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Interference in photons emitted from multiple atoms has been studied extensively. We show that a single atom can induce interference in its emitted light when tunnelling in a double-well potential coupled to an optical cavity. The phase in the cavity field interference can be modulated by the double-well spacing. By controlling the coherent tunnelling, blockade of single-photon excitations is found in the destructive interference regime, where super-Poissonian bunched light is generated. Furthermore, we show that the atomic flux of the coherent tunnelling motion generates chiral cavity fields. The direction of the chirality oscillates for many cycles before the decoherence of the atomic motion and the decay of the cavity photons. Our work opens new ways for manipulating photons with controllable quantum states of atoms for quantum information applications., 4 pages, 5 figures; SM: 6 pages, 2 figures

We investigate speeding up of relaxation of Markovian open quantum systems with the Liouvillian exceptional point (LEP), where the slowest decay mode degenerate with a faster decay mode. The degeneracy significantly increases the gap of the Liouvillian operator, which determines the timescale of such systems in converging to stationarity, and hence accelerates the relaxation process. We explore an experimentally relevant three level atomic system, whose eigenmatrices and eigenspectra are obtained completely analytically. This allows us to gain insights in the LEP and examine respective dynamics with details. We illustrate that the gap can be further widened through Floquet engineering, which further accelerates the relaxation process. Finally, we extend this approach to analyze laser cooling of trapped ions, where vibrations (phonons) couple to the electronic states. An optimal cooling condition is obtained analytically, which agrees with both existing experiments and numerical simulations. Our study provides analytical insights in understanding LEP, as well as in controlling and optimizing dissipative dynamics of atoms and trapped ions.

Trapped ions provide a platform for quantum technologies that offers long coherence times and high degrees of scalability and controllability. Here, we use this platform to develop a realistic model of a thermal device consisting of two laser-driven, strongly coupled Rydberg ions in a harmonic trap. We show that the translational degrees of freedom of this system can be utilized as a flywheel storing the work output that is generated by a cyclic thermodynamic process applied to its electronic degrees of freedom. Mimicking such a process through periodic variations of external control parameters, we use a mean-field approach underpinned by exact numerical and analytical calculations to identify relevant physical processes and to determine the charging rate of the flywheel. Our work paves the way for the design of microscopic thermal machines based on Rydberg ions that can be equipped with both many-body working media and universal work storages., 11 pages, 5 figures

Identifying high-quality webpages is fundamental for real-world search engines, which can fulfil users' information need with the less cognitive burden. Early studies of \emph{webpage quality assessment} usually design hand-crafted features that may only work on particular categories of webpages (e.g., shopping websites, medical websites). They can hardly be applied to real-world search engines that serve trillions of webpages with various types and purposes. In this paper, we propose a novel layout-aware webpage quality assessment model currently deployed in our search engine. Intuitively, layout is a universal and critical dimension for the quality assessment of different categories of webpages. Based on this, we directly employ the meta-data that describes a webpage, i.e., Document Object Model (DOM) tree, as the input of our model. The DOM tree data unifies the representation of webpages with different categories and purposes and indicates the layout of webpages. To assess webpage quality from complex DOM tree data, we propose a graph neural network (GNN) based method that extracts rich layout-aware information that implies webpage quality in an end-to-end manner. Moreover, we improve the GNN method with an attentive readout function, external web categories and a category-aware sampling method. We conduct rigorous offline and online experiments to show that our proposed solution is effective in real search engines, improving the overall usability and user experience., 10 pages, 5 figures

Multipartite entangled states involving non-locality are one of the most fascinating characteristics of quantum mechanics. In this work, we propose a generation of Schr\"{o}dinger cat states in Rydberg atom arrays against the thermal dephasing. Unlike the previous work for producing large-scale entanglement [A. Omran et al, Science 365, 570 (2019)], we encode logical 1 on dressed states rather than Rydberg states. Such treatment can increase the lifetime of multipartite entanglement coherence to around 3 times compared to the previous work [A. Omran et al, Science 365, 570 (2019)], at the same system size, and therefore induce solid fidelities of Schr\"{o}dinger cat states generation. The current work theoretically verifies the advantages of Rydberg dressed state in many-body quantum entanglement, which is meaningful for large-scale quantum computation and many-body Rydberg quantum simulation., Comment: 9 pages, 8 figures, 1 table

It is challenging to probe ergodicity breaking trends of a quantum many-body system when dissipation inevitably damages quantum coherence originated from coherent coupling and dispersive two-body interactions. Rydberg atoms provide a test bed to detect emergent exotic many-body phases and non-ergodic dynamics where the strong Rydberg atom interaction competes with and overtakes dissipative effects even at room temperature. Here we report experimental evidence of a transition from ergodic towards ergodic breaking dynamics in driven-dissipative Rydberg atomic gases. The broken ergodicity is featured by the long-time phase oscillation, which is attributed from the formation of Rydberg excitation clusters in limit cycle phases. The broken symmetry in the limit cycle is a direct manifestation of many-body interactions, which is verified by tuning atomic densities in our experiment. The reported result reveals that Rydberg many-body systems are a promising candidate to probe ergodicity breaking dynamics, such as limit cycles, and enable the benchmark of non-equilibrium phase transition.

Heterogeneous Graph Neural Networks (HGNNs) have gained significant popularity in various heterogeneous graph learning tasks. However, most HGNNs rely on spatial domain-based message passing and attention modules for information propagation and aggregation. These spatial-based HGNNs neglect the utilization of spectral graph convolutions, which are the foundation of Graph Convolutional Networks (GCN) on homogeneous graphs. Inspired by the effectiveness and scalability of spectral-based GNNs on homogeneous graphs, this paper explores the extension of spectral-based GNNs to heterogeneous graphs. We propose PSHGCN, a novel heterogeneous convolutional network based on positive noncommutative polynomials. PSHGCN provides a simple yet effective approach for learning spectral graph convolutions on heterogeneous graphs. Moreover, we demonstrate the rationale of PSHGCN in graph optimization. We conducted an extensive experimental study to show that PSHGCN can learn diverse spectral heterogeneous graph convolutions and achieve superior performance in node classification tasks. Our code is available at https://github.com/ivam-he/PSHGCN., Comment: 10 pages

Greenberger-Horne-Zeilinger and W states feature genuine tripartite entanglement that cannot be converted into each other by local operations and classical communication. Here, we present a dissipative protocol for deterministic interconversion between Greenberger-Horne-Zeilinger and W states of three neutral $^{87}$Rb atoms arranged in an equilateral triangle of a two-dimensional array. With three atomic levels and diagonal van der Waals interactions of Rydberg atoms, the interconversion between tripartite entangled states can be efficiently accomplished in the Floquet-Lindblad framework through the periodic optical pump and dissipation engineering. We evaluate the feasibility of the existing methodology using the experimental parameters accessible to current neutral-atom platforms. We find that our scheme is robust against typical noises, such as laser phase noise and geometric imperfections of the atom array. In addition, our scheme can integrate the Gaussian soft quantum control technique, which further reduces the overall conversion time and increases the resilience to timing errors and interatomic distance fluctuations. The high-fidelity and robust tripartite entanglement interconversion protocol provides a route to save physical resources and enhance the computational efficiency of quantum networks formed by neutral-atom arrays., Comment: 18 pages, 14 figures, accepted by Physical Review Applied

We propose a nontrivial two-qubit gate scheme in which Rydberg atoms are subject to designed pulses resulting from geometric evolution processes. By utilizing a hybrid robust non-adiabatic and adiabatic geometric operations on the control atom and target atom, respectively, we improve the robustness of two-qubit Rydberg gate against Rabi control errors as well as blockade errors in comparison with the conventional two-qubit blockade gate. Numerical results with the current state-of-the-art experimental parameters corroborates the above mentioned robustness. We also evaluated the influence induced by the motion-induced dephasing and the dipole-dipole interaction and imperfection excitation induced leakage errors, which both could decrease the gate fidelity. Our scheme provides a promising route towards systematic control error (Rabi error) as well as blockade error tolerant geometric quantum computation on neutral atom system., Comment: 14 pages, 13 figures, 2 tables. Accepted by Physical Review Applied

Multipartite entangled states involving non-locality are one of the most fascinating characteristics of quantum mechanics. In this work, we propose a generation of Schrödinger cat states in Rydberg atom arrays against the thermal dephasing. Unlike the previous work for producing large-scale entanglement [A. Omran et al, Science 365, 570 (2019)], we encode logical 1 on dressed states rather than Rydberg states. Such treatment can increase the lifetime of multipartite entanglement coherence to around 3 times compared to the previous work [A. Omran et al, Science 365, 570 (2019)], at the same system size, and therefore induce solid fidelities of Schrödinger cat states generation. The current work theoretically verifies the advantages of Rydberg dressed state in many-body quantum entanglement, which is meaningful for large-scale quantum computation and many-body Rydberg quantum simulation., 9 pages, 8 figures, 1 table

We study signatures of quantum chaos in dynamics of Rydberg dressed bosonic atoms held in a one dimensional triple-well potential. Long-range nearest-neighbor and next-nearest-neighbor interactions, induced by laser dressing atoms to strongly interacting Rydberg states, affect drastically mean field and quantum many-body dynamics. By analyzing the mean field dynamics, classical chaos regions with positive and large Lyapunov exponents are identified as a function of the potential well tilting and dressed interactions. In the quantum regime, it is found that level statistics of the eigen-energies gains a Wigner-Dyson distribution when the Lyapunov exponents are large, giving rise to signatures of strong quantum chaos. We find that both the time averaged entanglement entropy and survival probability of the initial state have distinctively large values in the quantum chaos regime. We further show that population variances could be used as an indicator of the emergence of quantum chaos. This might provide a way to directly probe quantum chaotic dynamics through analyzing population dynamics in individual potential wells., Comment: 13 pages, 7 figures

This doctoral thesis studies the Kondo effect of rare earth compounds measured by X-ray absorption spectroscopy (XAS). Two diluted intermetallic systems: A non-Kondo system Er0.025Pd0.975 and a Kondo system Yb0.005Au0.995 have been measured by XAS with circular polarized X-ray under strong magnetic field and weak magnetic field for temperatures from 0.2 K to 300 K. X-ray Magnetic Circular Dichroism (XMCD) spectra and X-ray Magnetic Linear Dichroism (XMLD) spectra have been extracted. The magnetic moment of the spin and of the orbit of the diluted impurity atom are obtained by applying the magneto-optical sum rules. Calculations by Ligand Field Multiplet (LFM) theory are performed to simulate the magnetic properties. The comparison between the Kondo system and the non-Kondo system, as well as the experimental measurements and the simulations allows the discovery of the local Kondo signature around the critical Kondo temperature TK for the Kondo system Yb0.005Au0.995. To achieve the experimental objective, part of this thesis has been devoted to instrumental developments. Hence a new 3He-4He dilution insert, named DICHRO50 which is able to cool the sample down to 180 mK, has been installed in the cryomagnet of DEIMOS beamline at Synchrotron SOLEIL; it is aimed to soft X-ray XAS-XMCD measurements. Moreover, a former dilution insert hosted in so-called TBT-mK cryomagnet has been upgraded to be installed on ID12 beamline at ESRF; it is aimed for hard X-ray XAS-XMCD measurements., Cette thèse doctorale étudie l’effet Kondo des composés de terre rare par spectroscopie d’absorption des rayons X (XAS). Deux systèmes intermétalliques dilués : un système non-Kondo d’Er0.025Pd0.975 et un système Kondo d’Yb0.005Au0.995 ont été mesurés par XAS avec des rayons X polarisés circulairement sous champ magnétique fort et aussi en champ magnétique faible pour une température variant de 0.2 K à 300 K. Les signaux de dichroïsme circulaire magnétique de rayons X (XMCD) et les spectres de dichroïsme linéaire magnétique de rayons X (XMLD) ont été extraits. Les moments magnétiques de spin et d'orbite ont été obtenus par application des règles de somme magnéto-optiques. Des calculs dans le cadre de la théorie des multiplets en champ de ligands (LFM) ont été faits pour simuler les signaux expérimentaux et ainsi remonter aux propriétés magnétiques. Dans le système Kondo, celui de l’ytterbium dans l’or, on observe pour des champs magnétiques ≤ 0.5 T et des températures inférieures à 1 K une différence prononcée entre l’aimantation attendue pour un atome isolé et celle observée expérimentalement : c’est le signe de l’effet Kondo. Pour arriver aux objectifs expérimentaux, une partie de travail de cette thèse a été consacrée à des développements instrumentaux. Un nouvel insert DICHRO50 qui fonctionne avec la dilution d’3He-4He a été installé dans le cryo-aimant de la ligne DEIMOS du Synchrotron SOLEIL. Cet instrument est développé pour des mesures de XAS, de XMCD ou des XMLD dans le domaine des rayons X mous. Il permet de refroidir un échantillon jusqu’à 180 mK. Un autre cryo-aimant, le TBT-mK, a été installé sur la ligne ID12 à l'ESRF où j’ai participé à des mesures de XMCD dans le domaine des rayons X durs.

We investigate the thermal Casimir-Polder (CP) potential of \textsuperscript{87}Rb atoms in Rydberg $n$S-states near single- and double-layer graphene. The dependence of the CP potential on parameters such as atom-surface distance, temperature, principal quantum number $n$ and graphene Fermi energy are explored. Through large scale numerical simulations, we show that, in the non-retarded regime, the CP potential is dominated by the non-resonant and evanescent-wave terms which are monotonic, and that, in the retarded regime, the CP potential exhibits spatial oscillations. We identify that the most important contributions to the resonant component of the CP potential come from the $n$S-$n$P and $n$S-$(n-1)$P transitions. Scaling of the CP potential as a function of the principal quantum number and temperature is obtained. A heterostructure comprising hexagonal boron nitride layers sandwiched between two graphene layers is also studied. When the boron nitride layer is sufficiently thin, the CP potential can be weakened by changing the Fermi energy of the top graphene layer. Our study provides insights for understanding and controlling CP potentials experienced by Rydberg atoms near single and multi-layer graphene-based van der Waals heterostructures.

We study steady state phases of a one-dimensional array of Rydberg atoms coupled by a microwave (MW) field where the higher energy Rydberg state decays to the lower energy one via single-body and collective (superradiant) decay. Using mean-field approaches, we examine the interplay among the MW coupling, intra-state van der Waals (vdW) interaction, and single-body and collective dissipation between Rydberg states. A linear stability analysis reveals that a series of phases, including uniform, antiferromagnetic, oscillatory, and bistable and multistable phases can be obtained. Without the vdW interaction, only uniform phases are found. In the presence of the vdW interaction, multistable solutions are enhanced when increasing the strength of the superradiant decay rate. Our numerical simulations show that the bistable and multistable phases are stabilized by superradiance in a long chain. The critical point between the uniform and multistable phases and its scaling with the atom number is obtained. Through numerically solving the master equation of a finite chain, we show that the mean-field multistable phase could be characterized by expectation values of Rydberg populations and two-body correlations between Rydberg atoms in different sites.

Stabilizing important physical quantities to atom-based standards lies at the heart of modern atomic, molecular and optical physics, and is widely applied to the field of precision metrology. Of particular importance is the atom-based microwave field amplitude stabilizer, the so-called atomic candle. Previous atomic candles are realized with atoms in their ground state, and hence suffer from the lack of frequency band tunability and small stabilization bandwidth, severely limiting their development and potential applications. To tackle these limitations, we employ microwave-dressed Rydberg atoms to realize a novel atomic candle that features multi-band frequency tunability and large stabilization bandwidth. We demonstrate amplitude stabilization of microwave field from C-band to Ka-band, which could be extended to quasi-DC and terahertz fields by exploring abundant Rydberg levels. Our atomic candle achieves stabilization bandwidth of 100 Hz, outperforming previous ones by more than two orders of magnitude. Our simulation indicates the stabilization bandwidth can be further increased up to 100 kHz. Our work paves a route to develop novel electric field control and applications with a noise-resilient, miniaturized, sensitive and broadband atomic candle.

International audience; In the past years, solution-processed organometallic perovskite based solar cells have emerged as a promising low-cost thin-film photovoltaic technology. 3D halide perovskite semiconductors and their 2D or OD nanostructures present specific symmetry and electronic properties, including giant spin-orbit coupling (SOC) effects. The ultrahigh softness of the halide perovskite lattice is also characteristic, and the role of the electron-phonon coupling, especially at temperatures relevant for device operation, is not fully understood. The presentation will focus on 2D perovskites, composed of perovskites layers sandwiched between two layers of large organic cations, described in the 90’s as self-assembled quantum and dielectric well systems.

National audience; The presentation will describe a few recent results on the structural and optoelectronic properties in 2D and 3D halide perovskites, focusing on some possibilities offered by nowadays neutron, X-rays and electron large scale scattering facilities.

Resonant laser excitation of multiple Rydberg atoms are prohibited, leading to Rydberg blockade, when the long-range van der Waals interactions are stronger than the laser-atom coupling. Rydberg blockade can be violated, i.e., simultaneous excitation of more than one Rydberg atom, by off-resonant laser excitation, causing an excitation antiblockade. Rydberg antiblockade gives rise to strongly correlated many-body dynamics and spin-orbit coupling and also finds quantum computation applications. Instead of commonly used van der Waals interactions, we investigate antiblockade dynamics of two Rydberg atoms interacting via dipole-dipole exchange interactions. We study typical situations in current Rydberg atom experiments, where different types of dipole-dipole interactions can be achieved by varying Rydberg state couplings. An effective Hamiltonian governing underlying antiblockade dynamics is derived. We illustrate that geometric gates can be realized with the Rydberg antiblockade which is robust against the decay of Rydberg states. Our study may stimulate new experimental and theoretical exploration of quantum optics and strongly interacting many-body dynamics with Rydberg antiblockade driven by dipole-dipole interactions.

The generation of squeezed light in semiconductor materials opens opportunities for building on-chip devices that are operated at the quantum level. Here we study theoretically a squeezed light source of polariton dark solitons confined in a geometric potential well of semiconductor microcavities in the strong coupling regime. We show that polariton dark solitons of odd and even parities can be created by tuning the potential depth. When driving the potential depth linearly, a bistability of solitons with the two different parities can be induced. Strong intensity squeezing is obtained near the turning point of the bistability due to the large nonlinear interaction, which can be controlled by Feshbach resonance. The phase diagram of the bistability and squeezing of the dark solitons is obtained through large scale numerical calculations. Our study contributes to the current efforts in realizing topological excitations and squeezed light sources with solid-state devices., 8 pages, 4 figures

The shaking table model test mainly focuses on the study of seismic response law, aseismic performance and seismic damping and isolation effect of bridges with a single or multi-platform shaking table. Basically, the plane principal axis direction is adopted for the seismic input of structural models. Little research effort considering multi-angle seismic input has been reported in the structural model test. In this paper we designed and conducted a small-scale shaking table model test to study the seismic response law of the curved girder bridges with seismic input at different angles, and provided experimental verification for the theoretical method of the most unfavorable angle of seismic input. The experimental results show that the variation trend of component response to variation of the seismic input direction is consistent with that of the numerical analysis, which indicates that the designed device is effective.

We study the population trapping extensively in a periodically driven Rydberg pair. The periodic modulation of the atom-light detuning effectively suppresses the Rabi couplings and, together with Rydberg-Rydberg interactions, leads to the state-dependent population trapping. We identify a simple yet general scheme to determine population trapping regions using driving-induced resonances, the Floquet spectrum, and the inverse participation ratio. Contrary to the single-atom case, we show that the population trapping in the two-atom setup may not necessarily be associated with level crossings in the Floquet spectrum. Further, we discuss under what criteria population trapping can be related to dynamical stabilization, taking specific and experimentally relevant initial states, which include both product and the maximally entangled Bell states. The behavior of the entangled states is further characterized by the bipartite entanglement entropy.

In recent years, owing to the outstanding performance in graph representation learning, graph neural network (GNN) techniques have gained considerable interests in many real-world scenarios, such as recommender systems and social networks. In recommender systems, the main challenge is to learn the effective user/item representations from their interactions. However, many recent publications using GNNs for recommender systems cannot be directly compared, due to their difference on datasets and evaluation metrics. Furthermore, many of them only provide a demo to conduct experiments on small datasets, which is far away to be applied in real-world recommender systems. To address this problem, we introduce Graph4Rec, a universal toolkit that unifies the paradigm to train GNN models into the following parts: graphs input, random walk generation, ego graphs generation, pairs generation and GNNs selection. From this training pipeline, one can easily establish his own GNN model with a few configurations. Besides, we develop a large-scale graph engine and a parameter server to support distributed GNN training. We conduct a systematic and comprehensive experiment to compare the performance of different GNN models on several scenarios in different scale. Extensive experiments are demonstrated to identify the key components of GNNs. We also try to figure out how the sparse and dense parameters affect the performance of GNNs. Finally, we investigate methods including negative sampling, ego graph construction order, and warm start strategy to find a more effective and efficient GNNs practice on recommender systems. Our toolkit is based on PGL https://github.com/PaddlePaddle/PGL and the code is opened source in https://github.com/PaddlePaddle/PGL/tree/main/apps/Graph4Rec., Comment: 8 pages, 4 figures

Additional file 1: Fig. S1. The root removal effect on microbial biomass by trenching and girdling methods. The numbers in the right of figure represents the number of case studies. Fig.S2. Effects of ALR and RE on dissolved organic carbon. The numbers in the right of figure represents the number of case studies. ALR, above-ground litter removal; RE, root exclusion. Table S1. Correlation coefficients of the effect size of sol microbial biomass and F/B ratio to above-ground litter removal (ALR) and root exclusion (RE) with climatic variables and soil properties

In this report, we (SuperHelix team) present our solution to KDD Cup 2021-PCQM4M-LSC, a large-scale quantum chemistry dataset on predicting HOMO-LUMO gap of molecules. Our solution, Lite Geometry Enhanced Molecular representation learning (LiteGEM) achieves a mean absolute error (MAE) of 0.1204 on the test set with the help of deep graph neural networks and various self-supervised learning tasks. The code of the framework can be found in https://github.com/PaddlePaddle/PaddleHelix/tree/dev/competition/kddcup2021-PCQM4M-LSC/.

Advertising click fraud detection plays one of the vital roles in current E-commerce websites as advertising is an essential component of its business model. It aims at, given a set of corresponding features, e.g., demographic information of users and statistical features of clicks, predicting whether a click is fraudulent or not in the community. Recent efforts attempted to incorporate attributed behavior sequence and heterogeneous network for extracting complex features of users and achieved significant effects on click fraud detection. In this paper, we propose a Multimodal and Contrastive learning network for Click Fraud detection (MCCF). Specifically, motivated by the observations on differences of demographic information, behavior sequences and media relationship between fraudsters and genuine users on E-commerce platform, MCCF jointly utilizes wide and deep features, behavior sequence and heterogeneous network to distill click representations. Moreover, these three modules are integrated by contrastive learning and collaboratively contribute to the final predictions. With the real-world datasets containing 2.54 million clicks on Alibaba platform, we investigate the effectiveness of MCCF. The experimental results show that the proposed approach is able to improve AUC by 7.2% and F1-score by 15.6%, compared with the state-of-the-art methods., Comment: Accepted to DeMal@WWW 2021

International audience; Gaining control over the grafting geometry is critically important for any application of surface-supported single-molecule magnets (SMMs) in data storage, spintronics, and quantum information science. Here, tetrairon(III) SMMs with a propeller-like structure are functionalized with thioacetyl-terminated alkyl chains to promote chemisorption on gold surfaces from solution and to evaluate differences in adsorption geometry and magnetic properties as a function of chain length. The prepared monolayers are investigated using X-ray absorption techniques with linearly and circularly polarized light to extract geometrical and magnetic information, respectively. All derivatives remain intact and form partially oriented monolayers on the gold surface. A ligand-field analysis of the observed X-ray natural linear dichroism shows that the threefold molecular axis is invariably biased toward the surface normal, in agreement with ab initio calculations. This preferential orientation is most pronounced in monolayers of the shortest-chain derivative, which are further studied with an ultralow temperature X-ray magnetic circular dichroism setup operating down to 350 mK. The isothermal field sweeps with the magnetic field at normal incidence show an open hysteresis loop below 1 K, while measurements at different incidence angles prove the magnetic anisotropy of the monolayers.

We analyze the excitation dynamics numerically in a one-dimensional Rydberg atomic chain, using the methods of discrete truncated Wigner approximation (dTWA) and artificial neural networks (ANN), for both van der Waals and dipolar interactions. In particular, we look at how the number of excitations dynamically grows or evolves in the system for an initial state where all atoms are in their electronic ground state. Further, we calculate the maximum number of excitations attained at any instant and the average number of excitations. For a small system size of ten atoms, we compare the results from dTWA and ANN with that of exact numerical calculations of the Schr\"odinger equation. The collapse and revival dynamics in the number of Rydberg excitations are also characterized in detail. Though we find good agreement at shorter periods, both dTWA and ANN failed to capture the dynamics accurately at longer times. By increasing the number of hidden units, the accuracy of ANN has improved but suffered by numerical instabilities, especially for large interaction strengths. Finally, we look at the dynamics of a large system size of two-hundred atoms using dTWA., Comment: 21 pages, 11 figures

The damage detection of the wind turbine (WT) blade is an important aspect of its health situation monitoring. In order to catch small damages, it is necessary to stitch the multi segment images of the blade to obtain a high resolution image. In image stitching, a blurring of the image is carried out to reduce the influence of noise. However, the preprocessing may decrease the amount of feature points and cannot avoid the interaction of feature points in the background and the target parts. To overcome these problems, a preprocessing method based on background removal is proposed. The idea of the method is to carry out image segmentation to get the background part, then the intensities of pixels in background part are replaced by a same value, such as average intensity. Employing the proposed preprocessing method, the image stitching is implemented on several groups of WT blade images. Feature points extraction result are compared between the proposed and the blurring preprocessing, which shows that the proposed method is more robust to the parameters in image stitching process. Moreover, the capability about image stitching and multi-image stitching of the proposed method is well verified by the experiment results.

Wind energy, as a renewable energy source, has attracted great attention of many countries. It is converted into electricity by the important machine, wind turbine (WT). With the fast growing of WT capacity in the world, the costs of monitoring and maintaining increase year by year. One necessary part of these costs is for blades health situation monitoring, which directly affects effectiveness and safety of WT. Thus, the damage detection of the blades is of great significance. The blades suffer from sunshine, acid rain, sand attack, and others, which may cause kinds of damages, such as skin abscission, surface crack, and sand hole. Aiming at surface damage detection of the blades, the paper proposed a method based on variational image segmentation model. At beginning, an idea that objects in an image are left along with detection of the background part is present, and it is changed into an optimization problem by using the level set method and 1-D Heaviside function. Then the corresponding gradient descent minimization algorithm is derived. In the experimental part, a large number of blade images with surface damages are tested by applying the proposed method, and damages are all detected successfully. Moreover, the segmentation results of the noise images show that our method is robust to noise. This paper can provide effective technical support for surface damage detection of WT blades in-service.

We propose a nonadiabatic non-Abelian geometric quantum operation scheme to realize universal quantum computation with mesoscopic Rydberg atoms. A single control atom entangles a mesoscopic ensemble of target atoms through long-range interactions between Rydberg states. We demonstrate theoretically that both the single qubit and two-qubit quantum gates can achieve high fidelities around or above 99.9% in ideal situations. Besides, to address the experimental issue of Rabi frequency fluctuation (Rabi error) in Rydberg atom and ensemble, we apply the dynamical-invariant-based zero systematic-error sensitivity (ZSS) optimal control theory to the proposed scheme. Our numerical simulations show that the average fidelity could be 99.98% for single ensemble qubit gate and 99.94% for two-qubit gate even when the Rabi frequency of the gate laser acquires 10% fluctuations. We also find that the optimized scheme can also reduce errors caused by higher-order perturbation terms in deriving the Hamiltonian of the ensemble atoms. To address the experimental issue of decoherence error between the ground state and Rydberg levels in Rydberg ensemble, we introduce a dispersive coupling regime between Rydberg and ground levels, based on which the Rydberg state is adiabatically discarded. The numerical simulation demonstrate that the quantum gate is enhanced. By combining strong Rydberg atom interactions, nonadiabatic geometric quantum computation, dynamical invariant and optimal control theory together, our scheme shows a new route to construct fast and robust quantum gates with mesoscopic atomic ensembles. Our study contributes to the ongoing effort in developing quantum information processing with Rydberg atoms trapped in optical lattices or tweezer arrays.

The rapid and accurate detection of partial discharge (PD) in AC metal enclosed switchgear (switchgear cabinet) is of great significance to ensure the safe operation of power grid and improve the reliability of power supply. At present, the main methods used to detect PD signal in high voltage (HV) switchgear cabinet are transient earth voltage (TEV), ultra high frequency (UHF) and ultrasonic emission (AE). Based on a simple comparison of the above three methods, this paper reviews the TEV detection method which is widely used and has formed many standards. The physical principle, instrument composition and requirements of TEV detection method and field technical standards are summarized. The related applications including comprehensive application analysis, multi-technologies joint detection, discharge power verification and positioning, PD transmission simulation and robot application are introduced. Finally, the technology prospect of integrated composite sensor and Internet of things (IOT) is given.

Quantum holonomic gates hold built-in resilience to local noises and provide a promising approach for implementing fault-tolerant quantum computation. We propose to realize high-fidelity holonomic $(N+1)$-qubit controlled gates using Rydberg atoms confined in optical arrays or superconducting circuits. We identify the scheme, deduce the effective multi-body Hamiltonian, and determine the working condition of the multiqubit gate. Uniquely, the multiqubit gate is immune to systematic errors, i.e., laser parameter fluctuations and motional dephasing, as the $N$ control atoms largely remain in the much stable qubit space during the operation. We show that $C_N$-NOT gates can reach same level of fidelity at a given gate time for $N\leq5$ under a suitable choice of parameters, and the gate tolerance against errors in systematic parameters can be further enhanced through optimal pulse engineering. In case of Rydberg atoms, the proposed protocol is intrinsically different from typical schemes based on Rydberg blockade or antiblockade. Our study paves a new route to build robust multiqubit gates with Rydberg atoms trapped in optical arrays or with superconducting circuits. It contributes to current efforts in developing scalable quantum computation with trapped atoms and fabricable superconducting devices., Comment: Accepted to publish in Physical Review Applied

Understanding and manipulating the non-Hermitian optical property based on coherent atomic gases is of great importance and has attracted much theoretical and experimental attentions. Advancing this study to the nonlinear optics regime is highly desirable due to its importance in fundamental physics and potential applications. In this work, we propose to realize a tunable electromagnetically induced grating (EIG) with parity-time (PT) symmetry in a cold gas of Rydberg atoms, where interatomic interactions between Rydberg states are mapped to strong and long-range optical interactions, and investigate nonlinear light diffractions in this system. We show that for far-field diffraction, laser beams incident upon the PT-symmetric EIG display distinctive asymmetric diffraction fringes, which can be actively manipulated through tuning the gain-absorption coefficient of the EIG, the incident intensity of the laser beam, and the nonlocality provided by Rydberg atoms. For near-field diffraction, the nonlinear Talbot diffraction carpets emerge and can be modulated by PT symmetry in the presence of strong nonlocal interactions, allowing the realization of controllable optical self-imaging. The results are not only imperative for the study of non-Hermitian nonlinear optics but also useful for characterizing the interatomic interaction in Rydberg gases and for designing new optical devices useful in optical information processing and transmission.

Supplementary material

Supplementary material

In this paper, we propose a scheme to implement the two-qubit controlled-Z gate via the Stark-tuned Förster interaction of Rydberg atoms, where the Förster defect is driven by a time-dependent electric field of a simple sinusoidal function while the matrix elements of the dipole-dipole interaction are time independent. It is shown that when the system is initially in a specific state, it makes a cyclic evolution after a preset interaction time, returning to the initial state, but picks up a phase, which can be used for realizing a two-atom controlled-Z gate. Due to the interference of sequential Landau-Zener transitions, the population and phase of the state is quasideterministic after the cyclic evolution and therefore the gate fidelity is insensitive to fluctuations of the interaction time and the dipole-dipole matrix elements. Feasibility of the scheme realized with Cs atoms is discussed in detail, which shows that the two-qubit gate via Landau-Zener control can be realized with the state-of-the-art experimental setup.

In this work, we prepared titanium matrix composites (TMCs) reinforced with in-situ polycarbosilane (PCS)-derived TiC particles. The effects of PCS addition on the microstructure, interface, hardness, and tribological properties were studied. The pyrolysis of PCS leads to the formation of in-situ TiC particles and Si solid-solution at a low PCS content (≤3 wt%). The TiC particles with a particle size of 4.8 μm are uniformly distributed in TMCs and have a well-bonded interface with the Ti matrix. The average grain size of α-Ti decreases from 100.5 μm in pure Ti to 16.1 μm in the Ti-3 wt% PCS composite. The presence of in situ synthesized TiC particles contributes to the excellent wear resistance of the Ti/PCS composites, which is ascribed to the increased hardness, superior load transfer capability, and oxidation wear resistance. The Ti-3 wt% PCS composite possesses the hardness of 4.72 GPa, elastic modulus of 169.23 GPa, and a low specific wear rate of 0.84 × 10−12 m3/(N·m) under constant conditions (3 N, 0.03 m/s). These values are all superior to those of Ti-6Al-4V alloy. This work sheds light on the design of high wear-resistant TMCs for industrial applications.

In this work, we developed a powder conditioning process that involves coating polycarbosilane (PCS) on Ti particles. After sintering, the conditioned Ti powder was converted into Ti composites. TiC was derived from the pyrolysis of PCS and forming an in-situ reinforcement. There exists a specific orientation relationship of ( 111 ) TiC∥ ( 10 1 ‾ 0 ) Ti and [ 11 2 ‾ ] TiC∥ [ 1 2 ‾ 10 ] Ti. The average grain size of α-Ti decreases significantly from 100.5 μm in pure Ti to 16.1 μm in the Ti-3 wt.% PCS composite. When the PCS content is 4 wt%, Ti3Si particles precipitate out, and they are combined with TiC forming an aggregated network architecture. Among these Ti composites, the 3 wt% PCS sample exhibits a high tensile strength of 861 MPa, high yield strength of 754 MPa and reasonably large elongation of 10.8%, respectively.

In HL-2 M tokamak, three-phase thyristor power supplies are utilized to output a direct current to energize the device coil to control the plasma current and shape configuration. Phase-controlled is currently the most effective control method in thyristor power supply. The quality of the synchronization signal is directly related to the performance of the thyristor power supply control. HL-2 M device uses a pulse generator with rectifier load to supply power to the device coil, it makes the thyristor power supply AC input voltage not only have a wide frequency variation but also a severe waveform distortion, so it is difficult to obtain the accurate synchronization signal of the thyristor power supply. In this paper, a real-time tracking and processing method for variable frequency synchronization signals are proposed, which applied the digital filter with point-to-point to process varying frequency synchronization signal, calculated the real-time frequency of the filtered data, obtained the delay angles at different input frequencies according to the phase-frequency characteristics of Butterworth low-pass filter, and reconstructed the synchronization signal by phase compensation. The system has been built to achieve a wide range of real-time frequency tracking from 70 to 110 Hz, and provides multiple synchronization signal output with 15° interval. The performance of the system was verified in the HL-2A experiment.

We present a robust and accurate numerical method to solve the modified Buckley-Leverett equation in two-phase porous media flow with dynamic capillary pressure effect. A symmetric interior penalty discontinuous Galerkin method is used to discretize the equation in the space direction. For accuracy and stability issues, the third-order strong stability preserving implicit-explicit Runge-Kutta method is adopted to solve the nonlinear semi-discrete system: the linear diffusion term is discretized implicitly while the nonlinear flux term is discretized explicitly. The spatial accuracy of the discontinuous Galerkin method depends on the limiters applied to the solution: we test a minmod-TVB limiter, a simple WENO limiter and a high-order shock-capturing moment limiter to demonstrate that a suitable shock capturing moment limiter leads to more accurate approximation of solution. A set of representative numerical experiments are presented to show the accuracy and efficiency of the proposed approach. The results indicate that the moment limiter proposed by Moe et al. [Arxiv:1507.03024, 2015] is the most suitable one to be used in solving the modified Buckley- Leverett equation, and high order schemes perform much better than lower order schemes. Our simulation results are consistent with the previous results in Kao et al.[J. Sci. Comput., 64(3) (2015), 837-857], Zhang and Zegeling [J. Comput. Phys., 345 (2017), 510-527 and Commun. Comput. Phys., 22(4) (2017), 935-964]., Comment: 20 pages, 10 figures, 4 tables

In this paper, we propose a scheme to implement the two-qubit controlled-Z gate via the Stark-tuned F��rster interaction of Rydberg atoms, where the F��rster defect is driven by a time-dependent electric field of a simple sinusoidal function while the matrix elements of the dipole-dipole interaction are time-independent. It is shown that when the system is initially in a specific state, it makes a cyclic evolution after a preset interaction time, returning to the initial state, but picks up a phase, which can be used for realizing a two-atom controlled-Z gate. Due to the interference of sequential Landau-Zener transitions, the population and phase of the state is quasi-deterministic after the cyclic evolution and therefore the gate fidelity is insensitive to fluctuations of the interaction time and the dipole-dipole matrix elements. Feasibility of the scheme realized with Cs atoms is discussed in detail, which shows that the two-qubit gate via Landau-Zener control can be realized with the state-of-the-art experimental setup., 8 pages, 8 figures

Realizing single light bullets and vortices that are stable in high dimensions is a long-standing goal in the study of nonlinear optical physics. On the other hand, the storage and retrieval of such stable high dimensional optical pulses may offer a variety of applications. Here we present a scheme to generate such optical pulses in a cold Rydberg atomic gas. By virtue of electromagnetically induced transparency, strong, long-range atom-atom interaction in Rydberg states is mapped to light fields, resulting in a giant, fast-responding nonlocal Kerr nonlinearity and the formation of light bullets and vortices carrying orbital angular momenta, which have extremely low generation power, very slow propagation velocity, and can stably propagate, with the stability provided by the combination of local and the nonlocal Kerr nonlinearities. We demonstrate that the light bullets and vortices obtained can be stored and retrieved in the system with high efficiency and fidelity. Our study provides a new route for manipulating high-dimensional nonlinear optical processes via the controlled optical nonlinearities in cold Rydberg gases.

Chemically bonded graphene/TiO2 nanorod hybrid composites with superior dispersity were synthesized by a one-step in situ hydrothermal method using graphene oxide (GO) and TiO2 (P25) as the starting materials. The as-prepared samples were characterized by XRD, XPS, TEM, FE-SEM, EDX, Raman, N2 adsorption, and UV–vis DRS techniques. Enhanced light absorption and a red shift of absorption edge were observed for the composites in the ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). Their effective photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light irradiation. An enhancement of photocatalytic performance was observed over graphene/TiO2 nanorod hybrid composite photocatalysts, as 3.7 times larger than that of pristine TiO2 nanorods. This work demonstrated that the synthesis of TiO2 nanorods and simultaneous conversion of GO to graphene “without using reducing agents” had shown to be a rapid, direct and clean approach to fabricate chemically bonded graphene/TiO2 nanorod hybrid composites with enhanced photocatalytic performance.

We demonstrate experimentally that Stark-tuned Förster resonances can be used to substantially increase the interaction between individual photons mediated by Rydberg interaction inside an optical medium. This technique is employed to boost the gain of a Rydberg-mediated single-photon transistor and to enhance the non-destructive detection of single Rydberg atoms. Furthermore, our all-optical detection scheme enables high-resolution spectroscopy of two-state Förster resonances, revealing the fine structure splitting of high-n Rydberg states and the non-degeneracy of Rydberg Zeeman substates in finite fields. We show that the ∣50S1/2,48S1/2⟩↔∣49P1/2,48P1/2⟩ pair state resonance in 87Rb enables simultaneously a transistor gain G>100 and all-optical detection fidelity of single Rydberg atoms F>0.8. We demonstrate for the first time the coherent operation of the Rydberg transistor with G>2 by reading out the gate photon after scattering source photons. Comparison of the observed readout efficiency to a theoretical model for the projection of the stored spin wave yields excellent agreement and thus successfully identifies the main decoherence mechanism of the Rydberg transistor.

The devil's staircase is a fractal structure that characterizes the ground state of one-dimensional classical lattice gases with long-range repulsive convex interactions. Its plateaus mark regions of stability for specific filling fractions which are controlled by a chemical potential. Typically such staircase has an explicit particle-hole symmetry, i.e., the staircase at more than half-filling can be trivially extracted from the one at less than half filling by exchanging the roles of holes and particles. Here we introduce a quantum spin chain with competing short-range attractive and long-range repulsive interactions, i.e. a non-convex potential. In the classical limit the ground state features generalized Wigner crystals that --- depending on the filling fraction --- are either composed of dimer particles or dimer holes which results in an emergent complete devil's staircase without explicit particle-hole symmetry of the underlying microscopic model. In our system the particle-hole symmetry is lifted due to the fact that the staircase is controlled through a two-body interaction rather than a one-body chemical potential. The introduction of quantum fluctuations through a transverse field melts the staircase and ultimately makes the system enter a paramagnetic phase. For intermediate transverse field strengths, however, we identify a region, where the density-density correlations suggest the emergence of quasi long-range order. We discuss how this physics can be explored with Rydberg-dressed atoms held in a lattice.