Metasurfaces, the two-dimensional analog of metamaterials, have exhibited unprecedented optical and thermal properties, including super-Planckian thermal radiation. Asymmetrically patterning two-dimensional materials has been proposed recently to excite additional surface hyperbolic modes, which can enhance radiative energy transport. In the present study, we further look into the effect of symmetric patterns. The graphene metasurfaces are selected as an example to present the improving role of symmetric patterning in radiative heat flux. Fluctuational electrodynamics that incorporates scattering matrix theory with rigorous coupled-wave analysis is employed to exactly calculate the near-field heat flux. It is shown that the radiative heat flux between graphene metasurfaces with square patterns performs a maximum 35-fold enhancement compared with the sheet counterpart, far exceeding the performance based on asymmetric patterning. The enhanced heat flux is dominated by a different mechanism through excitation and redshift of graphene-surface plasmon polaritons with high in-plane wavevector. The effects of substrate, vacuum-gap distance, and surface-geometry parameters between the two metasurfaces with symmetric pattern are also investigated. This work opens an alternative route to enhance and modulate the metasurface-based radiative heat transfer for efficient thermal-energy management at micro- and nanoscales.

We study magnon transmission in the sandwich structure of ferromagnetic insulators (FMIs), antiferromagnetic insulators (AFMI), and ferromagnetic insulators (FMI) by atomistic spin-model simulations. Magnon junction effects (MJEs), which have been reported in magnon junction (MJ) experiments, can be reproduced in this work, demonstrating the importance of spin-dependent magnon blocking effects (MBEs) in a MJ structure. Moreover, AFMI spacers with various structures are investigated. We show that the MJE is sensitive to the characteristics of the AFMI spacer such as orientation of Néel vector, types of AFMI spin configuration, and intrinsic exchange interaction. It is found that these phenomena are rooted in the magnon selection rules between two FMIs of different magnonic polarization. Based on the mechanism studied above, we further propose an in-plane MJE and give a feasible experimental prediction using nonlocal magnon-mediated current-drag measurement. Our work provides insight into magnon transmission in MJ and serves as a promising tool for future magnon circuits.

Axions are a popular dark-matter candidate that are often searched for in experiments known as “haloscopes,” which exploit a putative axion-photon coupling. These experiments typically rely on transverse-magnetic (TM) modes in resonant cavities to capture and detect photons generated via axion conversion. We present a study of a resonant-cavity design for application in haloscope searches, of particular use in the push to higher-mass axion searches (above approximately $60\mu \mathrm{eV}$). In particular, we take advantage of azimuthally varying ${\mathrm{TM}}_{m10}$ modes that, while typically insensitive to axions due to field nonuniformity, can be made axion sensitive (and frequency tunable) through the strategic placement of dielectric wedges, becoming a type of resonator known as a dielectric-boosted axion-sensitivity (DBAS) resonator. Results from finite-element modeling are presented and compared with a simple proof-of-concept experiment. The results show a significant increase in axion sensitivity for these DBAS resonators over their empty-cavity counterparts and high potential for application in high-mass axion searches when benchmarked against simpler more traditional designs that rely on fundamental TM modes.

On-chip integration fundamentally changes the way in which information is processed. The exploding communication capacity requires a high degree of integration of optical devices in a limited footprint. These requirements have pushed the minimization of optical chips almost to their physical limits. One potential way to break this limitation is to increase the number of functionalities in a module, for which the most critical issue is to expand the degree of freedom of information processing. Here, we propose a degree of freedom of information processing based on the basic mode vectors in the anti-parity-time-symmetry system. Based on our principle, adjacent whispering-gallery modes in a ring cavity are remarkably distinguished in their sensitivity to the signal intensity. What is more, the desired modes are labeled by individual resonance frequencies. This principle is demonstrated experimentally based on the wavelength-selective nonlinear excitation in microring resonators with the nonlinear material ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. In addition, the combination of this proposed degree of freedom and the signal-direction-dependent function is experimentally demonstrated. This research provides a degree of freedom for designing multifunction devices, which will fundamentally expand the capacity of on-chip information processing.

Nitrogen-vacancy (N-V) centers in diamond work as a quantum electrometer. Using an ensemble state of N-V centers, we propose vector electrometry and demonstrate measurements in a diamond electronic device. A transverse electric field applied to the N-V axis under a high voltage is measured, while applying a transverse magnetic field. The response of the energy-level shift against the electric field is significantly enhanced compared with that against an axial magnetic field. Repeating the measurement of the transverse electric field for multiple N-V axes, we obtain the components of the electric field generated in the device.

Structured-light lasers are highly topical due to not only their ability to tailor customized distribution of intensity, phase, orbital angular momentum (OAM), and other optical properties, but also the compact and simple at-the-source generation scheme. Here we propose a form of structured-light laser, intracavity mode convertor laser, with the ability to generate two-dimensional (2D) tunable high-order Hermite-Gaussian (HG) modes with a large indice range (up to 15). The mode convertor constituted by two cylindrical lenses is always used for external OAM conversion, but here we show that it can be inserted into a laser cavity as an intracavity element for symmetry-breaking control, which we also demonstrate with a complete matrix optics theory. The generated 2D HG modes can also be converted into Laguerre-Gaussian (LG) vortex beams with both tunable OAM and radial momentum. Moreover, we also show the ability to directly generate vortex beam from our laser cavity. Our approach meets the urgent necessity for a practical laser device for more versatile light, providing more alternative parametric space for structure control and fostering extended applications.

Combined diffusion, migration, and advection of ions in a binary electrolyte plays a role in various applications, including water electrolysis, electrodeposition, deionization, and electrophoresis. Here we analyze a dilute binary electrolyte with arbitrary ion valencies in a porous or nonporous medium using the one-dimensional Nernst-Planck equations. We examine how advection influences the limiting current, diffusion potential, and overall potential, deriving broadly useful analytical expressions. We provide experimental results for the electro-osmotic flow through a submicroporous separator in an alkaline water electrolysis setup. The time evolution of the potential is followed from the initial timescale of double-layer charging, followed by the diffusional timescale, to the time at which a limiting current is reached. For the longer timescales, a quasisteady model is shown to predict the time evolution of the advection-modified potential drop reasonably well. Additional interesting features arising due to electro-osmotic drag and unsteady diffusion are observed and explained.

We propose and demonstrate pump-probe spectroscopy of rubidium absorption that reveals the sub-Doppler hyperfine structure of the ${}^5{\mathrm{S}}_{1/2}\leftrightarrow {}^5{\mathrm{P}}_{3/2}$ (${\mathrm{D}}_2$) transitions. The counterpropagating pump and probe lasers are independently tunable in frequency, with the probe operating at the single-photon level. The two-dimensional spectrum measured as the laser frequencies are scanned shows fluorescence, Doppler-broadened absorption dips, and sub-Doppler features. The detuning between the pump and probe lasers allows compensation of the Doppler shift for all atomic velocities in the room-temperature vapor, meaning we observe sub-Doppler features for all atoms in the beam. We detail a theoretical model of the system that incorporates fluorescence, saturation effects, and optical pumping and compare this with the measured spectrum, finding a mean absolute percentage error of 3.11%. This high level of agreement allows us to extract the number density and temperature of the $\mathrm{Rb}$ vapor from the two-dimensional spectrum. In the future this technique could be used as an atomic frequency standard for calibrating and characterising a single-photon or low-light-level source.

Ferroelectric memristors are intensively studied due to their potential implementation in data storage and processing devices. In this work we show that the memristive behavior of metal–ferroelectric-oxide–metal devices relies on the competition of two effects: the modulation of metal-ferroelectric interface barriers by the switchable ferroelectric polarization and the electromigration of oxygen vacancies, with the depolarizing field playing a fundamental role in the latter. We simulate our experimental results with a phenomenological model that includes both effects and we reproduce several nontrivial features of the electrical response, including resistance relaxations observed after external poling. Besides providing insight into the underlying physics of these complex devices, our work suggests that it is possible to combine nonvolatile and volatile resistive changes in single ferroelectric memristors, an issue that could be useful for the development of neuromorphic devices.

Holonomic quantum computing has attracted much attention in achieving robust and high-fidelity quantum gates owing to its built-in noise-resilience features. Here in this work, we propose an experimentally feasible scheme to realize scalable nonadiabatic non-Abelian holonomic gates in Rabi lattices, where each building block favors ultrastrong coupling and accordingly is portrayed by a quantum Rabi model (QRM). The polariton states with the lowest two energies in the QRM effectively simulate a spin-half system and thus constitute a logical qubit. In contrast to the existing schemes of using ancillary levels, our holonomic operations are performed with the aid of neighboring QRMs acting as ancillary qubits. Employing the two-tone driving scheme onto the physical system, various noncommutable single-qubit and nontrivial two-qubit holonomic gates are applicable on the computational basis, in which all-resonant control is employed and this guarantees fast speed and consequently high fidelities. In addition, our scheme exhibits a unique advantage of being immune to dephasing noises as a result of intrinsic characteristics of the ultrastrong coupling and the QRM. Therefore, this scheme prompts the integration of ultrastrong coupling and geometric properties to mitigate the negative effect of errors and decoherence. Ultimately, holonomic quantum gates incorporated in QRMs with all-resonant control may enable reaching the accuracy threshold for scalable fault-tolerant quantum-information processing within and beyond the ultrastrong couping regime.

We experimentally study timing jitter of single-photon detection by NbN superconducting strips with width $w$ ranging from 190 nm to $3\mu \mathrm{m}$. We find that timing jitter of both narrow (190 nm) and micron-wide strips is about 40 ps at currents where internal detection efficiency $\eta$ saturates and it is close to our instrumental jitter. We also calculate intrinsic timing jitter in wide strips using the modified time-dependent Ginzburg-Landau equation coupled with a two-temperature model. We find that with increasing width the intrinsic timing jitter increases and the effect is most considerable at currents where a rapid growth of $\eta$ changes to saturation. We relate it with complicated vortex and antivortex dynamics, which depends on a photon’s absorption site across the strip and its width. The model also predicts that at current close to depairing current the intrinsic timing jitter of a wide strip could be about $\hslash /k_B{T}_c$ ($T_c$ is a critical temperature of superconductor), i.e., the same as for a narrow strip.

We present fast tunable superconducting microwave resonators fabricated from planar $\mathrm{Nb}\mathrm{N}$ on a sapphire substrate. The $3\lambda /4$ wavelength resonators are tuning fork shaped and tuned by passing a dc current that controls the kinetic inductance of the tuning fork prongs. The $\lambda /4$ section from the open end operates as an integrated impedance converter that creates a nearly perfect short for microwave currents at the dc terminal coupling points, thus preventing microwave energy leakage through the dc lines. We measure an internal quality factor $Q_{\mathrm{int}}>{10}^5$ over the entire tuning range. We demonstrate a tuning range of greater than $3\mathrm{\%}$ and tuning response times as short as 20 ns for the maximum achievable detuning. Because of the quasifractal design, the resonators are resilient to magnetic fields of up to 0.5 T.

We present a realistic phenomenological description of liquid transport through defective, layered membranes. We derive general expressions based on conventional models of laminar flow and extend the formalism to accommodate slip flow. We consider different types of defects including in-layer vacancies that provide an activation-free tortuous path through the membrane. Of the many factors that affect flow, the most important is the radius of in-layer vacancy defects, which enters in the fourth power in expressions for the flux density. We apply our formalism to water transport through defective multilayer graphene oxide membranes and find that the flow remains in the laminar regime. Our results show that observed high water permeability in this system can be explained quantitatively by a sufficient density of in-layer pores that shorten the effective diffusion path.

We investigate the effect of hypersonic ($>1$-GHz) acoustic phonon wave packets on electron transport in a semiconductor superlattice. Our quantum-mechanical simulations demonstrate that a gigahertz train of picosecond deformation-strain pulses propagating through a superlattice can generate current oscillations the frequency of which is many times higher than that of the strain pulse train, potentially reaching the terahertz regime. The shape and polarity of the calculated current pulses agree well with experimentally measured electric signals. The calculations also explain and accurately reproduce the measured variation of the induced-current-pulse magnitude with the strain-pulse amplitude and applied bias voltage. Our results open a route to developing acoustically driven semiconductor superlattices as sources of millimeter and submillimeter electromagnetic waves.

We investigate the mechanism of analoglike switching of ${\mathrm{Pt}}_{38}{\mathrm{Mn}}_{62}$/[$\mathrm{Co}$/$\mathrm{Ni}$] multilayers induced by spin-orbit torques. X-ray photoemission microscopy performed during magnetization reversal driven by current pulses shows that sequential switching of reproducible domain patterns can be achieved. Switching proceeds by domain-wall displacement starting from the edges of blocked ferromagnetic domains, which do not switch for either direction of the current and represent up to 24% of the total ferromagnetic area. The antiferromagnetic ${\mathrm{Pt}}_{38}{\mathrm{Mn}}_{62}$ layer has a granular texture, with the majority of the domains being smaller than 100 nm, whereas the ferromagnetic domains in $\mathrm{Co}$/$\mathrm{Ni}$ are typically larger than 200 nm. The blocked domains and the granular distribution of exchange bias constrain the origin as well as the displacement of the domain walls, thus leading to highly reproducible switching patterns as a function of the applied current pulses. These measurements clarify the origin of the memristive behavior in antiferromagnet-ferromagnet structures and provide clues for further optimization of spin-orbit torque switching and memristivity in these systems.