We study parametric oscillations of two capacitively coupled Kerr parametric oscillators (KPOs) with frequency-chirped two- and one-photon drives. The two-KPO system adiabatically evolves from the initial vacuum state to an oscillation state corresponding to a solution state in quantum-annealing applications. Frequency chirping dynamically changes the detuning between resonance and oscillation frequencies during parametric modulation and reduces unwanted population transfer to excited states caused by pure dephasing and photon loss. We observe that frequency chirping increases the success probability to obtain the solution state and that simulations taking into account pure dephasing reproduce experiments with and without frequency chirping. This study demonstrates the effectiveness and applicability of frequency chirping to a KPO-based quantum annealer.

Quantum states encoded in electromagnetic fields, also known as bosonic states, have been widely applied in quantum sensing, quantum communication, and quantum error correction. Accurate characterization is therefore essential yet difficult when states cannot be reconstructed with sparse Pauli measurements. Tomography must work with dense measurement bases, high-dimensional Hilbert spaces, and often sample-based data. However, existing convex optimization-based techniques are not efficient enough and scale poorly when extended to large and multimode systems. In this work, we explore convex optimization as an effective framework to address problems in bosonic state tomography, introducing three techniques to enhance efficiency and scalability: efficient displacement operator computation, Hilbert-space truncation, and stochastic convex optimization, which mitigate common limitations of existing approaches. Then we propose a sample-based, convex maximum-likelihood estimation method specifically designed for flying-mode tomography. Numerical simulations of flying four-mode and nine-mode problems demonstrate the accuracy and practicality of our methods. This method provides practical tools for reliable bosonic mode quantum state reconstruction in high-dimensional and multimode systems.

All-optical (AO) microwave-free magnetometry using nitrogen-vacancy ($\mathrm{N}$-$V$) centers in diamond is attractive due to its broad applicability and reduced experimental complexity. In this work, we investigate room-temperature AO photoluminescence (PL) at low magnetic fields ($<2$ mT) using diamonds with $\mathrm{N}$-$V$ ensembles at parts-per-million (ppm) concentrations. The measured AO-PL contrast features as a function of the applied magnetic field magnitude and direction are correlated with near-degenerate $\mathrm{N}$-$V$ electronic spin and hyperfine transitions from different $\mathrm{N}$-$V$ orientations within the diamond host. Reasonable agreement is found between low-field AO-PL measurements and model-based simulations of the effects of resonant dipolar interactions between $\mathrm{N}$-$V$ centers. The maximum observed AO-PL contrast depends on both the $\mathrm{N}$-$V$ concentration and the laser-illumination intensity at 532 nm. These results imply different optimal conditions for low-field AO $\mathrm{N}$-$V$ sensing compared to conventional optically detected magnetic resonance (ODMR) techniques, suggesting new research and application opportunities using AO measurements with lower system complexity, size, weight, and power.

Tunable-barrier dynamic quantum dots are known to generate very accurate single-electron-based currents and can be used as a source of single-electron wave packets for use in quantum metrology, sensing, or information processing. To realize their full technological potential, it is desirable to maximize their frequency of operation to increase the current; however, it has been observed that the mechanism of electron transfer across the quantum dot consistently breaks down for gigahertz frequencies, and this remains unexplained. Here, we present an analysis technique, combined with detailed modeling, to present a mechanism of high-frequency breakdown in this class of quantum dots as a rapidly imparted momentum impulse. Such understanding aids future design and operation protocols, allowing their use in high-frequency and real-time quantum measurements and technologies.

Thermal imaging in the long-wave infrared (LWIR) spectrum is crucial for surveillance, navigation, and medical diagnostics. However, the latency and power consumption of current infrared detectors are stumbling blocks for efficient heat-based object detection, recognition, and ranging. In this paper, we present the concept of a neural bolometer that integrates the recently developed spintronic ultrafast nanoscale bolometers with an artificial neural network architecture. Our approach enables long-wave infrared detectors to function as both imaging sensors and stochastic computing units. Our design significantly enhances processing speed and reduces power consumption, achieving LWIR MNIST (Modified National Institute of Standards and Technology) classification with an inference time of 2.82 $\text{μ}\mathrm{s}$ and power consumption of 1.9 $\text{μ}\mathrm{W}$, while maintaining a high accuracy of 92.5%. The proposed approach can usher in a new generation of thermal imagers with in-pixel computing for widespread applications in defense, surveillance, healthcare, and autonomous navigation.

Solar-blind ultraviolet (UV) communication has gained significant attention due to its low background noise, non-line-of-sight transmission, and high security. Achieving efficient solar-blind UV communication requires photodetectors with high sensitivity to weak solar-blind UV signals, low dark current, and excellent stability. In this study, an all-inorganic β-${\mathrm{Ga}}_2{\mathrm{O}}_3/\mathrm{Cu}\mathrm{O}/\mathrm{Ni}\mathrm{O}$ three-layer heterostructure was developed for self-powered solar-blind UV photodetectors. The introduction of a $\mathrm{Cu}\mathrm{O}$ electron-blocking layer effectively suppressed thermal carrier transport in the dark by creating a high conduction-band barrier, significantly reducing dark current. Compared to traditional β-${\mathrm{Ga}}_2{\mathrm{O}}_3/$p-$\mathrm{Ni}\mathrm{O}$ two-layer heterojunctions, the dark current of the β-${\mathrm{Ga}}_2{\mathrm{O}}_3/\mathrm{Cu}\mathrm{O}/\mathrm{Ni}\mathrm{O}$ photodetector is reduced by factors of 5.9 at 0 V and 19.2 at 20 V, respectively, along with a 77.6-fold and 5.9-fold increase in the photocurrent-to-dark current ratio. The device demonstrated a responsivity of 0.27 A/W under 254-nm illumination with a light power of 100 nW/${\mathrm{cm}}^2$ and robust stability across extreme temperatures (−170 °C to 100 °C). These results highlight the potential of the β-${\mathrm{Ga}}_2{\mathrm{O}}_3/\mathrm{Cu}\mathrm{O}/\mathrm{Ni}\mathrm{O}$-based photodetector for high-performance solar-blind UV communication systems.

In the “flopping-mode” regime of electron spin resonance, a single electron confined in a double quantum dot is electrically driven in the presence of a magnetic-field gradient. The increased dipole moment of the charge in the flopping mode significantly reduces the amount of power required to drive spin rotations; however, the susceptibility of flopping-mode spin qubits to charge noise, and consequently their overall performance, has not been examined in detail. In this work, we simulate single-qubit gate fidelities of electrically driven spin rotations in an ensemble of devices configured to operate in both the single-dot and flopping-mode regimes. Our model accounts for the valley physics of conduction-band electrons in silicon and realistic alloy disorder in the $\mathrm{Si}\text{−}\mathrm{Ge}$ barrier layers, allowing us to investigate device-to-device variability. We include charge and magnetic noise, as well as spin-relaxation processes arising from charge noise and electron-phonon coupling. We find that the two operating modes exhibit significantly different susceptibilities to the various noise sources, with valley splitting and spin-relaxation times also playing a role in their relative performance. For realistic noise strengths, we find that single-dot gate fidelities are limited by magnetic noise, while flopping-mode fidelities are primarily limited by charge noise and spin relaxation. For sufficiently long spin-relaxation times, flopping-mode spin operation is feasible with orders-of-magnitude lower drive power and gate fidelities that are on par with conventional single-dot electric dipole spin resonance.

Neutron detection materials are critical and irreplaceable in the fields of nuclear security monitoring, radioactive waste management, and particle physics research. The development of efficient neutron-gamma multimode scintillators that simultaneously offer high light yield, decent energy resolution, and efficient neutron-gamma discrimination capability remains a grand challenge. In this work, we report a neutron-gamma discrimination strategy by introducing ${}^6\mathrm{Li}$-enriched $\mathrm{Li}\mathrm{I}$ dopants, which has a high thermal neutron absorption cross section, into the highly efficient ${\mathrm{Cs}}_3{\mathrm{Cu}}_2{\mathrm{I}}_5:\mathrm{Tl}$ single crystals. The Bridgman-grown ${\mathrm{Cs}}_3{\mathrm{Cu}}_2{\mathrm{I}}_5:\mathrm{Tl},\mathrm{Li}$ single crystals demonstrate superior light yield of 81 000 photons/MeV under gamma irradiation and 200 000 photons/neutron under thermal neutron irradiation, respectively, higher than any reported multimode scintillators. Moreover, ${\mathrm{Cs}}_3{\mathrm{Cu}}_2{\mathrm{I}}_5:\mathrm{Tl},\mathrm{Li}$ single crystals possess a superior energy resolution of 4.2% at 662 keV, a decent neutron-gamma discrimination figure of merit of 2.35, and an intrinsic absence of radioactive background. By combining the density-functional-theory calculations, nuclear magnetic resonance, positron annihilation, and thermoluminescence measurements, the effects of ${}^6\mathrm{Li}$ codoping on the defect structure and scintillation performance were clarified. This work provides an alternative horizon for designing highly efficient neutron-gamma multimode scintillators.

Gradual modification of the magnetic properties in ferromagnetic films has recently been proposed as an effective method to channel and control spin waves for the development of alternative functionalities in magnonic devices. Here, we investigate graded $\mathrm{Fe}$:$\mathrm{N}$ films prepared by low-dose nitrogen implantation of $\mathrm{Fe}$ epitaxial thin films. Combining Brillouin light-scattering measurements and a spin-wave theoretical approach, we show that nitrogen implantation induces a graded profile of both the in-plane and the perpendicular anisotropies along the film thickness. This graduation leads to a significant modification of the spin-wave spatial localization across the thickness and generates a marked frequency asymmetry in the spin-wave dispersion. Moreover, we find that the anisotropy profile, and as a consequence the dispersion relation, can be tuned on changing the implantation dose, opening a way for the potential use of the graded $\mathrm{Fe}$:$\mathrm{N}$ films in magnonic applications.

The writing process of spin-orbit torque magnetic random-access memories (SOT-MRAMs) is considered deterministic when additional symmetry-breaking factors, such as the application of an external magnetic field aligned with the current, are present. Notably, the write probability exhibits a unique behavior as a function of the current: it drops to zero at high currents or even oscillates with the current. This phenomenon is attributed to back-switching, an intrinsic effect of magnetization reversal driven by spin-orbit torques. A systematic investigation of this back-switching phenomenon is conducted on sub-100-nm $\mathrm{Co}\mathrm{Fe}\mathrm{B}$ magnetic pillars positioned at the center of $\beta$-$\mathrm{W}$ Hall crosses. Using a statistical approach, the study examines the impact of various parameters, including the amplitude of current pulses and the application of magnetic fields in different directions. The findings reveal that the back-switching phenomenon is not statistically random. Macrospin simulations, employing realistic magnetic parameter values, accurately replicate the experimental observations and provide insights into the underlying mechanisms of back-switching. These simulations also explore strategies to mitigate the phenomenon, such as optimizing the shape of the writing pulses. Applying this approach to complete SOT-MRAM single cells achieves a write-error rate below $2\times {10}^{-6}$, demonstrating the effectiveness of this strategy in expanding the operational current range for write operations in SOT-MRAMs.

In this work we demonstrate a spin-orbit-torque (SOT) magnetic field sensor, designed as a $\mathrm{Ta}$/$\mathrm{Co}\mathrm{Fe}\mathrm{B}$/$\mathrm{Mg}\mathrm{O}$ structure, with high sensitivity and capable of active offset compensation in all three spatial directions. This is described and verified in experiment and simulation. The measurements of magnetic fields showed an offset of 35, 42, and $3\text{μ}\mathrm{T}$ for $x$-, $y$-, and $z$-fields respectively. Furthermore, the sensitivities of these measurements had values of 590, 580, and $490{\mathrm{V}\mathrm{A}}^{-1}{\mathrm{T}}^{-1}$ in the $x$-, $y$-, and $z$-direction, respectively. In addition, the robustness to bias fields is demonstrated via experiments and single-spin simulations by applying bias fields in the $y$-direction. Cross sensitivities were further analyzed via single-spin simulations, performing a parameter sweep of different bias fields in the $y$- and $z$-direction up to $\pm 1\mathrm{mT}$. The extraction of the SOT parameters ${\eta }_{\mathrm{DL}}$ and ${\eta }_{\mathrm{FL}}$ is shown via an optimization of a single-spin curve to the experimental measurements.

Owing to the spin Hall effect, an electric current flowing in a nonmagnetic conductor with a strong spin-orbit coupling creates a torque acting on spins in an adjacent ferromagnet or antiferromagnet. Such a spin-orbit torque provides the remarkable opportunity to generate steady-state auto-oscillations of spins in the magnetic nanolayer by a direct electric current. The frequency of the current-induced precession of spins in ferromagnetic spin Hall nano-oscillators (SHNOs) is well below 100 GHz, but it should increase up to the terahertz range in antiferromagnetic SHNOs. Further, in magnetoelastic antiferromagnets such as $\mathrm{Ni}\mathrm{O}$, spin oscillations should be accompanied by elastic vibrations. Here we describe the coupled magnetic and acoustic dynamics in $\mathrm{Ni}\mathrm{O}$-based SHNOs with the aid of micromagnetoelastic simulations. It is shown that the Néel-vector auto-oscillations excite high-frequency elastic vibrations inside the SHNO. Moreover, these vibrations may generate monochromatic terahertz elastic waves in the underlying nonmagnetic substrate. The frequency of the electrically excited longitudinal and transverse acoustic waves is 2 times higher than the frequency of spin oscillations, and their wave numbers comply with respective elastic dispersions. Our findings demonstrate that SHNOs comprising magnetoelastic antiferromagnets represent nanoscale sources of monochromatic coherent phonons with an electrically tunable frequency and wave number.

We demonstrate neutral gas-flow velocimetry by exploiting the optical dipole forces exerted by precisely tailored high-intensity laser fields on polarizable particles, in the form of single-shot coherent Rayleigh-Brillouin scattering (CRBS). This enables mapping of the velocity distribution function of the particles in a single laser shot of approximately 200 ns duration, allowing us to perform spectroscopic measurements in the time, rather than the frequency, domain. Importantly, CRBS results in a coherent signal beam, which renders the technique ideal for measurements in optically noisy environments. By correlating the time shift of the resulting spectrum to the Doppler shift caused by the bulk motion of particles, we perform neutral gas-flow velocimetry without the need to seed the flow, nondestructively, for a variety of gases, atomic or molecular. We demonstrate gas-flow velocimetry at flow velocities as low as $1\mathrm{m}{\mathrm{s}}^{-1}$, with similar velocity resolution, while temperature and gas density can also be estimated from the same single-shot spectra. To prove the effectiveness of the measurement technique, we benchmark it against Pitot tube measurements, which show excellent agreement.

We investigate the dynamics of mechanical resonators driven by excitations that include an oscillating or harmonic component with an amplitude that decays exponentially over time. We refer to these as complex-frequency excitations, and we show that the resulting response is quasisteady; i.e., after an appropriate transform, the response of the new variable corresponds to the steady-state behavior under a harmonic excitation. A procedure is presented to determine the amplitude-frequency response and effective quality factor based on this steady-state behavior. Optimal excitations are identified for both single- and multi-degree-of-freedom systems that result in the amplitude-frequency response approaching that of an undamped system. The feasibility of the proposed method is verified through numerical simulations. Experiments with cantilever beams made of acrylic show a 249-fold increase in the effective quality factor. Our method does not involve any structural modifications and opens avenues for improving detection sensitivity in nondestructive testing and enhancing resolution in micro- and nanoelectromechanical sensors.