To overcome the memory wall based on the von Neumann architecture, in-memory computing has been intensively studied as a potential solution. Recently, an alternative type of spintronic material, namely, bipolar magnetic semiconductors (BMSs), has attracted much attention because of its opposite spin-polarized valence and conduction bands, which have thus facilitated electrically tunable spin transport. Here, we propose a logic-in-memory device with a traditional field-effect-transistor (FET) configuration by making use of the ferromagnetic and semiconducting features of BMSs simultaneously. Two representative BMSs (2H-${\mathrm{VS}}_2$ and semihydrogenated graphene) are selected as the FET channels, and the transport properties of these devices are investigated by using ab initio quantum transport simulations. The spin polarization of the current reaches up to 98%, enabling the device to provide an ideal spin-polarization signal. The distinct electronic structures under the two magnetic states and the electrically tunable spin polarization allow the devices to perform logic operations directly in situ. Two-input logic, including xor and nonvolatile and or nor, can be realized with one and two BMS FETs, respectively, efficiently decreasing the integration density of logic circuits. This work provides an alternative route to realize fused storage and computing functions in a transistor.

The growing demand for ultrafast information transmission in integrated sensing and communications has fueled extensive research on spoof surface-plasmon polaritons (SSPPs). However, existing studies have been limited by structural design constraints, resulting in single-frequency phase modulation and hindered high-order modulation capabilities. Here, we propose a superthin programmable modulator utilizing SSPP waveguides and validate its performance through experimental verification. Our modulator enables phase control across a wider bandwidth by real-time manipulation of SSPP waveguides in a programmable manner, facilitating quadrature-phase-shift-keying modulation. Moreover, this modulator opens up possibilities for achieving higher-order modulation. Measurement results demonstrate the effectiveness of programmable plasma metamaterials in modulating surface electromagnetic waves, with significant implications for integrated sensing and communications applications.

Transparent light-converting ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}:\mathrm{Ce}$ (YAG:$\mathrm{Ce}$) ceramics have become promising materials for advanced light-emitting diode and laser-driven white-light-generation technology. However, their functionality is highly dependent on factors such as structural quality, uniformity of dopant distribution, the presence of defects, and the cost of fabrication. The emission of YAG:$\mathrm{Ce}$ ceramics remains thermally stable when high-power-density laser excitation is uniformly spread over the entire surface area of the ceramics due to light-scattering processes. The creation of light-scattering centers that can provide homogeneous white light in ceramics is crucial. One of the drawbacks of YAG:$\mathrm{Ce}$ as a material for converting ultraviolet emission into white light is the lack of a red component, which results in cold light and a low color rendering index. Therefore, the codoping of YAG:${\mathrm{Ce}}^{3+}$ with red-emitting ions (${\mathrm{Er}}^{3+}$, ${\mathrm{Ho}}^{3+}$, ${\mathrm{Nd}}^{3+}$, ${\mathrm{Pr}}^{3+}$, and ${\mathrm{Cr}}^{3+}$) was carried out and slight nonstoichiometry was induced in the present study to improve the photoconversion parameters. The phase purity of the studied ceramics was analyzed using powder x-ray diffraction and SEM combined with energy-dispersive spectroscopy (EDS). EDS studies revealed that nonstoichiometric ceramics contained ${\mathrm{Al}}_2{\mathrm{O}}_3$ phase inclusions that acted as light-scattering centers. Optical transmittance and absorption spectra measurements revealed the presence of light-scattering centers imposed by ${\mathrm{Al}}_2{\mathrm{O}}_3$ phase inclusions and nanodefects related to perturbations of the local lattice structure by dopants. EDS mapping and photoluminescence analysis showed the formation of $\mathrm{Ce}$-$\mathrm{Ln}$,$\mathrm{Cr}$ ($\mathrm{Cr}$ is a transition metal) pairs and the availability of energy transfer between the pair-forming ions. Intrinsic thermal quenching of ${\mathrm{Ce}}^{3+}$ luminescence started above 400 K. The nonstoichiometric YAG:$\mathrm{Ce},\mathrm{Nd}$ sample showed luminescence stability up to 650 K with a luminous efficacy of 198 lm/W. The photoconversion parameters of the transparent ceramic packaged with a blue light-emitting diode or a laser diode were compared. It was shown that the color temperature of ceramic emissions could be controlled by the spectral width of the excitation beam. Thermally stimulated luminescence was applied to investigate the deep trapping centers imposed by the codopants. A detailed EPR study revealed the presence of ${\mathrm{F}}^{+}$, ${\mathrm{O}}^{-}$, and ${\mathrm{Ce}}^{4+}$ centers.

Optimizing the cooperativity between two distinct particles is an important feature of quantum information processing. Of particular interest is the coupling between spin and phonon, which allows for integrated long-range communication between gates operating at gigahertz frequency. Using local light scattering, we show that, in magnetic planar geometries, this attribute can be tuned by adjusting the orientation and strength of an external magnetic field. The coupling strength is enhanced by about a factor of 2 for the out-of-plane magnetized geometry where the Kittel mode is coupled to circularly polarized phonons, compared to the in-plane one where it couples to linearly polarized phonons. We also show that the overlap between magnon and phonon is maximized by matching the Kittel frequency with an acoustic resonance that satisfies the half-wave-plate condition across the magnetic film thickness. Taking the frequency dependence of the damping into account, a maximum cooperativity of about 6 is reached in garnets for the normal configuration near 5.5 GHz.

In addition to the need for stable and precisely controllable qubits, quantum computers take advantage of good readout schemes. Superconducting qubit states can be inferred from the readout signal transmitted through a dispersively coupled resonator. This work proposes a readout classification method for superconducting qubits based on a neural network pretrained with an autoencoder approach. A neural network is pretrained with qubit readout signals as autoencoders in order to extract relevant features from the data set. Afterward, the pretrained-network inner-layer values are used to perform a classification of the inputs in a supervised manner. We demonstrate that this method can enhance classification performance, particularly for short- and long-time measurements where more traditional methods present inferior performance.

In conventional inductive wireless power devices, the energy is transferred via only reactive near fields, which is equivalent to nonradiative Förster energy transfer in optics. Radiation from transmitting and receiving coils is usually considered as a parasitic effect that reduces the power-transfer efficiency. As long as the distance between the two antennas is small compared to the antenna size, conventional wireless power-transfer devices offer rather high power-transfer efficiency, of the order of 80%–90%. However, for larger distances, the transfer efficiency dramatically drops, making such devices impractical. In this paper, we develop a dynamic theory of wireless power transfer between two small loop antennas, clarify the role of far-field radiation, and find a possibility to realize efficient wireless power transfer at large distances utilizing the regime of radiation suppression due to optimized mutual dynamic interactions between the transmitting and receiving antennas. The analytical results are validated by simulations and measurements, and they open a possibility to greatly expand the range of distances of compact wireless power-transfer devices. The developed theory can also be applied to coupling between antennas of different types and to energy transfer between nano-objects.

In this paper, we develop an exact analytical quantum theory for field emission from surfaces with a nearby quantum well, by solving the one-dimensional time-independent Schrödinger equation. The quantum well, which may be introduced by ions, atoms, nanoparticles, etc., is simplified as a square potential well with depth H, width d, and distance to the surface L. The theory is used to analyze the effects of the quantum well (d, H, and L), the cathode properties (work function W and Fermi energy $E_F$), and dc field F. It is found that the quantum well can lead to resonant tunneling enhanced field emission up to several orders of magnitude larger than that from bare cathode surfaces. In the meantime, the electron-emission-energy spectrum is significantly narrowed. The strong enhancement region is bounded by the conditions eFL + H ≥ W + C and eFL ≤ W, with e being the elementary charge (positive) and C a constant dependent on dc field F. It is also found that the linear shift of resonance peaks in the electron-emission-energy spectrum with dc field F follows ${\epsilon }_p={\epsilon }_{p0}-eFL$, with ${\epsilon }_{p0}$ being approximately the eigenenergies for electrons confined in a square potential well without a dc field. The theory provides insights for the design of high-efficiency field emitters, which can produce a high current and highly collimated electron beams.

Willis dynamic homogenization theory revealed that the effective linear momentum of elastic composites is coupled to their effective strain. Recent generalization of Willis dynamic homogenization theory to the case of piezoelectric composites further revealed that their effective linear momentum is also coupled to the effective electric field. Here, we introduce the simplest possible model—a one-dimensional discrete model—that exhibits this so-called electromomentum coupling in subwavelength composites. We utilize our model to elucidate the physical origins of this phenomenon, illustrate its mechanism, and identify local resonances which lead to elevated Willis and electromomentum coupling in narrow frequency bands. The results provide intuitive guidelines for the design of this coupling in piezoelectric metamaterials.

Temporal modulation unlocks possibilities to dynamically control and modify the response of electromagnetic systems. Employing explicit dependencies of circuit or surface parameters on time enables the engineering of systems with conventionally unachievable functionalities. Here, we propose an alternative approach that enables the emulation of electromagnetic systems that can have arbitrary frequency dispersion and nonlinear properties, including the non-Foster response. In particular, we show that a proper modulation of a time-varying capacitor allows one to mimic a static inductance, capacitance, or resistance having arbitrary values, both positive and negative. We discuss necessary modifications of determined ideal modulation functions that ensure the stability of the system. To demonstrate the applicability of the proposed method, we introduce and simulate an invisible sensor, i.e., a device that does not produce any scattering and is capable of sensing. Three different geometries are proposed and validated using full-wave simulations. In addition to that, we discuss the stability of the systems that are modulated externally. We believe that this study introduces an alternative paradigm of using time modulations to engineer system responses that can be applied not only to electromagnetic systems (in electronics, microwaves, and optics) but also in other branches of physics.

Unpaired electronic spins at diamond surfaces are ubiquitous and can lead to excess magnetic noise. They have been observed in several studies to date, but their exact chemical nature is still unknown. We propose a simple model to explain the existence and chemical stability of surface spins associated with the ${sp}^3$ dangling bond on the (100) diamond surface using density-functional theory. We find that the (111) facet, which is naturally generated at a step edge of (100) crystalline diamond surface, can sterically protect a spinful defect. Our study reveals a mechanism for annihilation of these surface spins upon annealing, consistent with recent experimental results. We also demonstrate that the Fermi-contact term in the hyperfine coupling is not negligible between the surface spins and the surrounding nuclear spins, and thus ab initio simulation can be used to devise a sensing protocol where the surface spins act as reporter spins to sense nuclear spins on the surface.

Understanding the fundamental heat-transport mechanisms across interfaces comprised of two-dimensional (2D) materials is crucial for the further development of the next generation of optoelectronic devices based on 2D heterostructures for which one of the main factors affecting the device performance is their poor thermal management. Here we use systematic atomistic simulations to unravel the influence of anharmonicity in dictating the thermal boundary conductance across graphene and ${\mathrm{Mo}\mathrm{S}}_2$-based 2D and three-dimensional (3D) interfaces. Specifically, we conduct nonequilibrium molecular dynamics simulations on computational domains with graphene or ${\mathrm{Mo}\mathrm{S}}_2$ layers encapsulated between crystalline or amorphous silicon leads across a wide temperature range (of 50–600 K). We show that while the interfacial conductance across a graphene and crystalline silicon interface demonstrates considerable temperature dependence, the conductance across a graphene and amorphous silicon interface has no significant temperature dependence. In contrast, the thermal boundary conductance for the ${\mathrm{Mo}\mathrm{S}}_2$-based heterostructures with both the crystalline and amorphous leads demonstrate no significant temperature dependence. Our spectral energy-density calculations along with our spectrally resolved heat-flux accumulation calculations on the various interfaces show that anharmonic coupling across the entire vibrational spectrum as well as the strong hybridization of a broader spectrum of the flexural modes with substrate Rayleigh waves in graphene heterostructures give rise to the relatively higher and drastically different heat-transport mechanisms across these interfaces as compared to the ${\mathrm{Mo}\mathrm{S}}_2$-based heterostructures. Through these understandings, we show that one strategy to enhance heat conductance across 2D-3D interfaces is to increase the anharmonic coupling between the acoustic and optic modes in the 2D materials by inducing a stronger interaction strength with the substrates. Our findings elucidate the fundamental heat-transfer mechanisms dictating thermal-boundary conductances across 2D-3D interfaces and will be crucial for heat dissipation in the next generation of optoelectronic devices where the utilization of 2D materials are becoming ubiquitous.

Vulnerabilities of components used in quantum-key-distribution systems affect its implementation security and must be taken into consideration during system development and security analysis. In this paper, we investigate transmission of fiber optical elements, which are commonly used in quantum-key-distribution systems for designing countermeasures against Trojan-horse attacks, in the $1500$–$2100$-$\mathrm{nm}$ range. As a result, we find loopholes in their transmission spectra that open possibilities for eavesdropping. We also consider a simple passive countermeasure based on the violation of total internal reflection in a single-mode fiber, that provides additional insertion losses of at least 60 dB for double-pass Trojan-horse probe pulses for wavelengths longer than 1830 nm.

We develop a theoretical model for calibrating the absorption imaging of cold atoms under high magnetic fields. Particularly it also works when the hyperfine structure is decoupled and cannot provide good quantum numbers anymore. Compared with zero or low magnetic fields, for high magnetic fields the efficiency of the absorption imaging is lower, while an additional correction factor is required to obtain the absolute atom number under the Beer-Lambert law. Our model is based on the rate equations and can account for many experimental imperfections, such as Zeeman level crossing, off-resonant couplings, and low repumping efficiency. On the basis of this method, we can precisely calculate the correction factor for atom-number measurement without any empirical or fitting parameters. Meanwhile, we use a cold-atom apparatus based on ${}^{85}\mathrm{Rb}$ to experimentally verify our model. In addition, we find our work can also serve as a benchmark to measure the polarization impurity of a circularly polarized laser beam with high sensitivity. We believe this work will be beneficial for most cold-atom experiments using absorption imaging.

As integrated-circuit (IC) geometry and packaging become more sophisticated with ongoing fabrication and design innovations, the electrical-engineering community needs increasingly powerful failure-analysis (FA) methods to meet the growing troubleshooting challenges of multilayer (with multiple metal layers) and multichip components. In this work, we investigate an electronics FA method using a quantum diamond microscope (QDM) to image the magnetic fields from short-circuit faults. After quantifying the performance by detecting short-circuit faults in a multilayer silicon die, we assess how a QDM would detect faults in a heterogeneously integrated (HI) die stack. This work hopefully establishes QDM-based magnetic imaging as a competitive technique for electronics FA, offering high spatial resolution, high sensitivity, and robust instrumentation. We anticipate these advantages to be especially useful for finding faults deep within chip-stack ICs with many metal layers, optically opaque layers, or optically scattering layers.

Bilayer graphene is an attractive material that hosts a high-quality two-dimensional electron gas with a controllable band gap. By utilizing the band gap, electrical gate tuning of the carrier is possible and formation of nanostructures such as quantum dots has been reported. To probe the dynamics of the electronic states and realize applications for quantum bit devices, radio-frequency (rf) reflectometry, which enables high-speed electrical measurements, is important. Here we demonstrate rf reflectometry in bilayer graphene devices. We utilize a microscale graphite back-gate and an undoped $\mathrm{Si}$ substrate to reduce the parasitic capacitance, which degrades the rf reflectometry measurement. We measure the resonance properties including the matching condition of a tank circuit, which contains the bilayer graphene device. We construct a demodulated rf reflectometry setup and compare the result with dc measurement, and confirm their consistency. The wide-range frequency-dependent noise behavior is also analyzed. From the noise analysis, we calculate the readout error rate of our device for single-electron detection and demonstrate that a vertically integrated charge sensor has the potential to achieve a low error rate. We also measure Coulomb diamonds of quantum dots possibly formed by bubbles and confirm that rf reflectometry of quantum dots can be performed. This technique enables high-speed measurements of bilayer graphene quantum dots and contributes to the study of bilayer-graphene-based quantum devices by fast readout of the states.

The fabrication of superconducting circuits requires multiple deposition, etching, and cleaning steps, each possibly introducing material property changes and microscopic defects. In this work, we specifically investigate the process of argon milling, a potentially coherence-limiting step, using niobium and aluminum superconducting resonators as a proxy for the surface-limited behavior of qubits. We find that niobium microwave resonators exhibit an order of magnitude decrease in quality factors after surface argon milling, while aluminum resonators are resilient to the same process. Extensive analysis of the niobium surface shows no change in the suboxide composition due to argon milling, while two-tone spectroscopy measurements reveal an increase in two-level system electrical dipole moments, indicating a structurally altered niobium oxide. However, a short dry etch can fully recover the argon-milling-induced losses on niobium, offering a potential route towards state-of-the-art overlap Josephson junction qubits with niobium circuitry.