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Metalenses have emerged as a new optical element or system in recent years, showing superior performance and abundant applications. However, the phase distribution of a metalens has not been measured directly up to now, hindering further quantitative evaluation of its performance. We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern. Based on the measured phase distribution, we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses. Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment. Furthermore, through phase distribution analysis, it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture, even though the metalens is ideal without any fabrication error. We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens. Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process, which will pave the way for metalenses in industrial applications.

Light and sound are the most ubiquitous forms of waves, associated with a variety of phenomena and physical effects such as rainbows and echoes. Light and sound, both categorized as classical waves, have lately been brought into unexpected connections with exotic topological phases of matter. We are currently witnessing the onset of a second wave of active research into this topic. The past decade has been marked by fundamental advances comprising two-dimensional quantum Hall insulators and quantum spin and valley Hall insulators, whose topological properties are characterized using linear band topology. Here, going beyond these conventional topological systems, we focus on the latest frontiers, including non-Hermitian, nonlinear and non-Abelian topology as well as topological defects, for which the characterization of the topological features goes beyond the standard band-topology language. In addition to an overview of the current state of the art, we also survey future research directions for valuable applications. The current state of the art of topological phenomena in photonics and acoustics is reviewed and future research directions for valuable applications are discussed.

Non-Abelian braiding is regarded as an essential process for realizing quantum logic. Its realizations in quantum systems often rely on the dynamic winding of anyons, which can be challenging to obtain. Implementing braiding in a classical system could, therefore, assist the experimental study of non-Abelian physics. Here we present the realization of the non-Abelian braiding of multiple degenerate acoustic waveguide modes. The dynamics of non-Abelian braiding can be captured by the non-Abelian Berry–Wilczek–Zee phase that connects the holonomic adiabatic evolutions of multiple degenerate states. The cyclic evolution of degenerate states induces a non-Abelian geometric phase, manifesting as the exchange of states. The non-Abelian characteristics are revealed by switching the order of two distinct braiding processes involving three modes. Our work demonstrates wave manipulations based on non-Abelian braiding and logic operations. Although it shows promise for applications, non-Abelian braiding is difficult to realize in electronic systems. Its demonstration using acoustic waveguides may provide a useful platform to study non-Abelian physics.

Non-Abelian braiding has attracted substantial attention because of its pivotal role in describing the exchange behaviour of anyons—candidates for realizing quantum logics. The input and outcome of non-Abelian braiding are connected by a unitary matrix that can also physically emerge as a geometric-phase matrix in classical systems. Hence it is predicted that non-Abelian braiding should have analogues in photonics, although a feasible platform and the experimental realization remain out of reach. Here we propose and experimentally realize an on-chip photonic system that achieves the non-Abelian braiding of up to five photonic modes. The braiding is realized by controlling the multi-mode geometric-phase matrix in judiciously designed photonic waveguide arrays. The quintessential effect of braiding—sequence-dependent swapping of photon dwell sites—is observed in both classical-light and single-photon experiments. Our photonic chips are a versatile and expandable platform for studying non-Abelian physics, and we expect the results to motivate next-generation non-Abelian photonic devices.Non-Abelian braiding—a candidate for realizing quantum logics—is demonstrated by controlling the geometric-phase matrix in a photonic chip, and its key characteristics are observed.

The ongoing new coronavirus pneumonia (Corona Virus Disease 2019, COVID-19) outbreak is spreading in China, but it has not yet reached its peak. Five million people emigrated from Wuhan before lockdown, potentially representing a source of virus infection. Determining case distribution and its correlation with population emigration from Wuhan in the early stage of the epidemic is of great importance for early warning and for the prevention of future outbreaks. The official case report on the COVID-19 epidemic was collected as of January 30, 2020. Time and location information on COVID-19 cases was extracted and analyzed using ArcGIS and WinBUGS software. Data on population migration from Wuhan city and Hubei province were extracted from Baidu Qianxi, and their correlation with the number of cases was analyzed. The COVID-19 confirmed and death cases in Hubei province accounted for 59.91% (5806/9692) and 95.77% (204/213) of the total cases in China, respectively. Hot spot provinces included Sichuan and Yunnan, which are adjacent to Hubei. The time risk of Hubei province on the following day was 1.960 times that on the previous day. The number of cases in some cities was relatively low, but the time risk appeared to be continuously rising. The correlation coefficient between the provincial number of cases and emigration from Wuhan was up to 0.943. The lockdown of 17 cities in Hubei province and the implementation of nationwide control measures efficiently prevented an exponential growth in the number of cases. The population that emigrated from Wuhan was the main infection source in other cities and provinces. Some cities with a low number of cases showed a rapid increase in case load. Owing to the upcoming Spring Festival return wave, understanding the risk trends in different regions is crucial to ensure preparedness at both the individual and organization levels and to prevent new outbreaks.

Adult hippocampal neurogenesis plays a critical role in memory and emotion processing, and this process is dynamically regulated by neural circuit activity. However, it remains unknown whether manipulation of neural circuit activity can achieve sufficient neurogenic effects to modulate behavior. Here we report that chronic patterned optogenetic stimulation of supramammillary nucleus (SuM) neurons in the mouse hypothalamus robustly promotes neurogenesis at multiple stages, leading to increased production of neural stem cells and behaviorally relevant adult-born neurons (ABNs) with enhanced maturity. Functionally, selective manipulation of the activity of these SuM-promoted ABNs modulates memory retrieval and anxiety-like behaviors. Furthermore, we show that SuM neurons are highly responsive to environmental novelty (EN) and are required for EN-induced enhancement of neurogenesis. Moreover, SuM is required for ABN activity-dependent behavioral modulation under a novel environment. Our study identifies a key hypothalamic circuit that couples novelty signals to the production and maturation of ABNs, and highlights the activity-dependent contribution of circuit-modified ABNs in behavioral regulation.Li et al. report a key brain region in the hypothalamus that effectively modulates the production and properties of new neurons generated in adulthood. These hypothalamic modified new neurons are critical for memory and anxiety-like behavior.

Infrared photodetectors are currently subject to a rapidly expanding application space, with an increasing demand for compact, sensitive and inexpensive detectors. Despite continued advancement, technological factors limit the widespread usage of such detectors, specifically, the need for cooling and the high costs associated with processing of iii–v/ii–vi semiconductors. Here, black phosphorous (bP)/MoS2 heterojunction photodiodes are explored as mid-wave infrared (MWIR) detectors. Although previous studies have demonstrated photodiodes using bP, here we significantly improve the performance, showing that such devices can be competitive with conventional MWIR photodetectors. By optimizing the device structure and light management, we demonstrate a two-terminal device that achieves room-temperature external quantum efficiencies (ηe) of 35% and specific detectivities (D*) as high as 1.1 × 1010 cm Hz1/2 W−1 in the MWIR region. Furthermore, by leveraging the anisotropic optical properties of bP we demonstrate the first bias-selectable polarization-resolved photodetector that operates without the need for external optics.

We present a theoretical study and experimental realization of a system that is simultaneously a four-dimensional (4D) Chern insulator and a higher-order topological insulator. The system sustains the coexistence of (4-1)-dimensional chiral topological hypersurface modes (THMs) and (4-2)-dimensional chiral topological surface modes (TSMs). Our study reveals that the THMs are protected by second Chern numbers, and the TSMs are protected by a topological invariant composed of two first Chern numbers, each belonging to a Chern insulator existing in subdimensions. With the synthetic coordinates fixed, the THMs and TSMs, respectively, manifest as topological edge modes and topological corner modes (TCMs) in the real space, which are experimentally observed in a 2D acoustic lattice. These TCMs are not related to quantized polarizations, making them fundamentally distinctive from existing examples. We further show that our 4D topological system offers an effective way for the manipulation of the frequency, location, and number of TCMs, which is highly desirable for applications.

Zinc-ion batteries have demonstrated promising potential for future energy storage, whereas drawbacks, including dendrite growth, hydrogen evolution reaction, and localized deposition, heavily hinder their development for practical applications. Herein, unlike elaborated structural design and electrolyte excogitation, we introduce an effective parts-per-million (ppm)-scale electrolyte additive, phosphonoglycolic acid (PPGA), to overcome the intrinsic issues of zinc negative electrode in mild acidic aqueous electrolytes. Profiting from absorbed PPGA on zinc surface and its beneficial interaction with hydrogen bonds of adjacent water molecules, stable symmetric stripping/plating of zinc in aqueous ZnSO 4 electrolyte at around 25  o C was achieved, procuring 362 and 350 days of operation at 1 mA cm -2 , 1 mAh cm -2 and 10 mA cm -2 , 1 mAh cm -2 , respectively. As a proof-of-concept, an Ah-level Zn||Zn 0.25 V 2 O 5 ·nH 2 O pouch cell examined the validity of PPGA and sustained 250 cycles at 0.2 A g -1 and around 25 o C without capacity loss. The Zn||Br 2 redox flow battery demonstrated an operation of over 800 h at 40 mA cm -2 , 20 mAh cm -2 with an average coulombic efficiency of 98%, which is attributed to restrained dendrite growth and side effects. This work is believed to open up new ways forward for knowledge of electrolyte additive engineering. Challenges of zinc electrodes imped their progress in energy storage. Here, authors propose a parts-per-million scale electrolyte additive, phosphonoglycolic acid, enabling Zn stripping/stripping for nearly a year in coin cells, and exhibiting high durability in pouch cells and redox flow batteries.

ObjectivesPreoperative prediction of microvascular invasion (MVI) in patients with hepatocellular cancer (HCC) is important for surgery strategy making. We aimed to develop and validate a combined intratumoural and peritumoural radiomics model based on gadolinium-ethoxybenzyl-diethylenetriamine (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) for preoperative prediction of MVI in primary HCC patients.MethodsThis study included a training cohort of 110 HCC patients and a validating cohort of 50 HCC patients. All the patients underwent preoperative Gd-EOB-DTPA-enhanced MRI examination and curative hepatectomy. The volumes of interest (VOIs) around the hepatic lesions including intratumoural and peritumoural regions were manually delineated in the hepatobiliary phase of MRI images, from which quantitative features were extracted and analysed. In the training cohort, machine-learning method was applied for dimensionality reduction and selection of the extracted features.ResultsThe proportion of MVI-positive patients was 38.2% and 40.0% in the training and validation cohort, respectively. Supervised machine learning selected ten features to establish a predictive model for MVI. The area under the receiver operating characteristic curve (AUC), sensitivity, specificity of the combined intratumoural and peritumoural radiomics model in the training and validation cohort were 0.85 (95% confidence interval (CI), 0.77–0.93), 88.2%, 76.2%, and 0.83 (95% CI, 0.71–0.95), 90.0%, 75.0%, respectively.ConclusionsWe evaluate quantitative Gd-EOB-DTPA-enhanced MRI image features of both intratumoural and peritumoural regions and provide an effective radiomics-based model for the prediction of MVI in HCC patients, and may therefore help clinicians make precise decisions regarding treatment before the surgery.Key Points• An effective radiomics model for prediction of microvascular invasion in HCC patients is established.• The radiomics model is superior to the radiologist in prediction of MVI.• The radiomics model can help clinicians in pretreatment decision making.