Spin-split superconductors exhibit an electron-hole asymmetric spin-resolved density of states, but the symmetry is restored upon averaging over spin. On the other hand, asymmetry appears again in tunneling junctions of spin-split superconductors with a spin-polarized barrier. As demonstrated recently in both theory and experiment, this fact leads to a particularly strong thermoelectric effect in superconductor-ferromagnet structures. In this work we show another important effect stemming from the electron-hole asymmetry: current rectification. We calculate the charge current in spin-polarized tunnel junctions of a normal metal and a spin-split superconductor with ac and dc voltage bias. In the dc case, the I-V curve is not fully antisymmetric and has a voltage-symmetric component due to spin polarization. This translates to the existence of a rectified current in the ac case, which is proportional to the spin polarization of the junction and strongly depends on the frequency of the applied bias. We discuss possible applications of the rectification effect, including a diode for superconducting electronics and radiation detectors. The analysis of the rectified charge current is supplemented by the discussion of heat current and relevant noise correlators, where electron-hole asymmetry also plays an important role, and which are useful for applications in detectors.

Mitigating greenhouse gas emissions by underground carbon dioxide storage or by coupling intermittent renewable energy with underground hydrogen storage are solutions essential to the future of energy. Of particular importance to the success of underground storage is the fundamental understanding of geochemical reactions with mineralogical phases and flow behavior at the length scale at which interfaces are well resolved. Fast synchrotron-based three-dimensional x-ray microcomputed tomography (µCT) of rocks is a widely used technique that provides real-time visualization of fluid flow and transport mechanisms. However, fast imaging results in significant noise and artifacts that complicate the extraction of quantitative data beyond the basic identification of solid and void regions. To address this issue, an image-processing workflow is introduced that begins with unpaired domain transfer by cycle-consistent adversarial network, which is used to transfer synchrotron-based µCT images containing fast-imaging-associated noise to long-scan high-quality µCT images that have paired ground truth labels for all phases. The second part of the workflow is multimineral segmentation of images using convolutional neural networks (CNNs). Four CNNs are trained using the transferred dynamic-style µCT images. A quantitative assessment of physically meaningful parameters and material properties is carried out. In terms of physical accuracy, the results show a high variance for each network output, which indicates that the segmentation performance cannot be fully revealed by pixel-wise accuracy alone. Overall, the integration of unpaired domain transfer with CNN-based multimineral segmentation provides a generalizable digital material framework to study the physics of porous materials for energy-related applications, such as underground ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2$ storage.

One of the main advantages of silicon spin qubits over other solid-state qubits is their inherent scalability and compatibility with the 300-mm complementary metal oxide semiconductor (CMOS) fabrication technology that is already widely used in the semiconductor industry, while maintaining high readout and gate fidelities. We demonstrate the detection of a single electron spin using energy-selective readout in a CMOS-fabricated nanowire device with an integrated charge detector. We measure a valley splitting of 0.3 meV and 0.16 meV in two similar devices. The anisotropy of the spin-valley mixing is measured and shown to follow the dependence expected from the symmetry of the local confinement, indicating low disorder in the region of the quantum dot. Finally the charge noise in the strong spin-valley coupling regime is investigated and found to induce fluctuations in the qubit energy in the range of $0.6\text{GHz}/\sqrt{\text{Hz}}$.

Defect spin qubits in silicon carbide have recently drawn widespread attention. Extraction of spin information in the presence of noise always requires multiple repeated measurements, which consumes a large amount of time resources. In this paper, we propose a deep-learning-enhanced method to extract effective parameters from continuous-wave optically detected magnetic resonance (ODMR) spectra and Rabi oscillations with less time consumption. Even if the signal-to-noise ratio is reasonably low, a well-trained convolutional neural network (CNN) can predict the resonance peaks of ODMR spectra or the period of Rabi oscillations. Because of the fast output of predictions by the CNN, this method can be used to sense the magnetic field in the environment and microwave intensities in real time.

Scattering of light by cloud, haze, and fog decreases the transmission efficiency of communication channels in quantum key distribution (QKD), reduces the system’s practical security, and thus constrains the deployment of free-space QKD. Here, we employ wave-front shaping technology to compensate distorted optical signals in high-loss scattering quantum channels and fulfill a polarization-encoded BB84 QKD experiment. With this quantum-channel compensation technology, we achieve a typical enhancement of about 250 in transmission efficiency and build a secure communication link even considering finite key length effect, while the link is impossible to share secure keys before optimization. The method applied in the QKD system shows the potential to expand the application range of QKD systems from lossless channels to highly scattered ones and therefore enhances the deployment ability of a global quantum communication network.

Two-dimensional (2D) materials with suitable electronic and optical properties offer various possibilities for photocatalytic applications. Although various 2D materials have hitherto been specified as adequate candidates, materials with high photocatalytic efficiency for water splitting are still minimal. In this study, we predict a 2D Janus $\mathrm{Ge}\mathrm{P}\mathrm{As}$ monolayer and examine its capability for photocatalytic water splitting by performing first-principles calculations. The $\mathrm{Ge}\mathrm{P}\mathrm{As}$ monolayer is shown to possess robust dynamic and thermal stability. The direct electronic band gap in the visible region and band-edge positions of the strain-free and strained monolayers are revealed to be convenient for redox reactions in wide pH ranges. The low recombination probability of charge carriers ensured by high and anisotropic carrier mobility enhances the material’s photocatalytic potential. Optical response calculations, including many-body interactions, indicate significant optical absorption capacity in the UV-visible range. Furthermore, low exciton binding energy facilitates dissociation into free electrons and holes, promoting photocatalytic reactions. Our study suggests that the $\mathrm{Ge}\mathrm{P}\mathrm{As}$ monolayer is an ideal and remarkably promising material to be utilized in visible-light-driven photocatalytic applications.

A general aging model of the double Schottky barrier was proposed to unveil the long-term aging behaviors of $\mathrm{Zn}\mathrm{O}$ varistor ceramics, especially for those ones with steadily decreasing power loss. For those samples, the barrier height and electrical properties were even enhanced rather than commonly deteriorated, which were beyond the classic ion migration model. In this paper, inspired by the unique reversible aging of them, interface states are proposed to remain stable in those samples. The major mobile ions, which have been in debate, are further identified to be ${\mathrm{Zn}}_i^{\cdot }$ ions. Based on these assumptions, a quantitative dynamic ion migration-diffusion model is proposed. The calculated power loss steadily decreases with aging time, which well supported our proposal. When the interface states are not combined with those mobile ions, the formation of a “U-shape” ion spatial distribution in depletion layers is found to be responsible for the unique aging phenomena, i.e., a reduction in the depletion layer and interfacial charge, a rise in the depletion layer width, and an increase in the barrier height. However, continuously increasing power loss would be generated if the mobile ions combined with the interface states. Therefore, a general mechanism on the aging of the double Schottky barrier is unveiled that it is a competition process between consumption of the interface states and the dynamics of mobile ions in depletion layers.

We present a liquid-nitrogen-cooled $\mathrm{Ca}$${}^{+}$ optical clock with an overall systematic uncertainty of $3.0\times {10}^{-18}$. In contrast to the room-temperature $\mathrm{Ca}$${}^{+}$ optical clock that we have reported previously, the cryogenic black-body radiation (BBR) shield in vacuum is cooled to $82\pm 5$ K using liquid nitrogen. We also implement an ion trap with a reduced heating rate and improved laser cooling. This allows the ion temperature to fall to the Doppler-cooling limit during the clock operation and the systematic uncertainty associated with the secular (thermal) motion of the ion is reduced to $<1\times {10}^{-18}$. The uncertainty arising from the probe laser light shift and the servo error is also reduced to $<1\times {10}^{-19}$ and $4\times {10}^{-19}$ with the hyper-Ramsey method and the higher-order servo algorithm, respectively. By comparing the output frequency of the cryogenic clock to that of a room-temperature clock, the differential BBR shift between the two is determined with a fractional statistical uncertainty of $7\times {10}^{-18}$. The differential BBR shift is used to calculate the static differential polarizability and the result is found to be in excellent agreement with our previous measurement using a different method. This work suggests that the BBR shift of optical clocks can be suppressed well in a liquid-nitrogen environment. Systems similar to what is presented here can also be used to suppress the BBR shift significantly in other types of optical clocks, such as $\mathrm{Yb}$${}^{+}$, $\mathrm{Sr}$${}^{+}$, $\mathrm{Yb}$, Sr, etc.

We theoretically demonstrate near-field radiative thermal switching between two nanoparticles located above a multilayered slab. We propose a multilayered structure composed of $\mathrm{Si}\mathrm{C}$ and the phase transition material ${\mathrm{VO}}_2$. The high tunability of the multilayered structure enables the active modulation of surface polaritons when combined with the phase transition feature of ${\mathrm{VO}}_2$, overcoming the intrinsic resonance of the thermal radiation of ${\mathrm{VO}}_2$. Utilizing this feature, the surface polaritons enormously excited at the particle’s resonant frequency above the multilayer can be switched on or off, resulting in the efficient modulation of heat flux between nanoparticles. The effects of interparticle distance and multilayer parameters on thermal switching ratios are investigated. We demonstrate that the multilayer with metallic ${\mathrm{VO}}_2$ can significantly inhibit the heat flux between particles as a result of the destructive interference between direct and reflected waves. The excited surface modes above the multilayer with insulating ${\mathrm{VO}}_2$ can still improve the heat flux between nanoparticles, resulting in a thermal switching ratio of ${10}^{-5}$ at the particle resonant frequency at a large interparticle distance.

Maxwell’s fish-eye lens (MFEL) with positive refraction has been shown to achieve perfect imaging, but with the cost of drain assistance. This has led to ongoing heated debates about the rigor of the physics of super-resolution phenomena in MFEL. In this work, we report that a MFEL embedded in an exterior coating, inspired by the solid immersion concept, can realize super-resolution imaging without a drain. Such a solution mitigates and bypasses the corresponding criticisms and debates of the past decades. We find that the total reflection at the outer solid-immersion interface and the native perfect focusing of MFEL synthetically contribute to a super-resolution image formed in the air. Moreover, this intuitive yet simple recipe can be robustly applied to other absolute instruments, such as the general Luneburg lens and more versatile superimaging systems are anticipated. We demonstrate the imaging performance in a solid immersion general Luneburg lens both numerically and experimentally, which indirectly verifies the imaging validity of the solid immersion MFEL without a drain.

The presence of a partially reflecting screen on top of a grounded dielectric slab strongly perturbs its modal spectrum. The modes supported by such structures have been investigated in the literature for some specific, yet relevant cases. Here, a comprehensive modal analysis is presented, which emphasizes the inductive or capacitive nature of the partially reflecting sheet. The results of this analysis not only provide a clear overview of a wide class of structures of relevance in applied electromagnetics, but also unveil the presence of some useful propagating regimes so far barely explored.

We theoretically and numerically study the terahertz auto-oscillations, or self-oscillations, in thin-film metallic noncollinear coplanar antiferromagnets (AFMs), such as ${\mathrm{Mn}}_3\mathrm{Sn}$ and ${\mathrm{Mn}}_3\mathrm{Ir}$, under the effect of antidamping spin torque with spin polarization perpendicular to the plane of the film. To obtain the order parameter dynamics in these AFMs, we solve three Landau-Lifshitz-Gilbert equations coupled by exchange interactions assuming both single- and multidomain (micromagnetics) dynamical processes. In the limit of a strong exchange interaction, the oscillatory dynamics of the order parameter in these AFMs, which have opposite chiralities, could be mapped to that of two damped-driven pendulums with significant differences in the magnitude of the threshold currents and the range of frequency of operation. The theoretical framework allows us to identify the input current requirements as a function of the material and geometry parameters for exciting an oscillatory response. We also obtain a closed-form approximate solution of the oscillation frequency for large input currents in the case of both ${\mathrm{Mn}}_3\mathrm{Ir}$ and ${\mathrm{Mn}}_3\mathrm{Sn}$. Our analytical predictions of threshold current and oscillation frequency agree well with the numerical results and thus can be used as compact models to design and optimize the auto-oscillator. Employing a circuit model, based on the principle of tunnel anisotropy magnetoresistance, we present detailed models of the output power and efficiency versus oscillation frequency of the auto-oscillator. Finally, we explore the spiking dynamics of two unidirectional as well as bidirectional coupled AFM oscillators using nonlinear damped-driven pendulum equations. Our results could be a starting point for building experimental setups to demonstrate auto-oscillations in metallic AFMs, which have potential applications in terahertz sensing, imaging, and neuromorphic computing based on oscillatory or spiking neurons.

Realistic modeling of qubit systems including noise and constraints imposed by control hardware is required for performance prediction and control optimization of quantum processors. We introduce qopt, a software framework for simulating qubit dynamics and robust quantum optimal control considering common experimental situations. To this end, we model open and closed qubit systems with a focus on the simulation of realistic noise characteristics and experimental constraints. Specifically, the influence of noise can be calculated using Monte Carlo methods, effective master equations or with the efficient filter function formalism, which enables the investigation and mitigation of autocorrelated noise. In addition, limitations of control electronics, including finite bandwidth effects as well as nonlinear transfer functions and drive-dependent noise, can be considered. The calculation of gradients based on analytic results is implemented to facilitate the efficient optimization of control pulses. The software easily interfaces with QuTiP, is published under an open-source license, is well tested, and features a detailed documentation.

The hydrogen-evolution reaction is an essential step in the electrochemical production of hydrogen without the emission of greenhouse gases. For this reaction, alternative catalyst materials that can replace the platinum of current catalysts are needed. Recent alternatives include two-dimensional materials such as transition metal dichalcogenides. Here, we show the electronic and electrochemical properties of the two-dimensional material palladium disulfide (${\mathrm{Pd}\mathrm{S}}_2$) with two crystal structures (phases) and the formation of native point defects. We analyze the differences between the pentagonal ($P$-${\mathrm{Pd}\mathrm{S}}_2$) phase and the octahedral ($1T$-${\mathrm{Pd}\mathrm{S}}_2$) phase, point defects and the Gibbs free energies for hydrogen adsorption from first-principles calculations. Our results show that the $1T$-${\mathrm{Pd}\mathrm{S}}_2$ phase has better catalytic activity than the $P$-${\mathrm{Pd}\mathrm{S}}_2$ phase in the pristine basal plane. In addition, the point defects of lower formation energy in the $1T$-${\mathrm{Pd}\mathrm{S}}_2$ phase, the $S$ vacancies, further improve the catalytic activity for hydrogen production.

Capillary adhesion is commonly present in ambient conditions. It can be measured in single-asperity contacts through atomic force microscopy using a sharp probe that is pulled off a smooth substrate. However, for macroscopic multiasperity interfaces, the measured adhesive force is always close to zero because of the elastic energy stored into the deformation of surface roughness; this is known as the adhesion paradox. Here, we experimentally show how capillary adhesion influences friction between macroscopic $\mathrm{Si}$-on-$\mathrm{Si}$ interfaces, covered with native oxide, in two vapor environments: humid air and isopropyl alcohol (IPA) vapor. To quantify the adhesion contribution to friction, we present a boundary element method that successfully models the interplay between capillary adhesion, surface topography, and friction without adjustable parameters and show that the evolution of the surface topography during sliding dramatically increases capillary adhesion and thus friction. Replacing the water vapor with an organic (IPA) vapor, we find a lower adhesion due to the smaller surface tension.

Static and dynamic magnetic properties of $\mathrm{Co}$-$\mathrm{Fe}$(10 nm)/$\mathrm{Ru}$$(t_{\mathrm{Ru}}=0-3\mathrm{nm})$/$\mathrm{Co}$-$\mathrm{Fe}$(5 nm) asymmetric trilayers are systematically investigated. The interlayer exchange coupling (IEC) strengths of bilinear $(J_1)$, biquadratic $(J_2)$, and their equivalent $(J_{\mathrm{eff}})$ terms are determined; they show a weak nonmonotonic behavior with $t_{\mathrm{Ru}}$. Interestingly, the magnetic remanence ratio η of hard axis to easy axis has two distinct peaks; this can reasonably be interpreted by taking the strong $J_2$ term into account. Various pump-laser fluences are utilized to modulate the static IEC during the time-resolved magneto-optical Kerr effect measurements, by which individual magnetization precessions of the two $\mathrm{Co}$-$\mathrm{Fe}$ layers are achieved and the effects of dynamic IEC through mutual spin currents are highlighted. With the increase in $t_{\mathrm{Ru}}$, the magnetic damping factors of both layers display the same nonmonotonic behavior, which has been mainly ascribed to the spin pumping damping ${\alpha }_{\mathrm{SP}}$ associated with the dynamic IEC. Moreover, it is found that the variation trend of damping difference $\mathrm{\Delta }{\alpha }_{\mathrm{SP}}$ between the two $\mathrm{Co}$-$\mathrm{Fe}$ layers is similar to that of $J_{\mathrm{eff}}$, revealing that the dynamic IEC effect is actually dominated by the static IEC and thereupon a theoretical formula is proposed to describe the correlation between $\mathrm{\Delta }{\alpha }_{\mathrm{SP}}$ and $J_{\mathrm{eff}}$. These results suggest the feasibility of efficient control of spin pumping damping through controlled IEC, which has great significance for microwave spintronic devices based on asymmetric trilayer structures.

Magnetic-field-resilient superconducting circuits enable sensing applications and hybrid quantum computing architectures involving spin or topological qubits and electromechanical elements, as well as studying flux noise and quasiparticle loss. We investigate the effect of in-plane magnetic fields up to 1 T on the spectrum and coherence times of thin-film three-dimensional aluminum transmons. Using a copper cavity, unaffected by strong magnetic fields, we can probe solely the effect of magnetic fields on the transmons. We present data on a single-junction and a superconducting-quantum-interference-device (SQUID) transmon that are cooled down in the same cavity. As expected, the transmon frequencies decrease with increasing field, due to suppression of the superconducting gap and a geometric Fraunhofer-like contribution. Nevertheless, the thin-film transmons show strong magnetic field resilience: both transmons display microsecond coherence up to at least 0.65 T, and $T_1$ remains above $1\mu \text{s}$ over the entire measurable range. SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude that thin-film aluminum Josephson junctions are suitable hardware for superconducting circuits in the high-magnetic-field regime.

The magneto-optical trap (MOT) is an essential tool for collecting and preparing cold atoms with a wide range of applications. We demonstrate a planar-integrated MOT by combining an optical grating chip with a magnetic coil chip. The flat grating chip simplifies the conventional six-beam configuration down to a single laser beam, and the flat coil chip replaces the conventional anti-Helmholtz coils of cylindrical geometry. Up to ${10}^6$ cold ${}^{87}\mathrm{Rb}$ atoms are trapped by the planar-integrated MOT, with the atom cloud being approximately $6\mathrm{mm}$ above the chip surface. This configuration effectively reduces the volume, weight, and complexity of the MOT, bringing benefits to applications including gravimeter, clock, and quantum memory devices.