Due to the contribution of photon tunneling, the output power of near-field thermophotovoltaic (NFTPV) devices can surpass that of far-field thermophotovoltaic devices by several orders of magnitude, which has recently drawn extensive attention. Previous research explores the enhancement brought by hyperbolic materials, but little investigation has been done on the frequency shift of hyperbolic bands. Hyperbolic metamaterials acquire the hyperbolic properties through complex nanofabrication processes. However, calcite (${\mathrm{Ca}\mathrm{CO}}_3$), as a natural hyperbolic material, possesses hyperbolic properties without the need for expensive processing. Despite this, ${\mathrm{Ca}\mathrm{CO}}_3$ is rarely chosen as the thermal emitter in NFTPV devices. In this work, we propose an NFTPV device using ${\mathrm{Ca}\mathrm{CO}}_3$ as the thermal emitter and an $\mathrm{In}\mathrm{Sb}$ p-n junction as the PV cell. Furthermore, we compare the performance of four structures to analyze the effect of the graphene layer on the ${\mathrm{Ca}\mathrm{CO}}_3$-$\mathrm{In}\mathrm{Sb}$ NFTPV devices we propose. The numerical results demonstrate that the ${\mathrm{Ca}\mathrm{CO}}_3$/$\mathrm{graphene}/\mathrm{In}\mathrm{Sb}$ structure exhibits the best performance based on the assumption of considering only radiative recombination. The ${\mathrm{Ca}\mathrm{CO}}_3$/$\mathrm{graphene}/\mathrm{In}\mathrm{Sb}$ structure simultaneously achieves 41% efficiency and 94 W/${\mathrm{cm}}^2$ output power density when the temperature of the thermal emitter is 900 K. The physical mechanism of the significantly improved performance of the NFTPV device arises from the frequency coupling between the hyperbolic resonance and the interband transition of the $\mathrm{In}\mathrm{Sb}$ p-n junction, where the surface plasmon polaritons excited in graphene make a promotion role. Moreover, we discuss the impact of the gap distance, the temperature of the thermal emitter, and the thickness of the thermal emitter on the performance of NFTPV devices. Our research contributes to understanding the coupling of surface plasmon polaritons and hyperbolic phonon polaritons and the design of high-performance thermophotovoltaic device.

III-V semiconductor quantum dots (QDs) are near-ideal and versatile single-photon sources. Because of the capacity for monolithic integration with photonic structures as well as optoelectronic and optomechanical systems, they are proving useful in an increasingly broad application space. Here, we develop monolithic circular dielectric gratings on bulk substrates—as opposed to suspended or wafer-bonded substrates—for greatly improved photon collection from $\mathrm{In}\mathrm{As}$ quantum dots. The structures utilize a unique two-tiered distributed-Bragg-reflector structure for vertical electric field confinement over a broad angular range. Opposing “openings” in the cavities induce strongly polarized QD luminescence without harming collection efficiencies. We describe how measured enhancements depend on the choice of collection optics. This is important to consider when evaluating the performance of any photonic structure that concentrates far-field emission intensity. Our cavity designs are useful for integrating QDs with other quantum systems that require bulk substrates, such as surface acoustic wave phonons.

The coexistence and coupling of multiple ferroics may not only cause some novel physical phenomena but also provide new means for the detection and control of electronic degrees of freedom. In recent years, two-dimensional (2D) ferroelectricity and ferromagnetism have been experimentally confirmed in van der Waals materials but their coexistence and coupling have rarely been demonstrated in single-phase materials. Here, a general mechanism for the coexistence and coupling of three ferroics has been demonstrated in van der Waals monolayer ferromagnets lacking inversion symmetry, in which spin-orbit coupling leads to spin-direction-dependent ferroelectricity and ferrovalley. This causes the emergence of some interesting phenomena, such as the anomalous valley Hall effect without an applied electric field. The ferroelectric polarization induced in a 2D ferromagnet with strong spin-orbit coupling can be close to the largest known spin-induced polarization. Importantly, the magnetoelectric coupling effect enables the cross control of ferroic order parameters by external fields, such as controlling magnetization by an electric field and polarization by a magnetic field.

While light-matter interaction mediated by strong exciton-plasmon coupling has been demonstrated to increase the absorbance and spontaneous emission in coupled transition-metal dichalcogenide and metal nanostructures, incorporating it in an optoelectronic device in a controlled manner is challenging. Here we report that the exciton-plasmon coupling can be tuned in a chemically synthesized hybrid of ${\mathrm{WS}}_2$ and $\mathrm{Ag}$ nanoparticles (NPs) capped with an insulating polyvinylpyrrolidone (PVP) layer by controlling the coverage area and the PVP layer thickness. Furthermore, we decorate large-area single-layer graphene with these nanostructures to create the hybrid channel for a three-terminal phototransistor. The fabricated device exhibits superior gate tunability and extremely high photoresponsivity (up to 3.2 × ${10}^4$ A/W), which is more than 5 times higher than for the bare $\mathrm{graphene}$/${\mathrm{WS}}_2$ hybrid device, along with a low noise equivalent power (approximately ${10}^{-13}$ $\text{W}/{\text{Hz}}^{0.5}$) and higher specific detectivity of approximately ${10}^{10}$ Jones units in a wide wavelength range (325–730 nm). The additional PVP capping of $\mathrm{Ag}$ NPs helps to suppress the direct charge and heat transfer and, most importantly, increases the device stability by preventing the degradation of the ${\mathrm{WS}}_2$-$\mathrm{Ag}$ hybrid system. Our work demonstrates a strategy towards obtaining an environmentally friendly, scalable, high-performance broadband phototransistor by tuning of the exciton-plasmon coupling for next-generation optoelectronic devices.

The manipulation of topological states in topological systems can be achieved through gain-loss domain walls, offering flexibility and reconfigurability within the bulk. However, this typically necessitates a global non-Hermitian modulation, involving the modulation of all lattice points within each domain, thereby increasing the complexity of system modulation. In this study, we propose a local-non-Hermitian-modulation approach to inducing photonic topological states within topologically trivial systems. By solely modulating the lattice points along the domain boundary, we significantly reduce the complexity of modulation. We theoretically and experimentally demonstrate the generation of photonic topological states induced by local non-Hermitian modulation on a silicon chip in a one-dimensional system. This process is controlled precisely through an effective Hamiltonian. Furthermore, we extend this concept to generate higher-order topological corner states in two-dimensional systems. Our findings showcase the potential of local non-Hermitian modulation in facilitating the manipulation of photonic topological states, thereby offering new possibilities for higher-dimensional systems and other topological systems.

Magnetotransport measurements on two-dimensional van der Waals heterostructures have recently shown signatures of uniaxial anisotropy. Such measurements are almost exclusively performed in a Hall bar geometry, which makes it difficult to extract the full resistivity tensor. The goal of this paper is to theoretically analyze anisotropic magnetoconductance in a homogeneous disk geometry and to provide a closed-form expression for the electrical potential anywhere on the disk if the current source and drain are located somewhere on the circumference. This expression can then be used to experimentally extract the full conductivity tensor, and by a simple inversion, the full resistivity tensor.

Adaptive tomography has been widely investigated with the aim of achieving faster state tomography processing of quantum systems. Infidelity of the nearly pure states in a quantum information process generally scales as $O(1/\sqrt{N})$, which requires a large number of statistical ensembles in comparison to the infidelity scaling of $O(1/N)$ for mixed states. One previous report optimized the measurement basis in a photonic qubit system, whose state tomography uses projective measurements, to obtain an infidelity scaling of $O(1/N)$. However, this dramatic improvement cannot be applied to indistinct measurement systems in which two quantum states cannot be distinguished with perfect measurement fidelity. We introduce in this work an optimal measurement basis to achieve fast adaptive quantum state tomography and a minimum magnitude of infidelity in an indistinct measurement system. We expect that the adaptive quantum state tomography protocol can lead to a reduction in the number of required measurements of approximately 33.74% via analytical expectation without changing the $O(1/\sqrt{N})$ scaling. Experimentally, we find a 15.06% measurement number reduction in a superconducting circuit system.

Unidirectional magnetoresistance (UMR) is a magnetoresistance family that arises from spin-current generation in ferromagnet (FM)/nonmagnetic heavy metal (HM) bilayers. Because UMR exhibits asymmetric behavior owing to the current or external magnetic field directions, it is easy to quantify the amount of charge-to-spin conversion in a system and the sign of the spin current. UMR has been explained by two major mechanisms: spin accumulation at the FM/HM interface and electron-magnon scattering in an FM layer. In this study, we investigated the thickness and temperature dependence of the UMR of $\mathrm{Ta}/\mathrm{Co}$ and $\mathrm{Pt}/\mathrm{Co}$ bilayer structures and numerically analyzed the contribution of the electron-magnon scattering using a self-developed quantitative-analysis model. The magnon UMR was dominant in the $\mathrm{Pt}/\mathrm{Co}$ samples, and the spin-accumulation-UMR and magnon-UMR trends were separated in the $\mathrm{Ta}/\mathrm{Co}$ samples by thickness. The magnitude of the UMR strongly depends on the choice of the HM. Our findings provide a method to quantitatively separate the contributions of each mechanism.

Hydrophobic and superhydrophobic interactions can be characterized by measuring forces between drops and surfaces using force gauges that range from optical fibers to atomic force microscopy cantilevers. Here, we propose and implement an alternative methodology in which a nearly spherical drop itself serves as a force gauge. By obtaining dynamic contact angles, force constants of biological structures, and the force of adhesion on nonwettable surfaces, we demonstrate the robustness, wide applicability, and simplicity (neither profile fitting nor knowledge of the contact angle or area are required) of this technique.

Noninvasive surface-acoustic-wave (SAW) tweezers provide a powerful tool for on-chip object manipulation. However, the piezoelectric materials for generating SAWs are anisotropic with misaligned directions of wave momenta and energy flow, making the conventional interdigital transducer (IDT) inappropriate for perfect SAW control. Here we propose a holographic IDT for phase-velocity engineering, which improves the focusing quality of SAWs with smaller focal size, larger enhancement of intensity, and precise control of focal position. For the holographic IDT, the focal size is approximately 78.2 µm at 40 MHz, which is 36% smaller than the one produced by a circular IDT. About twofold enhancement of focal intensity and focal length of 10λ are further demonstrated for our design. Nonetheless, we show that the holographic SAW tweezers can implement accurate sorting for solid objects of different sizes as well as large active deformation for liquid droplets even at relatively low input power, which have important biomedical applications.

Computational imaging allows image formation with single-pixel detectors that have no spatial resolution. It has wide-ranging potential applications in fields ranging from biomedical imaging to remote sensing. However, the practical applications of computational imaging are limited due to the high sampling ratio, weak robustness, and low resolution. In this paper, we propose a robust superresolution computational imaging scheme with diffuser-refined illumination and multibucket detection. To increase the reconstruction efficiency, a dual-stream neural network incorporated with a physical model is developed for this imaging scheme, which can reconstruct a high-resolution image in ultralow-sampling-ratio (1.56%) and ultrahigh-noise (4 dB) environments without any data for pretraining. The experimental results demonstrate that the proposed method can increase the spatial resolution by a factor of 2.59 with respect to the diffraction limit of the original imaging system. We also successfully apply this method to image a real biomedical sample and believe that this study provides a computational-imaging framework for complicated practical applications.

${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$ semiconductors have promise for large-scale, monolithic, midinfrared photonics and optoelectronics. However, despite the successful demonstration of several ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$-based photodetectors and emitters, key fundamental properties of this material system are yet to be fully explored and understood. In particular, little is known about the role of the material properties in controlling the recombination mechanisms and their consequences for the carrier lifetime. Evaluating the latter is in fact fraught with large uncertainties that are exacerbated by the difficulty in investigating narrow-band-gap semiconductors. To alleviate these limitations, herein we demonstrate that the behavior of the radiative carrier lifetime can be evaluated from straightforward excitation power- and temperature-dependent photoluminescence measurements. To this end, a theoretical framework is introduced to simulate the measured spectra by combining the band structure calculations from the k.p theory and the envelope function approximation to estimate the absorption and spontaneous emission. The model computes explicitly the momentum matrix element to estimate the strength of the optical transitions in single bulk materials, unlike the joint density of states model that assumes a constant matrix element. Based on this model, the temperature-dependent emission from ${\mathrm{Ge}}_{0.83}{\mathrm{Sn}}_{0.17}$ samples at a biaxial compressive strain of $-1.3\mathrm{\%}$ is investigated. The simulated spectra reproduce accurately the measured data thereby enabling the evaluation of the steady-state radiative carrier lifetimes, which are found in the range 3–22 ns for temperatures between $10$ and 300 K at an excitation power of $0.9\mathrm{kW}/{\mathrm{cm}}^2$. For a lower power of $0.07\mathrm{kW}/{\mathrm{cm}}^2$, the obtained lifetime has a value of $1.9\mathrm{ns}$ at 4 K. The demonstrated approach yielding the radiative lifetime from simple emission spectra will provide valuable inputs to improve the design and modeling of ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$-based devices.

We consider a quadpartite hybrid system that incorporates a microwave cavity, a yttrium-iron-garnet (YIG) magnetic sphere resonator, a mechanical resonator, and an $LC$ electrical resonator. The entanglement and the quantum steering properties of this quadpartite system are thoroughly investigated by considering practical parameters. The microwave cavity mode is directly coupled to the magnon, mechanical, and electrical modes via Kittel magnetostatics, radiation pressure, and adjustable capacitance of the $LC$ configuration, respectively. We demonstrate tripartite entanglement among different modes, including indirectly coupled modes (such as magnon entanglement with mechanical and $LC$ electrical modes) for operating temperatures up to 2 K. Furthermore, we observe the presence of asymmetric one-way steering, revealing that the mechanical oscillator and the $LC$ resonant modes can steer the indirectly coupled magnon mode (yet in one direction while steering is not possible in the backward direction). The integration of the four interacting modes provides a variety of controlling degrees of freedom and makes the proposed quadpartite system an attractive approach for a wide range of applications, including data processing and communication, sensing, and quantum technologies.

Converting the medium-emitting infrared field to the visible band is an effective image-detection method. We propose a comprehensive theory of image up-conversion under continuous optical pumping, and discuss the relationship between the experimental parameters and imaging field of view, resolution, quantum efficiency, and conversion bandwidth. Theoretical predictions are given based on numerical simulations, which show good agreement with experimental results. In particular, coherent and incoherent light illumination are studied separately and the advantages and disadvantages of their imaging performance are compared and analyzed. This work provides a detailed study of the up-conversion image detection performance of the system, which is of great value in guiding the design of the detection system and bringing it to practical applications.