Kernel function plays a crucial role in machine learning algorithms such as classifiers. In this paper, we aim to improve the classification performance and reduce the reading out burden of quantum classifiers. We devise a universally trainable quantum feature mapping layout to broaden the scope of feature states and avoid the inefficiently straight preparation of quantum superposition states. We also propose an improved quantum support vector machine that employs partially evenly weighted trial states. In addition, we analyze its error sources and superiority. As a promotion, we propose a quantum iterative multiclassifier framework for one-versus-one and one-versus-rest approaches. Finally, we conduct corresponding numerical demonstrations in the qiskit package. The simulation result of trainable quantum feature mapping shows considerable clustering performance, and the subsequent classification performance is superior to the existing quantum classifiers in terms of accuracy and distinguishability.

In practical applications, achieving perfect transmission of electromagnetic waves despite reflections from a complex medium segment in waveguide systems is of great significance. Using a preinstalled antireflective artificial metastructure (ARAMS) to mitigate reflections caused by the presence of a complex medium is an effective solution. The inverse design of ARAMS in waveguide systems is an optimization process. Recent applications of the topology optimization method in designing ARAMS have demonstrated attractive performances [Nature 607, 281 (2022)]. Topology optimization necessitates frequent utilization of full-wave electromagnetic simulations, while designing from scratch for different functional devices incurs exceedingly high computational costs. To address this problem, we introduce a fast inverse design method for ARAMS based on the internal multiport model (IMPM). Based on a single full-wave electromagnetic simulation dataset, IMPM abstracts the ARAMS electromagnetic field model into a microwave network, analytically establishing connections between actual excitation ports and fictitious internal ports while greatly reducing computational costs in optimization design. Furthermore, once IMPM is established, it can be reused for the rapid optimization design of various functional ARAMS devices in the same complex medium-filled waveguide environment. The cases presented in the paper validate the efficiency of this method in providing effective solutions for the perfect transmission of electromagnetic waves in waveguide systems filled with complex medium.

It has recently been shown how computing operations such as high-speed switching, routing, and solving partial differential equations can be performed by exploiting perfect splitting of electromagnetic waves in networks of waveguides from microwaves to the optical regime. Here we propose a technique to achieve perfect splitting of electromagnetic waves using junctions of rectangular waveguides. The structure consists of N air-filled rectangular waveguides interconnected at a junction. They are designed to have their cutoff frequency above the cutoff frequency of a further N waveguides used as inputs. The proposed structure is studied theoretically with use of transmission-line models, and it is demonstrated that perfect splitting can occur at frequencies below the cutoff frequency of the interconnected waveguides (evanescent coupling). Numerical results are used to validate the designs, and it is demonstrated that the theoretical model fits the numerical data well. As examples of computing operations, it is shown how the proposed structure can be used to compare the amplitude of two incident signals (comparison operation) and also for routing of information to different output ports by exploiting the linear superposition of scattered waves excited at the junction of rectangular waveguides, opening new opportunities and possibilities for future exploration and exploitation of electromagnetic waves for high-speed computing.

Wide-band-gap two-dimensional semiconductors have extensive applications in high-power electronics and optoelectronics in the blue to ultraviolet region. In this study, we investigate the electronic, mechanical, transport, and photoelectric properties of $\mathrm{Sc}$X$\mathrm{I}$ (X = $\mathrm{S}$, $\mathrm{Se}$, $\mathrm{Te}$) monolayers using a first-principles method. Some conceptual nanodevices based on $\mathrm{Sc}$X$\mathrm{I}$ monolayers are constructed, such as p-n-junction diodes, field-effect transistors (FETs), and phototransistors. Their multifunctional properties are subsequently revealed. The results indicate that $\mathrm{Sc}$X$\mathrm{I}$ monolayers, all of which are semiconductors with a moderate direct band gap of 2.42–1.34 eV, show many interesting properties, such as high dynamical, thermal, and mechanical stabilities, low cleavage energy, significant mechanical anisotropy, relatively low stiffness, and electronic properties that are tunable via applying strain. Additionally, the p-n-junction diodes of the $\mathrm{Sc}$X$\mathrm{I}$ monolayers display a strong rectifying effect and remarkable electrical anisotropy behavior. Moreover, the gate voltages effectively regulate the current through the FETs of the $\mathrm{Sc}$X$\mathrm{I}$ monolayers. $\mathrm{Sc}$X$\mathrm{I}$ monolayers and their phototransistors also show good photoelectric responses in the visible and ultraviolet regions. Strain can tune the device transport and photoelectric properties of the $\mathrm{ScSI}$ monolayers. Our results suggest that $\mathrm{Sc}$X$\mathrm{I}$ monolayers can be an alternative platform for flexible applications in microelectronic nanodevices, especially in photoelectric sensors.

Efficient interconnection between distant semiconductor spin qubits with the help of photonic qubits offers exciting new prospects for future quantum communication applications. In this paper, we optimize the extraction efficiency of a novel interface between a singlet-triplet-spin-qubit and a photonic-qubit. The interface is based on a 220-nm-thick $\mathrm{Ga}\mathrm{As}/(\mathrm{Al},\mathrm{Ga})\mathrm{As}$ heterostructure membrane and consists of a gate-defined double quantum dot (GDQD) supporting a singlet-triplet qubit, an optically active quantum dot (OAQD) consisting of a gate-defined exciton trap, a photonic crystal cavity providing in-plane optical confinement, efficient outcoupling to an ideal free-space Gaussian beam while accommodating the gate wiring of the GDQD and OAQD, and a bottom gold reflector to recycle photons and increase the optical extraction efficiency. All the essential components can be lithographically defined and deterministically fabricated on the $\mathrm{Ga}\mathrm{As}/(\mathrm{Al},\mathrm{Ga})\mathrm{As}$ heterostructure membrane, which greatly increases the scalability of on-chip integration. According to our simulations, the interface provides an overall coupling efficiency of 28.7% into a free-space Gaussian beam, assuming a ${\mathrm{Si}\mathrm{O}}_2$ interlayer fills the space between the reflector and the membrane. The performance can be further increased by undercutting this ${\mathrm{Si}\mathrm{O}}_2$ interlayer below the photonic crystal. In this case, the overall efficiency is calculated to be 48.5%.

Pursuing nonradiating sources and radiationless motion for accelerated charged particles has captivated physicists for generations. Nonradiating sources represent intricate current-charge configurations that do not emit radiation beyond their source domain. This study investigates a single nonradiating source comprising a low-index dielectric disk excited by a split-ring resonator. Employing analytical and numerical methods, we demonstrate that this configuration supports an anapole state, exhibiting minimal or no radiation, effectively representing a nonradiating source. The radiation suppression is accomplished through the destructive interference of electric dipoles excited on the metallic and dielectric components of the proposed prototype. Transforming the design into a cost-effective device capable of suppressing radiation, we achieve excellent numerical and experimental agreement, affirming the formation of the anapole state using the lowest-order multipoles. Moreover, the devised anapole device is remarkably compact, constructed from a low-index dielectric, and employs readily available components. As a versatile platform, the proposed device can spearhead anapole research for diverse applications, including sensing, wireless charging, radio frequency identification tags, and other nonlinear applications.

The synthetic antiferromagnet (SAF) offers a versatile platform to couple with various quasiparticles that is an indispensable element for the realization of hybrid quantum computing systems. In this work, we found that the magnon-magnon coupling strength in layered SAFs, consisting of repeated layers of $[{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Ru}{]}_n$, is highly dependent on the finite layer number n. In particular, the self-hybridizations of individual acoustic or optical modes in the even-layers lead to the opening of local anticrossing gaps within the same type of mode in the resonance spectra. With the structural asymmetry of the odd-layers, a global gap between different modes can be generated whose size is found to decrease with increasing layer number. By combining the static linear chain model with the dynamically coupled Landau-Lifshitz equations, we further formulated a theoretical approach to qualitatively describe such highly layer-dependent behaviors of magnon-magnon coupling in SAFs. It is clear that the layer number is a significant factor that influences both the number of excited modes and the associated mode hybridizations. Our findings shed light on the magnon-magnon coupling in layered antiferromagnets that may invigorate the development of magnonics.

The number of superconducting qubits contained in a single quantum processor is increasing steadily. However, to realize a truly useful quantum computer, it is inevitable to increase the number of qubits much further by distributing quantum information among distant processors using flying qubits. A key element towards this goal is a deterministic quantum interaction between superconducting-atom and propagating microwave-photon qubits. Here, we confirm the bidirectional state transfer between them, which completes by simply reflecting the photon at the atom. The averaged fidelity of the photon-to-atom (atom-to-photon) state transfer reaches 0.826 (0.801), limited mainly by the lifetime of the atom qubit. The present technology would be useful for future distributed quantum computation with superconducting qubits.

Here, we propose the construction of acoustic Weyl semimetals in synthetic dimensions based on a 2D coupling waveguide array under external dynamic modulations. The type-I, type-II, and line node acoustic Weyl semimetals can be realized in one lattice array and the associated transitions between different phases can be implemented by flexibly adjusting the dynamic modulations. The correspondence between different phases and symmetries is analyzed. The results clearly show that the spectra of topological surface states undergo bidirectional or unidirectional shifts in the frequency domain according to the type of Weyl points. Our work opens the door for studying acoustic Weyl physics in the synthetic dimensions and may have impacts on acoustic wave manipulation in both spatial and frequency domains.

Diamond tin-vacancy centers have emerged as a promising platform for quantum information science and technology. A key challenge for their use in more-complex quantum experiments and scalable applications is the ability to prepare the center in the desired charge state with the optical transition at a predefined frequency. Here we report on heralding such successful preparation using a combination of laser excitation, photon detection, and real-time logic. We first show that fluorescence photon counts collected during an optimized resonant probe pulse strongly correlate with the subsequent charge state and optical-transition frequency, enabling real-time heralding of the desired state through threshold photon counting. We then implement and apply this heralding technique to photoluminescence-excitation measurements, coherent optical driving, and an optical Ramsey experiment, finding strongly increased optical coherence with increasing threshold. Finally, we demonstrate that the prepared optical frequency follows the probe laser across the inhomogeneous linewidth, enabling tuning of the transition frequency over multiple homogeneous linewidths.

State-of-the-art miniature atomic clocks (MACs) are based on the phenomenon of coherent population trapping (CPT) in alkali-metal atomic vapors ($\mathrm{Rb}$ or $\mathrm{Cs}$). Improving the stability of the clock frequency is a crucial issue; resolving it would result in significant progress in numerous applications. Here, we examine the configuration of the light field, which is composed of two bichromatic beams with opposing handedness of circular polarization. The beams are in resonance with optical transitions in the $\mathrm{Cs}$ $D_1$ line ($\lambda \approx 895$ nm). This configuration has previously been shown to produce observed CPT resonances with higher contrast than a standard single-beam scheme; however, our scheme implements pump and probe beams that operate independently, with the transmission of the probe beam being monitored separately. This approach differs from previous studies. The experiments are carried out using a cubic $5\times 5\times 5{\mathrm{mm}}^3$ vapor cell filled with buffer gas. It is shown that the line shape of the resonance acquires an asymmetry that can be efficiently controlled by a microwave (Raman) phase between the beams. As a proof of concept, we study the way in which this asymmetry can help to mitigate the influence of the ac Stark (light) shift on the long-term frequency stability of CPT clocks based on vapor microcells ($V\ll 1{\mathrm{cm}}^3$). Experimental verification is performed with both a distributed-Bragg-reflector laser and a vertical-cavity surface-emitting laser. The latter is of particular importance for the development of MACs. The experimental results are in qualitative agreement with the analytical theory based on a double-$\mathrm{\Lambda }$ scheme of atomic energy levels.

The study of the anisotropic magnetoresistance (AMR) in antiferromagnetic materials is essential due to their superior properties, which have led to a broader application of antiferromagnets in spintronic devices. In this work, we examine the impact of substitutional doping on the antiferromagnetic AMR of $\mathrm{Fe}\mathrm{Rh}$. We discover that $\mathrm{Pt}$-$\mathrm{Rh}$ substitution can markedly enhance the antiferromagnetic AMR of $\mathrm{Fe}\mathrm{Rh}$. With a 7.7% $\mathrm{Pt}$-$\mathrm{Rh}$ substitution, the AMR increases up to fivefold compared to that of pristine $\mathrm{Fe}\mathrm{Rh}$ films. Conversely, $\mathrm{Mn}$-$\mathrm{Fe}$ substitution results in a decrease in the antiferromagnetic AMR of $\mathrm{Fe}\mathrm{Rh}$. First-principles calculations are employed to comprehend the distinct effects of the substitution on the electronic band structures. Compared to the $\mathrm{Mn}$-$\mathrm{Fe}$ substitution, the $\mathrm{Pt}$-$\mathrm{Rh}$ substitution leads to a greater difference in electrical transport between parallel and perpendicular orientations, culminating in a larger AMR. This is because the replacement with $\mathrm{Pt}$-$\mathrm{Rh}$ increases the spin-orbit coupling interaction and s-d scattering in the system, whereas the substitution with $\mathrm{Mn}$-$\mathrm{Fe}$ reduces the spin-orbit coupling. Our research offers valuable insights into the underlying mechanisms controlling the AMR in antiferromagnetic materials and establishes a foundation for further enhancing their functionality.

The dielectric loss of silicon nitride (${\mathrm{Si}}_3{\mathrm{N}}_4$) limits the performance of microwave-frequency devices that rely on this material for sensing, signal processing, and quantum communication. Using superconducting resonant circuits, we measure the cryogenic loss tangent of either as-deposited or high-temperature annealed stoichiometric ${\mathrm{Si}}_3{\mathrm{N}}_4$ as a function of drive strength and temperature. The internal loss behavior of the electrical resonators is largely consistent with the standard tunneling model of two-level systems (TLSs), including damping caused by resonant energy exchange with TLSs and by the relaxation of nonresonant TLSs. We further supplement the TLS model with a self-heating effect to explain an increase in the loss observed in as-deposited films at large drive powers. Critically, we demonstrate that annealing remedies this anomalous power-induced loss, reduces the relaxation-type damping by more than 2 orders of magnitude, and reduces the resonant-type damping by a factor of 3. Employing infrared absorption spectroscopy, we find that annealing reduces the concentration of hydrogen in ${\mathrm{Si}}_3{\mathrm{N}}_4$, suggesting that hydrogen impurities cause substantial dissipation.

We have investigated the carrier-transport properties of diamond using a first-principles approach. We have employed a full-band Monte Carlo model based on an electronic structure obtained from density-functional theory (DFT) augmented with Heyd-Scuseria-Ernzerhof (HSE) hybrid functionals. We have computed the carrier-phonon interaction directly employing the DFT electronic structure and phonon dispersion. Effective acoustic and optical scattering models have been calibrated against the ab initio results to obtain a computationally efficient transport model that retains the accuracy of the first-principles approach. Using the DFT-derived full-band structure and the calculated carrier-phonon scattering rates, we have evaluated the field-dependent drift velocities and impact-ionization coefficients and compared them to the available experimental data. We have also analyzed the temperature dependence of the carrier drift velocity up to 500 K and developed analytical models that can be used to perform device simulation based on the drift-diffusion method.

Increasing the separation between semiconductor quantum dots offers scaling advantages by facilitating gate routing and the integration of sensors and charge reservoirs. Elongated quantum dots have been utilized for this purpose in GaAs heterostructures to extend the range of spin-spin interactions. Here, we study a MOS device where two quantum dot arrays are separated by an elongated quantum dot (340 nm long, 50 nm wide). We monitor charge transitions of the elongated quantum dot by measuring radiofrequency single-electron currents to a reservoir to which we connect a lumped-element resonator. We operate the dot as a single-electron box to achieve charge sensing of remote quantum dots in each array, separated by an edge-to-edge distance of 480 nm. Charge detection on both ends of the elongated dot at a coinciding setpoint demonstrates that the charge states are well distributed across its nominal length, supported by the simulated quantum mechanical electron density. Likewise, we show elongated-peripheral quantum dot tunnel couplings can exceed $20\mathrm{GHz}$, above the electron temperature, fulfilling the requirement for mediated exchange. Our results illustrate how single-electron boxes can be realized with versatile footprints that may enable compact quantum processor layouts, offering distributed charge sensing in addition to the possibility of mediated coupling.

Quantum state readout plays a pivotal role in quantum technologies, spanning applications in sensing, computation, and secure communication. In this work, we introduce an approach for efficiently reading populations of hybrid-spin states in the nitrogen-vacancy center of diamond using a single laser pulse, which utilizes the excited-state-level anticrossing mechanism at around 500 Gs. Reading spin-state populations through this approach achieves the same outcome as traditional quantum state diagonal tomography but significantly reduces the experimental time by an order of magnitude while maintaining fidelity. Moreover, this approach may be extended to encompass full-state tomography, thereby obviating the requirement for a sequence of spin manipulations and mitigating errors induced by decoherence throughout the procedure.

We propose a superconducting diode device comprising a central superconducting film flanked by two wires carrying an applied dc bias, suitably chosen so as to generate different asymmetric field profiles. Through numerical simulations of the coupled Ginzburg-Landau and heat-diffusion equations, we show that this design is capable of efficiently breaking the reciprocity of the critical current in the central superconductor, thus promoting the diode effect in response to an applied ac. By adjusting the dc bias in the wires, we find the optimum inhomogeneous field profile that facilitates the entrance of vortices and antivortices in a given polarity of the applied ac and impede their entrance in the other polarity. This way, the system behaves as a superconducting half-wave rectifier, with diode efficiencies surpassing 70%. Furthermore, we detail the behavior and diode efficiency of the system under different experimental conditions, such as the substrate heat-transfer coefficient and the sweep rate of the external current.

Exploring reconfigurable axial trapping within perovskite nanoparticles can advance our understanding of their dynamic behaviors, but fine research tools are needed for precise control and modulation. We present a method to study the interaction between perovskite particles and optical fields at the single-particle level, proposing an autofocusing cusp-catastrophe Bessel beam (CCBB) with reconfigurable multiple foci along the propagation direction. The CCBB displays multiple autofocusing with quasi-diffraction-free features. The geometric parameters of the beam can precisely control the quasi-diffraction-free distances, the focus positions, the peak intensities, the trapping forces, etc. Our theoretical proposal for the CCBB has been experimentally corroborated through the generation of the CCBB. We further apply the CCBB to trap ${\mathrm{Cs}}_3{\mathrm{Cu}}_2{\mathrm{I}}_5$ perovskite particles ranging from micrometers to nanometers at multiple longitudinal foci and evaluate the trapping forces at the respective focus. The CCBB offers a potent tool for optical trapping and manipulation, playing a pivotal role in uncovering the interactions between perovskite materials and optical fields.