We design superinductors made of strongly disordered superconductors for implementation in “hybrid” superconducting quantum circuits. The superinductors are fabricated as meandered nanowires made from granular aluminum films. Optimization of the device geometry enables the realization of superinductors with an inductance of approximately 1 $\mu \mathrm{H}$ and a self-resonance frequency of over 3 GHz. These compact superinductors are attractive for a wide range of applications, from superconducting circuits for quantum computing to microwave elements of cryogenic parametric amplifiers and kinetic inductance photon detectors.

We analyze the dynamics of passively mode-locked integrated external-cavity surface-emitting lasers (MIXSELs) using a first-principles dynamical model based on delay algebraic equations. We show that the third-order dispersion stemming from the lasing microcavity induces a train of decaying satellites on the leading edge of the pulse. Due to the nonlinear interaction with carriers, these satellites may get amplified, thereby destabilizing the mode-locked states. In the long-cavity regime, the localized structures that exist below the lasing threshold are found to be deeply affected by this instability. As it originates from a global bifurcation of the saddle-node infinite-period type, we explain why the pulses exhibit forms of behavior characteristic of excitable systems. Using the multiple-time-scale and the functional-mapping methods, we derive rigorously a master equation for MIXSELs in which third-order dispersion is an essential ingredient. We compare the bifurcation diagrams of the two models and assess their good agreement.

Magnetic skyrmions, which are a topologically nontrivial spin texture, have been considered as promising information carriers in future electronic devices because of their nanoscale size, low depinning current density, and high motion velocity. Despite the broad interest in skyrmion racetrack memory, researchers have recently been exploiting logic functions enabled by using the particlelike behavior of skyrmions. These functions can be applied to unconventional computing, such as stochastic computing (SC), which treats data as probabilities and is superior to binary computing due to its simplicity of logic operation. In this paper, we demonstrate SC implemented by the use of skyrmionic logic devices. We propose a skyrmionic and-or logic device as a multiplier in the stochastic domain and two skyrmionic multiplexer (MUX) logic devices as stochastic adders. With the assistance of voltage-controlled magnetic anisotropy (VCMA), precise control of skyrmion collisions is not required in the skyrmionic and-or logic device, thus improving the operational robustness. In the two MUX logic devices, skyrmions can be driven by the Zhang-Li torque or the spin-orbit torque (SOT). In particular, we can regulate the skyrmion motion flexibly by using VCMA or voltage-controlled Dzyaloshinskii-Moriya interaction in the SOT case. Furthermore, a 3-bit stochastic multiplier and adder are demonstrated by micromagnetic simulations. Simulations in synthetic antiferromagnets show that the performance of our skyrmionic logic gates can be optimized through the use of advanced materials. Our work opens up possibilities for implementing SC using skyrmionic logic devices.

We present a plenoptic microscopy configuration for three-dimensional (3D) snapshot imaging, which is dual telecentric and can directly record true projection images corresponding to different viewing angles. It also allows the blocking of high-angle stray rays without sacrificing the light collection efficiency. This configuration, which we call snapshot projection optical tomography (SPOT), arranges an objective lens and a microlens array (MLA) in a $4F$ telecentric configuration (where F denotes the focal length of the lens) and places an aperture stop at the back focal plane of a relay lens. We develop a forward imaging model for SPOT, which can also be applied to existing light-field microscopy techniques using a MLA as a tube lens. Using the developed system, we demonstrate snapshot 3D imaging of various fluorescent beads and a biological cell, which confirms the capability of SPOT for imaging specimens with an extended fluorophore distribution as well as isolated fluorochromes. The transverse and vertical resolutions are measured to be $0.8\mu \mathrm{m}$ and $1.6\mu \mathrm{m}$, respectively.

The fundamental thermal limit of magnetic field sensing using the resonance-enhanced magnetoelectric (ME) effect in strain-coupled ferroic composite cantilevers is investigated theoretically with results applied to $({\mathrm{Fe}}_{90}{\mathrm{Co}}_{10}{)}_{78}{\mathrm{Si}}_{12}{\mathrm{B}}_{10}/\mathrm{Si}/\mathrm{Al}\mathrm{N}$ using experimental material parameters. An analytic theory of the ME response and noise from thermal vibrations, Johnson-Nyquist noise from dielectric losses in $\mathrm{Al}\mathrm{N}$, and amplifier electronics is given to yield the magnetic field detection limit for the first bending mode. A systematic investigation of scaling behavior of ME response, sensitivity, noise components, and detection limit with cantilever size, layer thicknesses, quality factor $Q_f$, and resonance frequency $f$ is presented emphasizing the low-frequency small-size regime essential for biomagnetic sensing applications. Thermal vibrations are found to dominate all investigated noise sources for practical composite sizes except at low quality factors. Detection limit scaling inversely with functional layer thickness, as $1{/\mathrm{size}}^2$ for constant $f$ and $Q_f$, and as $Q_f^{-1/2}$ (constant size and $f$) is found. Achievable detection limits below $100\mathrm{fT}/\mathrm{H}{\mathrm{z}}^{1/2}$ are predicted for $({\mathrm{Fe}}_{90}{\mathrm{Co}}_{10}{)}_{78}{\mathrm{Si}}_{12}{\mathrm{B}}_{10}/\mathrm{Si}/\mathrm{Al}\mathrm{N}$ composite cantilevers at sizes below $10\mathrm{mm}$ (and even lower without size constraint) with $f=1\mathrm{kHz}$, $Q_f=1000$, and $({\mathrm{Fe}}_{90}{\mathrm{Co}}_{10}{)}_{78}{\mathrm{Si}}_{12}{\mathrm{B}}_{10}$ layers of $50\mu \mathrm{m}$. The scaling behavior implies the absence of an absolute detection limit for thick ferroic layers within the range of validity of the experimental material parameters observed at $\sim 2\dots 4\mu \mathrm{m}$.

Understanding the sources of energy loss in organic photovoltaic cells can ultimately lead to increasing their power-conversion efficiency. Here we explore energy losses at the interface between an archetype structure comprising a vacuum-deposited tetraphenyldibenzoperiflanthene/${\mathrm{C}}_{70}$ bulk-heterojunction active layer and several anode buffer layers (ABLs) using a combination of experimental and computational tools. The composition of the active organic region adjacent to the ABL interface is controlled independently from that in the bulk to determine energy losses that are attributed to charge transfer between the organic active region and the ABL. The open-circuit voltage ($V_{\mathrm{OC}}$) can be varied over a range of 120 meV without affecting the short-circuit current and fill factor by growing an interface layer whose composition ranges from 100% ${\mathrm{C}}_{70}$ to 0% ${\mathrm{C}}_{70}$ in tetraphenyldibenzoperiflanthene at the active-region–ABL interface. Kinetic Monte Carlo simulations are used to quantitatively evaluate the magnitude of the interfacial energy loss and change in $V_{\mathrm{OC}}$ with various interface-layer compositions. When the interface layer consists of neat ${\mathrm{C}}_{70}$ that permits nondissipative hole tunneling into the ABL, the interfacial energy loss is reduced and $V_{\mathrm{OC}}$ increases by 20–40 mV compared with conventional devices with a homogenous mixed active region.

We theoretically study plasmonic antennas featuring areas of extremely concentrated electric or magnetic field, known as hot spots. We combine two types of electric-magnetic complementarity to increase the degree of freedom for the design of the antennas: bowtie and diabolo duality and Babinet’s principle. We evaluate the figures of merit for different plasmon-enhanced optical spectroscopy methods and optical trapping: field enhancement, decay rate enhancement, quality factor of the plasmon resonances, and trapping potential depth. The role of Babinet’s principle in interchanging electric and magnetic field hot spots and its consequences for practical antenna design are discussed. In particular, diabolo antennas exhibit slightly better performance than bowties in terms of larger field enhancement and larger $Q$ factor. For specific resonance frequency, diabolo antennas are considerably smaller than bowties, which makes them favorable for the integration into more complex devices but also makes their fabrication more demanding in terms of spatial resolution. Finally, we propose a Babinet-type dimer antenna featuring electromagnetic hot spot with both the electric and magnetic field components treated on an equal footing.

Anomalous Nernst effect in epitaxially grown $L{1}_0$-ordered $\mathrm{Fe}\mathrm{Pd}{}_{1-x}\mathrm{Pt}{}_x$ alloy films is systematically investigated both experimentally and theoretically. It is found that the anomalous Nernst coefficient and anomalous Hall resistivity both increase monotonically with the increase of $\mathrm{Pt}$ composition. By subtracting the Seebeck contribution, the anomalous Nernst conductivity (${\alpha }_{xy}^A$) is obtained. By comparison with first-principles Berry-phase-theory calculations, it is interesting to find that the anomalous Nernst conductivity is dominated by the intrinsic contribution from heavy metal $\mathrm{Pt}$-$\mathrm{Pd}$ with large spin-orbit coupling strength. Moreover, the first-principles calculations also predict a large spin Nernst counductivity for both $L{1}_0$-ordered $\mathrm{Fe}\mathrm{Pd}$ and $\mathrm{Fe}\mathrm{Pt}$. Thus, the present results may shed light in searching materials with large thermally driven Hall and spin currents.

A single-photon source is an essential tool for the emerging field of quantum technologies. Ideally, it should be spectrally compatible with other photonic devices while providing a high flux of narrow-band photons. The single organic dye molecule dibenzanthanthrene under cryogenic conditions possesses the given characteristics and therefore constitutes a prominent single-photon source. Nevertheless, the implementation of such a single-photon source requires a complex experimental setup involving a cryostat with a confocal microscope for the effective collection of the molecular emission. In the approach presented here we use a single emitter coupled directly to the end facet of an optical fiber. This has the potential to transfer a single-photon source based on a quantum emitter from a proof-of-principle type of setup to a scalable “plug-and-play” device. We present successful coupling of a single organic molecule to an optical fiber and record the excitation spectrum, measure the saturation curve, and analyze the contributions of Raman background fluorescence. The single-photon nature is proven by an antibunched autocorrelation recording, which reveals coherent Rabi oscillations.

We propose Qubit4Sync, a synchronization method for quantum-key-distribution (QKD) setups, based on the same qubits exchanged during the protocol and without requiring additional hardware other than that necessary to prepare and measure the quantum states, in a similar fashion to the clock recovery used in classical communications. Our approach introduces a cross-correlation algorithm with low computational complexity for high channel losses. We test the robustness of our scheme in a real QKD implementation, and we believe it may find application in other quantum communication protocols.

The superconducting transition leads to a sharp resistance drop in a temperature interval that can be a small fraction of the critical temperature $T_c$. A superconductor exactly at $T_c$ is thus very sensitive to all kinds of thermal perturbation, including the heat dissipated by the measurement current. We show that the interaction between electrical and thermal currents leads to a sizable imaginary impedance at frequencies of the order of tens of hertz at the resistive transition of single crystals of the layered material $2H$-${\mathrm{Nb}\mathrm{Se}}_2$. We explain the result using models developed for transition-edge sensors. By measuring under magnetic fields and at high currents, we find that the imaginary impedance is strongly influenced by the heat associated with vortex motion and out-of-equilibrium quasiparticles.

Epitaxial magnetic heterostructures of $\mathrm{Mg}\mathrm{O}(001)//\mathrm{Pd}/{\mathrm{Co}}_2\mathrm{Fe}\mathrm{Al}/\mathrm{Mg}\mathrm{O}$ are grown by magnetron sputtering and the current-induced spin-orbit torques are quantified using harmonic Hall measurements. We demonstrate efficient current-induced spin-orbit-torque switching in perpendicularly magnetized samples. The advantage of such heterostructures for spin-orbit-torque magnetic random-access memory devices is that they allow a combination of critical ingredients: (i) the low resistivity required for reduced electric energy consumption during writing, (ii) the compatibility with a high tunnel magnetoresistive ratio required for efficient reading, and (iii) strong perpendicular magnetic anisotropy for increased thermal stability.

We present a method for efficient spin-wave guiding within the magnonic nanostructures. Our technique is based on the anomalous refraction in the metamaterial flat slab. The gradual change of the material parameters (saturation magnetization or magnetic anisotropy) across the slab allows tilting the wavefronts of the transmitted spin waves and controlling the refraction. Numerical studies of the spin-wave refraction are preceded by the analytical calculations of the phase shift acquired by the spin wave due to the change of material parameters in a confined area. We demonstrate that our findings can be used to guide the spin waves smoothly in curved waveguides, even through sharp bends, without reflection and scattering between different waveguide’s modes, preserving the phase, the quantity essential for wave computing.

Electromagnetic waves carrying orbital angular momentum (OAM) have attracted much interest due to their capacity to enhance communication capabilities. In this work, the OAM-mode-dispersion (OMD) phenomenon is analyzed by decomposing the vortex wave into a series of plane waves based on the spectral-domain method. Specifically, the OMD phenomenon induced by off-axis transmission is analyzed in detail, which clearly demonstrates that the vortex wave with a single OAM mode is spread to multiple OAM modes after off-axis propagation. To avoid the performance degradation of the OAM system due to OMD (e.g., interchannel crosstalk and signal-to-noise ratio reduction), a method for alleviating the OMD based on the reflective metasurface is proposed to transmit or receive the vortex waves with multiple OAM modes. Theoretical formulas for the phase distribution are developed in order to construct the metasurface. As proof-of-concept demonstrations, two metasurface prototypes are designed, fabricated, and measured to verify the proposed method in the radio-frequency range. The experimental results agree very well with the full-wave simulation results, validating the design methodology.

This paper presents an elastic metasurface that can entrap the elastic wave energy of both longitudinal and shear wave modes in a lossy region, resulting in almost no reflection environment, which we call a reflectionless metasurface. Unlike previous attempts in acoustics, elastic waves are governed by different physics, such as mode conversion, and different behavior of shear waves. Accordingly, achieving a reflectionless elastic metasurface requires a different approach to that of previous studies on acoustic metasurfaces for sound absorption. Here, physics for entrapping the elastic wave energy is proposed by combining two phenomena: the local resonance of metasurface unit cells and the surface wave conversion. As a result, the elastic wave energy originating from an incident longitudinal wave can be highly concentrated in the metasurface, and energy dissipation can be significantly increased if any damping is implemented in the metasurface region. To realize the idea, a reflectionless metasurface, consisting of rod-shaped unit cells with various lengths, is designed. Numerical and experimental investigations show that the proposed reflectionless metasurface, with a small amount of loss, can effectively reduce both the reflected longitudinal and shear waves under longitudinal wave incidence with broad angles. We expect that the proposed idea, based on a thin artificial elastic layer, will provide an alternative route to design ultrasonic absorbers.

Rydberg-assisted atomic electrometry using alkali-metal atoms contained inside a vacuum environment for detecting external electric fields at frequencies below a few kilohertz has been quite challenging due to the low-frequency electric-field-screening effect that is caused by the alkali-metal atoms adsorbed on the inner surface of the container. We report a very slow electric-field-screening phenomenon with a time scale up to the order of seconds on a rubidium-vapor cell that is made of monocrystalline sapphire. Using this sapphire rubidium-vapor cell with an optically induced, internal bias electric field, we demonstrate vapor-cell-based, low-frequency atomic electrometry that responds to the electric field strength linearly. Limited by the given experimental conditions, this demonstrated atomic electrometer uses an active volume of $11{\mathrm{mm}}^3$ and delivers a spectral noise floor of around $0.34\mathrm{mV}/\mathrm{m}\sqrt{\mathrm{Hz}}$ and a 3-dB low cutoff frequency of around 770 Hz inside the vapor cell. This work investigates a regime of vapor-cell-based atomic electrometry that was seldom studied before, which may enable more applications that use atomic electric-field-sensing technology.

To ascertain the feasibility of large-scale quantum computing, the performance and quantum resource of a practical quantum-computing situation needs to be analyzed. However, most of the analyses reported so far have focused on the statistical examination that simply calculates the performance and resource based on individual quantum-computing components. In this work, we propose an integrated analysis methodology that models a large-scale fault-tolerant quantum-computing system based on three components: algorithm, error correction, and device. Furthermore, to implement the proposed methodology, we develop a quantum-computing software platform composed of three functional layers: compile, system, and building block. By using our platform, we observe that it takes $8.78\times {10}^5\mathrm{h}$, which is much longer than previous estimations, for factoring a 512-bit integer with Shor’s factoring algorithm. We also discuss whether the proposed platform can play a significant role in finding an optimal concatenation level and/or code distance of quantum error-correcting code.