In this work we report on the extensive characterization of amorphous silicon carbide ($a$-SiC) coatings prepared by physical deposition methods. Our investigation is performed within the perspective application of $a$-SiC as an optical material for high-precision optical experiments and, in particular, in gravitational wave interferometry. We compare the results obtained with two different sputtering systems [a standard radio frequency (rf) magnetron sputtering and an ion-beam sputtering] to grasp the impact of two different setups on the repeatability of the results. After a thorough characterization of structural, morphological, and compositional characteristics of the prepared samples, we focus on a detailed study of the optical and mechanical losses in those materials. Mechanical losses are further investigated from a microscopic point of view by comparing our experimental results with molecular dynamic simulations of the amorphous SiC structure: first we define a protocol to generate a numerical model of the amorphous film, capturing the main features of the real system; then we simulate its dynamical behavior upon deformation in order to obtain its mechanical response.

We theoretically demonstrate generation of the Stokes temporal localized structure (TLS) by exploiting its Raman interaction in space and time within an optical potential well shared with another dark pulse. Excitation of the Stokes TLSs is feasible in both the normal and anomalous group-velocity dispersion regime, with a single modulated pump source. Stimulated Raman scattering constitutes influences on the stability and physical feature of the generated Stokes TLS (STLS). Particularly, breathing STLSs are also observed due to the periodic energy transfer between the primary and the Stokes fields. These findings could deepen the understanding of complex nonlinear dynamics in resonators and facilitate the excitation of different types of TLSs in potential platforms.

Fiber-based quantum communication networks are currently limited without quantum repeaters. Satellite-based quantum links have been proposed to extend the network domain. We develop a quantum communication system, suitable for realistic satellite-to-ground communication. With this system, we execute an entanglement-based quantum key distribution (QKD) protocol developed by Bennett, Brassard, and Mermin (BBM92), achieving quantum bit-error rates (QBERs) below 2% in all bases. More importantly, we demonstrate low-QBER execution of a higher-dimensional hyperentanglement-based QKD protocol, using photons simultaneously entangled in polarization and time bin, leading to significantly higher secure key rates, at the cost of increased technical complexity and system size. We show that our protocol is suitable for a space-to-ground link, after incorporating Doppler-shift compensation, and verify its security using a rigorous finite-key analysis. Additionally, we discuss system-engineering considerations relevant to those and other quantum communication protocols and their dependence on what photonic degrees of freedom are utilized.

Superconducting circuits are a leading platform for quantum computing. However, their coherence times are still limited and exhibit temporal fluctuations. Those phenomena are often attributed to the coupling between qubits and material defects that can be well described as an ensemble of two-level systems (TLSs). Among them, charge fluctuators inside amorphous oxide layers contribute to both low-frequency $1/f$ charge noise and high-frequency dielectric loss, causing fast qubit dephasing and relaxation. Moreover, spectral diffusion from mutual TLS interactions varies the noise amplitude over time, fluctuating the qubit lifetime. Here, we propose to mitigate those harmful effects by engineering the relevant TLS noise spectral densities. Specifically, our protocols smooth the high-frequency noise spectrum and suppress the low-frequency noise amplitude via depolarizing and dephasing the TLSs, respectively. As a result, we predict a drastic stabilization in qubit lifetime and an increase in qubit pure dephasing time. Our detailed analysis of feasible experimental implementations shows that the improvement is not compromised by spurious coupling from the applied noise to the qubit.

Hamiltonians of the superconducting qubits of transmon type involve nonzero $ZZ$ interaction terms due to their finite and small anharmonicities. These terms might lead to the unwanted accumulation of spurious phases during the execution of the two-qubit gates. Exact calculation of the $ZZ$ interaction rates requires the full diagonalization of the circuit Hamiltonians, which very quickly becomes computationally demanding as the number of the modes in the coupler circuit increases. Here we propose a direct analytical method for the accurate estimation of the $ZZ$ interaction rates between low-anharmonicity qubits in the dispersive limit of the multimode circuit quantum electrodynamics (circuit QED). We observe very good agreement between the predictions of our method and the measurement data collected from the multiqubit devices.

Understanding the dynamic behaviors of magnetic skyrmions has great potential in the application of spintronics. This is especially the case for the interaction between two skyrmions. In the literature, the attractive and repulsive skyrmion-skyrmion interactions are demonstrated as strongly related to the distance of two skyrmions and external magnetic fields. However, as a natural property, the temperature effect on skyrmion-skyrmion interactions is unclear, which lacks understanding from thermodynamics, and accordingly its driving force equation is absent. Here, we employ a temperature-related phase-field simulation and demonstrate that the skyrmion-skyrmion interaction is dramatically changed by temperature (e.g., a temperature change of only a few kelvins results in an eightfold higher interaction), which can lead to critical temperature behavior of skyrmion phase. Detailed analysis shows the interaction potential decreases exponentially with an increase of temperature, and this pronounced temperature dependence originates from the temperature-related skyrmion structure. Then, an equation is proposed to describe the skyrmion interaction at finite temperatures. Therefore, this study provides a deeper understanding of the skyrmion kinetic behavior and explores the temperature control of skyrmion interactions coupled with other sources of interaction, which is a guidance for future study of skyrmions and their applications.

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.