The strain-mediated method is considered to be a promising solution for implementing energy-efficient magnetization rotation. However, current methods strictly require a voltage clock. Here, a multiferroic nanomagnet composed of bicomponent magnetic materials (Terfenol-D:$\mathrm{Ni}$ = 1:2) is developed to study strain-mediated magnetization switching behavior. With micromagnetic simulations, what is demonstrated is that the strict requirements for a precise applied voltage period can be overcome in such a bicomponent nanomagnet, where the threshold of the square-wave voltage pulse width required for complete and repeated magnetization reversal is only 0.42 ns if the amplitude of the voltage is 1 V. Besides deterministic magnetization switching, further study shows that the unique strain-mediated stochastic magnetization reversal behavior of the designed device can be used to mimic the biological neuron. With the application of the derived neural device parameters, a three-layer artificial neural network is further constructed to recognize a handwritten dataset, based on which, an accuracy of more than 98% can be achieved. Overall, these results open an intriguing way toward straintronic memory and neuromorphic systems.

Cavity photons and ferromagnetic spin excitations can exchange information coherently in hybrid architectures, at speeds set by their mutual coupling strength. Speed enhancement is usually achieved by optimizing the geometry of the electromagnetic cavity. Here we show that the geometry of the ferromagnet also plays a role, by setting the fundamental frequency of the magnonic resonator. Using focused ion-beam patterning, we vary the aspect ratio of different Permalloy samples reaching operation frequencies above 10 GHz while working at low external magnetic fields. Additionally, we perform broadband ferromagnetic resonance measurements and cavity experiments that demonstrate that the light-matter coupling strength can be estimated using either open transmission lines or resonant cavities, yielding very good agreement. Finally, we describe a simple theoretical framework based on electromagnetic and micromagnetic simulations that successfully accounts for the experimental results. This approach can be used to design hybrid quantum systems exploiting magnetostatic mode excited in ferromagnets of arbitrary size and shape and to tune their operation conditions.

Localizing an intruder submerged in a strongly scattering medium, such as a dense granular suspension, is a practical challenge. Here we extract the coherent ultrasonic echo from a steel ball submerged in a dense glass-bead packing saturated by water, by using a standard single-element ultrasonic transducer thanks to a configuration averaging process. Different configurations of the granular packing are created by the nonaffine motion of the beads with a mixing blade, akin to the Brownian motion, in the vicinity of the intruder. We investigate the efficiency of this process to reduce the so-called material noise from multiply scattered ultrasound, as a function of the configuration number, the shear rate and the blade-intruder distance. Nonaffine motions of the beads in the shear zone induced by the blade are then analyzed on the basis of a split-bottom rotating shear cell. This method helps to develop not only ultrasonic imaging tools of buried objects in turbid marine sediments, but also the local rheology based on a ball falling monitored by ultrasonic tracking.

The emergence of localized structures originating from instabilities is of particular interest to scientists interested in exploring the rich nonlinear dynamics associated with complex dynamical systems. In the context of ultrafast lasers, the localized structures can be broadly divided into two categories: coherent structures of the dissipative soliton (DS) and incoherent structures such as the noiselike pulse (NLP). These two different types of structures have unique properties and applications and their physical origins are markedly different. Having both in a single fiber laser is an intriguing but challenging problem. Here we demonstrate the formation of the DS and NLP in a bidirectional ultrafast fiber laser and study their buildup dynamics from $Q$-switched instabilities. The clockwise light is a DS while the counterclockwise light is a NLP. The synchronized buildup dynamics of a DS or NLP from $Q$-switched instabilities provides vital evidence of the $Q$-switched instabilities as a universal indicator for the generation of localized structures in ultrafast lasers. The evenly spaced $Q$-switched spikes before the onset of a DS (NLP) exhibit intensity fluctuations, which is strikingly different than in the mode-locking regime in unidirectional oscillators, hence providing decisive evidence of the interaction between the counterpropagating light fields in the bidirectional lasers. The spectra cross-correlation and the histogram of the spectral intensity confirm the concurrent formation of a DS and NLP. Numerical simulations confirmed experimental observations. These findings help deepen understanding of the behavior of bidirectional ultrafast lasers and also demonstrate their potential as multifunctional ultrafast laser sources.

A complete simulation scheme is established to model the terahertz (THz) properties of vanadium dioxide (${\mathrm{VO}}_2$) from ab initio to computational electromagnetic method. For the monoclinic insulating phase of ${\mathrm{VO}}_2$, dielectric properties are computed by Hubbard-corrected density functional perturbation theory. Meanwhile, the electron-phonon interactions are studied to model the electronic transport properties of the tetragonal metallic phase of ${\mathrm{VO}}_2$. In order to build a bridge from the microscopic effects of first-principles calculations to the macroscopic THz properties, the Drude model and effective medium theory are applied to model the dispersion properties of the material. To validate the proposed model, a ${\mathrm{VO}}_2$ film grown on a sapphire substrate is fabricated and measured by a terahertz time-domain spectroscopy system. The measurement results have excellent agreements with the proposed simulations. Further, a ${\mathrm{VO}}_2$-based THz metamaterial modulator is simulated by using the proposed model, in great agreement with the reported measurement result. Our ab initio computational scheme improves the simulation accuracy of design, which provides a solid THz modeling approach to the ${\mathrm{VO}}_2$ and other insulator-metal transition metal oxides.

Recently, real-space representations, revealing in depth the duality of topological descriptions in real and momentum space, have been applied to show multidimensional crystalline topology. Here we propose nontrivial phononic crystals by constructing different Wannier configurations based on real-space representations. We experimentally achieve the symmetry-protected interface topology in multiple dimensions containing anomalous interface states and higher-order corner states. Nontrivial acoustic pseudospin polarizations are critical to the interface states and have been directly observed in experiment. In a consistent frame, the higher-order corner states arising from the fractional charge anomaly are further observed. Our study provides a scheme based on Wannier configurations for designing topological metamaterials, which is fruitful for characterizing and manipulating multidimensional topological states and can be generalized to other classical systems.

Spin-wave transport across multidimensional networks of magnonic waveguides represents a crucial and necessary aspect of prospective densely packed three-dimensional spin-wave architectures. Here, we report the results of investigations of spin-wave propagation through magnonic waveguides extending along and bending across two and three dimensions. We consider three designs of in-plane two-dimensional bends, namely with right-angled, diagonal, and curved geometries. Our numerical and experimental results show that such bends facilitate the conversion of spin-wave types, with the output modal number depending on the spin-wave frequency. At the same time, variation of the width of lateral magnonic bends enables the spin-wave wavelength to be modified. When propagating across three-dimensional waveguide bends in the form of out-of-plane junctions, the spin-wave wavelength can similarly be tuned by adjusting the stripe’s thickness. Our results show that magnonic waveguides can serve not only as passive conduits but also as active elements in modifying the properties of the transmitted spin wave in three-dimensional magnonic networks.

Fault-tolerant quantum information processing with flawed qubits and gates requires highly efficient, quantum nondemolition qubit readout. In superconducting circuits, qubit readout using coherent light with fidelity above 99% has been achieved by using quantum limited parametric amplifiers such as the Josephson parametric converter (JPC). However, further improvement of such measurement faces many challenges, including the vacuum fluctuation of the coherent light that limits measurement fidelity. In this work we demonstrate dispersive qubit readout with a two-mode squeezed light interferometer formed by two JPCs. The first JPC generates two-mode squeezed vacuum at its output, which is coherently recombined by the second JPC after one branch is phase shifted and displaced by its interaction with the qubit-cavity system on that arm of the interferometer. We observe a 31% improvement in the power signal-to-noise ratio (SNR) of projective readout after replacing vacuum fluctuation in the readout cavity with two-mode squeezed vacuum containing on average one photon. This demonstrates a more efficient way of improving SNR than by increasing readout power. Furthermore, we investigate the quantum properties of the two-mode squeezed light in the system through weak measurement. Surprisingly, we find that tuning the interferometer to be less projective increases the measurement efficiency relative to the optimum setting for projective measurement. These enhancements may enable remote entanglement with lower efficiency components in a system with qubits in both arms of the interferometer.

Understanding the interaction of a kilojoule picosecond laser pulse with long-scale-length preplasma or homogeneous near-critical-density (NCD) plasma is crucial for guiding experiments at national short-pulse laser facilities. Using full three-dimensional particle-in-cell simulations, we demonstrate that in this regime, cross-filament stochastic acceleration is an important mechanism that contributes to the production of superponderomotive high-flux electron beams. Since the laser power significantly exceeds the threshold of the relativistic self-focusing, multiple filaments are generated and can propagate independently over a long distance. Electrons jump across the filaments during the acceleration and their motion becomes stochastic. We find that the effective temperature of electrons increases with the total interaction time following a scaling like $T_{\mathrm{eff}}\propto {\tau }_i^{0.65}$. By irradiating a submillimeter-thick NCD target, the space charge of electrons with energy above 2.5 MeV reaches tens of microcoulombs. Such high-flux electrons with superponderomotive energies significantly facilitate applications in high-energy-density science, nuclear science, secondary sources, and diagnostic techniques.

For decades, researchers have been exploring pattern-forming instabilities in free surface thin films in the hope of developing alternative lithographic techniques for applications only requiring resolution limits in the submicron range. Previous studies have shown how the pitch and shape of elements in an array can be varied by adjusting the magnitude of surface forces and growth time prior to solidification in situ. Since the formations emerge naturally from an initial flat molten film, the final arrays exhibit ultrasmooth interfaces and are therefore ideally suited to beam-shaping applications such as thin-film micro-optics. Progress in this field has stalled, however, due to the very nature of the formation process. Even when great care is taken to ensure that initial films are defect-free, final arrays still exhibit unacceptable variability in pitch, shape, and height due to ubiquitous sources of noise responsible for instability and growth. In this work, we focus on a thermocapillary instability in slender molten films exposed to a very large thermal gradient. We begin with a discussion and demonstration of why this instability inextricably leads to highly disordered arrays even if initialized by a film with very small amplitude surface roughness. We then demonstrate how spatially periodic modulation of the thermal field, implemented in three different ways, can induce synchronous growth of highly uniform periodic arrays despite noisy initial conditions. Results based on linear and weakly nonlinear stability analysis, Bloch wave analysis, and direct numerical simulation of the interface equation reveal how resonant wavelength excitations occurring between the modulation and instability driving fields are responsible for such rapid and coherent growth. An additional benefit is that the modulation field can be selected to yield an array pitch much smaller than in unmodulated systems.

Corner states (CSs) in higher-order topological insulators (HOTIs) have recently been of great interest in both crystals and quasicrystals. In contrast to electronic systems, HOTIs have not been found in photonic quasicrystals (PQCs). Here, we systemically study the higher-order topology in the two-dimensional Thue-Morse photonic quasicrystals (TM PQCs). Not only the topological phase transition and the nontrivial CSs with fractional charge induced by multipole moments, but also another type of CSs are found due to the complex structure of TM PQCs near corners. The different origins of these CSs are also analyzed based on the tight-binding model. Our work opens the door to explore richer HOT physics beyond photonic crystals and the robustness of CSs in PQC shows the potential for applications.

Dynamic hysteresis effects have been long known to occur in the current density-voltage characteristics of perovskite solar cells, with the ionic migration being identified as the primary factor. The hysteretic effects impacted early studies by the uncertainty in the evaluation of the power conversion efficiency, while currently, potential links to degradation mechanisms are the focus. Therefore, understanding ion migration is a central goal, typically addressed by performing a combined large and small signal analysis. The reported large capacitive and inductive effects created controversies with respect to the underlying mechanisms, yielding essentially two classes of models, one based on the large accumulation capacitances and the other based on the ionic modulation of the collected current. We introduce here an equivalent circuit model and interpret these phenomena in terms of recombination current modulation, identifying the distinct contributions from ion current and ionic charge accumulations. These contributions to the recombination current are associated with capacitive and inductive effects, respectively, and we corroborate the numerical simulations with electrochemical impedance spectroscopy measurements. These show the role of the recombination currents of photogenerated carriers in producing both capacitive and inductive effects as the illumination is varied. Moreover, we provide a bridging point between the two classes of models and suggest a framework of investigation of defect states based on the observed inductive behavior, which would further aid the mitigation of the degradation effects.

Two-dimensional (2D) magnetic semiconductor materials with the electric-field-tunable spin polarization and carrier-transport anisotropy are of great significance for the fundamental physics and device application. Here we propose a general strategy to tune the spin polarization and anisotropic effective mass in a 2D A-type antiferromagnetic (AFM) bilayer system. We take the A-type AFM bilayer $\mathrm{CrSBr}$ (with the intralayer ferromagnetic and interlayer AFM coupling) as an example to confirm this design principle. Firstly, a vertical electric field can lift the spin degeneracy in the A-type AFM bilayer $\mathrm{CrSBr}$. By flipping the direction of electric field, the spin polarization direction can be reversed. Secondly, in the A-type AFM bilayer $\mathrm{CrSBr}$ with an interlayer twist angle of 90°, both the spin direction and the carrier-transport anisotropy can be tuned simultaneously by applying a vertical electric field due to the in-plane anisotropic carrier effective mass in each $\mathrm{CrSBr}$ monolayer. This opens an opportunity for controlling the spin polarization as well as carrier-transport anisotropy in the 2D magnetic van der Waals layered materials by interlayer twist and electric field, and provides an idea for utilizing A-type AFM semiconductors to design spintronic devices.

The Airy beam has the characteristics of nondiffraction, self-bending, and self-healing, so it is of great significance to wireless power transfer (WPT) and wireless communication in the radio-frequency (rf) field. This paper proposes the generation and modulation method of the two-dimensional (2D) Airy beams based on a holographic tensor metasurface, which can generate 2D Airy beams with different trajectories. A multidimensional controllable tensor metasurface unit operating at 10 GHz is designed to concentrate the electromagnetic energy to achieve the linearly polarized Airy beam. The unit with tiny size can also precisely regulate both the amplitude and the phase of the electromagnetic wave so that the high-performance 2D Airy beams can be generated by the holographic tensor metasurface in the microwave band. Meanwhile, the Airy beams with varying deflected angles are designed based on beam-steering theory to obtain different energy transmission trajectories for WPT. The simulation and measurement results show that the deflected 2D Airy beam still maintains the characteristics of nondiffraction and self-bending.

Ferroelectric hafnium oxide films are one of the most promising functional materials for a new generation of nonvolatile memory for data storage because of a number of excellent performance features, including nanosecond speed, high endurance, low power consumption, full scalability, and perfect compatibility with Si technology. However, the commercialization of this memory is hindered by its limited retention time, which still does not meet the 10-year electronics-industry standard. To date, much effort has been focused on the improvement of retention via material and interface engineering. Meanwhile, the evaluation and comparison of engineering results have been hampered, since there is still no unified retention test. Indeed, a specific feature of the retention performance is that it cannot be measured directly, because 10 years is required to measure the actual polarization loss. In this paper, we present a physical model that predicts the retention loss in ${\mathrm{Hf}\mathrm{O}}_2$-based memory during long-term information storage. The time-dependent polarization loss originates from the phenomenon of polarization imprint, which consists in the temporal development of a preferential polarization state in a poled ferroelectric. For high reliability of the retention calculation, the model takes into account the specific features of imprint evolution in the ferroelectric material ${\mathrm{Hf}\mathrm{O}}_2$. Among these is the origin of the imprint in this material, which consists in the interplay of two physical mechanisms, specifically, charge injection into interface traps and migration of mobile charged defects across the functional layer. The second property of ${\mathrm{Hf}\mathrm{O}}_2$ taken into account is the different rates of imprint evolution in two types of ${\mathrm{Hf}\mathrm{O}}_2$ film that exist within each memory cell. These two types of film originate from two populations of domains that appear during crystallization of the ${\mathrm{Hf}\mathrm{O}}_2$ and persist during the whole lifetime of the memory cell. The high accuracy of the retention model makes it possible to implement an express retention test, i.e., to predict the retention time in record short time (1 h) for any particular sample, whereas usually a retention test takes at least several days. For ${\mathrm{Hf}}_{0.5}{\mathrm{Zr}}_{0.5}{\mathrm{O}}_2$-based capacitors, the retention model shows excellent agreement with experimental results. The proposed model can serve not only for the implementation of this express retention test, but also as a tool for intelligent material engineering in the field of nonvolatile ferroelectric memory.

Semiconductor spin qubits may be coupled through a superconducting cavity to generate an entangling two-qubit gate. However, the fidelity of such an operation will be reduced by a variety of error mechanisms such as charge and magnetic noise, phonons, cavity loss, transitions to nonqubit states, and, for electrons in silicon, excitation into other valley eigenstates. Here, we model the effects of these error sources and the valley degree of freedom on the performance of a cavity-mediated two-qubit $\mathrm{i}$swap gate. For valley splittings inadequately large relative to the interdot tunnel coupling within each qubit, we find that valley excitation may be a limiter to the fidelity of this two-qubit gate. In addition, we show trade-offs between gating times and exposure to various error sources, identifying optimal operating regimes and device improvements that would have the greatest impact on the fidelity of the cavity-mediated spin $\mathrm{i}$swap gate. Importantly, we find that, while the impact of charge noise and phonon relaxation favor operation in the regime where the qubits are most spinlike to reduce sensitivity to these sources of noise, the combination of hyperfine noise and valley physics shifts the optimal regime to chargelike qubits with stronger effective spin-photon coupling so that gate times can be made as short as possible. In this regime, the primary limitation is the need to avoid Landau-Zener transitions as the gate is implemented.