Here we present the nonreciprocal propagation of caustic beams and channeling of the backward volume spin wave in an yttrium-iron-garnet structure with the longitudinal symmetry axis and broken translational symmetry. The experimental method of Brillouin spectroscopy and the numerical micromagnetic methods are used to study the mechanisms of control of the nonreciprocal spin-wave signal propagation in a T-shaped junction with a partially metallized surface. It is shown that the partial metallization of the surface together with the reversal of the magnetic field direction can serve as a way to control the propagation of spin-wave beams. The formation of the spin-wave channel between the metal stripe and the edge of the magnetic film is observed experimentally and demonstrated by numerical solution of the Landau-Lifshitz-Gilbert equation and Maxwell’s equations. The proposed theoretical analysis explains the experimental results and provides useful technical information for the fabrication of reconfigurable magnonic devices, which utilize the spin-wave beam formation in the region of the junction of the magnonic waveguides with different widths. The proposed structure can be used as a functional element of signal branching and/or power division in magnonic networks and signal-processing devices based on them.

Solid-state refrigeration holds promise for environmentally friendly cooling with high energy efficiency and downsize scalability. However, its refrigeration performance is notably inferior in comparison with commercial refrigerants due to the lack of scientific guidance for material discovery and performance improvement. Here, we provide an efficient approach to investigate caloric effect under external factors (i.e., electric fields, magnetic fields, and mechanical fields). Using the electrocaloric material ${\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_3$ (PTO) as a prototype and employing ab initio calculations combined with deep potential machine learning, we demonstrate the field-dependent isothermal entropy change ΔS and adiabatic temperature change ΔT, along with the coefficient of performance near the phase transitions temperature ($T_c$). Through analysis of the evolution of microscopic dynamics, we clarify that the refrigeration process involves heat absorption by a transition from a low-potential-energy to a high-potential-energy state. This transition, in a more general case, can be defined as a conventional caloric effect driven by temperature when T > $T_c$, or an inverse caloric effect driven by external field when T < $T_c$. Importantly, this approach is successfully applied to magnetocaloric, elastocaloric, and barocaloric materials, from which we further showcase the regulation of caloric effect in multicaloric refrigeration process. This work establishes an effective and universal method for predicting key refrigeration parameters, which can be applied to extensive caloric materials, that provide important insights for material design in solid-state cooling technology.

We model and experimentally demonstrate the full time-dependent counting statistics of photons emitted by a single nitrogen-vacancy ($\mathrm{N}$-$V$) center in diamond under nonresonant laser excitation and resonant microwave control. A generalization of the quantum jump formalism for the seven electronic states involved in the fast intrinsic dynamics of a $\mathrm{N}$-$V$ center provides a self-contained model that allows the characterization of its emission and clarifies the relation between the internal states of the $\mathrm{N}$-$V$ center and the measurable detected photon counts. The model allows the elaboration of detection protocols to optimize the energy and time resources while maximizing the system sensitivity to magnetic field measurements.

We report the observation of frequency nonlinearity within a gain-embedded resonator. A coupling model, integrating the van der Pol–Duffing oscillator, is theoretically proposed. The proposed model is substantiated through experimental verification in coupled LRC circuits, demonstrating bistable behavior. Furthermore, by application of the van der Pol–Duffing oscillator to a gain-embedded microwave cavity, our model is demonstrated as an alternative theoretical perspective for understanding the gain-driven polariton.

The tunnel magnetoresistance (TMR) sensor is a highly sensitive magnetic field sensor that is expected to be applied in various fields, such as magnetic recording, industrial sensing, and biomedical sensing. To improve the detection capability of TMR sensors in the low-frequency regime, it is necessary to suppress the $1/f$ noise. We theoretically study the $1/f$ noise of a tiny TMR sensor using the macrospin model. Starting from the generalized Langevin equation, the $1/f$ noise power spectrum and the Hooge parameter are derived. The calculated Hooge parameter of a tiny TMR sensor is much smaller than that of a conventional TMR sensor with large junction area. The results provide a new perspective on magnetic $1/f$ noise and will be useful for improving TMR sensors.

Compared with traditional electric-field-controlled resistive random-access memory, optoelectronic resistive random-access memory (ORRAM) can be modulated in more dimensions by applying a laser; this is identified as a potential device to meet the demands of neuromorphic vision sensors. As a device with a wide range of application prospects, ORRAM still faces many challenges, such as an unclear mechanism and poor performance. Using the photosensitive properties of ${\mathrm{Ti}\mathrm{O}}_2$ and the effects of the oxygen vacancy in anatase ${\mathrm{Ti}\mathrm{O}}_2$, we successfully obtain the giant laser-induced resistance effect in the $\mathrm{Ag}/{\mathrm{Ti}\mathrm{O}}_x/p$-$\mathrm{Si}$ structure, and its electrical conductivity is enhanced by about 4000 times with a response time of less than 24 µs (the response time of most ${\mathrm{Ti}\mathrm{O}}_2$ thin-film devices is in the order of milliseconds to seconds), which greatly improves the performance of ORRAM. This work provides a scalable strategy for the development of ORRAM devices and brings ORRAM closer to practical applications.

Solid-state devices used for quantum computation and quantum sensing applications are adversely affected by loss and noise caused by spurious, charged two-level systems (TLS) and stray paramagnetic spins. These two sources of noise are interconnected, exacerbating the impact on circuit performance. We use an on-chip electron spin resonance (ESR) technique, with niobium nitride ($\mathrm{Nb}\mathrm{N}$) superconducting resonators, to study surface spins on silicon and the effect of postfabrication surface treatments. We identify two distinct spin species that are characterized by different spin-relaxation times and respond selectively to various surface treatments (annealing and hydrofluoric acid). Only one of the two spin species has a significant impact on the TLS-limited resonator quality factor at low-power (near-single-photon) excitation. We observe a three- to fivefold reduction in the total density of spins after surface treatments and demonstrate the efficacy of ESR spectroscopy in developing strategies to mitigate loss and decoherence in quantum systems.

Computational ghost imaging is widely used in classical cryptographic key distribution (CKD) because its measurement and reconstruction are equivalent to the encoding and decoding of signals. Although the measurement efficiency and key-generation rate can be improved by using snapshot compressive ghost-imaging technique, it is still hard to deal with the risk of private key leakage. In this paper, we propose a cascade snapshot CKD protocol over a public network. In each round of communication, multiframe binary block diagrams embedded with cryptographic keys, Arnold transform parameters (derived from the checksum data of recovered images in the previous communication), and users’ authentication information are superimposed into one image frame that is measured within a single exposure of an array detector, here the Arnold transformation is applied to randomly disrupt the previously used modulation patterns according to the above parameters, which greatly enhances the nonstealability of private keys and makes the temporary intrusion of a fake identity nowhere to hide. Both simulation and experimental results have demonstrated the feasibility of this protocol and its ability to detect illegal attacks. We believe that the introduction of the cascade idea will accelerate the practicalization process of snapshot CKD.

Quantum master equations are commonly used to model the dynamics of open quantum systems, but their accuracy is rarely compared with the analytical solution of exactly solvable models. In this work, we perform such a comparison for the damped Jaynes-Cummings model of a qubit in a leaky cavity, for which an analytical solution is available in the one-excitation subspace. We consider the non-Markovian time-convolutionless master equation up to the second (Redfield) and fourth orders as well as three types of Markovian master equations: the coarse-grained, cumulant, and standard rotating-wave approximation (RWA) Lindblad equations. We compare the exact solution to these master equations for three different spectral densities: impulse, Ohmic, and triangular. We demonstrate that the coarse-grained master equation outperforms the standard RWA-based Lindblad master equation for weak coupling or high qubit frequency (relative to the spectral density high-frequency cutoff ${\omega }_c$), where the Markovian approximation is valid. In the presence of non-Markovian effects characterized by oscillatory, nondecaying behavior, the time-convolutionless approximation closely matches the exact solution for short evolution times (in units of ${\omega }_c^{-1}$) even outside the regime of validity of the Markovian approximations. For long evolution times, all master equations perform poorly, as quantified in terms of the trace-norm distance from the exact solution. The fourth-order time-convolutionless master equation achieves the top performance in all cases. Our results highlight the need for reliable approximation methods to describe open-system quantum dynamics beyond the short-time limit.

We present a novel method for the suppression of laser intensity noise and pulse-to-pulse energy fluctuation, based on second-harmonic generation. This method is broadband, passive, has low complexity, and suppresses noise uniformly over the noise spectrum. We theoretically model, analytically analyze, and numerically simulate this technique’s performance for cw and nanosecond pulse lasers with different pulse shapes. We demonstrate broadband relative intensity noise suppression of up to 48 dB, and pulse-to-pulse energy fluctuation suppression of up to 50 dB, and highlight the significance of these findings for extending atom trap storage time, e.g., for quantum information processing.

We apply principal component analysis (PCA) to a set of electrical output signals from a commercially available superconducting nanowire single-photon detector (SNSPD) to investigate their photon-number-resolving capability. We find that the rising edge as well as the amplitude of the electrical signal have the most dependence on photon number. Accurately measuring the rising edge while simultaneously measuring the voltage of the pulse amplitude maximizes the photon-number resolution of SNSPDs. Using an optimal basis of principal components, we show unambiguous discrimination between one- and two-photon events, as well as partial resolution up to five photons. This expands the use case of SNSPDs to photon-counting experiments, without the need of detector multiplexing architectures.

Unlike conventional imaging with two-dimensional array sensors featuring millions of pixels, ghost imaging enables the use of advanced detector technologies, giving advantages such as high signal-to-noise ratio, wide spectral range, and robustness to light scattering. However, this involves an extremely time-consuming measurement process, which means that it is difficult to meet the needs of high-quality real-time imaging. This paradox becomes notable especially in the context of utilizing non-orthogonal modulation patterns, such as the speckles generated by rotating ground glass. Efficient modulation patterns and advanced reconstruction algorithms are widely studied as two main ideas to solve the above problem. Here, we perform real-time, high-fidelity differential ghost imaging (DGI) at a low sampling ratio of 6.25% by proposing a compact physically guided single-layer neural network with the DGI algorithm embedded. Simulations and experiments show that, once the learned modulation patterns are obtained, our scheme can achieve fast, high-quality, and noise-robust DGI without the need for complex iterative optimization algorithms or subsequent optimization neural networks. Our scheme opens up new horizons for exploring more efficient modulation patterns for ghost imaging by deeply combining physical priors.

A dynamic trapping of Lamb modes with a frequency cutoff was achieved through local heating of an elastic plate using a cw laser. The relatively small variations in material stiffness resulting from the temperature rise proved effective at capturing waves within the heated region, which behaved like a potential well for specific Lamb modes. These trapped modes corresponded precisely to discrete frequencies predicted by the time-independent Schrödinger equation, reminiscent of the principle quantum number. The number of trapped modes hinges on both the width and depth of the laser-induced thermal potential well, with these variables interrelated via Heisenberg’s uncertainty principle. Furthermore, we observed a high-quality factor ($Q$ factor of approximately 260) attributed to the trapped wave motion within the potential well, offering significant promise for highly precise nondestructive evaluation of thermal and mechanical properties of materials.

Many correlated oxides feature an insulator-to-metal transition as the temperature is increased. In thin films, this transition can be electrically induced by localized Joule heating, resulting in volatile resistive switching. Considering the importance of thermal effects, the thermal conductivity of the underlying substrate is expected to play a key role. Despite this, its influence has not been experimentally explored. Here, we compare the resistive switching of ${\mathrm{VO}}_2$ films grown on two substrates with very different thermal conductivities k: sapphire [k ∼ 50 W/(m K)] and mica [k ∼ 0.5 W/(m K)]. While the overall features of the electrical switching are similar, the ${\mathrm{VO}}_2\text{−}$mica devices need around one order of magnitude less power to be switched, and their switching time is shorter. This can be understood by the improved thermal insulation offered by the substrate, which keeps the heat within the film. Our work shows that thermal insulators, such as mica, are a promising platform for energy-efficient volatile resistive switching.

Visible-band polarization-entangled photon sources (VBPEPSs) are preferred in quantum microscopy, imaging, and light-matter interactions with solid-state quantum memories, $\mathrm{N}$-$V$ centers, and trapped ions. They can be generated directly via spontaneous parametric down-conversion. However, that requires a high-power deep-ultraviolet pump laser. Additionally, the required ultraviolet-band nonlinear crystal is inefficient compared to periodically poled potassium titanyl phosphate or periodically poled lithium niobate crystals. The quantum frequency transduction of a near-infrared polarization-entangled photon source (NIPEPS) provides an effective way to overcome the drawbacks of direct generation. We demonstrate 634-nm VBPEPS generation via polarization-independent frequency transduction of 1080-nm NIPEPS. High-quality entanglement in the visible band is verified via two-photon polarization interference, Bell-inequality, and quantum-state tomography. This method could be applied to other visible wavelengths or be extended to the ultraviolet, which is difficult to generate directly. It has promising applications in quantum imaging, networks, and spectroscopy.

An appropriately parametrized analytical equation (APAE) is suggested to account for charge-carrier mobility in organic disordered semiconductors. This equation correctly reproduces the effects of temperature $T$, carrier concentration $n$, and electric field $F$ on the carrier mobility $\mu (T,F,n)$, as evidenced by comparison with analytical theories and Monte Carlo simulations. The set of material parameters responsible for charge transport is proven to be at variance with those used in the so-called extended-Gaussian-disorder-model (EGDM) approach, which is widely exploited in commercially distributed device-simulation algorithms. While the EGDM is valid only for cubic lattices with a specific choice of parameters, the APAE describes charge transport in systems with spatial disorder in a wide range of parameters. The APAE is user-friendly and, thus, suitable for incorporation into device-simulation algorithms.

Microwave ablation is a therapeutic procedure to eliminate abnormal tissue within a body selectively. There are two types of ablation; thermal ablation aims to raise the temperature at the target, while nonthermal ablation induces a temporarily high electric field at the target to disrupt cellular membrane integrity. This work identifies the fundamental bounds of the efficiency for each type of ablation and the sources to achieve them. For both types, the bounds exceed the performance of existing solutions tenfold, showing large room for improvement. Finally, the optimal source for thermal ablation is physically realized with an $11\times 11$ dipole array, the performance of which closely approaches the bound.