The influence of mechanical strain on the static and dynamic properties of chiral domain walls (DWs) in perpendicularly magnetized strips is investigated using micromagnetic simulations and a one-dimensional model. While a uniform strain allows one to reversibly switch the domain-wall configuration at rest between Bloch and Néel patterns, strain gradients are suggested as an energy-sustainable means to drive domain-wall motion without the need for magnetic fields or electrical currents. It is shown that an in-plane strain gradient creates a force on a domain wall that drives it towards a region of higher tensile (compressive) strain for materials with positive (negative) magnetostriction. Moreover, due to the dependence of the domain-wall internal energy on the in-plane strain, a damping torque proportional to the local strain arises during motion that opposes the precessional torque due to the driving force, which is proportional to the strain gradient. After a transient period, where both the internal DW angle and the velocity change nonmonotonically, reaching their maximum values asynchronously, the two torques balance each other. This compensation prevents the onset of turbulent domain-wall dynamics, and steady domain-wall motion with a constant velocity is asymptotically reached for an arbitrarily large strain gradient. Despite this complex dynamics, our work shows that average domain-wall velocities in the range of 500 m/s can be obtained using voltage-induced strain in piezoelectric/ferromagnetic devices under realistic conditions.

Information reconciliation (IR), which corrects the errors in the sifted keys, directly determines the secure key rate and the link distance of quantum key distribution (QKD) systems. In this paper, we propose an appending information reconciliation (AIR) scheme based on polar codes, which achieves high efficiency and ultralow failure probability simultaneously, by gradually disclosing the bit values of the polarized channels with high error probability. The experimental results show that the efficiency of the proposed AIR scheme is closer to the Shannon limit, compared with the state-of-the-art implemented polar-code-based IR schemes, with the overall failure probability around ${10}^{-8}$, especially when performed with smaller block sizes. Moreover, the efficiency of the proposed AIR scheme is 1.046, when the block size is 1 Gb and the quantum bit error rate of 0.02. Therefore, the proposed AIR scheme can further eradicate the performance gap between theory and implementation for QKD systems.

Undoped and N-doped $\mathrm{Zn}\mathrm{O}$ films are grown by atomic layer deposition under O-rich conditions. Scanning photoelectron microscopy studies carried out on the films cross sections with a state-of-the-art resolution of 130 nm, allowed the study of the electronic structure of individual crystallites. In has been found that crystallites can be divided into two types, that differ in the electronic structure of the valence band. This finding, together with the cathodoluminescence images showing clustering the acceptor- and donor-related emission, unveiled that acceptors and donors are grouped in separate regions of the $\mathrm{Zn}\mathrm{O}$ and $\mathrm{Zn}\mathrm{O}$:$\mathrm{N}$ films. Density-functional-theory (DFT) calculations reveal that the complexes involving zinc vacancy, hydrogen, and nitrogen (in the case of $\mathrm{Zn}\mathrm{O}$:$\mathrm{N}$) modify the density of states in the valence-band region, so the experimentally observed differences in photoelectron spectra between crystallites evidence the grouping of acceptor complexes in some crystallites. DFT calculations also suggest that shallow acceptor states might be of $n\cdot V_{\mathrm{Zn}}$ origin. Nitrogen willingly joins such complexes and facilitates their formation. The separation of donors and acceptors and its tendency to group along the growth columns is of great relevance for future applications, as it indicates that eventual electronic devices should rather be constructed in a vertical architecture.

In this work, we theoretically explore the spin- and valley-resolved transport in monolayer transition-metal dichalcogenide (TMDC) planar heterojunctions. We propose two types of ${\mathrm{Mo}\mathrm{S}}_2{/\mathrm{WS}}_2$ planar heterojunctions based on the position of the optical modulation. Spin- and valley-resolved transmission is realized and transmission spectra look quite different between the two types of heterojunctions due to the spin-valley-dependent effective potential, which results from the off-resonant circularly polarized light (CPL) and the band offset. Specifically, fully valley-polarized transport is demonstrated in Type-1 heterojunction (optical modulation on ${\mathrm{WS}}_2$). However, transmission in Type-2 heterojunction (optical modulation on ${\mathrm{Mo}\mathrm{S}}_2$) experiences a dramatic change with respect to CPL intensity, where the system can be switched from perfect valley-polarized “on” state to nearly nonpolarized “off” state only by adjusting the CPL intensity. As a result, we propose pure optically controlled valley filter and valley transistor based on the two types of planar heterojunctions, respectively. This work may shed light on potential application of valleytronic devices based on TMDC planar heterojunctions.

The majority of sources of coherent optical radiation rely on laser oscillators driven by population inversion. Despite their technological importance in communications, medicine, industry, and other fields, it remains a challenge to access the spectral range of 0.1–10 THz (the “terahertz gap”), a frequency band for applications ranging from spectroscopy to security and high-speed wireless communications. Here, we propose a way to produce coherent radiation spanning the THz gap by efficient second-harmonic generation in low-loss dielectric structures, starting from technologically mature electronic oscillators in the approximately 100 GHz range. To achieve this goal, we introduce hybrid THz-band dielectric cavity designs that combine (1) extreme field concentration in high-quality-factor resonators with (2) nonlinear materials enhanced by phonon resonances. We theoretically predict conversion efficiencies of $>{10}^3\mathrm{\%}/$W and the potential to bridge the THz gap with 1 W of input power. This approach enables efficient, cascaded parametric frequency converters, and light sources extensible into the mid-IR spectrum and beyond.

Multispin interactions can be engineered with artificial quantum spins. However, it is challenging to verify such interactions experimentally. Here, we describe two methods to characterize the $n$-local coupling of $n$ spins. First, we analyze the variation of the transition energy of the static system as a function of local spin fields. Standard measurement techniques are employed to distinguish $n$-local interactions between up to five spins from lower-order contributions in the presence of noise and spurious fields and couplings. Second, we show a detection technique that relies on time-dependent driving of the coupling term. Generalizations to larger system sizes are analyzed for both static and dynamic detection methods and we find that the dynamic method is asymptotically optimal when increasing the system size. The proposed methods enable robust exploration of multispin interactions across a broad range of both coupling strengths and qubit modalities.

Imaging through an opaque scattering medium, such as biological tissue, is of broad interest for many applications from physics to life sciences. Measuring the transmission matrix (TM) of the scattering medium is a versatile tool for this purpose. Previously, researchers are used to improving the image resolution by measuring a gigantic TM with a long sampling time. However, the low resolution and low SNR of the reconstructed images are still two obstacles to the adoption of such a technique. The foveal centralis of the human eye produces sharper vision than that from the retina’s peripheral region. Inspired by this feature, we report the implementation of foveated scattering imaging with a multiresolution TM whose space-variant resolution feature can be flexibly adjusted. The enhancement of linear resolution and SNR of the foveated scattering imaging system by factors of 4 and 8.3, respectively, is demonstrated experimentally. Our bioinspired imaging method heuristically introduces foveal vision into scattering imaging, and thus paves the way for both high resolution and high SNR imaging through scattering medium concurrently monitoring the entire field of view.

Defects play a crucial role in the physical properties of crystals, whether for classical or quantum systems. For example, in photonic and phononic crystals, defects can serve as precise guidance for and localization of classical electromagnetic or mechanical waves. Rainbow concentrating, an exotic wave localization, exploits defects to enable the collection and frequency routing of weak signals in real space. Here, using a solid-state phononic crystal (PnC) plate, we experimentally verify this phenomenon by deliberately infusing a homogeneously graded dislocation, i.e., a line defect, into the PnC. Two PnCs separated by the defect will breed deterministic interface states along with the defect, offering rainbow trapping and concentrating for elastic waves. Our PnC-based rainbow trappers and concentrators are scalable and configurable, and thus, are promising for advancing applications like energy harvesting, information processing, and acoustofluidic manipulation.

Quantum adiabatic transfer is widely used in quantum computation and quantum simulation. However, the transfer speed is limited by the quantum adiabatic approximation condition, which hinders its application in quantum systems with a short decoherence time. Here we demonstrate quantum adiabatic state transfers that jump along geodesics in one-qubit and two-qubit superconducting transmons. This approach possesses the advantages of speed, robustness, and high-fidelity compared with the usual adiabatic process. Our protocol provides feasible strategies for improving state manipulation and gate operation in superconducting quantum circuits.

Unraveling real eigenfrequencies in non-Hermitian $\mathcal{P}\mathcal{T}$-symmetric Hamiltonians has opened avenues in quantum physics, photonics, and most recently, phononics. However, the existing literature squarely focuses on exploiting such systems in the context of scattering profiles (i.e., transmission and reflection) at the boundaries of a modulated waveguide, rather than the rich dynamics of the non-Hermitian medium itself. In this work, we investigate the wave propagation behavior of a one-dimensional non-Hermitian elastic medium with a universal complex stiffness modulation that encompasses a static term in addition to real and imaginary harmonic variations in both space and time. Using a plane-wave expansion, we conduct a comprehensive dispersion analysis for a wide set of subscenarios to quantify the onset of complex conjugate eigenfrequencies, and set forth the existence conditions for gaps that emerge along the wave-number space. Upon defining the hierarchy and examining the asymmetry of these wave-number gaps, we show that both the position with respect to the wave-number axis and the imaginary component of the oscillatory frequency largely depend on the modulation type and gap order. Finally, we demonstrate the coalescence of multiple Bloch-wave modes at the emergent exceptional points where significant direction-dependent amplification can be realized by triggering specific harmonics through a process that is detailed herein.

With the increasing demand for miniaturized devices and integrated circuits, ultrasmall-scale device units have attracted increasing attention. However, the short-channel effects severely limit the development of high-performance micro- and nanodevices. Here, we design sub-5-nm dual-gate monolayer $\mathrm{Ga}\mathrm{Se}$ metal-oxide-semiconductor field-effect transistors (MOSFETs) and systemically analyze the transmission spectrum, local density of states, on-state current ($I_{on}$), and subthreshold swing (SS), considering different dielectric layer thicknesses, dielectric constants, and underlap lengths. The results show that, with decreasing equivalent oxide thickness, the SS ($I_{on}$) shows a downward (uptrend) trend. Compared with ${\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{Hf}\mathrm{O}}_2$ substrates, the SS and $I_{on}$ can be modified obviously through the dielectric layer thickness for 3-nm $\mathrm{Ga}\mathrm{Se}$ MOSFETs with ${\mathrm{Si}\mathrm{O}}_2$ substrate. The $I_{on}$ can be tuned from 904 to 1766 µA/µm, which is about 2 times higher than the high-performance requirements of the International Technology Roadmap for Semiconductors (ITRS) (900 µA/µm) for 2028. Meanwhile, the SS is upgraded from 134.8 to 62.7 mV/dec, closing the Boltzmann tyranny (60 mV/dec). Therefore, this work provides a route to realize ultrashort-scale MOSFETs with an ultralow subthreshold swing and a high on-state current through engineering the dielectric layer.

Magic angles, namely, relative rotations between two parallel graphene flakes that create bigger periodic superlattices, are recently found to inherit the bilayer structure with exotic properties totally unknown to a single isolated graphite sheet. An electromagnetic analog to these regimes is provided by modeling the two monolayers of the same two-dimensional medium as anisotropic surface conductivities, which, if properly tilted, give substantial enhancement for the fields across the formed cavity. Such results may apply the paradigm of twistronics to nanophotonic design involving stacked optical materials, for serving a wide range of applications: from electromagnetic sensing and signal processing to radiative heat transfer and light harvesting.

The measurement of ac susceptibility $\chi (\omega )$ down to $0.1\mathrm{mHz}$ of test masses is vital for TianQin, a Chinese space-based gravitational-wave detection mission, since the magnetic induced disturbing force is one of the main contributors to residual acceleration noise of test masses. Here we report a method based on a torsion pendulum with dual magnetic field modulation to measure $\chi (\omega )$ of centimeter-scale test mass from $50\mu \mathrm{Hz}$ to $80$ Hz. The measurement resolution can reach a level of ${10}^{-8}$, meeting the requirements of TianQin. Meanwhile, this method also provides an important ground-validation approach for the down-converted effects [Phys. Rev. Lett. 120, 061101 (2018)] from ac magnetic fields, potentially reducing the risk of failure in space.

The generation and control of surface acoustic waves (SAWs) in a magnetic material are objects of an intense research effort focused on magnetoelastic properties, with fruitful ramifications in spin-wave-based quantum logic and magnonics. We implement a transient grating setup to optically generate SAWs also seeding coherent spin waves via magnetoelastic coupling in ferromagnetic media. In this work we report on SAW-driven ferromagnetic resonance (FMR) experiments performed on polycrystalline Ni thin films in combination with time-resolved Faraday polarimetry, which allows extraction of the value of the effective magnetization and of the Gilbert damping. The results are in full agreement with measurements on the very same samples from standard FMR. Higher-order effects due to parametric modulation of the magnetization dynamics, such as down-conversion, up-conversion, and frequency mixing, are observed, testifying the high sensitivity of this technique.

We numerically demonstrate a general method to achieve acoustic high absorption in water with a wide range of incident angles and a broad frequency bandwidth. Different from previous studies considering local resonances with a narrow bandwidth or porous materials with a gradient design, we show that flat multilayer solid composites can be engineered to be perfectly impedance matched with water over a wide range of angles and a broad spectrum. By adding a proper loss factor to the composites, sound waves can be gradually dissipated and high absorption can be realized. Such a method is robust and adaptive to a broad range of material parameters. Our work could promise broad underwater applications.

The study of helicity in the context of light-matter interactions is an increasing area of research. However, some fundamental aspects of the helicity content of light fields inside scatterers have been overlooked. In this work, we demonstrate that the helicity of light fields inside lossless spherical cavities cannot be either conserved or sign flipped as a result of a scattering event. The underlying reason is that the internal electric and magnetic Mie coefficients cannot simultaneously oscillate with equal amplitude and equal or opposite phase. Our analytical demonstration is fulfilled regardless of the refractive index, sphere size, and multipolar order. In addition, we show that the helicity of light fields inside lossy spheres can be conserved. This fact is in striking contrast to the behavior of the scattered field, whose helicity content cannot be conserved precisely when the sphere has losses. Finally, we show that the helicity content of internal fields can be flipped for materials with gain.

The optical anisotropy of $r$-plane $\mathrm{Al}$${}_x$$\mathrm{Ga}$${}_{1-x}$$\mathrm{N}$/$\mathrm{Al}\mathrm{N}$ quantum wells (QWs) is investigated theoretically and experimentally. Theoretical calculations predict that as the $\mathrm{Al}$ composition is increased from 0 to 1, the in-plane polarization switches from $\mathbf{E}\perp$ [11$\overline{2}$0] to $\mathbf{E}\perp$ [1$\overline{1}$01] at an $\mathrm{Al}$ composition of approximately 0.2. The polarization properties are nearly independent of the well width, particularly when the well width is thicker than approximately $1.5\mathrm{nm}$. Photoluminescence spectroscopy of the fabricated $r$-plane $\mathrm{Al}$${}_x$$\mathrm{Ga}$${}_{1-x}$$\mathrm{N}$/$\mathrm{Al}\mathrm{N}$ QWs experimentally confirms the theoretical prediction. The $\mathbf{E}\perp$ [1$\overline{1}$01] polarization enables the emitted light to propagate along the [11$\overline{2}$0] direction. Using this property, photopumped lasing at approximately 250-nm wavelength at 11 K is demonstrated from an $r$-plane $\mathrm{Al}$${}_x$$\mathrm{Ga}$${}_{1-x}$$\mathrm{N}$/$\mathrm{Al}\mathrm{N}$ QW with the cleaved (11$\overline{2}$0) $a$ planes as cavity mirrors.

Neutron beams are unique tools to probe samples in many fields, such as biology medicine and fusion research. Access to such sources is traditionally limited to large particle accelerators. However, laser-driven pulsed neutron sources have attracted attention in recent years due to their compactness and cost savings. Although, in practical applications, the major obstacle is terribly low neutron flux due to the isotropic scattering. Here we propose a roadmap for laser-driven neutron sources based on “kinematic focusing,” which is ideal for producing highly collimated neutron beams and leads to the neutron-flux enhancement by more than 1 order of magnitude. Such a good collimation is conducive to the detection of samples located several meters from neutron sources, and it becomes feasible to place sensitive detectors adjacent to the neutron sources without the necessity of heavy shielding. A theoretical model for kinematic focusing and supporting two-dimensional particle-in-cell simulations are presented. It is shown that a well-collimated neutron beam, with the maximal divergence angle of about ${30}^{\circ }$, is generated by bombardment of a hydrogen target with ${\mathrm{Li}}^{3+}$ beams, which come from a metallic lithium foil irradiated by a short laser pulse at an intensity of $5.5\times {10}^{20}\mathrm{W}{\mathrm{cm}}^{-2}$. This proposed method can be achieved by present-day petawatt laser facilities.