Brownian thermal noise associated with highly reflective coatings is a fundamental limit for several precision experiments, including gravitational-wave detectors. Research is currently ongoing to find coatings with low thermal noise that also fulfill strict optical requirements such as low absorption and scatter. We report on the optical and mechanical properties of ion-beam-sputtered magnesium fluoride thin films and we discuss the application of such coatings in current and future gravitational-wave detectors.

Superconducting boron-doped silicon is a promising material for integrated silicon quantum devices. In particular, its low electronic density and moderate disorder make it a suitable candidate for the fabrication of large inductances with low losses at microwave frequencies. We study experimentally the electrodynamics of superconducting silicon thin layers using coplanar waveguide resonators, focusing on the kinetic inductance, the internal losses, and the variation of these quantities with the resonator readout power. We report the observation in a doped semiconductor of microwave resonances with internal quality factors of a few thousand. As expected in the BCS framework, superconducting silicon presents a large sheet kinetic inductance in the 50–500-pH range, comparable to that of strongly disordered superconductors. The temperature dependence of the kinetic inductance is well described by the Mattis-Bardeen theory. However, we find an unexpectedly strong nonlinearity in the complex surface impedance that cannot be satisfactorily explained either by depairing or by quasiparticle heating.

Adiabatic quantum-control schemes are widely used in the areas of quantum-information processing and quantum sensing. The very requirement of adiabaticity in these schemes often leads to problems of low efficiency and being sensitive to decoherence. To address such issues, various methods have been developed for accelerating adiabatic processes, but they often need to be designed on an $adhoc$ basis. Here we propose and experimentally demonstrate an inverse-engineering approach, where a parameterized state of the Schrödinger equation is employed for constructing desired evolutions. Within a single and simple frame, the user-defined passages can be flexibly customized for different objectives and systems. To experimentally benchmark its performance, we implement this approach in a task of coherent state transfer in a superconducting Xmon device. We find that our method completed the transfer with the fastest speed and highest efficiency (>99.5%) among all recent experiments performed in similar configurations.

Intercalation-type batteries based on the alkali metal $\mathrm{K}$, an earth-abundant element, are attracting increasing attention as alternatives to $\mathrm{Li}$-ion batteries. However, the lack of a high-performance anode limits the success of $\mathrm{K}$-ion batteries. Here, we study the performance of monolayer ${\mathrm{C}}_5\mathrm{N}$ as a potential building block for the anode. Our theoretical data show that the metallic monolayer can accommodate 2.25 K atoms per formula unit, which corresponds to a specific capacity of 814 mA h ${\mathrm{g}}^{-1}$, and provides a low diffusion barrier of only 0.11 eV. The volume change of bulk ${\mathrm{C}}_5\mathrm{N}$ (47%) is found to be smaller than that of graphite (61%; commercial anode material). These predictions will serve the design of future anode materials for $\mathrm{K}$-ion batteries.

We envision the use of an indium tin oxide (ITO) thin film as part of a bilayered silicon-photonics subwavelength device to boost nonlinearity-assisted all-passive and ultrafast nonreciprocal behavior. Asymmetric $p$-polarized oblique excitation of a mode near the epsilon-near-zero frequency, with a highly confined and enhanced normal electric field component and large absorption, allows one to harness the strong subpicosecond nonlinear response of ITO for the generation of notable nonreciprocal performance in an ultracompact two-port element. Although the results are limited by loss, we find the optimal operational point and the maximum attainable nonreciprocal transmittance ratio of the metasurface versus light intensity—including an apparent upper bound slightly over 2—and we perform exhaustive numerical simulations considering nonlinear processes of both anharmonic and thermal nature that validate our predictions, including steady-state and pulsed-laser excitation.

Ghost imaging in terahertz range has proved that amplitude and phase holographic imaging could be realized by detecting time-resolved electromagnetic waves, which shows application potential in several areas, such as nondestructive evaluation, biological sample imaging, etc. Compared with terahertz electromagnetic waves, ultrasound is easier to emit, modulate, and detect, and its shorter wavelength can produce higher phase and spatial-imaging resolutions. Here, we investigate ultrasonic holographic ghost imaging (UHGI). A linear-array ultrasonic transducer is used to emit ultrasonic waves, which travel through the sample closely attached to the transducer, then propagate for a certain distance in water, and finally are received by a hydrophone. By encoding the ultrasonic waves emitted by the linear-array transducer and correlating the ultrasonic waves received by the hydrophone and prearranged sampling patterns, holographic imaging of transmittance and phase shift can be realized. Combined with near-field imaging, the spatial resolution (determined by the element size of the transducer) can reach 0.3 mm. The UHGI experiment is easy to carry out and can add more capabilities to ultrasonic medical imaging, nondestructive evaluations, and the imaging of acoustic metasurfaces.

The purpose of this study is to develop a method for directly measuring the sheet resistance of a junction partner for a chalcogenide light absorber in a thin-film solar cell. The developed method is applied to $\mathrm{Cd}\mathrm{S}$ in a $\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{Se}}_2$ (CIGS) thin-film solar cell as a proof of concept. The suggested method utilizes a combination of the lateral photocurrent flowing along $\mathrm{Cd}\mathrm{S}$ in a custom-designed cell and the current density–voltage curve of a lab-scale CIGS solar cell. By combining an equivalent circuit analysis and a derived approximate equation, a semiempirical formula is proposed for directly measuring the sheet resistance of $\mathrm{Cd}\mathrm{S}$ in the CIGS thin-film solar cell. The semiempirical formula is a function of the basic characteristics (fill factor, short-circuit current density, open-circuit voltage) of the CIGS solar cell, and the linear lateral photocurrent density measured in the custom-designed cell. The proposed semiempirical formula is validated by measuring the sheet resistance of a $\mathrm{Zn}\mathrm{O}:\mathrm{Al}$ thin film in a custom-modified cell. The sheet resistance value agrees well with the sheet resistance value measured by a four-point probe. This method can be easily extended to ${\mathrm{Cu}}_2{\mathrm{Zn}\mathrm{Sn}\mathrm{S}}_4$, $\mathrm{Sn}\mathrm{S}$, and ${\mathrm{Sb}}_2{\mathrm{Se}}_3$ thin-film solar cells, which have very similar device structures to a CIGS thin-film solar cell.

Acoustic and elastic metamaterials with time- and space-dependent material properties have received great attention recently as a means to break reciprocity for propagating mechanical waves, achieving greater directional control. One nonreciprocal device that has been demonstrated in the fields of acoustics and electromagnetism is the circulator, which achieves unirotational transmission through a network of ports. This work investigates an elastic wave circulator composed of a thin elastic ring with three semi-infinite elastic waveguides attached, creating a three-port network. Nonreciprocity is achieved for both longitudinal and transverse waves by modulating the elastic modulus of the ring in a rotating fashion. Two numerical models are derived and implemented to compute the elastic wave field in the circulator. The first is an approximate model based on coupled-mode theory, which makes use of the known mode shapes of the unmodulated system. The second model is a finite-element approach that includes a Fourier expansion in the harmonics of the modulation frequency and radiation boundary conditions at the ports. The coupled-mode model shows excellent agreement with the finite-element model and the conditions on the modulation parameters that enable a high degree of nonreciprocity are presented. This work demonstrates that it is possible to create an elastic wave circulator that enables nonreciprocal mode-splitting of an incident longitudinal wave into outgoing longitudinal and transverse waves.

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.