Electron tomography offers useful three-dimensional (3D) structural information, which cannot be observed by two-dimensional imaging. By combining annular dark-field scanning transmission electron microscopy (ADF STEM) with aberration correction, the resolution of electron tomography has reached atomic resolution. However, tomography based on ADF STEM inherently suffers from several issues, including a high electron-dose requirement, poor contrast for light elements, and artifacts from image-contrast nonlinearity. Here, we develop an alternative method called multislice electron tomography (MSET) based on four-dimensional STEM tilt series. Our simulations show that multislice-based 3D reconstruction can effectively reduce undesirable reconstruction artifacts from the nonlinear contrast, allowing precise determination of atomic structures with improved sensitivity for low-Z elements, at considerably low electron-dose conditions. We expect that the MSET method can be applied to a wide variety of materials, including radiation-sensitive samples and materials containing light elements whose 3D atomic structures have never been fully elucidated due to electron-dose limitations or nonlinear imaging contrast.

A ferroelectric field-effect transistor (FEFET) with a cylindrical ferroelectric (FE) nanopillar embedded in the gate oxide stack is proposed and investigated. The device utilizes the multiple polar topological states, which can be stabilized in a nanoscale regime. To correctly simulate the proposed FEFET, a full three-dimensional phase-field-based quantum transport model is developed where nonequilibrium Green’s function, Poisson, and time-dependent Ginzburg-Landau equations are self-consistently solved. Using the in-house tool, we theoretically demonstrate that the nanopillar FEFET exhibits multibit operation of six-level states with a reasonable memory window (MW) and sufficiently large difference in the current between the states. We also investigate the short-channel effect on the proposed FEFET and assess its scalability. MW linearly increases as the gate length decreases, because the polarization bound charges of the FE nanopillar induce the quasi-bound-states on the channel region and thus degrade the gate controllability.

High-dimensional quantum key distribution (HD-QKD) possesses a higher noise-tolerance ability and secure key rate. In the work presented here, by developing a mapping method for multiple degrees of freedom (DOFs), we propose and implement a HD-QKD system with a quantum bit error rate as low as 0.57%. Our HD-QKD system can stably achieve high secure key rates and is composable, allowing one to build HD quantum networks compatible with multiple DOFs. The results indicate that the proposed scheme could bridge HD and two-dimensional terminals encoded in different DOFs and could support large-scale deployment of quantum networks with high performance. Our work significantly enhances the performance of HD-QKD and strengthens the practical applications of large-scale quantum networks in a hybrid way.

The interaction between light and an atom causes perturbations in the atom’s energy levels, known as the light shift. These light shifts are a key source of inaccuracy in atomic clocks, and can also deteriorate their precision. We present a study of light shifts and associated dynamic polarizabilities for a two-photon atomic clock based on the $5S_{1/2}$–$5D_{5/2}$ transition in rubidium-87 over the range 770–800 nm. We determine experimental and theoretical values for a magic wavelength in this range and the electric dipole (E1) matrix element for the $5P_{3/2}$–$5D_{5/2}$ transition. We find a magic wavelength of 776.179(5) nm (experimental) and 776.21 nm (theoretical) in the vicinity of the $5P_{3/2}$–$5D_{5/2}$ resonance, and the corresponding reduced E1 matrix element $1.80(6)e{a}_0$ (experimental) and $1.96(15)e{a}_0$ (theoretical). These values resolve a previous discrepancy between theory and experiment.

Designing the giant-performance explosive energy conversion of lead-free ferroelectrics attracts increasing attention from the medical, energy, defense, and mining industries, whereas the underlying physics mechanism remains ambiguous. Here, chemical modification and pressure engineering are utilized to induce a structural competition between polar and nonpolar structures to achieve a superior explosive energy conversion ($34.57\mathrm{J}/{\mathrm{cm}}^3$) from lead-free (${\mathrm{Ag}}_{0.935}{\mathrm{K}}_{0.065}){\mathrm{Nb}\mathrm{O}}_3$ ceramics, enabling a sharp mechanical-stimulating pulse current within microseconds and having excellent thermal stability of phase structure. We reveal that these merits are related to a local structural heterogeneity on the atomic length scale. Pressure-regulating ferroelectric-antiferroelectric order is responsible for its explosive energy conversion, in which the evolution of oxygen octahedron distortion and electronic transition dynamics under the stress field have been specified. This work reveals the physical origin of the excellent energy-conversion performance of $(\mathrm{Ag},\mathrm{K}){\mathrm{Nb}\mathrm{O}}_3$, and draws a clear scenario for developing the advanced lead-free ferroelectrics device with high-performance energy conversion.

Using pulsed acoustic waves could provide a superior selectivity for microscale acoustic tweezers. However, the theory for the radiation force of pulsed acoustic waves has only been recently derived and no numerical implementations are available. In this paper, we present a finite-element implementation of this model to simulate the transient acoustic radiation force on small spheres. We use the model to simulate laser-guided acoustic tweezers and optimize their performance. By enabling numerical simulations of the transient radiation force, this work may accelerate the rational design of pulse-based high-selectivity acoustic tweezer devices.

We experimentally demonstrate a transverse magnetic (TM) mode laser in a photonic crystal (PhC) slab structure at room temperature. This study proposes a PhC nanobeam (NB) cavity to support a high-quality-factor ($Q$-factor) TM mode. For a large and complete photonic band gap, the PhC NB structures consist of large air holes in a thick dielectric slab. The PhC NB cavity is optimized numerically for a high-$Q$-factor TM mode of over 1 000 000 by reducing the radii of the air holes quadratically from the center to the edge of the PhC NB. A single-TM-mode lasing action is observed in an In-Ga-As-P quantum well (QW)-embedded optimized PhC NB cavity structure at room temperature via optical pulse pumping, where the QW layer is lightly etched. We believe that the TM mode lasers in PhC NB cavities with a lightly etched QW can be good candidates for a surface plasmon excitation source or a highly sensitive optical sensor.

We study spin-current-induced magnetodynamics in a planar nanogap spin Hall nano-oscillator (SHNO) based on $\mathrm{Pt}/[\mathrm{Co}/\mathrm{Ni}{]}_4$ with a large perpendicular magnetic anisotropy (PMA) at in-plane field geometry. Two distinct dynamic modes are observed in the spin-torque ferromagnetic resonance (FMR) and the generated microwave spectra. The primary mode has a frequency above the FMR frequency and a significant blueshift of the frequency with the increasing current $I$, consistent with the propagating spin-wave mode. The secondary higher-frequency mode with a much weaker power intensity, discrete frequency jump, and a slight redshift of frequency is only observed at low fields below the saturation field of 2 kOe, suggesting that it is likely related to the emerged domain region with in-plane magnetization due to grain-boundary defects, which is further supported by the frequency enhancement with reducing temperature. The primary propagating mode decreases its frequency and broadens its minimum linewidth by reducing the temperature, indicating that the frequency-drift instability dominates its dynamical decoherence due to the boundary-pinning effect. Furthermore, the micromagnetic simulation reproduces the experimentally observed propagating spin-wave and in-plane domain modes, and provides their spatial characteristics. Our demonstrated propagating spin waves in a SHNO with an out-of-plane magnetization extended bilayer can facilitate long-distance mutual synchronization in the SHNO network arrays for enhancing coherence and power as spin-wave sources in magnon-based devices or spin-based neuromorphic computing.

Accurate control of qubits is the central requirement for building functional quantum processors. For the current superconducting quantum processor, high-fidelity control of qubits is mainly based on independently calibrated microwave pulses, which could differ from each other in frequencies, amplitudes, and phases. With this control strategy, the needed physical resource could be challenging, especially when scaling up to large-scale quantum processors is considered. Inspired by Kane’s proposal for spin-based quantum computing, here, we explore theoretically the possibility of baseband flux control of superconducting qubits with only shared and always-on microwave drives. In our strategy, qubits are by default far detuned from the drive during system idle periods, qubit readout and baseband flux-controlled two-qubit gates can thus be realized with minimal impacts from the always-on drive. By contrast, during working periods, qubits are tuned on resonance with the drive and single-qubit gates can be realized. Therefore, universal qubit control can be achieved with only baseband flux pulses and always-on shared microwave drives. We apply this strategy to the qubit architecture where tunable qubits are coupled via a tunable coupler, and the analysis shows that high-fidelity qubit control is possible. Besides, the baseband control strategy needs fewer physical resources, such as control electronics and cooling power in cryogenic systems, than that of microwave control. Of note, the flexibility of baseband flux control could be employed for addressing the nonuniformity issue of superconducting qubits, potentially allowing the realization of multiplexing and cross-bar technologies and thus controlling large numbers of qubits with fewer control lines. We thus expect that baseband control with shared microwave drives can help build large-scale superconducting quantum processors.

Exciton polaritons in metallic nanocavities and transition-metal dichalcogenide monolayers has led to striking discoveries, ranging from Bose-Einstein condensation to slowing light. Although plasmonic nanocavities offer small mode volumes, the intrinsic losses of plasmonic nanocavities remain an open challenge in exciton-polariton devices. Consequently, dielectric nanocavities are used as an alternative candidate due to their low intrinsic losses. However, large mode volumes are a central bottleneck in dielectric nanocavities. Here, we theoretically propose to use a hybrid dielectric-metallic nanocavity to enhance light-matter interactions between the excitons of the ${\mathrm{WS}}_2$ monolayer and the hybrid nanocavity. Such a hybrid nanoresonator inherits the advantages of both dielectric and metallic nanocavities, including ultrasmall mode volume, ultralow losses, and reasonably-high-Q factor. It is demonstrated that the thickness and material of the central gap film together with the thickness of the metallic substrate play vital roles in governing the coupling strength between 1L-${\mathrm{WS}}_2$ excitons and the cavity. After optimizing the geometry and material parameters, the Rabi splitting is increased to 113 meV, almost twice that in dielectric metasystems. The significant improvement can be attributed to the greatly enhanced near field and the ultrasmall mode volume. Furthermore, we show that Rabi splitting can be further boosted to 151 meV by increasing the number of layers of ${\mathrm{WS}}_2$ and h-$\mathrm{BN}$ film in the nanocavity.

Quantum entanglement has become an essential resource in quantum information processing. Existing works employ entangled quantum states to perform various tasks, while little attention is paid to the control of the resource. In this work, we propose a simple protocol to upgrade an entanglement source with access control through phase randomization at the optical pump. The enhanced source can effectively control all users in utilizing the entanglement resource to implement quantum cryptography. In addition, we show this control can act as a practical countermeasure against memory attack on device-independent quantum key distribution at a negligible cost. To demonstrate the feasibility of our protocol, we implement an experimental setup using just off-the-shelf components and characterize its performance accordingly.

${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_2$ has recently attracted significant interest as a promising candidate for applications in green light-emitting diodes and photovoltaic absorbers. However, the experimentally synthesized ${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_2$ samples suffer from a high concentration of unintentionally doped electrons, and their origin is not fully understood yet. By performing first-principles calculations, we investigate the properties of intrinsic point defects and oxygen impurities in cation-ordered and -disordered wurtzite ${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_2$. It is found that the cation antisite defect ${\mathrm{Sn}}_{\mathrm{Mg}}$ is the predominant donor defect, contributing an electron concentration as high as ${10}^{17}{\mathrm{cm}}^{-3}$ to cation-ordered ${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_2$. However, this value is 2–3 orders of magnitude lower than experimental observations (${10}^{19}-{10}^{20}{\mathrm{cm}}^{-3}$). We further show that cation disorder significantly decreases the formation energies of defects, leading to a much higher electron concentration (${10}^{19}{\mathrm{cm}}^{-3}$) than in the case of the cation-ordered phase. The reduced formation energy can be understood by the energy gain due to the creation of energetically favorable local motif structures after the formation of defects. Hence, reducing the degree of cation disorder is beneficial for decreasing the densities of defects and self-doped carriers.

Inspired by the neurosynaptic frameworks in the human brain, neuromorphic computing is expected to overcome the bottleneck of traditional von Neumann architecture and be used in artificial intelligence. Here, we predict a class of potential candidate materials, $M{\mathrm{Cu}}_3{X}_4$ ($M$ = $\mathrm{V}$, $\mathrm{Nb}$, $\mathrm{Ta};X=\mathrm{S},\mathrm{Se},\mathrm{Te}$), for neuromorphic computing applications through first-principles calculations based on density-functional theory. We find that when $M{\mathrm{Cu}}_3{X}_4$ are inserted with $\mathrm{Li}$ atom, the systems would transform from semiconductors to metals due to the considerable electron filling [approximately 0.8 electrons per formula unit (f.u.)] and still maintain well-structural stability. Meanwhile, the inserted $\mathrm{Li}$ atom also has a low diffusion barrier (approximately 0.6 eV/f.u.), which ensures the feasibility to control the insertion and extraction of $\mathrm{Li}$ by gate voltage. These results establish that the system can achieve the reversible switching between two stable memory states, i.e., high or low resistance state, indicating that it could potentially be used to design synaptic transistor to enable neuromorphic computing. Our work provides inspiration for advancing the search of candidate materials related to neuromorphic computing from the perspective of theoretical calculations.

Space-time-varying metamaterials based on uniform-velocity modulation have spurred considerable interest over the past decade. We present here an extensive investigation of accelerated-modulation space-time metamaterials. Using the tools of general relativity, we establish their electrodynamic principles and describe their fundamental phenomena, in comparison with the physics of moving-matter media. We show that an electromagnetic beam propagating in an accelerated-modulation metamaterial is bent in its course, which reveals that such a medium curves space-time for light, similarly to gravitation. Finally, we illustrate the vast potential diversity of accelerated-modulation metamaterial by demonstrating related Schwarzschild holes.