Achromatic lenses are crucial to light focusing and imaging. However, conventional achromatic lenses are restricted by the Abbe diffraction limit. Although superresolution optical lenses have been demonstrated to overcome the limit, the correction of chromatic aberration in continuous broadband for superresolution lenses still remains challenging. To address this issue, we propose a generalized strategy of constructing a frequency-dependent phase profile of linear dispersion for achromatic superresolution focusing in a continuous broad bandwidth. Specifically, based on an arbitrary wavelength-independent discrete phase profile of a monochromatic superresolution lens optimized at a given single optical frequency, a frequency-dependent phase profile of an achromatic superresolution lens can be constructed as the sum of the given discrete phase profile and a linear dispersion phase term. Based on the proposed approach, broadband achromatic superresolution metalenses are designed and demonstrated in the terahertz regime. The proposed method can be applied to visible and infrared optical spectra, which could have promising potential in various superresolution-related applications.

The concept of photonic frequency-momentum ($\omega$-$q$) dispersion has been extensively studied in artificial dielectric structures such as photonic crystals and metamaterials. However, the $\omega$-$q$ dispersion of electrodynamic waves hosted in natural materials at the atomistic level is far less explored. Here, we develop a Maxwell Hamiltonian theory of matter combined with the quantum theory of atomistic polarization to obtain the electrodynamic dispersion of natural materials interacting with the photon field. We apply this theory to silicon and discover the existence of anomalous atomistic waves. These waves occur in the spectral region where propagating waves are conventionally forbidden in a macroscopic theory. Our findings demonstrate that natural media can host a variety of yet to be discovered waves with subnanometer effective wavelengths in the picophotonics regime.

Any architecture for practical quantum computing must be scalable. An attractive approach is to create multiple cores, computing regions of fixed size that are well spaced but interlinked with communication channels. This exploded architecture can relax the demands associated with a single monolithic device: the complexity of control, cooling and power infrastructure, as well as the difficulties of crosstalk suppression and near-perfect component yield. Here we explore interlinked multicore architectures through analytic and numerical modeling. While elements of our analysis are relevant to diverse platforms, our focus is on semiconductor electron spin systems in which numerous cores may exist on a single chip within a single fridge. We model shuttling and microwave-based interlinks and estimate the achievable fidelities, finding values that are encouraging but markedly inferior to intracore operations. We therefore introduce optimized entanglement purification to enable high-fidelity communication, finding that $99.5\mathrm{\%}$ is a very realistic goal. We then assess the prospects for quantum advantage using such devices in the noisy intermediate-scale quantum era and beyond: we simulate recently proposed exponentially powerful error mitigation schemes in the multicore environment and conclude that these techniques impressively suppress imperfections in both the inter- and intracore operations.

Nonlinear Cherenkov radiation, an intriguing noncollinear optical parametric process with versatile longitudinal phase matching, is commonly realized in engineered nonlinear photonic structures. Here, we report on the observation of ultrabroadband rainbow Cherenkov second-harmonic generation (UBR CSHG) in a single periodically poled lithium niobate (PPLN) nonlinear crystal driven by a near-infrared high-peak-power ultrashort femtosecond pump laser. Multiple colored nonlinear radiation bands along the direction of Cherenkov conical angles are simultaneously exhibited, leading to a beautifully colorful rainbow picture never reported before. We systematically analyze the multicolor spectral characteristics of the UBR CSHG in the whole conical direction and explicitly clarify their phase-matching conditions. We show that this UBR CSHG interaction is subject to remarkable spectral broadening owing to both the third-order nonlinearity effect induced by the high-peak-power ultrashort pump laser and the reciprocal lattice vector of the PPLN crystal, which eventually enables the generation of three bright dominating colors—red, orange-yellow, and green bands—and their automatic dispersion in space. The experimental results suggest rich physics of nonlinear optical interactions and indicate the possibility to engineer broadband nonlinear frequency conversion for applications in compact colored laser sources and others.

We present results of in situ optical detection of ultrasonic waves generated in stainless steel and graphite samples mounted in a flat plate model during hypersonic flow in the 31-Inch Mach 10 wind tunnel at NASA Langley Research Center. Longitudinal waves are excited in the stainless steel and graphite sample inserts by using a contact piezoelectric transducer and the normal displacement on the surface of the sample, exposed to hypersonic fluid flow, is measured optically using a Sagnac interferometer. Measurements are consistent at different Reynolds numbers both with and without a turbulent trip strip present. Additionally, optical detection of laser-generated surface acoustic waves in a stainless-steel sample during flow is presented. These results are a demonstration of laser-based ultrasonics as an in situ material characterization technique in hypersonic flow, enabling potential applications of in situ monitoring of defect initialization and morphology in hypersonic environments.

Soft materials that respond to external stimuli, such as moisture, heat, and light, can convert the environmental energy into mechanical motions, and thus can be considered engines. The energy-conversion process within the soft-materials-based engines is fundamentally different from that of conventional heat engines utilizing gaseous media, but has been rarely studied to date. Here we construct a theoretical framework to analyze the thermodynamic performance of humidity-responsive soft actuators, as a canonical model of soft engines, which operate in a similar manner to such motile plants as wild wheat seeds and pine cones. Considering the free-energy change and the work generation through a four-process cycle, we define a work ratio as the work of actual engines relative to that of a so-called hygro-Carnot cycle going through reversible changes of volume and chemical energy. We propose an explanation why natural motile plants exhibit higher work ratios than common artificial hygroscopic actuators based on the time scales of soft actuation and the environmental humidity change. Our thermodynamic model can be extended to a range of soft engines driven by diffusion of stimulus, e.g., solvent, heat, and ions, into soft media.

We propose and analyze a nonunitary variant of the continuous time Grover search algorithm based on frequent Zeno-type measurements. We show that the algorithm scales similarly to the pure quantum version by deriving tight analytical lower bounds on its efficiency for arbitrary database sizes and measurement parameters. We also study the behavior of the algorithm subject to noise, and find that under certain oracle and operational errors our measurement-based algorithm outperforms the standard algorithm, showing robustness against these noises. Our analysis is based on deriving a non-Hermitian effective description of the algorithm, which yields a deeper insight into components responsible for the quantum and the classical operation of the protocol.

Developing schemes for efficient and broadband frequency conversion of quantum signals is an ongoing challenge in the field of modern quantum information. The coherent conversion between microwave and optical signals is an especially important milestone towards long-distance quantum communication. In this work, we propose a two-stage conversion protocol, employing a resonant interaction between magnetic and mechanical excitations as a mediator between microwave and optical photons. Based on estimates for the coupling strengths under optimized conditions for yttrium iron garnet, we predict close to unity conversion efficiency without the requirement of matching cooperativities. We predict a conversion bandwidth in the regions of largest efficiency of the order of magnitude of the coupling strengths that can be further increased at the expense of reduced conversion efficiency.

Simple and smart directional transport of impacting droplets is of great significance for future life and industry, but there are still many challenges due to complex hydrodynamics. Inspired by Setaria viridis leaves, we propose an efficient strategy to manipulate the split and transport of impacting droplets based on the simple design of liquid-repellent surfaces decorated with a ridge, and we report the large-scale, high-speed, and fast-response bidirectional transport of split droplets. Upon impacting on a wirelike ridge, the droplet splits into two parts, which have considerable horizontal transport velocity up to 34% of the initial impact velocity. The transport distance can exceed 1 order of magnitude longer than the droplet size and the response time is reduced by 50% compared to the contact time on flat surfaces. The splitting of the impacting droplet is the precondition for this bidirectional movement, and the time required for splitting strongly correlates to the horizontal transport velocity. A model is developed to accurately predict the splitting time, and a scaling law is proposed to illustrate the quantitative relationship between the horizontal transport velocity and impact parameters. These findings provide a route for using macrostructures to achieve precise droplet manipulation for diverse applications, such as anti-icing and chemical detection.

Electric fields arising from the distribution of charge in metal-halide perovskite solar cells are critical for understanding the many weird and wonderful optoelectronic properties displayed by these devices. Mobile ionic defects are thought to accumulate at interfaces to screen electric fields within the bulk of the perovskite semiconductor on application of external bias, but tools are needed to directly probe the dynamics of this process. Here, we show that electroabsorption measurements allow the electric field within the active layer to be tracked as a function of frequency or time. The magnitude of the electroabsorption signal, corresponding to the strength of the electric field in the perovskite layer, falls off for externally applied low-frequency voltages or at long times following voltage steps. Our observations are consistent with drift-diffusion simulations, impedance spectroscopy, and transient photocurrent measurements. They indicate charge redistribution on timescales ranging from 10 ms to 100 s, depending on the device interlayer material, perovskite composition, dominant charged defect, and illumination conditions. The method can be used on typical solar-cell structures and has the potential to become a routine characterization tool for optimizing hybrid perovskite devices.

We report pseudospin-dependent hybrid topological acoustic metamaterials constructed from tunable acoustic metamaterials and honeycomb-latticed sonic crystals. Using a theoretical model analogous to electrostatic interactions, we provide an efficient approach to evaluate intra- and interlattice couplings, whose competition is the major physical reason arousing the quantum spin Hall effect. The intralattice coupling is from the intrinsic design of the acoustic metamaterial, and the interlattice coupling is affected by multiple scattering among periodic scatterers. By independently manipulating the acoustic metamaterial and sonic crystal, we can successfully induce topological phase transitions at will. An alternative type of topological material is thus realized with great tunability. With identical building blocks for all hybrid topological acoustic metamaterials, a simple tuning of the corotation angle of each acoustic metamaterial can directly induce a topological phase transition, which makes the reconfiguration of the topological domains very convenient. A tunable multiport acoustic power divider is designed and demonstrated using numerical simulations and experiments. An alternative method to control the transmission rate and direction is thus reached and alternative routes for designing hybrid topological acoustic metamaterials with different functionalities and versatile applications are thus paved.

Topological crystalline insulators (TCIs) capable of supporting topological states protected by spatial symmetries have given rise to a promising platform for wave manipulation due to their robustness. Unfortunately, the methods to control the group velocity of topological states in classical wave systems are rarely discussed, which is an important issue in practical applications. In this work, we propose a method to change the frequency and propagation speed of topological edge states through on-site potential and realize a prototype of topological rainbow concentrator in a resonant acoustic system at subwavelength, which can separate different frequency components of propagating sound waves. The concepts of classical wave systems are combined with condensed matter physics, and the rigorous correspondence of TCIs and their analogs in acoustic resonant systems is demonstrated to design topological acoustic devices. Further, the implementation of controlling the group velocity of topological states precisely in a two-dimensional Su-Schrieffer-Heeger model is presented in detail, which can be extended to other TCI models and higher dimensions. We hope this work will enlarge possible applications of topological phenomena and the manufacture of acoustic devices.

We propose a free-space, inverse design of a nanostructure’s effective mode-matching fields via a backward propagation of tightly focused vector beams to the pupil plane of an aplanatic system of high numerical aperture. First, we study the nanostructure’s eigenmodes without considering any excitation fields and then extract the modal near fields in the focal plane. Each modal field is then taken as the desired focal field, the band-limited waves of which are backward propagated to the pupil plane via a reversal of the Richards-Wolf vector diffraction formula. The pupil fields can be designed to be genuinely paraxial by associating the longitudinal electric or magnetic field component with the radial one on the reference sphere. The inversely designed pupil field in turn is propagated forwardly into the focal region to generate the designed focal field, whose distribution over the nanostructure’s surface is used to evaluate the overlap between the designed focal field and the modal fields, i.e., the modal expansion coefficients. Studies for a silicon nanodisk monomer, dimer, and tetramer demonstrate the ability of our inverse approach to design the necessary tightly focused vector field that can effectively and exclusively match a certain eigenmode of interest. Compared with the forward beam-shaping method, the inverse design approach tends to yield quantitatively more precise mode-matching field profiles. This work can have a significant impact on optical applications that rely on controllable and tunable mode excitation and light scattering.

To detect a specific radio-frequency (rf) magnetic field, rf optically pumped magnetometers (OPMs) require a static magnetic field to set the Larmor frequency of the atoms equal to the frequency of interest. However, unshielded and variable magnetic field environments (e.g., an rf OPM on a moving platform) pose a problem for rf OPM operation. Here, we demonstrate the use of a natural-abundance rubidium vapor to make a comagnetometer to address this challenge. Our implementation builds upon the simultaneous application of several OPM techniques within the same vapor cell. First, we use a modified implementation of an OPM variometer based on ${}^{87}$$\mathrm{Rb}$ to detect and actively cancel unwanted external fields at frequencies $⪅60\mathrm{Hz}$ using active feedback to a set of field control coils. We exploit this stabilized field environment to implement a high-sensitivity rf magnetometer using ${}^{85}$$\mathrm{Rb}$. Using this approach, we demonstrate the ability to measure rf fields with a sensitivity of approximately $9\mathrm{fT}{\mathrm{Hz}}^{-1/2}$ inside a magnetic shield in the presence of an applied field of approximately $20\mu \mathrm{T}$ along three mutually orthogonal directions. This demonstration opens up a path toward completely unshielded operation of a high-sensitivity rf OPM.

Laser-driven ion acceleration is an attractive technique to generate compact high-energy ion sources. Currently, among various physical and technical issues to be solved, boosting the ion energy and reducing the energy spread represent the key challenges with this technique. Here we present a scheme to tackle these challenges by using a hundred-terawatt-class laser pulse irradiating a cone target. Three-dimensional particle-in-cell simulations show that a large number of electrons are dragged out of the cone walls and accelerated to hundreds of MeV by the laser fields inside the cone. When these energetic dense electron beams pass through the cone target tip into vacuum, a very high bunching acceleration field, up to tens of TV/m, quickly forms. Protons are accelerated and simultaneously bunched by this field, resulting in quasimonoenergetic proton beams with 100 MeV energy and low energy spread of about 2%. Results exploring the scaling of the proton beam energy with laser and target parameters are presented, indicating that the scheme is robust. This opens an efficient route for compact high-energy proton sources for fundamental research and biomedical applications.

Recently, higher-order topological insulators with both gapped edge states and in-gap corner states, have been simulated and observed. However, multiple higher-order extensible topological states have not yet been witnessed. Here, we fabricate two acoustic samples, each consisting of double sandwichlike heterostructures, a sonic crystal with a gapless state is inset between two sonic crystals with opposite topological phases in each heterostructure. We theoretically simulate and experimentally obtain the higher-order extensible topological states, which are induced by the Jackiw-Rebbi mechanism, and also demonstrate the robustness of the higher-order extensible topological states via experiment and numerical simulations. The distributions of the pressure fields of the higher-order extensible topological states localized within a certain range of the vertical direction, rather than at a corner, and decay exponentially in the horizontal direction. At the same time, by adjusting the number of layers of the middle sonic crystal in the double acoustic sandwichlike structures, we witness the multiple higher-order extensible topological states protected by band topology. Although the width of the middle sonic crystal is limited by the size of the sample, we provide a feasible solution for different energy harvesting, and enrich the understanding of higher-order topological states.