The coherence of state-of-the-art superconducting qubit devices is predominantly limited by two-level-system defects, which are found primarily at amorphous interface layers. Reducing microwave loss from these interfaces by proper surface treatments is key to pushing the device performance forward. Here, we study niobium resonators after removing the native oxides with a hydrofluoric acid etch. We investigate the reappearance of microwave losses introduced by surface oxides that grow after exposure to air. We find that microwave loss in resonators are reduced by approximately an order of magnitude: internal Q factors increase from 1 × ${10}^6$ to 7 × ${10}^6$ in the single-photon regime when oxides are removed and device exposure to air is no longer than 16 min. Furthermore, we observe that ${\mathrm{Nb}}_2{\mathrm{O}}_5$ is the only surface oxide that grows significantly within the first 200 h, following the extended Cabrera-Mott growth model. In this time, microwave losses scale linearly with the ${\mathrm{Nb}}_2{\mathrm{O}}_5$ thickness, with an extracted loss tangent, $\tan {\delta }_{\mathrm{N}{\mathrm{b}}_2{\mathrm{O}}_5}$, of about $1\times {10}^{-2}$. Our findings are of particular interest for devices spanning from superconducting qubits, quantum-limited amplifiers, and microwave kinetic inductance detectors to single-photon detectors.

Superconducting resonators enable fast characterization and readout of mesoscopic quantum devices. Finding ways to perform measurements of interest on such devices using resonators only is therefore of great practical relevance. We report an experimental investigation of an $\mathrm{In}\mathrm{As}$ nanowire multiquantum dot device by probing gigahertz resonators connected to the device. First, we demonstrate accurate extraction of the dc conductance from measurements of the high-frequency admittance. Because our technique does not rely on dc calibration, it could potentially obviate the need for dc measurements in semiconductor qubit devices. Second, we demonstrate multiplexed gate sensing and the detection of charge tunneling on microsecond timescales. The gigahertz detection of dispersive resonator shifts allows rapid acquisition of charge stability diagrams, as well as resolving charge tunneling in the device with a signal-to-noise ratio of up to 15 in $1\mu \mathrm{s}$. Our measurements show that gigahertz-frequency resonators may serve as a universal tool for fast tuneup and high-fidelity readout of semiconductor qubits.

A model is developed to predict how the effective thermal boundary conductance (TBC) of a metal cap–metal contact–dielectric junction varies with the contact thickness. Two-temperature-model molecular-dynamics (MD) simulations are applied to qualitatively recreate the experimental observation that the junction TBC increases and then saturates as the contact thickness increases. The MD simulations reveal a strong correlation between the junction TBC and the fraction of the electron-phonon coupling that occurs in the contact versus that in the cap. This correlation is then combined with insights gained from an analytical solution to the two-temperature model in the cap and contact to propose a model that predicts how the TBC varies with contact thickness. The model, which contains no fitting parameters, is validated against more than 100 experimental measurements from the literature on a variety of cap-contact-dielectric junctions. By normalizing the TBC and the contact thickness, all the experimental data collapse onto a single curve, with 92% of it lying within $\pm 10$% of the model. Through physically motivated approximations, the model reduces to a simple thermal circuit that maintains high predictive ability. The population-weighted phonon density of states extracted from the MD simulations suggests that the TBC contact-thickness dependence is strongly influenced by electron-phonon coupling in the contact. The model provides guidance for streamlining the design of thermally efficient electrical contacts.

Low-noise fully depleted charge-coupled devices have been identified as a unique tool for dark-matter searches, low-energy neutrino physics, and x-ray detection. The charge-collection efficiency (CCE) for these detectors is a critical performance parameter for current and future experiments. We present a technique to characterize the CCE in back-illuminated CCDs based on soft x rays. This technique is used to study two different detector designs. The results demonstrate the importance of the backside processing for the detection of charge packages near threshold, showing that a recombination layer of a few microns significantly distorts the low-energy spectrum. The studies demonstrate that the region of partial charge collection can be reduced to a thickness of less than $1\mu \mathrm{m}$ with adequate backside processing.

The voltage-gate-assisted spin-orbit-torque (VGSOT) writing scheme combines the advantages from voltage control of magnetic anisotropy (VCMA) and spin-orbit-torque (SOT) effects, enabling multiple benefits for magnetic random-access-memory (MRAM) applications. In this work, we give a complete description of the VGSOT writing properties on perpendicular magnetic tunnel junction (PMTJ) devices, and we propose a detailed methodology for their electrical characterization. The impact of gate assistance on the SOT switching characteristics is investigated using electrical pulses down to 400 ps. The VCMA coefficient $(\xi )$ extracted from the current-switching scheme is found to be the same as that from the magnetic-field-switch method, which is in the order of 15 fJ/Vm for 80–150-nm devices. Moreover, as expected from the pure electronic VCMA effect, $\xi$ is revealed to be independent of the writing speed and gate length. We observe that SOT switching current characteristics are modified linearly with gate voltage $(V_g)$, similar to that for the magnetic properties. We interpret this linear behavior as the direct modification of perpendicular magnetic anisotropy induced by VCMA. At $V_g=1\mathrm{V}$, the SOT write current is decreased by 25%, corresponding to a 45% reduction in total energy down to 30 fJ/bit at 400 ps speed for the 80-nm devices used in this study. To test the operation reliability, we investigate the gate-SOT pulse configurations and overlays, and we find that an extended gate duration is able to preserve maximized gate benefit and selectivity. Furthermore, the device-scaling criteria are proposed, and we reveal that the VGSOT scheme is of great interest, as it can mitigate the complex material requirements of achieving high SOT and VCMA parameters for scaled MTJs. Finally, we perform design-to-technology co-optimization analysis to show that VGSOT MRAM can enable high-density arrays close to two-terminal geometries, with high-speed performance and low-power operation, showing great potential for embedded memories as well as in memory computing applications at advanced technology nodes.

Group-IV color centers in diamond have attracted significant attention as solid-state spin qubits because of their excellent optical and spin properties. Among these color centers, the tin-vacancy ($\mathrm{Sn}$-$V^{-}$) center is of particular interest because its large ground-state splitting enables long spin coherence times at temperatures above 1 K. However, color centers typically suffer from inhomogeneous broadening, which can be exacerbated by nanofabrication-induced strain, hindering the implementation of quantum nodes emitting indistinguishable photons. Although strain and Raman tuning have been investigated as promising tuning techniques to overcome the spectral mismatch between distinct group-IV color centers, other approaches need to be explored to find methods that can offer more localized control without sacrificing emission intensity. Here, we study the electrical tuning of $\mathrm{Sn}$-$V^{-}$ centers in diamond via the direct-current Stark effect. We demonstrate a tuning range beyond 1.7 GHz. We observe both quadratic and linear dependence on the applied electric field. We also confirm that the tuning effect we observe is a result of the applied electric field and is distinct from thermal tuning due to Joule heating. Stark tuning is a promising avenue toward overcoming detunings between emitters and enabling the realization of multiple identical quantum nodes.

The energetic landscape of charge-transfer (CT) states at the interface of electron donating and electron accepting domains in organic optoelectronic devices is crucial for their performance. Central questions—such as the role of static energetic disorder and vibrational effects—are under ongoing dispute. This study provides an in-depth analysis of temperature-dependent broadening of the spectroscopic absorption and emission features of CT states in devices with small molecule-fullerene blends. We confirm the validity of the electro-optical reciprocity relation between the photovoltaic external quantum efficiency and electroluminescence, enabling us to validate the device temperature during the experiment. The validated temperature allows us to fit our experimental data with several models, and compare extracted CT state energies with the corresponding open-circuit voltage limit at 0 K. Our findings reveal that the absorption and emission characteristics are usually not symmetric, and dominated by temperature-activated broadening (vibrational) effects instead of static disorder.

A skyrmionic programmable logic device (SPLD) with complete Boolean logic functions is proposed and analyzed by micromagnetic simulations. The SPLD is based on an antiferromagnet-ferromagnet bilayer structure, in which the antiferromagnetic layer supports the interfacial Dzyaloshinskii-Moriya interaction and the out-of-plane exchange-bias field for stabilizing a zero-field skyrmion. By varying the local exchange-bias field, artificial pinning sites are introduced to trap skyrmions. Depending on the input currents and initial position of skyrmions at different pinning sites, different logic functions can be realized. Micromagnetic simulations show that the proposed SPLD has a robust performance, even under thermal fluctuations and inhomogeneity effects. Our work can provide insights for the design of programmable spin-logic devices.

We use three-terminal magnetic tunnel junctions (MTJs) designed for field-free switching by spin-orbit torques (SOTs) to systematically study the impact of dual voltage pulses on the switching performance. We show that the concurrent action of an SOT pulse and an MTJ bias pulse allows for reducing the critical switching energy below the level typical of spin-transfer-torque while preserving the ability to switch the MTJ on the subnanosecond time scale. By performing dc and real-time electrical measurements, we discriminate and quantify three effects arising from the MTJ bias: the voltage-controlled change of the perpendicular magnetic anisotropy, current-induced heating, and the spin-transfer torque. The experimental results are supported by micromagnetic modeling. We observe that, depending on the pulse duration and the MTJ diameter, different effects take a lead in assisting the SOTs in the magnetization-reversal process. Finally, we present a compact model that allows for evaluating the impact of each effect due to the MTJ bias on the critical switching parameters. Our results provide input to optimize the switching of three-terminal devices as a function of time, size, and material parameters.

Accurate modeling of charge transport and both thermal and luminescent radiation is crucial to the understanding and design of radiative thermal energy converters. Charge-carrier dynamics in semiconductors are well-described by the Poisson-drift-diffusion equations, and thermal radiation in emitter-absorber structures can be computed using multilayer fluctuational electrodynamics. These two types of energy flows interact through radiation absorption or luminescence and charge-carrier generation or recombination. However, past research has typically only assumed limited interaction, with thermal radiation absorption as an input for charge-carrier models to predict device performance. To examine this assumption, we develop a fully coupled iterative model of charge and radiation transport in semiconductor devices, and we use our model to analyze near-field and far-field $\mathrm{Ga}\mathrm{Sb}$ thermophotovoltaic and thermoradiative systems. By comparing our results with past methods that do not consider cross-influences between charge and radiation transport, we find that a fully coupled approach is necessary to accurately model photon recycling and near-field enhancement of external luminescence. As these effects can substantially alter device performance, our modeling approach can aid in the design of efficient thermophotovoltaic and thermoradiative systems.

Neutron resonance transmission analysis (NRTA) is a spectroscopic technique that uses the resonant attenuation of epithermal neutrons to infer the isotopic composition of an object. NRTA is particularly well suited for applications requiring nondestructive analysis of objects containing mid- and high-$Z$ elements. To date, NRTA has required large expensive accelerator facilities to achieve precise neutron beams and has not been suitable for on-site applications. In this study, we provide an experimental demonstration showing that NRTA can be performed using a compact low-cost deuterium-tritium (DT) neutron generator to analyze neutron resonances in the 1–50-eV range. The neutron transmission spectra for five single-element targets—silver, cadmium, tungsten, indium, and depleted uranium—each show uniquely identifiable resonant attenuation dips in measurement times on the order of tens of minutes. Closely spaced resonances of approximately 1-cm-thick multielement targets can be easily differentiated with 1-eV resolution up to neutron energies of 10 eV and 5-eV resolution up to neutron energies of 30 eV. These results demonstrate the viability of compact NRTA measurements for isotopic identification and have the potential to significantly broaden the applicability of the technique across materials science, engineering, and nuclear security.

We explore a two-qubit system defined on valley isospins of two electrons confined in a gate-defined double quantum dot created within a ${\mathrm{Mo}\mathrm{S}}_2$ monolayer flake. We show how to initialize, control, interact, and read out such valley qubits by only electrical means using voltages applied to the local planar gates, which are layered on the top of the flake. By demonstrating the two-qubit exchange or readout via the Pauli blockade, we prove that valley qubits in the transition-metal-dichalcogenide semiconductor family fulfill the universality criteria and represent a scalable quantum-computing platform. Our numerical experiments are based on the tight-binding model for a ${\mathrm{Mo}\mathrm{S}}_2$ monolayer, which gives single-electron eigenstates that are then used to construct a basis of Slater determinants for the two-electron configuration space. We express screened electron-electron interactions in this basis by calculating the Coulomb matrix elements using localized Slater-type orbitals. Then we solve the time-dependent Schrödinger equation and obtain an exact time evolution of the two-electron system. During the evolution we simultaneously solve the Poison equation, finding the confinement potential controlled via voltages applied to the gates.

We present a hybrid semiconductor-based superconducting qubit device that remains coherent at magnetic fields up to 1 T. The qubit transition frequency exhibits periodic oscillations with the magnetic field, consistent with interference effects due to the magnetic flux threading the cross section of the proximitized semiconductor nanowire junction. As the induced superconductivity revives, additional coherent modes emerge at high magnetic fields, which we attribute to the interaction of the qubit and low-energy Andreev states.

An important requirement for spin-based quantum information processing is reliable and fast readout of electron spin states, allowing for feedback and error correction. However, common readout techniques often require additional gate structures, hindering device scaling, or impose stringent constraints on the tuning configuration of the sensed quantum dots. Here, we operate an in-line charge sensor within a triple quantum dot, where one of the dots is coupled to a microwave cavity and used to readout the charge states of the other two dots. Owing to the proximity of the charge sensor, we observe a near-digital sensor response with a power signal-to-noise ratio greater than $450$ at an integration time of $t_{\mathrm{int}}=1\mu \mathrm{s}$. Despite small singlet-triplet splittings of approximately 40 $\mu \mathrm{eV}$, we further utilize the sensor to measure the spin relaxation time of a singlet-triplet qubit, achieving an average single-shot spin readout fidelity greater than 99%. Our approach enables high-fidelity spin readout, combining minimal device overhead with flexible qubit operation in semiconductor quantum devices.

Naturally random devices that exploit ambient thermal noise have recently attracted attention as hardware primitives for accelerating probabilistic computing applications. One such approach is to use a low barrier nanomagnet as the free layer of a magnetic tunnel junction (MTJ), the magnetic fluctuations of which are converted to resistance fluctuations in the presence of a stable fixed layer. Here, we propose and theoretically analyze a MTJ with no fixed layers but two free layers that are circularly shaped disk magnets. We use an experimentally benchmarked model that accounts for finite-temperature magnetization dynamics, bias-dependent charge, and spin-polarized currents as well as the dipolar coupling between the free layers. We obtain analytical results for statistical averages of fluctuations that are in good agreement with the numerical model. We find that the free layers with low diameters fluctuate to randomize the resistance of the MTJ in an approximately bias-independent manner. We show how such MTJs can be used to build a binary stochastic neuron (or a $p$-bit) in hardware. Unlike earlier stochastic MTJs that need to operate at a specific bias point to produce random fluctuations, the proposed design can be random for a wide range of bias values, independent of spin-transfer-torque pinning. Moreover, in the absence of a carefully optimized stabled fixed layer, the symmetric double-free-layer stack can be manufactured using present-day magnetoresistive random-access memory (MRAM) technology by minimal changes to the fabrication process. Such devices can be used as hardware accelerators in energy-efficient computing schemes that require a large throughput of tunably random bits.

Wave-based computing has attracted extensive attention recently due to the benefits of parallel processing. In particular, several acoustic wave computing devices have been demonstrated to carry out classical algorithms and mathematical operations. Here, we extend acoustic wave computing to simulate a quantum algorithm, by proposing an integrated acoustic gradient metasurface system supporting spoof surface acoustic waves to implement the Grover quantum search algorithm. We show that this integrated metadevice can achieve a designed subdiffraction and transmission phase, which can be used to simulate operations used in a quantum algorithm, such as the Hadamard transformation and the inverse about the average. Numerical simulations demonstrate promising searching abilities of this device, including a quadratic speedup over classical algorithms and subwavelength searching accuracy. We anticipate that our results will inspire alternative design schemes for on-chip integrated metadevices for more quantum-inspired acoustic analog computations.

There is an increased interest in topologically nontrivial magnetic spin textures such as skyrmions and chiral domain-wall solitons, both from a point of fundamental physics understanding as well as potential technological interest in low-power memory applications. In order to control their behavior, it is necessary to understand their complex spin texture at the nanoscale. Lorentz transmission electron microscopy (LTEM) is a suitable technique for studying these systems due to its high spatial resolution and capability to simultaneously characterize magnetic texture and microstructure. In this work, we present the application of PyLorentz, an open-source software suite that we have developed, for quantitative image analysis of Néel-type skyrmions in thin-film heterostructures. PyLorentz enhances LTEM capabilities by enabling reconstruction of magnetic induction maps from experimental images, as well as simulating LTEM images using micromagnetic simulation data. We demonstrate this for simulated Néel skyrmions as well as experimental data from [$\mathrm{Pt}$/$\mathrm{Co}$/$\mathrm{W}$] multilayer heterostructures. We also show how simulation-assisted LTEM analysis is crucial for understanding these complex magnetic spin textures, in which the reconstructed magnetic induction map (seen in the LTEM images) differs significantly from the magnetization configuration.

Quasi-bound states in the continuum (BICs) of metasurfaces are electromagnetic resonances with a high-quality ($Q$) factor embedded in a radiative continuum. The magnetic dipole type of the quasi-BIC (quasi-MDBIC) is associated with resonant enhancement of magnetic field near the metasurface. Here we show that the quasi-MDBIC of a compact dielectric metasurface can provide resonant enhancement of wireless power transfer (WPT) to single and multiple receivers. Furthermore, the proposed physical mechanism can also be applied in the resonant coupling WPT systems. It is anticipated that our results can be generalized and applied in other physical systems.

Liquid-metal ion sources (LMIS) are widely used for ion implantation in semiconductors, focused ion-beam systems for lithographic patterning and now even small in-space thruster units for precision pointing. Above a critical field strength, a liquid metal just prior to ion emission forms a conical protrusion, which undergoes accelerated sharpening of the tip due to field self-enhancement. Despite decades of interest in this phenomenon, the influence of inertial effects on the shape and flow field prior to emission remain poorly understood. Zubarev [Formation of conic cusps at the surface of liquid metal in electric field, JETP Lett. 73, 544 (2001)] showed that when local Maxwell and capillary forces prevail at an electrified tip of a perfectly conducting liquid in inviscid flow, the asymptotic behavior of the potential fields and interface shape far from the tip can be described by a one-parameter family of self-similar series solutions describing a dynamic Taylor cone with radially convergent flow toward the tip. The Maxwell and capillary pressure undergo divergent growth in finite time, characteristic of blowup phenomena in self-focusing singularity flows. Suvorov and Zubarev [Formation of the Taylor cone on the surface of liquid metal in the presence of an electric field, J. Phys. D: Appl. Phys. 37, 289 (2004)] later found solutions that retained inertial effects and showed that the self-focusing, divergent dynamics leading to power-law growth are preserved. In this work, we focus especially on the influence of inertial effects and extend the analysis to include time-reversal symmetry. We provide an interweaved procedure for calculating the coefficients of the series expansions for the potential fields and interface shape and use these to deduce a compact relation for bounds on the minimum and maximum liquid apex height achievable. We then develop a boundary integral patching technique, which yields the complete self-similar solution, valid throughout the near- and far-field domain. The resulting two-parameter family of numerical solutions reveals a multiplicity of fluid configurations, which we coin subconical, superconical, and mixed conical, that exhibit not only tip sharpening but tip bulging, tip separation flow, interface stagnation points, and receding shapes reminiscent of recoil after capillary pinchoff. The existence of such multiple configurations may ultimately help explain experimental observations during LMIS operation involving tip pulsation, droplet emission, liquid recoil and collapse.

We investigate the inversion process of magnetic domain walls (DWs) propagating through synthetic noncollinear magnetic textures, whereby an up-down DW can be transformed into a down-up DW and vice versa. We exploit the lateral coupling between out-of-plane and in-plane magnetic regions induced by the interfacial Dzyaloshinskii-Moriya interaction in $\mathrm{Pt}/\mathrm{Co}/{\mathrm{Al}\mathrm{O}}_x$ trilayers to realize both field-driven and current-driven magnetic DW inverters. The inverters consist of narrow in-plane magnetic regions embedded in out-of-plane DW racetracks. Magnetic imaging and micromagnetic simulations provide an insight into the DW inversion mechanism, showing that DW inversion proceeds by annihilation of the incoming domain on one side of the in-plane region and nucleation of a reverse domain on the opposite side. By changing the shape of the in-plane magnetic region, we show that the DW inversion efficiency can be tuned by adjusting the ratio between the chiral coupling energy at the inverter boundary and the energy cost of nucleating a reverse domain. Finally, we realize an asymmetric DW inverter that has nonreciprocal inversion properties and demonstrate that such a device can operate as a DW diode. Our results provide input for the versatile manipulation of DWs in magnetic racetracks and the design of efficient DW devices for nonvolatile magnetic logic schemes.