The nitrogen-vacancy ($\mathrm{N}$-$V$) defect in diamond is a versatile quantum sensor, being able to measure physical quantities such as magnetic field, electric field, temperature, and pressure. In the present work, we demonstrate multiplexed sensing of magnetic field and temperature using a N-V ensemble in diamond. The dual-frequency-driving technique we employ is based on frequency-division multiplexing, which enables the sensing of both measurables in real time. The pair of $\mathrm{N}$-$V$ resonance frequencies for dual-frequency driving must be selected to avoid coherent population trapping of $\mathrm{N}$-$V$ spin states. With enhanced optical collection efficiency higher than 50% and a type 1b diamond crystal with a natural abundance of ${}^{13}\mathrm{C}$ spins, we achieve sensitivities of about $70\mathrm{pT}/\sqrt{\mathrm{Hz}}$ and $25\mu \mathrm{K}/\sqrt{\mathrm{Hz}}$ simultaneously. We demonstrate a high isolation factor of 34 dB in the $\mathrm{N}$-$V$ thermometry signal against the magnetic field; and we provide a theoretical description for the isolation factor. This work paves the way for extending the application of $\mathrm{N}$-$V$ diamond sensors into more demanding conditions.

The Ising machine is an unconventional computing architecture that can be used to solve NP-hard combinatorial optimization problems more efficiently than traditional von Neumann architectures. Fast, compact oscillator networks that provide programmable connectivities among arbitrary pairs of nodes are highly desirable for the development of practical oscillator-based Ising machines. Here we propose using an electrically coupled array of gigahertz spin Hall nano-oscillators to realize such a network. By developing a general analytical framework that describes injection locking of spin Hall oscillators with large precession angles, we explicitly show the mapping between the coupled oscillators’ properties and the Ising model. We integrate our analytical model into a versatile Verilog-A device that can emulate the coupled dynamics of spin Hall oscillators in circuit simulators. With this abstract model, we analyze the performance of the spin Hall oscillator network at the circuit level using conventional electronic components and considering phase noise and scalability. Our results provide design insights and analysis tools toward the realization of a CMOS-integrated spin Hall oscillator Ising machine operating with a high degree of time, space, and energy efficiency.

We report microwave spectroscopy of co-trapped ${}^9$$\mathrm{Be}$${}^{+}$ and ${}^{40}$$\mathrm{Ca}$${}^{+}$ ions within a compact permanent-magnet-based Penning ion trap. The trap is constructed with a reconfigurable array of $\mathrm{Nd}$-$\mathrm{Fe}$-$\mathrm{B}$ rings providing a 0.654-T magnetic field that is near the 0.6774-T magnetic-field-insensitive hyperfine transition in ${}^9$$\mathrm{Be}$${}^{+}$. Performing Ramsey spectroscopy on this hyperfine transition, we demonstrate nuclear spin coherence with a contrast decay time of >1 s. The ${}^9$$\mathrm{Be}$${}^{+}$ is sympathetically cooled by a Coulomb crystal of ${}^{40}$$\mathrm{Ca}$${}^{+}$, which minimizes ${}^9$$\mathrm{Be}$${}^{+}$ illumination and thus mitigates reactive loss. Introducing a unique high-magnetic-field optical-detection scheme for ${}^{40}$$\mathrm{Ca}$${}^{+}$, we perform spin-state readout without a 729-nm shelving laser. We record a fractional trap magnetic field instability below 20 ppb (<13 nT) at 43 s of averaging time with no magnetic shielding and only passive thermal isolation. We discuss potential applications of this compact reconfigurable Penning trap.

Ising machines (IMs) are physical systems designed to find solutions to combinatorial optimization (CO) problems mapped onto the IM via the coupling strengths between its binary spins. Using its intrinsic dynamics and different annealing schemes, the IM relaxes over time to its lowest-energy state, which is the solution to the CO problem. IMs have been implemented on different platforms, and interacting nonlinear oscillators are particularly promising candidates. Here we demonstrate a pathway towards an oscillator-based IM using arrays of nanoconstriction spin Hall nano-oscillators (SHNOs). We show how SHNOs can be readily phase binarized and how their resulting microwave power corresponds to well-defined global phase states. To distinguish between degenerate states, we use phase-resolved Brillouin-light-scattering microscopy and directly observe the individual phase of each nanoconstriction. Micromagnetic simulations corroborate our experiments and confirm that our proposed IM platform can solve CO problems, showcased by how the phase states of a $2\times 2$ SHNO array are solutions to a modified max-cut problem. Compared with the commercially available D-Wave ${\mathrm{Advantage}}^{\mathrm{TM}}$, our architecture holds significant promise for faster sampling, substantially reduced power consumption, and a dramatically smaller footprint.

By measuring the elastic slow dynamics behavior of various consolidated granular materials and metallic alloys, we show that the evolution of the wave velocity as a function of time can be reproduced by using a continuous relaxation-time spectrum, whose main features can be extracted from the experiments. Here we propose to adopt a Weibull distribution of the relaxation times, that we find to display a maximum, which is related to the material grain size and independent of the conditioning amplitude. These results show that the role of the grain-size distribution is fundamental to quantify slow dynamics effects, as well as to clarify its mesoscopic physical origin. Moreover, they can pave the way for the implementation of advanced characterization methods or nondestructive testing techniques capable of retrieving information on the different spatial scales or defects in the materials under investigation.

Based on full quantum-transport simulations, we report a comprehensive study of the evaporative cooling process in a double-barrier semiconductor heterostructure thermionic refrigerator. Our model, which self-consistently solves the nonequilibrium Green’s function framework and the heat equation, is capable of calculating the electron temperature and electrochemical potential inside the device. By investigating the dependence of those thermodynamic parameters as a function of the barrier thickness and height, we answer open questions on evaporative cooling in solid-state systems, and give a clear recipe to reach high electron refrigeration. In particular, simulation results demonstrate that the best cooling is obtained when (i) the device operates at the maximum resonant condition; (ii) the quantum well state is symmetrically coupled with the contacts. The present results then shed light on physical properties of evaporative cooling in semiconductor heterostructures and will allow the development of thermionic cooling devices towards unprecedented performances to be sped up.

We measure the terahertz conductivity of doped ceria by terahertz time-domain spectroscopy at different temperatures to characterize the shape of the potential associated with microscopic ion hopping. The experimental results for $\mathrm{Gd}$- and $\mathrm{La}$-doped ceria show that the activation energy in doped ceria is larger than that in stabilized zirconia. This result can be explained by a simple rigid-body model with the assumption of doping-induced lattice expansion, i.e., by considering the gap between cations. Our results for conventional fluorite-type solid-oxide electrolytes show that terahertz spectroscopy can be used to investigate fast microscopic ionic conduction in various electrolytes, which cannot be accessed through conventional impedance measurements.

In this study, we theoretically explore the probability distribution of the write-error rate (WER) of a voltage-controlled magnetoresistive random-access memory (VC MRAM). A probability density function (PDF) of the WER is analytically obtained using the change-of-variable technique with the assumption that the anisotropy constant of the VC MRAM follows the normal distribution. Furthermore, we assume that the WER of a single memory cell forms a parabola as a function of the anisotropy constant, resulting from numerical simulations by solving the Landau-Lifshitz-Gilbert equation based on the macrospin model. Theoretical analysis facilitates in identifying types of the PDF: a monotonic decreasing function with a peak at the smallest WER, and a function with local maximum.

Colloid separation from dilute solutions is of significant relevance in a multitude of technological applications. Here we use numerical simulations to investigate a recently proposed particle separation technique based on diffusiophoresis. Diffusiophoresis refers to the chemotactic migration of particles induced by local chemical gradients that allows for efficient particle manipulation. It can act in a cooperating or competing manner with respect to fluid advection, and is usually accompanied by diffusioosmosis that refers to the bulk flow adjacent to a solid surface. We consider a microfluidic setup with cocurrent flow in two horizontal channels connected by vertical diverging nanochannels, where the top flow contains suspended colloidal particles and solute at a low concentration and the bottom flow contains solute at a higher concentration. We analyze the fluid, solute, and particle dynamics to show that the particle motion is driven into the diverging nanochannels under the combined influence of fluid advection and diffusiophoresis, the latter arising due to the imposed solute gradient. Selective separation and characterization of the particles based on their size and surface charge can be achieved, whose efficiency can be improved by controlling the diffusiophoretic mobility of the particle, solute Péclet number, and imposed solute gradient. Diffusioosmosis can enhance or inhibit the diffusiophoretic separation, depending on the surface charge of the solid surfaces.

Except for a few cases to which sophisticated techniques are applicable, it is difficult to observe experimentally local electric fields or near fields associated with excitation of electromagnetic modes supported by building blocks of nanostructures. Although elucidating the behavior of the local electric fields or near fields is very useful to develop potential applications of the nanostructures, in many cases, their behaviors have been only speculated from simulations based on the electromagnetic theory. Here, we develop a simple technique that allows us to study experimentally the average behavior of the local electric fields inside two planar waveguide layers interacting with each other in all-dielectric multilayer structures. The study is made possible by doping the two waveguide layers with two different fluorophores. Fluorescence intensities detected at two different wavelengths allow us to study separately the behaviors of the local electric fields inside each waveguide layer. Angle-scan fluorescence excitation spectra are measured for two different series of multilayer samples by exciting the samples in an attenuated total reflection geometry. The line shapes observed are in good agreement with theoretical ones calculated based on the electromagnetic theory, confirming that the experimental fluorescence excitation spectra reflect well the average behaviors of the local electric fields. Applying the developed technique, we investigate systematically the changes in the local electric fields inside the waveguide layers caused by the change in the strength of coupling between the two waveguide modes. In one series of the samples, a gradual transition in the behavior of the local electric fields, from a Fano-resonant behavior to a double-peak behavior, is demonstrated with increasing the coupling strength. In another series of the samples, the coupling strength is widely changed and the formation of the coupled modes in a strong coupling regime is clearly observed. The observed changes in the local electric fields can be reproduced very well by simple analytical calculations based on a coupled oscillator model. The model is helpful to gain physical insights into the coupling of the waveguide modes, which cannot be obtained by the electromagnetic calculations.

In this work, we study the Schottky-barrier height (SBH) at the junction between $\beta$-${\mathrm{Ga}}_2{\mathrm{O}}_3$ and platinum, a system of great importance for the next generation of high-power and high-temperature electronic devices. Specifically, we obtain interfacial atomic structures at different orientations using our structure-matching algorithm and compute their SBH using electronic structure calculations based on hybrid density-functional theory. The orientation and strain of platinum are found to have little impact on the barrier height. In contrast, we find that decomposed water molecules ($\mathrm{H}$.$\mathrm{OH}$), which could be present at the interface from ${\mathrm{Ga}}_2{\mathrm{O}}_3$ substrate preparation, has a strong influence on the SBH, in particular in the ($\overline{2}01$) orientation. The SBH can range from approximately $2$ eV for a pristine interface to nearly zero for a full $\mathrm{H}$.$\mathrm{OH}$ coverage. This result suggests that a SBH of approximately $2$ eV can be achieved for the ${\mathrm{Ga}}_2{\mathrm{O}}_3(\overline{2}01)/\mathrm{Pt}$ junction using the substrate-preparation methods that can reduce the amount of adsorbed water at the interface.

In this work, we demonstrate nonreciprocal acoustic wave transmission in two-cascaded Fabry-Perot-like slab resonators undergoing time modulation of their effective density. A phase difference is introduced into the time modulation between the two coupled resonators to produce spatial bias to access unidirectional wave propagation. A theoretical model based on plane-wave expansion and the transfer-matrix method is developed to study the Fabry-Perot-based system. The theoretical model allows rapid and precise characterization of the acoustic dispersion, with results in excellent agreement with finite-element-based numerical simulations. We demonstrate acoustic nonreciprocity behavior for the fundamental acoustic mode and further show that, with proper optimization, the coupled Fabry-Perot-based device can achieve nonreciprocal acoustic frequency conversion. This work could inspire the design of simple and compact nonreciprocal acoustic devices for efficient wave control.

Crystal-damage events such as tracks and point defects have been used to record and detect radiation for a long time and recently they have been proposed as a means for dark-matter detection. Color centers can be read out optically and we propose a scheme based on selective plane illumination microscopy for micrometer-scale imaging of large volumes corresponding to kilogram mass detectors. This class of detectors would be passive and would operate at room temperature and we call this the passive low-energy optical color-center nuclear-recoil (PALEOCCENE) detection method. We apply these concepts to the detection of reactor neutrinos using coherent elastic neutrino nucleus scattering (CE$\nu$NS). Crystal-damage formation energies are intrinsically on the order of 25 eV, resulting in similarly low nuclear-recoil thresholds. This would enable the observation of reactor-neutrino CE$\nu$NS with detectors as small as 10 g. Additionally, a competitive search for spin-dependent dark-matter scattering down to a dark-matter mass of $0.3$ GeV could be possible. Passive crystal detectors might also be attractive for nuclear-nonproliferation safeguards if used to monitor reactor power and to put limits on plutonium production. The passive nature and small footprint of the proposed detectors implies that these might fit well within accepted reactor-safeguards operations.