Off-axis vortex beams are generated by superposing a Gaussian beam onto a symmetric optical vortex beam of unit topological charge in a single-path interferometer with a control of their relative intensities and phases. The radial displacement of the point vortex from the center of the beam is controlled by varying the relative intensity of the superposed beams, while the azimuthal displacement of the vortex is controlled by the phase difference between the superposed beams. This phase difference is employed through the Pancharatnam-Berry geometric phase by different cyclic evolutions of the polarization states of the superposed beams on the Poincaré sphere. Interferometric field reconstruction of the resultant beams from experiment, simulation, and numerical calculations are used to obtain the transverse linear momentum density. The net transverse linear momentum vector and the resulting extrinsic orbital angular momentum in an off-axis vortex beam is demonstrated to be related to the radial and azimuthal position of the vortex across the beam. Controlling the Pancharatnam-Berry geometric phase and intensity ratio of the component beams is thus proposed as an effective and robust technique to tune the extrinsic orbital angular momentum of off-axis vortex beams. The presented results can be useful in applications ranging from optical manipulation of trapped microparticles, controlling micromachines using light with orbital angular momentum to enabling more flexibility in superresolution microscopy and controlled asymmetric interaction of light with atom, molecule, and Bose-Einstein condensate.

The possibility of making an object invisible for detectors has become a topic of considerable interest over the past decades. Most of the studies so far focused on reducing the visibility by reshaping the electromagnetic scattering in the spatial domain. In fact, by manipulating the electromagnetic scattering in the time domain, the visibility of an object can also be reduced. Importantly, unlike previous studies on phase-switched screens and time-varying metasurfaces, where the effect is narrow band due to the dispersive resonance, for microwave frequency range, we introduce a broadband switchable metasurface integrated with $p$-$i$-$n$ diodes. The reflection phase of the metasurface can be changed by approximately $\pi$ over a fractional bandwidth of $76\mathrm{\%}$. By modulating the metasurface quasirandomly in the time domain, the incident narrow-band signal is spread into a white-noiselike spectrum upon reflection, creating a spectral camouflage. The broadband feature of the proposed time-varying metasurface can provide practical insight for various applications, including radar stealth and ultrawide-band wireless communication.

Nonlinear processes in the quantum regime are essential for many applications, such as quantum-limited amplification, measurement, and control of quantum systems. In particular, the field of quantum error correction relies heavily on high-order nonlinear interactions between various modes of a quantum system. However, the required order of nonlinearity is often not directly available or weak compared to dissipation present in the system. Here, we experimentally demonstrate a route to obtain higher-order nonlinearity by combining more easily available lower-order nonlinear processes, using a generalization of the Raman transition. In particular, we show a transformation of four photons of a high-$Q$ superconducting resonator into two excitations of a superconducting transmon mode and two pump photons, and vice versa. The resulting eight-wave mixing process is obtained by cascading two fourth-order nonlinear processes through a virtual state. We expect this type of process to become a key component of hardware-efficient quantum error correction using continuous-variable error-correction codes.

Conventional impurity doping of deeply nanoscale silicon (dns-$\mathrm{Si}$) used in ultra-large-scale integration (ULSI) faces serious challenges below the 14-nm technology node. We report on a fundamental effect in theory and experiment, namely the electronic structure of dns-$\mathrm{Si}$ experiencing energy offsets of approximately 1 eV as a function of ${\mathrm{Si}\mathrm{O}}_2$ versus ${\mathrm{Si}}_3{\mathrm{N}}_4$ embedding with a few monolayers (MLs). An interface charge transfer (ICT) from dns-$\mathrm{Si}$ specific to the anion type of the dielectric is at the core of this effect and is arguably nested in the quantum-chemical properties of oxygen ($\mathrm{O}$) and nitrogen ($\mathrm{N}$) versus $\mathrm{Si}$. We investigate the size up to which this energy offset defines the electronic structure of dns-$\mathrm{Si}$ by density-functional theory (DFT), considering the interface orientation, the embedding-layer thickness, and approximants featuring two $\mathrm{Si}$ nanocrystals (NCs), one embedded in ${\mathrm{Si}\mathrm{O}}_2$ and the other in ${\mathrm{Si}}_3{\mathrm{N}}_4$. Working with synchrotron ultraviolet- (UV) photoelectron spectroscopy (UPS), we use ${\mathrm{Si}\mathrm{O}}_2$- versus ${\mathrm{Si}}_3{\mathrm{N}}_4$-embedded $\mathrm{Si}$ nanowells (NWells) to obtain their energy of the top valence-band states. These results confirm our theoretical findings and gauge an analytic model for projecting maximum dns-$\mathrm{Si}$ sizes for NCs, nanowires (NWires), and NWells where the energy offset reaches full scale, yielding a clear preference for electrons or holes as majority carriers in dns-$\mathrm{Si}$. Our findings can replace impurity doping for $n$- or $p$-type dns-$\mathrm{Si}$ as used in ultra-low-power electronics and ULSI, eliminating dopant-related issues such as inelastic carrier scattering, thermal ionization, clustering, out-diffusion, and defect generation. As far as majority-carrier preference is concerned, the elimination of those issues effectively shifts the lower size limit of $\mathrm{Si}$-based ULSI devices to the crystallization limit of $\mathrm{Si}$ of approximately 1.5 nm and also enables them to work under cryogenic conditions.

Phase transitions of condensed matter have long been a spotlight issue studied by extensive theoretical and experimental investigations. Machine learning can build an integral model-dominant workflow to statistically analyze the collective dynamics of materials and deduce the structure. We use a support-vector-machine algorithm to propose an effective method to recognize the orthorhombic, tetragonal, and cubic phases as well as to construct the phase diagram in ferroelectric crystals by mining and learning the behavioral vectors of the phonon vibrations in a crystalline lattice from Raman scattering, which is a tool typically used to detect structural properties at the molecular level. This study creates a unifying framework including material synthesis and characterization, feature engineering and principal-component analysis, learner evaluation and optimization, structure prediction, and future development of the model. It paves the way to the application of a generic approach for predicting unexplored structures and materials in the future.

Asymmetric wave manipulation has attracted growing interest due to its great importance in practical applications. We design and demonstrate a planar acoustic metamirror for realizing asymmetric sound absorption with a controllable retroreflection coefficient, which is absent in conventional lossless metasurfaces. We design the metamirror by realizing the required theoretical surface impedance profile, and then numerically and experimentally demonstrate its asymmetric response. The measured and simulated acoustic fields agree well with each other, which shows that the proposed metamirror can yield strongly asymmetric sound absorption: retroreflection and nearly full absorption for two opposite incident angles. In addition, the measured retroreflection coefficient and retroreflection angle are very close to the design values. We find that the asymmetrical excitation of evanescent waves plays a key role in the realization of asymmetric absorption. The proposed metamirror enriches the functionalities for acoustic wave manipulation and has prospective applications in many fields, such as acoustic antennas, acoustic sensing, and angle-encoded steganography.

Graph states and hypergraph states are of wide interest in quantum information processing and foundational studies. Efficient verification of these states is a key to various applications. Here we propose a simple method for verifying hypergraph states, which requires only two distinct Pauli measurements for each party, yet its efficiency is comparable to the best strategy based on entangling measurements. For a given state, the overhead is bounded by the chromatic number and degree of the underlying hypergraph. Our protocol is dramatically more efficient than all previous protocols based on local measurements, including tomography and direct-fidelity estimation. It enables the verification of hypergraph states and genuine multipartite entanglement of thousands of qubits. The protocol can also be generalized to the adversarial scenario, while achieving almost the same efficiency. This merit is particularly appealing to demonstrating blind measurement-based quantum computation and quantum supremacy.

We introduce a conceptual design of a free-space thin-sheet isolator with an unlimited aperture and the possibility of a broadband omnidirectional rejection of the backward-propagating light. The proposed design involves a multilayered resonant cavity incorporating subwavelength magnetic layers, dichroic nanolayers, and an optional metallic nanolayer. The cavity resonance enhances the Faraday rotation produced by the subwavelength magnetic layers, while providing nearly total absorption of the backward-propagating light by the dichroic nanolayers. The latter is a necessary and the most challenging condition for a thin-sheet isolator with an unlimited aperture to function. The (optional) metallic nanolayer provides rejection of the obliquely incident light, which otherwise would be partially transmitted in either direction. Our numerical simulations and quasioptical measurements at millimeter-wave frequencies illustrate how the key elements of the layered-sheet isolator work. Our approach can be scaled down to long- and midinfrared wavelengths.

This Paper introduces analyzing and modeling dual silicon-oxy-nitride [${\mathrm{Si}\mathrm{O}}_x{\mathrm{N}}_y$] racetrack resonators (RRs) for biosensing applications. The geometric configuration of the resonators and design of alternative small sensing windows result in the realization of optical biosensors with a highly improved intrinsic limit of detection (ILOD). A small sensing window, located above the coupling region of dual RRs, can be used to maximize the total quality factor (minimized ILOD). The best characteristics for each optical component in the parallel-coupled RR-based biosensors are single-mode-channel waveguides with dimensions of $35\times 1\mu {\mathrm{m}}^2$; the radius of curvature $90\mu \mathrm{m}$ and quality factors up to approximately $5.53\times {10}^6$ for RRs. The biosensing performance of our proposed configuration is compared with other experimental and simulated biosensor devices. Our structure shows an ILOD of approximately $1.81\times {10}^{-6}$ refractive index units (r.i.u.), which significantly improved 100 times compared with the traditional single ${\mathrm{Si}\mathrm{O}}_x{\mathrm{N}}_y$ RR biosensor. This ultra-improved ILOD parameter is found in the dynamic refractive index range of 1.332–1.350 r.i.u. It shows that the proposed biosensor could be a promising diagnostic candidate for analyzing different components of blood samples, which is especially important in the early detection of some critical diseases such as prostate cancer.

High-quality epitaxial ferrites, such as low-damping $\mathrm{Mg}\mathrm{Al}$-ferrite (MAFO), are promising nanoscale building blocks for all-oxide heterostructures driven by pure spin current. However, the impact of oxide interfaces on spin dynamics in such heterostructures remains an open question. Here, we investigate the spin dynamics and chemical and magnetic depth profiles of 15-nm-thick MAFO coherently interfaced with an isostructural 1–8-nm-thick overlayer of paramagnetic ${\mathrm{Co}\mathrm{Cr}}_2{\mathrm{O}}_4$ (CCO) as an all-oxide model system. Compared to MAFO without an overlayer, effective Gilbert damping in MAFO/CCO is enhanced by a factor of $>3$, irrespective of the CCO overlayer thickness. We attribute this damping enhancement to spin scattering at the approximately 1-nm-thick chemically disordered layer at the MAFO-CCO interface, rather than spin pumping or proximity-induced magnetism. Our results indicate that damping in ferrite-based heterostructures is strongly influenced by interfacial chemical disorder, even if the thickness of the disordered layer is a small fraction of the ferrite thickness.

We experimentally demonstrate the ability of a nonlinear self-channeling beam to resist turbulence-induced spreading and scintillation. Spatio-temporal data is presented for an 850-m long, controlled turbulence range that can generate weak to strong turbulence on demand. At this range, the effects of atmospheric losses and dispersion are significant. Simulation results are also presented and show good agreement with experiment.

The simple quantum setup of a Fabry-Perot interferometer is found to exhibit very high directional preference to impinging particle beams, with use of realistic media. Numerous optimized designs, acting as extremely sharp angular filters of matter waves, are determined by trying and testing every single combination of actual materials picked from a long list. Two types of resonances are identified whose different mechanisms are demonstrated through the spatial distribution of wave-function magnitude and probability current, while their robustness with respect to fabrication defects is also examined. Such findings offer additional degrees of freedom when designing architectures for a broad range of quantum-engineering applications that involve beam tunneling and provide a set of limits for the angular selectivity that can be achieved with the considered geometry.

One long-term goal of phononic communications is to achieve the controlled transport of elastic wave signals with enhanced information capacity and improved robustness, which is still challenging given the complexity of elastic waves in terms of vectorial movement and multiple polarizations. Here, we present our theoretical and experimental study of the robust transport of elastic wave signals along interfaces between distinct topological phases. These topological edge states are robust against defects and disorders because they are jointly protected by both pseudospin and valley degrees of freedom (DOFs); thus naturally providing doubled information carriers within a single channel. A topology-based beam splitter is experimentally demonstrated, where the signal's propagation path is uniquely determined and topologically protected. Edge states between distinct topological phases not only offer a route towards new topological phenomena, but also open up an avenue for the design of high-capacity and robust phononic communication devices through discrete DOF multiplexing.

While wired-power-transfer devices ensure robust power delivery even if the receiver position or load impedance changes, achieving the robustness of wireless power transfer (WPT) is challenging. Conventional solutions are based on additional control circuits for dynamic tuning. Here we propose a robust WPT system in which no additional tuning circuitry is required for robust operation. This is achieved by our systematically designing the load and the coupling link to be parts of the feedback circuit. Therefore, the WPT operation is automatically adjusted to the optimal working condition under a wide range of load and receiver positions. In addition, pulsed oscillations instead of single-harmonic oscillation are adopted to increase the overall efficiency. An example system is designed with use of a capacitive coupling link. It realizes a virtual, nearly-ideal oscillating voltage source at the load site, giving efficient power transfer comparable to that of the ideal wired-connection scenario. We numerically and experimentally verify the robustness of the WPT system under the variations of load and coupling, where coupling is changing by our varying the alignment of aluminum plates. The working frequency and the transferred power agree well with analytical models. The proposed paradigm can have a significant impact on future high-performance WPT devices. The designed system can also work as a smart table supporting multiple receivers with robust and efficient operation.

Coupling-enabled frequency synchronization is essential for an array of light sources operating in a photonic system. Using a two-dimensional nonlinear oscillator model of a laser, we analyze the role of two distinct types of coupling, dispersive and dissipative, in promoting frequency locking between two nonidentical lasers. In both scenarios the two oscillators synchronize into a frequency-locked state when the coupling level exceeds a critical value. We show that the onset of dispersive and dissipative synchronization processes is associated with hard and soft frequency transitions, respectively. Through analysis and numerics, we demonstrate that the dispersive coupling yields bistable synchronization modes, accompanied by asymmetric intensities, and the frequency controlled by the coupling strength. In contrast, dissipative coupling induces monostable synchronization with symmetric intensities and a coupling-independent frequency. Our results are expected to provide a basis for understanding the coupling mechanisms of frequency locking toward controlling synchronization in laser arrays.

We investigate, both theoretically and experimentally, the drift, diffusion, and recombination of excitons in the strain field of an edge threading dislocation intersecting the $\mathrm{Ga}\mathrm{N}${0001} surface. We calculate and measure hyperspectral cathodoluminescence maps around the dislocation outcrop for temperatures between 10 and 200 K. Contrary to common belief, the cathodoluminescence intensity contrast is only weakly affected by exciton diffusion but is caused primarily by exciton dissociation in the piezoelectric field at the dislocation outcrop. Hence, the extension of the dark spots around dislocations in the luminescence maps cannot be used to determine the exciton diffusion length. However, the cathodoluminescence energy contrast, which reflects the local band-gap variation in the dislocation strain field, does sensitively depend on the exciton diffusion length and hence enables its experimental determination.

Radiant energy-flow control and privacy control are two important features for smart windows (or glass). Current smart window technologies can, however, only control one of them: radiant energy flow or privacy. Therefore, a dual-mode smart window is highly desirable. Here, we report a dual-mode switchable liquid-crystal window that can control both radiant energy flow and privacy. The switchable liquid-crystal window makes use of dielectric and flexoelectric effects. In the absence of an applied voltage, the window is clear and transparent, and radiant energy can flow through it and the scenery behind the window can be seen. When a low-frequency (50 Hz) voltage is applied, the window is switched to an optical scattering and absorbing state by a flexoelectric effect, and thus, privacy is protected. When a high-frequency (1 kHz) voltage is applied, the window is switched to an optical absorbing but nonscattering state through a dielectric effect, and thus, radiant energy flow is controlled.

We propose a p-n junction diode based on the adsorption of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) molecules on a monolayer of boron phosphide (MBP). We use density functional theory and a simple tight-binding model to investigate atomic configuration, electronic properties, and transport characteristics of the TCNQ/MBP/TTF structure. The p-n mechanism is achieved by the full coverage of MBP with TCNQ and TTF molecules, which are coupled by weak van der Waals forces. The adsorption of each individual molecule on MBP provides localized electronic states close to the valence and conduction bands; this is characteristic of p- and n-type semiconductors. To understand the charge-carrier dynamics, we also examine the evaluation of energy bands, together with localized states, local potential, charge redistribution, and charge transfer under the influence of an external electric field. Our results show that the adsorption of both molecules on the surfaces of MBP results in the behavior of a p-n junction with a rectifying current through the junction in the proposed van der Waals device. Moreover, the optical response to electromagnetic radiation is also analyzed through density functional theory by considering the independent-particle approximation. We show that, with a remarkable absorption band in the infrared region, TCNQ/MBP/TTF is a potential candidate as a component of next-generation optoelectronic devices.

The successful testing of non-Abelian statistics not only serves as a milestone in fundamental physics but also provides a quantum-gate operation in topological quantum computation. An accurate and efficient readout scheme of a topological qubit is an essential step toward the experimental confirmation of non-Abelian statistics. In the current work, we propose a protocol to read out the quantum state of a Majorana vortex qubit on a topological superconductor island. The protocol consists of four Majorana zero modes trapped in spatially well-separated vortex cores on the two-dimensional surface of a Coulomb blockaded topological superconductor. Our proposed measurement is implemented by a pair of weakly coupled Majorana modes separately in touch with two normal-metal leads and the readout is realized by observing the conductance-peak location in terms of the gate voltage. Using this protocol, we can further test the non-Abelian statistics of Majorana zero modes in the two-dimensional platform. A successful readout of a Majorana qubit is a crucial step toward the future application of topological quantum computation. In addition, this Coulomb-blockaded setup can distinguish Majorana zero modes from Caroli–de Gennes–Matricon modes in vortex cores.

We present a simple protocol for which Alice and Bob must only decide to either send out a coherent state or not send out a coherent state to Charlie. No switching of bases occurs. We demonstrate that this protocol is both source-state side-channel free and measurement-device independent. We do not have to exactly control the whole space of the state of the light pulse, which is an impossible task in practice. The protocol is immune to all adverse effects caused by quantum-state imperfections in the side-channel space, such as the photon frequency spectrum, emission time, propagation direction, spatial angular momentum, and so on. Numerical simulation shows that our scheme can reach a side-channel-free result for quantum key distribution over distances exceeding 200 km, given the single-photon interference-misalignment error rate of 20%.