bias the domain wall velocity. To tune the chiral torques, the design of the magnetic racetracks can be modified by varying the width of the tracks or the width of the transition region between noncollinear magnetizations, reaching effective chiral magnetic fields of up to 7.8 mT. Furthermore, we show how the magnitude of the chiral torques can be estimated by measuring asymmetric domain wall velocities, and demonstrate spontaneous domain wall motion propelled by intrinsic torques even in the absence of any external driving force.

The characterization and radiography of special nuclear materials (SNMs) such as plutonium and uranium is essential in various scenarios in the context of nonproliferation and national security. However, existing techniques are not sufficient in and of themselves for rapid isotope-sensitive interrogation of SNMs. In the present study, we propose an interrogation method, called scattering-nuclear-resonance-fluorescence-based computer tomography (SNRF CT), to reveal concealed SNMs with simultaneous measurements of the isotopic composition and tomographic distribution. Monte Carlo simulations show that three NRF signatures at 1802, 1846, and 1862 keV from a uranium target composed of ${\hspace{0.17em}}^{235}\mathrm{U}$ and ${\hspace{0.17em}}^{238}\mathrm{U}$, irradiated by a quasimonochromatic $\gamma$-ray beam of high intensity, can be identified. For different target configurations, sinograms of the SNRF signatures are obtained, and the tomographic distributions are reconstructed with appreciable image contrast and spatial precision. It is found that the tomographic patterns of ${\hspace{0.17em}}^{235}\mathrm{U}$ and ${\hspace{0.17em}}^{238}\mathrm{U}$ hidden in a 30-mm-diameter iron rod can be clearly visualized. Compared with transmission NRF CT (TNRF CT), SNRF CT has the advantage that it does not need a witness target or calibration of the notch-refill effect. Furthermore, the imaging time for SNRF CT is 20 times shorter than that for TNRF CT, assuming a low missed-detection rate of ${10}^{-4}$. We conclude that, using an intense $\gamma$-ray beam, the proposed SNRF CT technique is capable of simultaneous identification and tomographic imaging of the isotopic content of SNMs in a realistic measurement time. This imaging method could be extended to other applications in spent-fuel management and screening of cargo for explosives, drugs, and toxic chemicals.

Scalable quantum information processing requires the ability to tune multiqubit interactions. This makes the precise manipulation of quantum states particularly difficult for multiqubit interactions because tunability unavoidably introduces sensitivity to fluctuations in the tuning parameters, leading to erroneous multiqubit gate operations. The performance of quantum algorithms may be severely compromised by coherent multiqubit errors. It is therefore imperative to understand how these fluctuations affect multiqubit interactions and, more importantly, to mitigate their influence. In this study, we demonstrate how to implement dynamical-decoupling techniques to suppress the two-qubit analogue of the dephasing on a superconducting quantum device featuring a compact tunable coupler, a trending technology that enables the fast manipulation of qubit-qubit interactions. The pure-dephasing time shows up to an approximate 14 times enhancement on average when using robust sequences. The results are in good agreement with the noise generated from room-temperature circuits. Our study further reveals the decohering processes associated with tunable couplers and establishes a framework to develop gates and sequences robust against two-qubit errors.

The transtor and memtranstor are the fourth basic linear and memory elements, respectively, which allow direct coupling of charge (q) to magnetic flux (φ) via linear and nonlinear magnetoelectric (ME) effects, respectively. It is found here that a large variation of magnetization by an electric field is realized in both linear and nonlinear hysteretic styles in a magnetoelectric Y-type hexaferrite ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{1.5}{\mathrm{Zn}}_2({\mathrm{Fe}}_{0.92}{\mathrm{Al}}_{0.08}{)}_{12}{\mathrm{O}}_{22}$ single crystal. Moreover, based on the spin-current model, the underlying microscopic mechanisms for generating the two types of linear and nonlinear M versus E curves are understood to be E-induced changes to the cone angle and sign of P, respectively, establishing the charge-driven transtor and memtranstor in the Y-type hexaferrite system. This work points to a promising pathway to develop alternative circuit functionalities using magnetoelectric materials.