A wavy dielectric grating hosts bound states in the continuum (BICs) at nonzero Bloch wave number. For an oblique incident optical field with parameters near to the BICs, the reflectance spectrum exhibits an ultrasharp Fano line shape, and the reflected beam has a large negative Goos-Hänchen shift, due to excitation of the corresponding quasi-BIC with negative group velocity. Under incidence of a Gaussian beam with a sizable beam width, the excited quasi-BIC could travel a long distance along the direction of the Goos-Hänchen shift, designated as $L_{\mathrm{GH}}$, before the energy is completely radiated. If the length between the termination of the wavy shape and the focus of the incident Gaussian beam is smaller than $L_{\mathrm{GH}}$, sizable energy flux can be coupled into the waveguide mode of the flat dielectric slab that is connected to the wavy dielectric grating. Measurement of the energy flux of the waveguide mode can sense the variation of the refractive index of the background medium. The proposed sensing scheme can be integrated with a waveguide in an optical circuit.

Isometric feature mapping (Isomap) is a nonlinear dimensionality reduction algorithm based on the concept of manifold learning. The algorithm is widely used in neuroimaging, spectral analysis, and other fields. While Isomap performs well in certain scenarios, it still faces the challenge of time complexity when dealing with large-scale data sets. In this paper, we proposed a quantum Isomap algorithm that runs with quadratic dependence on the number of data points. Technically, our algorithm is based on two subroutines, quantum Floyd’s algorithm and quantum multidimensional scaling. They are of independent interest and may serve as potential tools for addressing other problems.

We investigate the dynamic properties of elastic lattices defined by tessellations of a curved hyperbolic space. The lattices are obtained by our projecting nodes of a regular hyperbolic tessellation onto a flat disk and then connecting those sites with simple linkages. Numerical and experimental investigations illustrate how their vibrational spectral properties are characterized by a high density of modes that are localized at the domain boundaries. Such properties govern the propagation of waves induced by broadband inputs. This suggests the potential for applications seeking the protection of bulk media from boundary-incident perturbations. We uncover the boundary-dominated nature of an exemplary hyperbolic lattice through the evaluation and analysis of its integrated density of states and vibrational spectrum. The dynamics of the lattice are also contextualized by our comparing them with those of continuous disks characterized by Euclidean and hyperbolic property distributions, which confirms that the lattice retains the boundary-dominated spectrum observed in the hyperbolic plane. We then numerically investigate the response of the lattice to transient pulses incident on the boundary and find that edge-confined wave propagation occurs. The modal and transient pulse-propagation behavior of the lattice is experimentally validated in a milled aluminum sample. By leveraging hyperbolic geometry, our mechanical lattice ushers in a novel class of mechanical metamaterials with boundary-dominated wave phenomena reminiscent of topologically protected systems suitable for applications in advanced wave control.

Pseudomagnetic fields are promising for manipulating classical waves, including optic, acoustic, and elastic waves. One fascinating phenomenon is the presence of Landau energy levels and the involved quantum Hall effect, which are usually considered to exist only in quantum systems. Unlike using synthetic Landau gauge fields, as in existing works, here we successfully create a symmetric gauge field to achieve a large-area uniform pseudomagnetic field in a two-dimensional phononic crystal by introducing linear variations in the single-cell parameters of the scatterer along both the x and y directions. Discrete Landau levels are generated near the Dirac cone region, and the unidirectional propagation of acoustic waves along the domain wall, i.e., quantum Hall transport, is observed in experiment. The proposed structure offers greater flexibility by allowing free choice of the effective vector potential. Our study expands the application perspective of artificial acoustic devices that rely on a pseudomagnetic field.

Spectral and band topologies have different degrees of freedom, usually treated separately. Recent studies have shown that spectral topology is not only related to the topological phase transition of bulk bands but can also influence the original boundary states. However, the interplay of these two topologies remains elusive, and the rich phase transitions resulting from their combination have yet to be explored. Here, we construct a two-dimensional non-Hermitian topological acoustic model using honeycomb-lattice cavity-tube configurations with controllable in-plane hopping and out-of-plane radiation losses. The phase diagram obtained is based on the interaction between trivial and nontrivial topological bands and unbroken and broken parity-time symmetry, depending on the hopping difference and loss strength trade-off. We experimentally observe novel exceptional points of topological boundary states, indicating that the energy band attraction effect is more substantial for the boundary than for the bulk. These results enrich non-Hermitian topological physics and may lead to robust yet ultrasensitive sensing applications by taking advantage of both topological and parity-time systems.

Recent advances in glass fabrication technology have allowed for the development of high-precision inertial sensors in devices weighing of the order of grams. Gram-scale inertial sensors can be used in many applications with tight space or weight requirements. A key element of these devices’ performance is the behavior of a mechanical resonator. We present a detailed study on the design of resonators for such sensors. First, we consider how the mechanical parameters of a resonator couple with an inertial sensor’s performance. Then, we look at how to geometrically design resonators to achieve specific mechanical behavior without undergoing brittle failure. Both analytic tools and finite element analysis are used to this end. We then derive expressions that can be used to optimize the performance of an inertial sensor for a specific sensitive bandwidth. A simple geometry used throughout the field is studied as an example. However, the results are presented in a general form so that they can be easily adapted to any required geometry and use case. Ultimately, the results presented here guide the design of gram-scale inertial sensors and will improve the performance of devices that follow them.

Optical beam deflection is a popular method to measure the deformation of micromechanical devices. As it measures mostly a local slope, its sensitivity depends on the location and size of the optical spot. We present a method to evaluate precisely these parameters, using the relative amplitude of the thermal noise–induced vibrations. With a case study of a microcantilever, we demonstrate the accuracy of the approach, as well as its ability to fully characterize the sensitivity of the detector and the parameters (mass and stiffness) of the resonator.

We propose the design of single-layer, double-layer, and triple-layer configurations of magnonic ring couplers, which perform spin-wave mode filtering and provide interlayer signal transmission in three-dimensional architectures of magnonic integrated circuits. We study the characteristics of spin-wave dynamics in coupled magnonic structures with a ring resonator in planar and vertical configurations using Brillouin light scattering and the micromagnetic simulation method based on numerical solution of the Landau–Lifshitz–Gilbert equation. The mechanisms of backward and forward coupling control of spin-wave transport in yttrium iron garnet stripe placed in the proximity of the magnonic microring resonator are elucidated. The possibility of reversing the direction of spin-wave propagation with simultaneous selection of transverse spin-wave modes is demonstrated. It is shown that, in the proposed structure, multistream selection of a spin-wave signal is possible due to spatial frequency and simultaneous mode separation. Lateral and vertical magnonic rings could be used for magnonic logic application with the variation of the phase and amplitude of signals. We also demonstrate that the spin-wave mode order is an additional parameter that can be used to simultaneously control the transmission of the ring coupler with the facility to encode the logical state “0” or “1” with the width mode order. The multistream selection of a spin-wave signal and the spatial frequency and simultaneous mode separation lie behind the application of the proposed magnonic ring coupler as a multiport interconnection element and/or functional logical unit in reconfigurable integral blocks of magnonic networks.

Classification, the computational process of categorizing an input into preexisting classes, is now a cornerstone in modern computation in the era of machine learning. Here, we propose an approach for a quantum physical computer; a quantum classifier, based on quantum transport of particles in a trained quantum network. The classifier is based on sending a quantum particle into a network and measuring the exit point of the particle, which serves as a “class” and can be determined by changing the network parameters, differing from standard quantum computers as no gate operations are required to perform the computation. Using this scheme, we demonstrate three examples of classification. In the first, wave functions are classified according to their overlap with predetermined (random) groups. In the second, we classify wave functions according to their level of localization. Both examples use small training sets and achieve over 95% precision and recall. The third classification scheme is a “real-world problem,” concerning classification of catalytic aromatic aldehyde substrates according to their reactivity. Using experimental data, the quantum classifier reaches an average 86% classification accuracy. We show that the quantum classifier outperforms its classical counterpart for these examples and demonstrates clear advantage, especially in the regime of “small data.” These results pave the way for a classification scheme that can be implemented as an algorithm and potentially realized experimentally on quantum hardware.

The design of a highly efficient planar focal lens with a near-unity numerical aperture remains a challenge, despite efforts made on this topic. In this paper, we propose a two-dimensional nonlocal transmission-type metasurface composed of subwavelength-sized channels and groove arrays, aiming to attain highly efficient acoustic focusing. We show that such a nonlocal structure can be efficiently designed by an inverse method based on the multistructural model, even when the number of constituent units becomes considerably large. As examples, metasurfaces both for the plane-wave source and for the point source have been designed. Numerical results show that our proposed nonlocal metasurface exhibits a much higher focusing efficiency than the corresponding structures based on the principle of the generalized Snell law. The structure designed for the point source has also been verified experimentally, showing good agreement between the numerical and experimental results. Our design contributes an alternative idea for wave control, which should be useful in acoustic sensors, energy harvesting, and so on.

Photonic reservoir computing has been successfully utilized in time-series prediction as the need for hardware implementations has increased. Prediction of chaotic time series remains a significant challenge, an area where the conventional reservoir computing framework encounters limitations of prediction accuracy. We introduce an attention mechanism to the reservoir computing model in the output stage. This attention layer is designed to prioritize distinct features and temporal sequences, thereby substantially enhancing the prediction accuracy. Our results show that a photonic reservoir computer enhanced with the attention mechanism exhibits improved prediction capabilities for smaller reservoirs. These advancements highlight the transformative possibilities of reservoir computing for practical applications where accurate prediction of chaotic time series is crucial.

We report spin-wave diffraction, caustic beam emission, and the formation of Talbot carpets in an yttrium iron garnet (YIG) film equipped with magnonic Fabry-Perot resonators. The resonator structures are created by patterning cobalt iron boron ($\mathrm{Co}$-$\mathrm{Fe}$-$\mathrm{B}$) nanostripes on the YIG film. Small gaps in the $\mathrm{Co}$-$\mathrm{Fe}$-$\mathrm{B}$ nanostripes generate a magnetic field profile within the YIG film, functioning as a slit grating when the resonators block incoming spin waves at specific frequencies. We employ super-Nyquist sampling magneto-optical Kerr effect (SNS-MOKE) microscopy to image the transport of spin waves through the slits and supplement our experimental observations with micromagnetic simulations. For a single slit, we observe a transition from spin-wave diffraction to caustic beam emission as the slit size decreases. These phenomena are influenced by the effective magnetic field within the slit, which varies with the direction of magnetization in either the YIG film or the $\mathrm{Co}$-$\mathrm{Fe}$-$\mathrm{B}$ nanostripes. For multiple slits, we detect self-imaging of spin-wave profiles and the formation of Talbot carpets. Furthermore, we demonstrate active tuning of spin-wave interference patterns through magnetic switching in the Fabry-Perot resonators or by rotating the in-plane magnetization of the YIG film. The magnonic grating system described here integrates low-loss spin-wave transport and programmable spin-wave interference, offering potential applications in advanced magnonic computing devices.

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.