Showing 1–50 of 89 results for author: Wen, X

Imaginary Gauge Fields for One-Way Transparency and Absorption in a Passive Metasurface

Authors: Qingdong Yang, Zhongfu Li, Xinhua Wen, Oubo You, Yi Wang, Shuang Zhang

Abstract: Electromagnetic nonreciprocity enables waves to respond differently when their propagation direction is reversed, forming the basis of isolation, directional routing, and asymmetric energy control. A central challenge is to achieve high transmission in one direction while inducing strong absorption in the opposite direction within a single passive element, as passive material dissipation typically… ▽ More Electromagnetic nonreciprocity enables waves to respond differently when their propagation direction is reversed, forming the basis of isolation, directional routing, and asymmetric energy control. A central challenge is to achieve high transmission in one direction while inducing strong absorption in the opposite direction within a single passive element, as passive material dissipation typically attenuates both propagation channels equally. Here we demonstrate that an imaginary artificial gauge field can redistribute net dissipation between opposite directions in a passive structure. By synthesizing a moving-type magnetoelectric response from gyromagnetic elements and subwavelength metallic resonators, we realize a polarization-independent metasurface in which the forward wave weakly excites the dissipative resonance through destructive current interference, whereas the backward wave strongly activates the same lossy mode through constructive interference. The fabricated metasurface transmits more than 80% of the incident power from one side while absorbing more than 80% from the opposite side, with low reflection from both directions. Near-field mapping of the surface electric field provides direct real-space evidence of this gauge-controlled, direction-dependent charge accumulation and dissipation. This work establishes imaginary gauge fields as a powerful route for engineering dissipative landscapes in open wave systems and opens a pathway toward compact, passive, reflectionless isolators and nonreciprocal absorbers. △ Less

Submitted 14 August, 2026; originally announced August 2026.

Comments: 19pages, 4 figures,

Hyperon-Nucleon Spectrometer

Authors: Xiaozhi Bai, Xu Cao, Zhe Cao, Jinhui Chen, Kai Chen, Qibo Chen, Shi Chen, Xin Chen, Yuquan Chen, Zhenyu Chen, Jianping Dai, Heng-Tong Ding, Dongshuo Du, Shuxian Du, Limin Duan, Zhe Duan, Anhui Feng, Jie Feng, Yicheng Feng, Jinlin Fu, Xiaofeng Fu, Chaosong Gao, Liang Ge, Wenwen Ge, Lisheng Geng , et al. (215 additional authors not shown)

Abstract: Chirality lies at the heart of low-energy QCD, governing the symmetry structure that shapes hadron masses and strong interaction dynamics. Among the most compelling open questions tied to chiral dynamics and spontaneous chiral symmetry breaking is the longstanding $Λ$ polarization puzzle, in which $Λ$ hyperons produced in unpolarized hadronic collisions exhibit a surprisingly large transverse pola… ▽ More Chirality lies at the heart of low-energy QCD, governing the symmetry structure that shapes hadron masses and strong interaction dynamics. Among the most compelling open questions tied to chiral dynamics and spontaneous chiral symmetry breaking is the longstanding $Λ$ polarization puzzle, in which $Λ$ hyperons produced in unpolarized hadronic collisions exhibit a surprisingly large transverse polarization that remains theoretically unexplained. This whitepaper presents the proposal for the Hyperon-Nucleon Spectrometer (H-NS) at the High-Intensity heavy-ion Accelerator Facility (HIAF). Leveraging the high energy and high intensity of HIAF's proton and heavy-ion beams, the H-NS experiment will perform systematic studies of hyperon polarization phenomena and their underlying mechanisms in proton-proton ($pp$), proton-nucleus ($pA$), and nucleus-nucleus ($AA$) collisions in the fixed target mode. A wide-range beam energy scan, including proton beams from 3 GeV up to 9.3 GeV (HIAF) and up to 32 GeV (upgraded HIAF), will be conducted to examine the dependence of polarization on collision energy. The spectrometer is designed with specialized detectors capable of high-precision reconstruction of final-state baryon polarizations. Among its many interesting and important measurements, H-NS will simultaneously measure hyperon and proton spin observables to explore the polarization mechanism in hadronic interactions and the spin structure of baryons. Furthermore, the use of $pA$ and $AA$ collisions will enable detailed investigations of cold and hot nuclear matter effects on spin polarization. Its physics program and detector development will significantly benefit the future Electron-ion Collider in China. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 69 pages, Hyperon-Nucleon Spectrometer (H-NS) white paper

Agentic Discovery of Exchange-Correlation Density Functionals

Authors: Titouan Duston, Jiashu Liang, Yuanheng Wang, Weihao Gao, Xuelan Wen, Nan Sheng, Weiluo Ren, Yang Sun, Yixiao Chen

Abstract: The development of accurate exchange-correlation (XC) functionals remains a longstanding challenge in density functional theory (DFT). The vast majority of XC functionals have been hand designed by human researchers combining physical insight, exact constraints, and empirical fitting. Recent advances in large language models enable a systematic, automated alternative to this human-driven design lo… ▽ More The development of accurate exchange-correlation (XC) functionals remains a longstanding challenge in density functional theory (DFT). The vast majority of XC functionals have been hand designed by human researchers combining physical insight, exact constraints, and empirical fitting. Recent advances in large language models enable a systematic, automated alternative to this human-driven design loop. This report presents an agentic search system in which an LLM proposes structured functional-form changes guided by evolutionary history. The system attempts to improve functional performance through an iterative plan-execute-summarize loop, where improvements are measurable by optimizing functional parameters against a standard thermochemistry dataset, then evaluating performance on a held-out subset. The strongest discovered functional, SAFS26-a (Seed Agentic Functional Search 2026), improves upon the gold-standard ωB97M-V baseline by ~9%. These results also surface a cautionary lesson for AI-assisted science: models powerful enough to discover genuine improvements are equally capable of exploiting unphysical shortcuts to game the benchmark; domain expertise translated into explicitly enforced constraints remains essential to keeping results scientifically grounded. △ Less

Submitted 6 May, 2026; originally announced May 2026.

Comments: 20 pages, 2 figues, 4 tables

Social Catalysts, Not Moral Agents: The Illusion of Alignment in LLM Societies

Authors: Yueqing Hu, Yixuan Jiang, Zehua Jiang, Xiao Wen, Tianhong Wang

Abstract: The rapid evolution of Large Language Models (LLMs) has led to the emergence of Multi-Agent Systems where collective cooperation is often threatened by the "Tragedy of the Commons." This study investigates the effectiveness of Anchoring Agents--pre-programmed altruistic entities--in fostering cooperation within a Public Goods Game (PGG). Using a full factorial design across three state-of-the-art… ▽ More The rapid evolution of Large Language Models (LLMs) has led to the emergence of Multi-Agent Systems where collective cooperation is often threatened by the "Tragedy of the Commons." This study investigates the effectiveness of Anchoring Agents--pre-programmed altruistic entities--in fostering cooperation within a Public Goods Game (PGG). Using a full factorial design across three state-of-the-art LLMs, we analyzed both behavioral outcomes and internal reasoning chains. While Anchoring Agents successfully boosted local cooperation rates, cognitive decomposition and transfer tests revealed that this effect was driven by strategic compliance and cognitive offloading rather than genuine norm internalization. Notably, most agents reverted to self-interest in new environments, and advanced models like GPT-4.1 exhibited a "Chameleon Effect," masking strategic defection under public scrutiny. These findings highlight a critical gap between behavioral modification and authentic value alignment in artificial societies. △ Less

Submitted 1 February, 2026; originally announced February 2026.

Comments: 7 pages, 5 figures

Spin-Adapted Neural Network Wavefunctions in Real Space

Authors: Ruichen Li, Yuzhi Liu, Du Jiang, Yixiao Chen, Xuelan Wen, Wenrui Li, Di He, Liwei Wang, Ji Chen, Weiluo Ren

Abstract: Spin plays a fundamental role in understanding electronic structure, yet many real-space wavefunction methods fail to adequately consider it. We introduce the Spin-Adapted Antisymmetrization Method (SAAM), a general procedure that enforces exact total spin symmetry for antisymmetric many-electron wavefunctions in real space. In the context of neural network-based quantum Monte Carlo (NNQMC), SAAM… ▽ More Spin plays a fundamental role in understanding electronic structure, yet many real-space wavefunction methods fail to adequately consider it. We introduce the Spin-Adapted Antisymmetrization Method (SAAM), a general procedure that enforces exact total spin symmetry for antisymmetric many-electron wavefunctions in real space. In the context of neural network-based quantum Monte Carlo (NNQMC), SAAM leverages the expressiveness of deep neural networks to capture electron correlation while enforcing exact spin adaptation via group representation theory. This framework provides a principled route to embed physical priors into otherwise black-box neural network wavefunctions, yielding a compact representation of correlated system with neural network orbitals. Compared with existing treatments of spin in NNQMC, SAAM is more accurate and efficient, achieving exact spin purity without any additional tunable hyperparameters. To demonstrate its effectiveness, we apply SAAM to study the spin ladder of iron-sulfur clusters, a long-standing challenge for many-body methods due to their dense spectrum of nearly degenerate spin states. Our results reveal accurate resolution of low-lying spin states and spin gaps in [Fe$_2$S$_2$] and [Fe$_4$S$_4$] clusters, offering new insights into their electronic structures. In sum, these findings establish SAAM as a robust, hyperparameter-free standard for spin-adapted NNQMC, particularly for strongly correlated systems. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Quantum Many-Body Simulations of Catalytic Metal Surfaces

Authors: Changsu Cao, Hung Q. Pham, Zhen Guo, Yutan Zhang, Zigeng Huang, Xuelan Wen, Ji Chen, Dingshun Lv

Abstract: Quantum simulations of metal surfaces are critical for catalytic innovation. Yet existing methods face a cost-accuracy dilemma: density functional theory is efficient but system-dependent in accuracy, while wavefunction-based theories are accurate but prohibitively costly. Here we introduce FEMION (Fragment Embedding for Metals and Insulators with Onsite and Nonlocal correlation), a systematically… ▽ More Quantum simulations of metal surfaces are critical for catalytic innovation. Yet existing methods face a cost-accuracy dilemma: density functional theory is efficient but system-dependent in accuracy, while wavefunction-based theories are accurate but prohibitively costly. Here we introduce FEMION (Fragment Embedding for Metals and Insulators with Onsite and Nonlocal correlation), a systematically improvable quantum embedding framework that resolves this challenge by capturing partially filled electronic states in metals. FEMION combines auxiliary-field quantum Monte Carlo for local catalytic sites with a global random phase approximation treatment of nonlocal screening, yielding a scalable approach across diverse catalytic systems. Employing FEMION, we address two longstanding challenges: determining the preferred CO adsorption site and quantifying the H2 desorption barrier on Cu(111). Furthermore, our calculations demonstrate that the recently discovered 10-electron-count rule can also be extended to the single-atom catalysis processes on 3d metal surfaces, resolving the controversies arising from density functional theory calculations. We thus open a predictive, first-principles route to modeling complex catalytic systems. △ Less

Submitted 9 April, 2026; v1 submitted 18 August, 2025; originally announced August 2025.

Comments: 12 pages, 5 figures

Neural Scaling Laws Surpass Chemical Accuracy for the Many-Electron Schrödinger Equation

Authors: Du Jiang, Xuelan Wen, Yixiao Chen, Ruichen Li, Weizhong Fu, Hung Q. Pham, Ji Chen, Di He, William A. Goddard III, Liwei Wang, Weiluo Ren

Abstract: We demonstrate, for the first time, that neural scaling laws can deliver near-exact solutions to the many-electron Schrödinger equation across a broad range of realistic molecules. This progress is enabled by the Lookahead Variational Algorithm (LAVA), an effective optimization scheme that systematically translates increased model size and computational resources into greatly improved energy accur… ▽ More We demonstrate, for the first time, that neural scaling laws can deliver near-exact solutions to the many-electron Schrödinger equation across a broad range of realistic molecules. This progress is enabled by the Lookahead Variational Algorithm (LAVA), an effective optimization scheme that systematically translates increased model size and computational resources into greatly improved energy accuracy for neural network wavefunctions. Across all tested cases, including benzene, the absolute energy error exhibits a systematic power-law decay with respect to model capacity and computation resources. The resulting energies not only surpass the 1 kcal/mol "chemical-accuracy" threshold but also achieve 1 kJ/mol subchemical accuracy. Beyond energies, the scaled-up neural network also yields better wavefunctions with improved physical symmetries, alongside accurate electron densities, dipole moments, and other important properties. Our approach offers a promising way forward to addressing many long-standing challenges in quantum chemistry. For instance, we improve energetic properties for systems such as the potential energy curve of nitrogen dimer as dissociation is approached and the cyclobutadiene automerization reaction barrier, producing definitive benchmarks, particularly in regimes where experimental data are sparse or highly uncertain. We also shed light on the decades-old puzzle of the cyclic ozone stability with highly accurate calculations for the cyclic-to-open ozone barrier. These results provide near-exact reference calculations with unprecedented accuracy, universal reliability and practical applicability, establishing a foundation for AI-driven quantum chemistry. △ Less

Submitted 5 August, 2025; v1 submitted 4 August, 2025; originally announced August 2025.

High-order virtual gain for optical loss compensation in plasmonic metamaterials

Authors: Fuxin Guan, Zemeng Lin, Sixin Chen, Xinhua Wen, Shuang Zhang

Abstract: Metamaterials exhibit extraordinary properties yet suffer from pronounced wave dissipation, particularly in optical imaging and sensing systems. Recent advances leveraging complex frequency wave excitations with virtual gain effect, synthesized by multi-monochromatic waves, offer promising solutions for optical loss compensation. However, this approach faces limitations in extreme loss scenarios.… ▽ More Metamaterials exhibit extraordinary properties yet suffer from pronounced wave dissipation, particularly in optical imaging and sensing systems. Recent advances leveraging complex frequency wave excitations with virtual gain effect, synthesized by multi-monochromatic waves, offer promising solutions for optical loss compensation. However, this approach faces limitations in extreme loss scenarios. The complex frequency wave requires sufficient virtual gain, i.e., temporal attenuation, to offset material loss, inevitably triggering rapid signal decay to zero before reaching a quasi-static state. To address this challenge, we introduce synthetic waves of high-order virtual gain to slow down the decay rate while preserving the loss compensation efficiency. We experimentally demonstrate 20-fold noise suppression in plasmonic resonance systems compared to conventional complex frequency excitations. This approach exhibits broad applicability across diverse fields, including imaging, biosensing, and integrated photonic signal processing. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Empowering Neural Network-based Quantum Monte Carlo with Local Pseudopotentials

Authors: Weizhong Fu, Ryunosuke Fujimaru, Ruichen Li, Yuzhi Liu, Xuelan Wen, Xiang Li, Kenta Hongo, Liwei Wang, Tom Ichibha, Ryo Maezono, Ji Chen, Weiluo Ren

Abstract: Neural Network-based Quantum Monte Carlo (NNQMC), an emerging method for solving many-body quantum systems with high accuracy, has been mainly applied to small systems due to demanding computation requirements. In this work, we introduce a framework based on local pseudopotentials to break through such limitation, improving the computational efficiency and scalability of NNQMC. The incorporation o… ▽ More Neural Network-based Quantum Monte Carlo (NNQMC), an emerging method for solving many-body quantum systems with high accuracy, has been mainly applied to small systems due to demanding computation requirements. In this work, we introduce a framework based on local pseudopotentials to break through such limitation, improving the computational efficiency and scalability of NNQMC. The incorporation of local pseudopotentials reduces the number of electrons treated in neural network and also achieves better relative energy accuracy than all electron NNQMC calculations for complex systems. This counterintuitive outcome is made possible by the distinctive characteristics inherent to NNQMC. Notably, by avoiding costly integration terms, this approach is also substantially more efficient than its widely used semilocal counterparts. Our approach enables the reliable treatment of large and challenging systems, such as the $\text{Fe}_4 \text{S}_4 (\text{SCH}_3)_4$ iron-sulfur cluster. Overall, our findings demonstrate that the synergy between NNQMC and local pseudopotentials substantially expands the scope of accurate ab initio calculations. △ Less

Submitted 17 July, 2026; v1 submitted 26 May, 2025; originally announced May 2025.

Research on Core Loss of Direct-drive 75kW Tidal Current Generator Using Machine Learning and Multi-objective Optimization Algorithms

Authors: Shuai Zu, Wanqiang Zhu, Fuli Zhang, Chi Xiao, Xiao Zhang, Yixiao Li, Xinze Wen, Yingying Qiao, Junyi Xu

Abstract: This paper presents a classification of generator excitation waveforms using principal component analysis (PCA) and machine learning models, including logistic regression, random forest, and gradient boosting decision trees (GBDT). Building upon the traditional Steinmetz equation, a temperature correction term is introduced. Through nonlinear regression and least squares parameter fitting, a novel… ▽ More This paper presents a classification of generator excitation waveforms using principal component analysis (PCA) and machine learning models, including logistic regression, random forest, and gradient boosting decision trees (GBDT). Building upon the traditional Steinmetz equation, a temperature correction term is introduced. Through nonlinear regression and least squares parameter fitting, a novel temperature correction equation is proposed, which significantly reduces the prediction error for core losses under high-temperature conditions. The average relative error is decreased to 16.03%, thereby markedly enhancing the accuracy. Using GBDT and random forest regression models, the independent and combined effects of temperature, excitation waveforms, and magnetic materials on core loss are analyzed. The results indicate that the excitation waveform has the most significant impact, followed by temperature, while the magnetic core material exhibits the least influence. The optimal combination for minimizing core loss is identified, achieving a core loss value of 35,310.9988 under the specified conditions. A data-driven predictive model for core loss is developed, demonstrating excellent performance with an R*R value of 0.9703 through machine learning regression analysis, indicating high prediction accuracy and broad applicability. Furthermore, a multi-objective optimization model considering both core loss and transmission magnetic energy is proposed. Genetic algorithms are employed for optimization, resulting in an optimal design scheme that minimizes core loss and maximizes transmission magnetic energy. Based on this model, the magnetic core compensation structure of a direct-drive 75kW tidal energy generator is optimized in practical applications, yielding satisfactory results. △ Less

Submitted 21 May, 2025; originally announced May 2025.

GECAM Discovery of Peculiar Oscillating Particle Precipitation Events

Authors: Chenwei Wang, Shaolin Xiong, Yi Zhao, Wei Xu, Gaopeng Lu, Xuzhi Zhou, Xiaocheng Guo, Wenya Li, Xiaochao Yang, Qinghe Zhang, Xinqiao Li, Zhenxia Zhang, Zhenghua An, Ce Cai, Peiyi Feng, Yue Huang, Min Gao, Ke Gong, Dongya Guo, Haoxuan Guo, Bing Li, Xiaobo Li, Yaqing Liu, Jiacong Liu, Xiaojing Liu , et al. (30 additional authors not shown)

Abstract: Charged particle precipitation typically manifests as a gradual increase and decrease of flux observed by space detectors. Cases with rapidly flux variation are very rare. Periodic events are even more extraordinary. These oscillating particle precipitation (OPP) events are usually attributed to the bounce motion of electrons, which are induced by lightning. Owing to the observation limitations, t… ▽ More Charged particle precipitation typically manifests as a gradual increase and decrease of flux observed by space detectors. Cases with rapidly flux variation are very rare. Periodic events are even more extraordinary. These oscillating particle precipitation (OPP) events are usually attributed to the bounce motion of electrons, which are induced by lightning. Owing to the observation limitations, there has been debate regarding whether these oscillations originate from temporal flux evolution or spatial structure evolution. Here we report three peculiar charged particle precipitation events detected by GECAM during a geomagnetic storm on March 21, 2024, with two exhibiting significant periodicity. These events were observed around the same region during three consecutive orbits. Through comprehensive temporal and spectral analyses, we revealed that one of the OPP events exhibited a transition in spectral lag of mini-pulses, shifting from "softer-earlier" to "softer-later" while showing no significant time evolution in overall frequency characteristics. And there is no association found between these two OPP events and lightning activity. Several possible scenarios are discussed to explain these charged particles with a life time of more than 3.5 hours, but the nature of these three events remains an enigma. We suggest that these GECAM-detected OPP events may represent a new type of particle precipitation event or a peculiar Lightning-induced Electron Precipitations (LEPs). △ Less

Submitted 9 May, 2025; originally announced May 2025.

Pitch Angle Measurement Method based on Detector Counts Distribution. -I. Basic conception

Authors: Chenwei Wang, Shaolin Xiong, Hongbo Xue, Yiteng Zhang, Shanzhi Ye, Wei Xu, Jinpeng Zhang, Zhenghua An, Ce Cai, Peiyi Feng, Ke Gong, Haoxuan Guo, Yue Huang, Xinqiao Li, Jiacong Liu, Xiaojing Liu, Xiang Ma, Liming Song, Wenjun Tan, Jin Wang, Ping Wang, Yue Wang, Xiangyang Wen, Shuo Xiao, Shenlun Xie , et al. (14 additional authors not shown)

Abstract: As an X-ray and gamma-ray all-sky monitor aiming for high energy astrophysical transients, Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) has also made a series of observational discoveries on burst events of gamma-rays and particles in the low Earth orbit. Pitch angle is one of the key parameters of charged particles traveling around geomagnetic field. However,… ▽ More As an X-ray and gamma-ray all-sky monitor aiming for high energy astrophysical transients, Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) has also made a series of observational discoveries on burst events of gamma-rays and particles in the low Earth orbit. Pitch angle is one of the key parameters of charged particles traveling around geomagnetic field. However, the usage of the GECAM-style instruments to measure the pitch angle of charged particles is still lacking. Here we propose a novel method for GECAM and similar instruments to measure the pitch angle of charged particles based on detector counts distribution. The basic conception of this method and simulation studies are described. With this method, the pitch angle of a peculiar electron precipitation event detected by GECAM-C is derived to be about 90$^\circ$, demonstrating the feasibility of our method. We note that the application of this method on GECAM-style instruments may open a new window for studying space particle events, such as Terrestrial Electron Beams (TEBs) and Lightning-induced Electron Precipitations (LEPs). △ Less

Submitted 9 May, 2025; originally announced May 2025.

Oblique rotational axis detection using elliptical optical vortex based on rotational Doppler effect

Authors: Xiangyang Zhu, Yuan Ren, Yaohui Fan, Xinyi Wen, Xiaocen Chen, Ruoyu Tang, You Ding, Zhengliang Liu, Tong Liu

Abstract: The rotational Doppler effect (RDE) of structured light carrying orbital angular momentum (OAM) has attracted widespread attention for applications in optical sensors and OAM spectrum detection. These studies, however, based on RDE, are mostly focused on the motion parameters of rotating objects; other equally important attitude characteristics, e.g., the tilt angle of the axis of rotation, have r… ▽ More The rotational Doppler effect (RDE) of structured light carrying orbital angular momentum (OAM) has attracted widespread attention for applications in optical sensors and OAM spectrum detection. These studies, however, based on RDE, are mostly focused on the motion parameters of rotating objects; other equally important attitude characteristics, e.g., the tilt angle of the axis of rotation, have rarely been considered. We observed an interesting phenomenon in the experiments: the rotational Doppler spectral distribution varies with the ellipticity of the elliptical optical vortex (EOV) and the tilt angle between the rotational axis and optical axis, which inspired us to wonder if it is possible to detect oblique rotational axis or compensate the rotational Doppler broadening effect induced by oblique incidence by utilizing the EOV. Here, we reveal the RDE quantitative relationship with tilt angle and ellipticity for the first time and report a novel approach for tilt angle measurement. By employing a series of EOV with periodically varying ellipticity to illuminate a rotating object and analyze the time-frequency spectral distribution of scattered light associated with ellipticity and tilt angle, the tilt angle can be acquired accurately based on the specific relationship between the tilt angle and ellipticity of the EOV. Furthermore, the spectrum broadening effect arising from oblique incidence in the actual scenario may be addressed through our scheme. The method may find applications in industrial manufacturing and target attitude measurement, and our results provide new insights for obtaining more information about objects. △ Less

Submitted 1 January, 2025; originally announced January 2025.

Advancing Surface Chemistry with Large-Scale Ab-Initio Quantum Many-Body Simulations

Authors: Zigeng Huang, Zhen Guo, Changsu Cao, Hung Q. Pham, Xuelan Wen, George H. Booth, Ji Chen, Dingshun Lv

Abstract: Predictive simulation of surface chemistry is of paramount importance for progress in fields from catalysis to electrochemistry and clean energy generation. Ab-initio quantum many-body methods should be offering deep insights into these systems at the electronic level, but are limited in their efficacy by their steep computational cost. In this work, we build upon state-of-the-art correlated wavef… ▽ More Predictive simulation of surface chemistry is of paramount importance for progress in fields from catalysis to electrochemistry and clean energy generation. Ab-initio quantum many-body methods should be offering deep insights into these systems at the electronic level, but are limited in their efficacy by their steep computational cost. In this work, we build upon state-of-the-art correlated wavefunctions to reliably converge to the `gold standard' accuracy in quantum chemistry for application to extended surface chemistry. Efficiently harnessing graphics processing unit acceleration along with systematically improvable multiscale resolution techniques, we achieve linear computational scaling up to 392 atoms in size. These large-scale simulations demonstrate the importance of converging to these extended system sizes, achieving a validating handshake between simulations with different boundary conditions for the interaction of water on a graphene surface. We provide a new benchmark for this water-graphene interaction that clarifies the preference for water orientations at the graphene interface. This is extended to the adsorption of carbonaceous molecules on chemically complex surfaces, including metal oxides and metal-organic frameworks, where we consistently achieve chemical accuracy compared to experimental references, and well inside the scatter of traditional density functional material modeling approaches. This pushes the state of the art for simulation of molecular adsorption on surfaces, and marks progress into a post-density functional era for more reliable and improvable approaches to first-principles modeling of surface problems at an unprecedented scale and accuracy using ab-initio quantum many-body methods. △ Less

Submitted 2 January, 2025; v1 submitted 24 December, 2024; originally announced December 2024.

Policy-relevance of a Model Inter-comparison: Switzerland in the European Energy Transition

Authors: Ambra Van Liedekerke, Blazhe Gjorgiev, Jonas Savelsberg, Xin Wen, Jérôme Dujardin, Ali Darudi, Jan-Philipp Sasse, Evelina Trutnevyte, Michael Lehning, Giovanni Sansavini

Abstract: The energy transition is reshaping electricity systems, bringing new challenges, and emphasizing the need for strategic planning. Energy policies play a crucial role in guiding this transition. However, assessing their impacts often requires robust modeling involving multiple models and going beyond a single country's scope, analyzing international interactions. In this study, we examine three Swi… ▽ More The energy transition is reshaping electricity systems, bringing new challenges, and emphasizing the need for strategic planning. Energy policies play a crucial role in guiding this transition. However, assessing their impacts often requires robust modeling involving multiple models and going beyond a single country's scope, analyzing international interactions. In this study, we examine three Swiss energy policies, analyzing their impacts on both the national energy system and the cross-border electricity flows. We use a model inter-comparison approach with four electricity system models to explore scenarios involving Swiss renewable generation targets, the Swiss market integration, and the Swiss winter import limitations, in the context of various European electricity developments. The results indicate that a renewable generation target leads to a reduction in net imports and electricity prices. Additionally, reduced market integration impacts both Swiss and European energy transitions by limiting trade benefits, underutilizing Variable Renewable Energy Sources (VRES), and increasing electricity supply costs. Lastly, we observe that limiting Swiss winter imports adversely affects electricity trading, driving up both supply costs and electricity prices. △ Less

Submitted 17 December, 2024; originally announced December 2024.

Comments: The main body of the paper has 16 pages, 11 figures and 4 tables. The supplementary material has 7 pages, 6 figures and no tables

Performance of the Gamma-ray Transient Monitor at the IHEP Electron-Beam Facility

Authors: Pei-Yi Feng, Zheng-Hua An, Yu-Hui Li, Qi Le, Da-Li Zhang, Xin-Qiao Li, Shao-Lin Xiong, Hong-Fei Guan, Cai-Yun Shao, Chen-Wei Wang, Chao Zheng, Jia-Cong Liu, Xiang-Yang Wen, Sheng Yang, Ke Gong, Ya-Qing Liu, Xiao-Jing Liu, Min Gao, Xiao-Yun Zhao, Fan Zhang, Jin-Zhou Wang, Xi-Lei Sun, Cong-Zhan Liu, Wei-Bin Liu, Jian-Li Wang , et al. (4 additional authors not shown)

Abstract: Gamma-Ray Transient Monitor (GTM) is an all-sky monitor onboard the Distant Retrograde Orbit-A (DRO-A) satellite, with the scientific objective of detecting gamma-ray bursts in the energy range of 20 keV to 1 MeV. GTM is equipped with five Gamma-Ray Transient Probes (GTPs), utilizing NaI(Tl) scintillators coupled with silicon photomultiplier (SiPM) arrays for signal readout. To test the performanc… ▽ More Gamma-Ray Transient Monitor (GTM) is an all-sky monitor onboard the Distant Retrograde Orbit-A (DRO-A) satellite, with the scientific objective of detecting gamma-ray bursts in the energy range of 20 keV to 1 MeV. GTM is equipped with five Gamma-Ray Transient Probes (GTPs), utilizing NaI(Tl) scintillators coupled with silicon photomultiplier (SiPM) arrays for signal readout. To test the performance of the GTP in detecting electrons, we used the IHEP Electron-Beam Facility (a continuous-energy-tunable, low-current, quasi-single-electron accelerator) for ground-based electron tests of the GTP. This paper provides a detailed description of the operating principles of the electron accelerator and presents the process and results of the GTP electron-beam tests. The test results show that the GTP has a dead time of less than 4 $μ$s for normal signals and approximately 70 $μ$s for overflow signals, consistent with the design specifications. The time-recording capability of the GTP was tested and found to be normal, with accurate recording of overflow events. The GTP's response to electrons in the 0.4-1.4 MeV range is also normal. Additionally, we used Geant4 to simulate the GTP's energy response and performed a comparative analysis of the simulation and experimental results. The performance tests and ground-based electron calibration validated the design of the GTP and enhanced the GTP's mass model, laying the foundation for payload development, in-orbit observation strategies, and scientific data analysis. △ Less

Submitted 25 March, 2026; v1 submitted 28 November, 2024; originally announced November 2024.

Comments: 14 pages, 16 figures

Lattice Energy Reservoir in Metal Halide Perovskites

Authors: Xiaoming Wen, Baohua Jia

Abstract: Metal halide perovskite-based technologies have been rapidly developed during the last decade. However, to date, the fundamental question, why are halide perovskites superior to conventional semiconductors? has remained elusive. Here, we propose a new theory of lattice energy reservoir (LER) in halide perovskites and elucidate that LER can comprehensively impact charge carrier dynamics and thus en… ▽ More Metal halide perovskite-based technologies have been rapidly developed during the last decade. However, to date, the fundamental question, why are halide perovskites superior to conventional semiconductors? has remained elusive. Here, we propose a new theory of lattice energy reservoir (LER) in halide perovskites and elucidate that LER can comprehensively impact charge carrier dynamics and thus enhance device performance, from hot carrier cooling, carrier recombination, anomalous upconversion fluorescence, illumination induced fluorescence enhancement (photobrightening), to high efficiency solar cells and light-emitting diodes. An LER is a dynamic nanodomain in halide perovskites with suppressed thermal transport that can accumulate energy from phonon coupling and then feedback to subgap carriers and result in subgap carrier upconversion. The LER directly results in slowed cooling of hot carriers and significantly prolonged carrier recombination, anomalous upconversion fluorescence, as usually termed as defect tolerance, as well as the anomalous ultraslow phenomena including persistent polarization, memory effect, and photobrightening. The LER theory rationalizes the superior optoelectronic properties and device performance and provides a novel physical understanding for anomalous phenomena observed uniquely in halide perovskites. △ Less

Submitted 26 June, 2024; originally announced June 2024.

Comments: 17 pages

Beam test results of the prototype of the multi wire drift chamber for the CSR external-target experiment

Authors: Zhi Qin, Zhoubo He, Zhe Cao, Tao Chen, Zhi Deng, Limin Duan, Dong Guo, Rongjiang Hu, Jie Kong, Canwen Liu, Peng Ma, Xianglun Wei, Shihai Wen, Xiangjie Wen, Junwei Yan, Herun Yang, Zuoqiao Yang, Yuhong Yu, Zhigang Xiao

Abstract: The half-size prototype of the multi wire drift chamber (MWDC) for the cooling storage ring (CSR) external-target experiment (CEE) was assembled and tested in 350 MeV/u Kr+Fe reactions on the heavy ion research facility in Lanzhou (HIRFL). The prototype consists of 6 sense layers, where the sense wires are stretched in three directions X, U and V, meeting $0^\circ$, $30^\circ$ and $-30^\circ$ with… ▽ More The half-size prototype of the multi wire drift chamber (MWDC) for the cooling storage ring (CSR) external-target experiment (CEE) was assembled and tested in 350 MeV/u Kr+Fe reactions on the heavy ion research facility in Lanzhou (HIRFL). The prototype consists of 6 sense layers, where the sense wires are stretched in three directions X, U and V, meeting $0^\circ$, $30^\circ$ and $-30^\circ$ with respect to the vertical axis, respectively. The sensitive area of the prototype is $76 {\rm cm} \times 76 {\rm cm}$. The amplified and shaped signals from the anode wires are digitized in a serial capacity array. Being operated with 1500 V high voltage on the anode wires, the efficiency for each layer is beyond 95\%. The tracking residual is about $301 \pm 2 \rm μm$. The performance meets the requirements of CEE. △ Less

Submitted 15 May, 2024; originally announced June 2024.

Tellegen responses in metamaterials

Authors: Qingdong Yang, Xinhua Wen, Zhongfu Li, Oubo You, Shuang Zhang

Abstract: Tellegen medium has long been a topic of debate, with its existence being contested over several decades. It was first proposed by Tellegen in 1948 and is characterized by a real-valued cross coupling between electric and magnetic responses, distinguishing it from the well-known chiral medium that has imaginary coupling coefficients. Significantly, Tellegen responses are closely linked to axion dy… ▽ More Tellegen medium has long been a topic of debate, with its existence being contested over several decades. It was first proposed by Tellegen in 1948 and is characterized by a real-valued cross coupling between electric and magnetic responses, distinguishing it from the well-known chiral medium that has imaginary coupling coefficients. Significantly, Tellegen responses are closely linked to axion dynamics, an extensively studied subject in condensed matter physics. Here, we report the realization of Tellegen metamaterials in the microwave region through a judicious combination of subwavelength metallic resonators, gyromagnetic materials, and permanent magnet discs. We observe the key signature of the Tellegen response, i.e. a Kerr rotation for reflected wave, while the polarization remains the same in the transmission direction. The retrieved effective Tellegen parameter is several orders of magnitude greater than that of natural materials. Our work opens door to a variety of nonreciprocal photonic devices and may provide a platform for studying axion physics. △ Less

Submitted 11 June, 2024; originally announced June 2024.

Comments: 19 pages, 4 figures

Symmetry enforced solution of the many-body Schrödinger equation with deep neural network

Authors: Zhe Li, Zixiang Lu, Ruichen Li, Xuelan Wen, Xiang Li, Liwei Wang, Ji Chen, Weiluo Ren

Abstract: The integration of deep neural networks with the Variational Monte Carlo (VMC) method has marked a significant advancement in solving the Schrödinger equation. In this work, we enforce spin symmetry in the neural network-based VMC calculation with modified optimization target. Our method is designed to solve for the ground state and multiple excited states with target spin symmetry at a low comput… ▽ More The integration of deep neural networks with the Variational Monte Carlo (VMC) method has marked a significant advancement in solving the Schrödinger equation. In this work, we enforce spin symmetry in the neural network-based VMC calculation with modified optimization target. Our method is designed to solve for the ground state and multiple excited states with target spin symmetry at a low computational cost. It predicts accurate energies while maintaining the correct symmetry in strongly correlated systems, even in cases where different spin states are nearly degenerate. Our approach also excels at spin-gap calculations, including the singlet-triplet gap in biradical systems, which is of high interest in photochemistry. Overall, this work establishes a robust framework for efficiently calculating various quantum states with specific spin symmetry in correlated systems, paving the way for novel discoveries in quantum science. △ Less

Submitted 3 June, 2024; originally announced June 2024.

Out-of-plane orientated self-trapped excitons enabled polarized light guiding in 2D perovskites

Authors: Junze Li, Junchao Hu, Ting Luo, Dongliang Chen, Yingying Chen, Zeyi Liu, Dingshan Gao, Xinglin Wen, Dehui Li

Abstract: Active optical waveguides combine light source and waveguides together in an individual component, which are essential for the integrated photonic chips. Although 1D luminescent materials based optical waveguides were extensively investigated, 2D waveguides allow photons to flow within a plane and serve as an ideal component for the ultracompact photonic circuits. Nevertheless, light guiding in 2D… ▽ More Active optical waveguides combine light source and waveguides together in an individual component, which are essential for the integrated photonic chips. Although 1D luminescent materials based optical waveguides were extensively investigated, 2D waveguides allow photons to flow within a plane and serve as an ideal component for the ultracompact photonic circuits. Nevertheless, light guiding in 2D planar structures normally relies on the precise control of molecular orientation, which is complicated and low yield. Here, we report a strategy to guide polarized light in 2D microflakes by making use of the out-of-plane (OP) orientation of self-trapped excitons in as-synthesized 2D perovskite microplates. A space confined crystallization method is developed to synthesize 2D perovskite microflakes with dominated broad self-trapped excitons emission at room temperature, which are highly OP orientated with a percentage of the OP component over 85%. Taking advantages of the negligible absorption coefficient and improved coupling efficiency of OP orientated self-trapped exciton emission to the planar waveguide mode of the as-synthesized perovskite microflakes, we have achieved a broadband polarized light guiding with a full width at half maximum over 120 nm. Our findings provide a promising platform for the development of ultracompact photonic circuits. △ Less

Submitted 7 April, 2024; originally announced April 2024.

Detector performance of the Gamma-ray Transient Monitor onboard DRO-A Satellite

Authors: Pei-Yi Feng, Zheng-Hua An, Da-Li Zhang, Chen-Wei Wang, Chao Zheng, Sheng Yang, Shao-Lin Xiong, Jia-Cong Liu, Xin-Qiao Li, Ke Gong, Xiao-Jing Liu, Min Gao, Xiang-Yang Wen, Ya-Qing liu, Xiao-Yun Zhao, Fan Zhang, Xi-Lei Sun, Hong Lu

Abstract: Gamma-ray Transient Monitor (GTM) is an all-sky monitor onboard the Distant Retrograde Orbit-A (DRO-A) satellite with the scientific objective of detecting gamma-ray transients ranging from 20 keV to 1 MeV. GTM is equipped with 5 Gamma-ray Transient Probe (GTP) detector modules, utilizing the NaI(Tl) scintillator coupled with a SiPM array. To reduce the SiPM noise, GTP makes use of a dedicated dua… ▽ More Gamma-ray Transient Monitor (GTM) is an all-sky monitor onboard the Distant Retrograde Orbit-A (DRO-A) satellite with the scientific objective of detecting gamma-ray transients ranging from 20 keV to 1 MeV. GTM is equipped with 5 Gamma-ray Transient Probe (GTP) detector modules, utilizing the NaI(Tl) scintillator coupled with a SiPM array. To reduce the SiPM noise, GTP makes use of a dedicated dual-channel coincident readout design. In this work, we firstly studied the impact of different coincidence times on detection efficiency and ultimately selected the 500 ns time coincidence window for offline data processing. To test the performance of GTPs and validate the Monte Carlo simulated energy response, we conducted comprehensive ground calibration tests using Hard X-ray Calibration Facility (HXCF) and radioactive sources, including energy response, detection efficiency, spatial response, bias-voltage response, and temperature dependence. We extensively presented the ground calibration results, and validated the design and mass model of GTP detector. These work paved the road for the in-flight observation and science data analysis. △ Less

Submitted 10 September, 2024; v1 submitted 15 January, 2024; originally announced January 2024.

Comments: 15 pages, 25 figures

Journal ref: Sci. China-Phys. Mech. Astron. 67, 111013 (2024)

The Energy Response of LaBr3(Ce), LaBr3(Ce,Sr) and NaI(Tl) Crystals for GECAM

Authors: Pei-Yi Feng, Xi-Lei Sun, Zheng-Hua An, Yong Deng, Cheng-Er Wang, Huang Jiang, Jun-Jie Li, Da-Li Zhang, Xin-Qiao Li, Shao-Lin Xiong, Chao Zheng, Ke Gong, Sheng Yang, Xiao-Jing Liu, Min Gao, Xiang-Yang Wen, Ya-Qing Liu, Yan-Bing Xu, Xiao-Yun Zhao, Jia-Cong Liu, Fan Zhang, Hong Lu

Abstract: The GECAM series of satellites utilize LaBr3(Ce), LaBr3(Ce,Sr), and NaI(Tl) crystals as sensitive materials for gamma-ray detectors (GRDs). To investigate the non-linearity in the detection of low-energy gamma rays and address errors in the E-C relationship calibration, comprehensive tests and comparative studies of the non-linearity of these three crystals were conducted using Compton electrons,… ▽ More The GECAM series of satellites utilize LaBr3(Ce), LaBr3(Ce,Sr), and NaI(Tl) crystals as sensitive materials for gamma-ray detectors (GRDs). To investigate the non-linearity in the detection of low-energy gamma rays and address errors in the E-C relationship calibration, comprehensive tests and comparative studies of the non-linearity of these three crystals were conducted using Compton electrons, radioactive sources, and mono-energetic X-rays. The non-linearity test results for Compton electrons and X-rays displayed substantial differences, with all three crystals showing higher non-linearity for X-rays and gamma-rays than for Compton electrons. Despite LaBr3(Ce) and LaBr3(Ce,Sr) crystals having higher absolute light yields, they exhibited a noticeable non-linear decrease in light yield, especially at energies below 400 keV. The NaI(Tl) crystal demonstrated excess light output in the 6~200 keV range, reaching a maximum excess of 9.2% at 30 keV in X-ray testing and up to 15.5% at 14 keV during Compton electron testing, indicating a significant advantage in the detection of low-energy gamma rays. Furthermore, this paper explores the underlying causes of the observed non-linearity in these crystals. This study not only elucidates the detector responses of GECAM, but also marks the inaugural comprehensive investigation into the non-linearity of domestically produced lanthanum bromide and sodium iodide crystals. △ Less

Submitted 27 December, 2023; originally announced December 2023.

Comments: 12pages, 16 figures

Nonreciprocal field transformation with active acoustic metasurfaces

Authors: X. Wen, C. Cho, X. Zhu, N. Park, J. Li

Abstract: Field transformation, as an extension of the transformation optics, provides a unique means for nonreciprocal wave manipulation, while the experimental realization remains a significant challenge as it requires stringent material parameters of the metamaterials, e.g., purely nonreciprocal bianisotropic parameters. Here, we develop and demonstrate a nonreciprocal field transformation in a 2D acoust… ▽ More Field transformation, as an extension of the transformation optics, provides a unique means for nonreciprocal wave manipulation, while the experimental realization remains a significant challenge as it requires stringent material parameters of the metamaterials, e.g., purely nonreciprocal bianisotropic parameters. Here, we develop and demonstrate a nonreciprocal field transformation in a 2D acoustic system, using an active metasurface that can independently control all constitutive parameters and achieve purely nonreciprocal Willis coupling. The field-transforming metasurface enables tailor-made field distribution manipulation, achieving localized field amplification by a predetermined ratio. Interestingly, the metasurface demonstrates the self-adaptive capability to various excitation conditions and can extend to other geometric shapes. The metasurface also achieves nonreciprocal wave propagation for internal and external excitations, demonstrating a one-way acoustic device. Such a field-transforming metasurface not only extends the framework of the transformation theory for nonreciprocal wave manipulation, but also holds significant potential in applications such as ultra-sensitive sensors and nonreciprocal communication. △ Less

Submitted 16 November, 2023; originally announced November 2023.

Comments: 20 pages, 4 figures

Stochastic spin-orbit-torque synapse and its application in uncertainty quantification

Authors: Cen Wang, Guang Zeng, Xinyu Wen, Yuhui He, Wei Luo, Shiwei Chen, Shiheng Liang, Yue Zhang

Abstract: Stochasticity plays a significant role in the low-power operation of a biological neural network. In an artificial neural network (ANN), stochasticity also contributes to critical functions such as the uncertainty quantification (UQ) for estimating the probability for the correctness of prediction. This UQ is vital for cutting-edge applications, including medical diagnostics, autopilots, and large… ▽ More Stochasticity plays a significant role in the low-power operation of a biological neural network. In an artificial neural network (ANN), stochasticity also contributes to critical functions such as the uncertainty quantification (UQ) for estimating the probability for the correctness of prediction. This UQ is vital for cutting-edge applications, including medical diagnostics, autopilots, and large language models. Thanks to high computing velocity and low dissipation, a spin-orbit-torque (SOT) device exhibits significant potential for implementing the UQ. However, up until now, the application of UQ for stochastic SOT devices remains unexplored. In this study, based on SOT-induced stochastic magnetic domain wall (DW) motion with varying velocity, we fabricated an SOT synapse that could emulate stochastic weight update following the Spike-Timing-Dependent-Plasticity (STDP) rule. Furthermore, we set up a stochastic Spiking-Neural-Network (SNN), which, when compared to its deterministic counterpart, demonstrates a clear advantage in quantifying uncertainty for diagnosing the type of breast tumor (benign or malignant). △ Less

Submitted 16 October, 2023; originally announced October 2023.

Non-standard power grid frequency statistics in Asia, Australia, and Europe

Authors: Xinyi Wen, Mehrnaz Anvari, Leonardo Rydin Gorjao, G. Cigdem Yalcin, Veit Hagenmeyer, Benjamin Schafer

Abstract: The power-grid frequency reflects the balance between electricity supply and demand. Measuring the frequency and its variations allows monitoring of the power balance in the system and, thus, the grid stability. In addition, gaining insight into the characteristics of frequency variations and defining precise evaluation metrics for these variations enables accurate assessment of the performance of… ▽ More The power-grid frequency reflects the balance between electricity supply and demand. Measuring the frequency and its variations allows monitoring of the power balance in the system and, thus, the grid stability. In addition, gaining insight into the characteristics of frequency variations and defining precise evaluation metrics for these variations enables accurate assessment of the performance of forecasts and synthetic models of the power-grid frequency. Previous work was limited to a few geographical regions and did not quantify the observed effects. In this contribution, we analyze and quantify the statistical and stochastic properties of self-recorded power-grid frequency data from various synchronous areas in Asia, Australia, and Europe at a resolution of one second. Revealing non-standard statistics of both empirical and synthetic frequency data, we effectively constrain the space of possible (stochastic) power-grid frequency models and share a range of analysis tools to benchmark any model or characterize empirical data. Furthermore, we emphasize the need to analyze data from a large range of synchronous areas to obtain generally applicable models. △ Less

Submitted 31 August, 2023; originally announced August 2023.

Comments: 7 pages; 7 figures

Forward Laplacian: A New Computational Framework for Neural Network-based Variational Monte Carlo

Authors: Ruichen Li, Haotian Ye, Du Jiang, Xuelan Wen, Chuwei Wang, Zhe Li, Xiang Li, Di He, Ji Chen, Weiluo Ren, Liwei Wang

Abstract: Neural network-based variational Monte Carlo (NN-VMC) has emerged as a promising cutting-edge technique of ab initio quantum chemistry. However, the high computational cost of existing approaches hinders their applications in realistic chemistry problems. Here, we report the development of a new NN-VMC method that achieves a remarkable speed-up by more than one order of magnitude, thereby greatly… ▽ More Neural network-based variational Monte Carlo (NN-VMC) has emerged as a promising cutting-edge technique of ab initio quantum chemistry. However, the high computational cost of existing approaches hinders their applications in realistic chemistry problems. Here, we report the development of a new NN-VMC method that achieves a remarkable speed-up by more than one order of magnitude, thereby greatly extending the applicability of NN-VMC to larger systems. Our key design is a novel computational framework named Forward Laplacian, which computes the Laplacian associated with neural networks, the bottleneck of NN-VMC, through an efficient forward propagation process. We then demonstrate that Forward Laplacian is not only versatile but also facilitates more developments of acceleration methods across various aspects, including optimization for sparse derivative matrix and efficient neural network design. Empirically, our approach enables NN-VMC to investigate a broader range of atoms, molecules and chemical reactions for the first time, providing valuable references to other ab initio methods. The results demonstrate a great potential in applying deep learning methods to solve general quantum mechanical problems. △ Less

Submitted 16 July, 2023; originally announced July 2023.

PT-symmetric feedback induced linewidth narrowing

Authors: Yuanjiang Tang, Chao Liang, Xin Wen, Weipeng Li, An-Ning Xu, Yong-Chun Liu

Abstract: Narrow linewidth is a long-pursuing goal in precision measurement and sensing. We propose a parity-time (PT )-symmetric feedback method to narrow the linewidths of resonance systems. By using a quadrature measurement-feedback loop, we transform a dissipative resonance system into a PT-symmetric system. Unlike the conventional PT-symmetric systems which typically require two or more modes, here the… ▽ More Narrow linewidth is a long-pursuing goal in precision measurement and sensing. We propose a parity-time (PT )-symmetric feedback method to narrow the linewidths of resonance systems. By using a quadrature measurement-feedback loop, we transform a dissipative resonance system into a PT-symmetric system. Unlike the conventional PT-symmetric systems which typically require two or more modes, here the PT-symmetric feedback system contains only a single resonance mode, which greatly extends the scope of applications. The method enables remarkable linewidth narrowing and enhancement of measurement sensitivity. We illustrate the concept in a thermal ensemble of atoms, achieving a 48-fold narrowing of the magnetic resonance linewidth. By applying the method in magnetometry, we realize a 22-times improvement of the measurement sensitivity. This work opens the avenue for studying non-Hermitian physics and high-precision measurements in resonance systems with feedback. △ Less

Submitted 16 May, 2023; v1 submitted 15 April, 2023; originally announced April 2023.

Comments: 5 pages, 5 figures

STCF Conceptual Design Report: Volume 1 -- Physics & Detector

Authors: M. Achasov, X. C. Ai, R. Aliberti, L. P. An, Q. An, X. Z. Bai, Y. Bai, O. Bakina, A. Barnyakov, V. Blinov, V. Bobrovnikov, D. Bodrov, A. Bogomyagkov, A. Bondar, I. Boyko, Z. H. Bu, F. M. Cai, H. Cai, J. J. Cao, Q. H. Cao, Z. Cao, Q. Chang, K. T. Chao, D. Y. Chen, H. Chen , et al. (413 additional authors not shown)

Abstract: The Super $τ$-Charm facility (STCF) is an electron-positron collider proposed by the Chinese particle physics community. It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of $0.5\times 10^{35}{\rm cm}^{-2}{\rm s}^{-1}$ or higher. The STCF will produce a data sample about a factor of 100 larger than that by the present $τ$-Charm factory -- the BEPCII,… ▽ More The Super $τ$-Charm facility (STCF) is an electron-positron collider proposed by the Chinese particle physics community. It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of $0.5\times 10^{35}{\rm cm}^{-2}{\rm s}^{-1}$ or higher. The STCF will produce a data sample about a factor of 100 larger than that by the present $τ$-Charm factory -- the BEPCII, providing a unique platform for exploring the asymmetry of matter-antimatter (charge-parity violation), in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions, as well as searching for exotic hadrons and physics beyond the Standard Model. The STCF project in China is under development with an extensive R\&D program. This document presents the physics opportunities at the STCF, describes conceptual designs of the STCF detector system, and discusses future plans for detector R\&D and physics case studies. △ Less

Submitted 5 October, 2023; v1 submitted 28 March, 2023; originally announced March 2023.

Journal ref: Front. Phys. 19(1), 14701 (2024)

Ground calibration of Gamma-Ray Detectors of GECAM-C

Authors: Chao Zheng, Zheng-Hua An, Wen-Xi Peng, Da-Li Zhang, Shao-Lin Xiong, Rui. Qiao, Yan-Qiu Zhang, Wang-Chen Xue, Jia-Cong Liu, Pei-Yi Feng, Ce. Cai, Min Gao, Ke Gong, Dong-Ya Guo, Dong-Jie Hou, Gang Li, Xin-Qiao Li, Yan-Guo Li, Mao-Shun Li, Xiao-Hua Liang, Ya-Qing Liu, Xiao-Jing Liu, Li-Ming Song, Xi-Lei Sun, Wen-Jun Tan , et al. (13 additional authors not shown)

Abstract: As a new member of GECAM mission, GECAM-C (also named High Energy Burst Searcher, HEBS) was launched onboard the SATech-01 satellite on July 27th, 2022, which is capable to monitor gamma-ray transients from $\sim$ 6 keV to 6 MeV. As the main detector, there are 12 gamma-ray detectors (GRDs) equipped for GECAM-C. In order to verify the GECAM-C GRD detector performance and to validate the Monte Carl… ▽ More As a new member of GECAM mission, GECAM-C (also named High Energy Burst Searcher, HEBS) was launched onboard the SATech-01 satellite on July 27th, 2022, which is capable to monitor gamma-ray transients from $\sim$ 6 keV to 6 MeV. As the main detector, there are 12 gamma-ray detectors (GRDs) equipped for GECAM-C. In order to verify the GECAM-C GRD detector performance and to validate the Monte Carlo simulations of detector response, comprehensive on-ground calibration experiments have been performed using X-ray beam and radioactive sources, including Energy-Channel relation, energy resolution, detection efficiency, SiPM voltage-gain relation and the non-uniformity of positional response. In this paper, the detailed calibration campaigns and data analysis results for GECAM-C GRDs are presented, demonstrating the excellent performance of GECAM-C GRD detectors. △ Less

Submitted 30 May, 2023; v1 submitted 1 March, 2023; originally announced March 2023.

Comments: third version

The performance of SiPM-based gamma-ray detector (GRD) of GECAM-C

Authors: Dali Zhang, Chao Zheng, Jiacong Liu, Zhenghua An, Chenwei Wang, Xiangyang Wen, Xinqiao Li, Xilei Sun, Ke Gong, Yaqing Liu, Xiaojing Liu, Sheng Yang, Wenxi Peng, Rui Qiao, Dongya Guo, Peiyi Feng, Yanqiu Zhang, Wangchen Xue, Wenjun Tan, Ce Cai, Shuo Xiao, Qibin Yi, Yanbing Xu, Min Gao, Jinzhou Wang , et al. (20 additional authors not shown)

Abstract: As a new member of GECAM mission, the GECAM-C (also called High Energy Burst Searcher, HEBS) is a gamma-ray all-sky monitor onboard SATech-01 satellite, which was launched on July 27th, 2022 to detect gamma-ray transients from 6 keV to 6 MeV, such as Gamma-Ray Bursts (GRBs), high energy counterpart of Gravitational Waves (GWs) and Fast Radio Bursts (FRBs), and Soft Gamma-ray Repeaters (SGRs). Toge… ▽ More As a new member of GECAM mission, the GECAM-C (also called High Energy Burst Searcher, HEBS) is a gamma-ray all-sky monitor onboard SATech-01 satellite, which was launched on July 27th, 2022 to detect gamma-ray transients from 6 keV to 6 MeV, such as Gamma-Ray Bursts (GRBs), high energy counterpart of Gravitational Waves (GWs) and Fast Radio Bursts (FRBs), and Soft Gamma-ray Repeaters (SGRs). Together with GECAM-A and GECAM-B launched in December 2020, GECAM-C will greatly improve the monitoring coverage, localization, as well as temporal and spectral measurements of gamma-ray transients. GECAM-C employs 12 SiPM-based Gamma-Ray Detectors (GRDs) to detect gamma-ray transients . In this paper, we firstly give a brief description of the design of GECAM-C GRDs, and then focus on the on-ground tests and in-flight performance of GRDs. We also did the comparison study of the SiPM in-flight performance between GECAM-C and GECAM-B. The results show GECAM-C GRD works as expected and is ready to make scientific observations. △ Less

Submitted 7 March, 2023; v1 submitted 1 March, 2023; originally announced March 2023.

Comments: 18 pages, 16 figures

Fundamental cause for superior optoelectronic properties in halide perovskites

Authors: Xiaoming Wen, Baohua Jia

Abstract: Halide perovskites have emerged as revolutionary materials for high performance photovoltaics and optoelectronics due to their superior optoelectronic properties. The physical origin for the superior optoelectronic properties of halide perovskites so far is still poorly understood. Here we propose and demonstrate a hypothesis that electron upconversion (detrapping) driven by ionic energy reservoir… ▽ More Halide perovskites have emerged as revolutionary materials for high performance photovoltaics and optoelectronics due to their superior optoelectronic properties. The physical origin for the superior optoelectronic properties of halide perovskites so far is still poorly understood. Here we propose and demonstrate a hypothesis that electron upconversion (detrapping) driven by ionic energy reservoir is the fundamental cause for the superior optoelectronic properties of halide perovskites. We fully consider ionic influence on the electronic dynamics in mixed ionic-electronic conduction system by introducing new concepts of ionic energy reservoir, ion-electron coupling and ion-phonon scattering. We clarified that the ionic beneficial effect originates from the different mechanisms from that of the detrimental effect of mobile ion. Our hypothesis consistently interprets that the electron detrapping directly leads to significantly enhanced fluorescence efficiency, prolonged carrier lifetime, and increased diffusion length, as well as the anomalous phenomena of defect healing and defect tolerance, which are responsible for the excellent device performance of halide perovskites. By adding the ion-electron coupling into the rate equations, we establish the physical correlation between electronic dynamics in the timescale of nanosecond-microsecond and ionic dynamics in the timescales of second to hour. This finding adds the missing puzzle into the holistic physics picture and provides a deep understanding of halide perovskites and ion-electron interaction in mixed ionic-electronic semiconductors. Our results suggest the possibility of maximizing the potential of halide perovskite devices through enhancing ion-electron coupling. △ Less

Submitted 2 August, 2023; v1 submitted 25 January, 2023; originally announced January 2023.

Comments: 28 pages, 5 figures

Flamelet modeling of thermo-diffusively unstable hydrogen-air flames

Authors: Hannes Böttler, Haris Lulic, Matthias Steinhausen, Xu Wen, Christian Hasse, Arne Scholtissek

Abstract: In order to reduce CO2 emissions, hydrogen combustion has become increasingly relevant for technical applications. In this context, lean H2-air flames show promising features but, among other characteristics, they tend to exhibit thermo-diffusive instabilities. The formation of cellular structures associated with these instabilities leads to an increased flame surface area which further promotes t… ▽ More In order to reduce CO2 emissions, hydrogen combustion has become increasingly relevant for technical applications. In this context, lean H2-air flames show promising features but, among other characteristics, they tend to exhibit thermo-diffusive instabilities. The formation of cellular structures associated with these instabilities leads to an increased flame surface area which further promotes the flame propagation speed, an important reference quantity for design, control, and safe operation of technical combustors. While many studies have addressed the physical phenomena of intrinsic flame instabilities in the past, there is also a demand to predict such flame characteristics with reduced-order models to allow computationally efficient simulations. In this work, a H2-air spherical expanding flame, which exhibits thermo-diffusive instabilities, is studied with flamelet-based modeling approaches both in a-priori and a-posteriori manner. A recently proposed Flamelet/Progress Variable (FPV) model, with a manifold based on unstretched planar flames, and a novel FPV approach, which takes into account a large curvature variation in the tabulated manifold, are compared to detailed chemistry (DC) calculations. First, both FPV approaches are assessed in terms of an a-priori test with the DC reference dataset. Thereafter, the a-posteriori assessment contains two parts: a linear stability analysis of perturbed planar flames and the simulation of the spherical expanding flame. Both FPV models are systematically analyzed considering global and local flame properties in comparison to the DC reference data. It is shown that the new FPV model, incorporating large curvature variations in the manifold, leads to improved predictions for the microstructure of the corrugated flame front and the formation of cellular structures, while global flame properties are reasonably well reproduced by both models. △ Less

Submitted 17 January, 2023; originally announced January 2023.

Numerical modeling of pulverized iron flames in a multidimensional hot counterflow burner

Authors: Xu Wen, Arne Scholtissek, Jeroen van Oijen, Jeffery Bergthorson, Christian Hasse

Abstract: Pulverized iron flames stabilized in a multidimensional hot counterflow burner are simulated using a numerical model, which is extended from the state-of-the-art model developed by Hazenberg and van Oijen (PCI, 2021) considering unsteady effects. The results are compared to available experimental data (McRae et al., PCI, 2019), including particle image velocimetry measurements, a direct flame phot… ▽ More Pulverized iron flames stabilized in a multidimensional hot counterflow burner are simulated using a numerical model, which is extended from the state-of-the-art model developed by Hazenberg and van Oijen (PCI, 2021) considering unsteady effects. The results are compared to available experimental data (McRae et al., PCI, 2019), including particle image velocimetry measurements, a direct flame photo, the flow field velocity and the flame speed for different iron and oxygen concentrations. The comparison shows that the particle dynamics and flame shape can be reasonably well predicted. The flow field velocity and flame speed also show quantitative agreement between the simulation and the experiment. Based on the validated simulation results, the iron combustion characteristics, including the thermal structures and the multidimensional effects, are analyzed for different oxidizer environments. The analysis shows that the iron particles undergo a transition from kinetic-controlled regime (up to ignition) to a diffusion-controlled regime (burning) at the central axis for both environments with the particle temperature being higher than the gas temperature at the flame front, which is indicated by the Damköhler number. For the hot counterflow burner, there exist multidimensional effects, i.e., the temperature and Damköhler number change along the radial direction. △ Less

Submitted 20 December, 2022; originally announced December 2022.

Journal ref: Volume 248, February 2023, 112572

Ultrashort dissipative Raman solitons in Kerr resonators driven with phase-coherent optical pulses

Authors: Zongda Li, Yiqing Xu, Sophie Shamailov, Xiaoxiao Wen, Wenlong Wang, Xiaoming Wei, Zhongmin Yang, Stéphane Coen, Stuart G. Murdoch, Miro Erkintalo

Abstract: External driving of passive, nonlinear optical resonators has emerged over the past decade as a novel route for the generation of ultrashort optical pulses and corresponding broadband frequency combs. Whilst the pulse formation dynamics in such systems differ dramatically from those manifesting themselves in conventional mode-locked lasers, the demarcation between the two traditionally distinct pa… ▽ More External driving of passive, nonlinear optical resonators has emerged over the past decade as a novel route for the generation of ultrashort optical pulses and corresponding broadband frequency combs. Whilst the pulse formation dynamics in such systems differ dramatically from those manifesting themselves in conventional mode-locked lasers, the demarcation between the two traditionally distinct paradigms has recently begun to blur, with demonstrations of hybrid systems incorporating both external driving and active media shown to offer specific advantages. Here we explore a new pathway for ultrashort pulse generation at the interface of externally-driven passive resonators and lasers. By leveraging the nonlinear Raman gain inherent to fused silica, we achieve deterministic generation of low-noise dissipative solitons with durations well below 100 fs via phase-coherent pulsed driving of resonators made of standard, commercially-available optical fibre. We explore and explain the physics of the new dissipative Raman soliton states, identifying scaling laws that govern the pulses' characteristics and that allow output repetition rates to be scaled at will without influencing the soliton duration. The scheme explored in our work enables the shortest ever pulses generated in resonators (active or passive) made from a single commercially-available optical fibre, and it has the potential to be transferred into a chip-scale format by using existing dispersion-engineered silica microresonators. △ Less

Submitted 15 December, 2022; originally announced December 2022.

Comments: 15 pages, 7 figures

Acoustic amplifying diode using non-reciprocal Willis coupling

Authors: Xinhua Wen, Heung Kit Yip, Choonlae Cho, Jensen Li, Namkyoo Park

Abstract: We propose a concept called acoustic amplifying diode in combining both signal isolation and amplification in a single device. The signal is exponentially amplified in one direction with no reflection and is completely absorbed in another. In this case, the reflection is eliminated from the device in both directions due to impedance matching, preventing backscattering to the signal source. Here, w… ▽ More We propose a concept called acoustic amplifying diode in combining both signal isolation and amplification in a single device. The signal is exponentially amplified in one direction with no reflection and is completely absorbed in another. In this case, the reflection is eliminated from the device in both directions due to impedance matching, preventing backscattering to the signal source. Here, we experimentally demonstrate the amplifying diode using an active metamaterial with non-reciprocal Willis coupling. We also discuss the situation with the presence of both reciprocal and non-reciprocal Willis couplings for more flexibility in implementation. The concept of acoustic amplifying diode will enable applications in sound isolation, sensing and communication, in which non-reciprocity can play an important role. △ Less

Submitted 29 October, 2022; originally announced October 2022.

Comments: 13 pages, 4 figures

Fe-assisted epitaxial growth of 4-inch single-crystal transition-metal dichalcogenides on c-plane sapphire without miscut angle

Authors: Hui Li, Junbo Yang, Xiaohui Li, Mo Cheng, Wang Feng, Ruofan Du, Yuzhu Wang, Luying Song, Xia Wen, Lei Liao, Yanfeng Zhang, Jianping Shi, Jun He

Abstract: Epitaxial growth and controllable doping of wafer-scale single-crystal transition-metal dichalcogenides (TMDCs) are two central tasks for extending Moore's law beyond silicon. However, despite considerable efforts, addressing such crucial issues simultaneously under two-dimensional (2D) confinement is yet to be realized. Here we design an ingenious epitaxial strategy to synthesize record-breaking… ▽ More Epitaxial growth and controllable doping of wafer-scale single-crystal transition-metal dichalcogenides (TMDCs) are two central tasks for extending Moore's law beyond silicon. However, despite considerable efforts, addressing such crucial issues simultaneously under two-dimensional (2D) confinement is yet to be realized. Here we design an ingenious epitaxial strategy to synthesize record-breaking 4-inch single-crystal Fe-doped TMDCs monolayers on industry-compatible c-plane sapphire without miscut angle. In-depth characterizations and theoretical calculations reveal that the introduction of Fe significantly decreases the formation energy of parallel steps on sapphire surfaces and contributes to the edge-nucleation of unidirectional TMDCs domains (>99%). The ultrahigh electron mobility (~86 cm2 V -1 s-1) and remarkable on/off current ratio (~108) are discovered on 4-inch single-crystal Fe-MoS2 monolayers due to the ultralow contact resistance and perfect Ohmic contact with metal electrodes. This work represents a substantial leap in terms of bridging the synthesis and doping of wafer-scale single-crystal 2D semiconductors without the need for substrate miscut, which should promote the further device downscaling and extension of Moore's law. △ Less

Submitted 16 September, 2022; originally announced September 2022.

Comments: 17 pages, 5 figures

Quantum support vector machines for aerodynamic classification

Authors: Xi-Jun Yuan, Zi-Qiao Chen, Yu-Dan Liu, Zhe Xie, Xian-Min Jin, Ying-Zheng Liu, Xin Wen, Hao Tang

Abstract: Aerodynamics plays an important role in aviation industry and aircraft design. Detecting and minimizing the phenomenon of flow separation from scattered pressure data on airfoil is critical for ensuring stable and efficient aviation. However, since it is challenging to understand the mechanics of flow field separation, the aerodynamic parameters are emphasized for the identification and control of… ▽ More Aerodynamics plays an important role in aviation industry and aircraft design. Detecting and minimizing the phenomenon of flow separation from scattered pressure data on airfoil is critical for ensuring stable and efficient aviation. However, since it is challenging to understand the mechanics of flow field separation, the aerodynamic parameters are emphasized for the identification and control of flow separation. It has been investigated extensively using traditional algorithms and machine learning methods such as the support vector machine (SVM) models. Recently, a growing interest in quantum computing and its applications among wide research communities sheds light upon the use of quantum techniques to solve aerodynamic problems. In this paper, we apply qSVM, a quantum SVM algorithm based on the quantum annealing model, to identify whether there is flow separation, with their performance in comparison to the widely-used classical SVM. We show that our approach outperforms the classical SVM with an 11.1% increase of the accuracy, from 0.818 to 0.909, for this binary classification task. We further develop multi-class qSVMs based on one-against-all algorithm. We apply it to classify multiple types of the attack angles to the wings, where the advantage over the classical multi-class counterpart is maintained with an accuracy increased from 0.67 to 0.79, by 17.9%. Our work demonstrates a useful quantum technique for classifying flow separation scenarios, and may promote rich investigations for quantum computing applications in fluid dynamics. △ Less

Submitted 15 August, 2022; originally announced August 2022.

Comments: 12 pages, 4 figures, 3 supplementary figures

Journal ref: Intelligent Computing 2, 57 (2023)

A data management system for machine learning research of tokamak

Authors: Chenguang Wan, Zhi Yu, Xiaojuan Liu, Xinghao Wen, Xi Deng, Jiangang Li

Abstract: In recent years, machine learning (ML) research methods have received increasing attention in the tokamak community. The conventional database (i.e., MDSplus for tokamak) of experimental data has been designed for small group consumption and is mainly aimed at simultaneous visualization of a small amount of data. The ML data access patterns fundamentally differ from traditional data access pattern… ▽ More In recent years, machine learning (ML) research methods have received increasing attention in the tokamak community. The conventional database (i.e., MDSplus for tokamak) of experimental data has been designed for small group consumption and is mainly aimed at simultaneous visualization of a small amount of data. The ML data access patterns fundamentally differ from traditional data access patterns. The typical MDSplus database is increasingly showing its limitations. We developed a new data management system suitable for tokamak machine learning research based on Experimental Advanced Superconducting Tokamak (EAST) data. The data management system is based on MongoDB and Hierarchical Data Format version 5 (HDF5). Currently, the entire data management has more than 3000 channels of data. The system can provide highly reliable concurrent access. The system includes error correction, MDSplus original data conversion, and high-performance sequence data output. Further, some valuable functions are implemented to accelerate ML model training of fusion, such as bucketing generator, the concatenating buffer, and distributed sequence generation. This data management system is more suitable for fusion machine learning model R\&D than MDSplus, but it can not replace the MDSplus database. The MDSplus database is still the backend for EAST tokamak data acquisition and storage. △ Less

Submitted 18 November, 2022; v1 submitted 16 June, 2022; originally announced June 2022.

Formulations of Hydrodynamic Force in the Transition Stage of the Water Entry of Linear Wedges with Constant and Varying Speeds

Authors: Xueliang Wen, Peiqing Liu, Alessandro Del Buono, Qiulin Qu, Alessandro Iafrati

Abstract: There is an increasing need to develop a two-dimensional (2D) water entry model including the slamming and transition stages for the 2.5-dimensional (2.5D) method being used on the take-off and water landing of seaplanes, and for the strip theory or 2D+t theory being used on the hull slamming. Motivated by that, this paper numerically studies the transition stage of the water entry of a linear wed… ▽ More There is an increasing need to develop a two-dimensional (2D) water entry model including the slamming and transition stages for the 2.5-dimensional (2.5D) method being used on the take-off and water landing of seaplanes, and for the strip theory or 2D+t theory being used on the hull slamming. Motivated by that, this paper numerically studies the transition stage of the water entry of a linear wedge with constant and varying speeds, with assumptions that the fluid is incompressible, inviscid and with negligible effects of gravity and surface tension, and the flow is irrotational. For the constant speed impact, the similitude of the declining forces of different deadrise angles in the transition stage are found by scaling the difference between the maximum values in the slamming stage and the results of steady supercavitating flow. The formulation of the hydrodynamic force is conducted based on the similitude of the declining forces in the transition stage together with the linear increasing results in the slamming stage. For the varying speed impact, the hydrodynamic force caused by the acceleration effect in the transition stage is formulated by an added mass coefficient with an averaged increase of 27.13% compared with that of slamming stage. Finally, a general expression of the hydrodynamic forces in both the slamming and transition stages is thus proposed and has good predictions in the ranges of deadrise angles from 5 deg to 70 deg for both the constant and varying speed impacts. △ Less

Submitted 3 January, 2022; originally announced January 2022.

Comments: 47 pages, 32 figures, 3 tables

Ultra-wideband electrostrictive mechanical antenna

Authors: Jianchun Xu, Zhao Li, Xuchao Pan, Xi Wen, Jinqing Cao, Wen Gong, Shaolong Yang, Ming Lei, Fangzhou Yao, Ke Bi

Abstract: Conventional mechanical antennas provide a strategy in long-wave communication with a surprisingly compact size below 1/1,000 of the wavelength. However, the narrow bandwidth and weak field intensity seriously hamper its practical applications. Here, we present a mechanical antenna based on the electrostrictive effect of PMN-PT-based relaxor ferroelectric ceramic to improve radiation capacity and… ▽ More Conventional mechanical antennas provide a strategy in long-wave communication with a surprisingly compact size below 1/1,000 of the wavelength. However, the narrow bandwidth and weak field intensity seriously hamper its practical applications. Here, we present a mechanical antenna based on the electrostrictive effect of PMN-PT-based relaxor ferroelectric ceramic to improve radiation capacity and achieve ultra-wideband characteristics (10 kHz - 1 MHz, the relative bandwidth is beyond 196%). Determined by the different underlying mechanism, the mechanical antenna based on the electrostrictive effect exhibits excellent communication properties from traditional mechanical antennas. The functions of signal coding, transmitting, receiving, and decoding were experimentally demonstrated. This approach offers a promising way of constructing mechanical antennas for long-wave communication. △ Less

Submitted 30 December, 2021; originally announced December 2021.

Comments: 28 pages, 10 figures,

The Design and Performance of Charged Particle Detector onboard the GECAM Mission

Authors: Y. B. Xu, X. L. Sun, S. Yang, X. Q. Li, W. X. Peng, K. Gong, X. H. Liang, Y. Q. Liu, D. Y. Guo, H. Wang, C. Y. Li, Z. H. An, J. J. He, X. J. Liu, S. L. Xiong, X. Y. Wen, Fan Zhang, D. L. Zhang, X. Y. Zhao, C. Y. Zhang, C. Cai, Z. Chang, G. Chen, C. Chen, Y. Y. Du , et al. (25 additional authors not shown)

Abstract: The Gravitational Wave highly energetic Electromagnetic Counterpart All-sky Monitor (GECAM) is dedicated to detecting gravitational wave gamma-ray bursts. It is capable of all-sky monitoring over and discovering gamma-ray bursts and new radiation phenomena. GECAM consists of two microsatellites, each equipped with 8 charged particle detectors (CPDs) and 25 gamma-ray detectors (GRDs). The CPD is us… ▽ More The Gravitational Wave highly energetic Electromagnetic Counterpart All-sky Monitor (GECAM) is dedicated to detecting gravitational wave gamma-ray bursts. It is capable of all-sky monitoring over and discovering gamma-ray bursts and new radiation phenomena. GECAM consists of two microsatellites, each equipped with 8 charged particle detectors (CPDs) and 25 gamma-ray detectors (GRDs). The CPD is used to measure charged particles in the space environment, monitor energy and flow intensity changes, and identify between gamma-ray bursts and space charged particle events in conjunction with GRD. CPD uses plastic scintillator as the sensitive material for detection, silicon photomultiplier (SiPM) array as the optically readable device, and the inlaid Am-241 radioactive source as the onboard calibration means. In this paper, we will present the working principle, physical design, functional implementation and preliminary performance test results of the CPD. △ Less

Submitted 9 December, 2021; originally announced December 2021.

Comments: accepted to RDTM

Inflight performance of the GECAM Gamma-ray and Charge particle Detectors

Authors: X. Q. Li, X. Y. Wen, S. L. Xiong, K. Gong, D. L. Zhang, Z. H. An, Y. B. Xu, Y. Q. Liu, C. Cai, Z. Chang, G. Chen, C. Chen, Y. Y. Du, M. Gao, R. Gao, D. Y. Guo, J. J. He, D. J. Hou, Y. G. Li, C. Li, C. Y. Li, G. Li, L. Li, Q. X. Li, X. F. Li , et al. (34 additional authors not shown)

Abstract: The GECAM mission consists of two identical microsatellites (GECAM-A and GECAM-B). Each satellite is equipped with 25 gamma-ray detectors (GRD) and 8 charged particle detectors (CPD). The main scientific objective of the GECAM mission is to detect gamma-ray bursts (GRBs) associated with the gravitational wave events produced by the merging of binary compact stars. After the launch on Dec. 10, 2020… ▽ More The GECAM mission consists of two identical microsatellites (GECAM-A and GECAM-B). Each satellite is equipped with 25 gamma-ray detectors (GRD) and 8 charged particle detectors (CPD). The main scientific objective of the GECAM mission is to detect gamma-ray bursts (GRBs) associated with the gravitational wave events produced by the merging of binary compact stars. After the launch on Dec. 10, 2020 , we carried out a series of on orbit tests. This paper introduces the test results of the GECAM-B satellite. According to the in-flight performance, the energy band for gamma-ray detection of GECAM-B is from about 7 keV to 3.5 MeV. GECAM-B can achieve prompt localization of GRBs. For the first time, GECAM-B realized a quasi-real-time transmission of trigger information using Beidou-3 RDSS. Keywords GECAM, gamma-ray burst, gravitational wave, GRD, CPD △ Less

Submitted 9 December, 2021; originally announced December 2021.

Comments: 16 pages, 8 figures

Quantum-enhanced rubidium atomic magnetometer based on Faraday rotation via 795-nm Stokes operator squeezed light

Authors: Lele Bai, Xin Wen, Yulin Yang, Lulu Zhang, Jun He, Yanhua Wang, Junmin Wang

Abstract: With the help of Stokes operator S2 squeezed state (also called polarization squeezed state (PSS)) of 795-nm light, rubidium-87 (87Rb) atomic magnetometer based on Faraday rotation has been implemented and characterized.The PSS of Stokes operator S2 of 795-nm light has been prepared by means of coherently combining the polarization coherent state (PCS) of a linearly p-polarized bright 795-nm light… ▽ More With the help of Stokes operator S2 squeezed state (also called polarization squeezed state (PSS)) of 795-nm light, rubidium-87 (87Rb) atomic magnetometer based on Faraday rotation has been implemented and characterized.The PSS of Stokes operator S2 of 795-nm light has been prepared by means of coherently combining the polarization coherent state (PCS) of a linearly p-polarized bright 795-nm light beam and a linearly s-polarized squeezed vacuum state (SVS) generated by a 397.5-nm ultraviolet laser pumped sub-threshold optical parametric oscillator (OPO) with a PPKTP bulk crystal inside the OPO cavity.PSS with a squeezing level of -3.7 has been achieved around the analysis frequency of 10 kHz. At different transitions of D1 line, various frequency detuning, and reasonable atomic vapor cells temperature, Faraday rotation has been measured and compared.To decrease absorption (scattering) losses and the back-action from atomic spin noise to the probe beams polarization noise for maintaining the quantum properties of PSS of Stokes operator S2 of 795-nm light, we had to run our magnetometer with 87Rb vapor cells temperature below 60, at which the PSS was almost destroyed.The sensitivities of magnetic field measurement were characterized via measuring signal-to-noise ratio of the alternating current (AC) calibrated magnetic field signal with a balanced polarimeter. Under the conditions of the atomic number density of 5.8*1010 /cm3 and the probe beam with a detuning of - 400 MHz relative to the 5S1/2 (Fg=2) - 5P1/2 (Fe=1) transition of 87Rb D1 line, a typical sensitivity of 19.5 pT/Hz1/2 has been achieved employing PSS of Stokes operator S2 as the probe, compared with a sensitivity of 28.3 pT/Hz1/2 using PCS as the probe.We preliminarily demonstrated that the quantum-enhanced sensitivity in a Faraday-rotation-based 87Rb atomic magnetometer with the help of PSS of 795-nm light. △ Less

Submitted 5 December, 2021; v1 submitted 30 November, 2021; originally announced December 2021.

Comments: 8 pages, 5 figures J. Opt. 23 (2021) 085202

Enhancement of spin noise spectroscopy of rubidium atomic ensemble by using of the polarization squeezed light

Authors: Lele Bai, Lulu Zhang, Yongbiao Yang, Rui Chang, Yao Qin, Jun He, Xin Wen, Junmin Wang

Abstract: We measured the spin noise spectroscopy (SNS) of rubidium atomic ensemble with two different atomic vapor cells (filled with the buffer gases or coated with paraffin film on the inner wall), and demonstrated the enhancement of signal to noise ratio (SNR) by using of the polarization squeezed state (PSS) of 795 nm light field with Stokes operator S2 squeezed. PSS is prepared by locking the relative… ▽ More We measured the spin noise spectroscopy (SNS) of rubidium atomic ensemble with two different atomic vapor cells (filled with the buffer gases or coated with paraffin film on the inner wall), and demonstrated the enhancement of signal to noise ratio (SNR) by using of the polarization squeezed state (PSS) of 795 nm light field with Stokes operator S2 squeezed. PSS is prepared by locking the relative phase between the squeezed vacuum state of light obtained by a sub-threshold optical parametric oscillator and the orthogonal polarized local oscillator beam by means of the quantum noise lock. Under the same conditions, PSS can be employed not only to improve SNR, but also to keep the full width at half maximum (FWHM) of SNS unchanged, compared with the case of using polarization coherent state (PCS), and the enhancement of SNR is positively correlated with the squeezing level of PSS. With the increase of probe laser power and atomic number density, the SNR and FWHM of SNS will increase correspondingly. With the help of PSS of Stokes operator S2, quantum enhancement of both SNR and FWHM of SNS signal has been demonstrated by controlling optical power of the S2 polarization squeezed light beam or atomic number density in our experiments. △ Less

Submitted 18 November, 2021; originally announced November 2021.

Gain stabilization and consistency correction approach for multiple SiPM-based gamma-ray detectors on GECAM

Authors: Dali Zhang, Xinqiao Li, Xiangyang Wen, Shaolin Xiong, Zhenghua An, Xilei Sun, Rui Qiao, Zhengwei Li, Ke Gong, Dongjie Hou, Yanguo Li, Xiaohua Liang, Xiaojing Liu, Yaqing Liu, Wenxi Peng, Sheng Yang, Fan Zhang, Xiaoyun Zhao, Ce Cai, Chaoyang Li, Jiacong Liu, Shuo Xiao, Chenwei Wang, Qibin Yi, Chao Zheng

Abstract: Each satellite of the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM, mission) consists of 25 SiPM based gamma-ray detectors (GRDs). Although SiPM based GRD has merits of compact size and low bias-voltage, the drift of the SiPM gain with temperature is a severe problem for GRD performance. An adaptive voltage supply source was designed to automatically adjust the… ▽ More Each satellite of the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM, mission) consists of 25 SiPM based gamma-ray detectors (GRDs). Although SiPM based GRD has merits of compact size and low bias-voltage, the drift of the SiPM gain with temperature is a severe problem for GRD performance. An adaptive voltage supply source was designed to automatically adjust the SiPM bias voltage to compensate the temperature effects and keep the gain stable. This approach has been proved to be effective during both the on-ground and in-flight tests. The in-flight measured variation of the SiPM gain is within 2%. To reduce the gain non-uniformity of GRDs, an iterative bias voltage adjustment approach is proposed and implemented. The gain non-uniformity is reduced from 17% to 0.6%. In this paper, the gain stabilization and consistency correction approach are presented and discussed in detail. △ Less

Submitted 9 December, 2021; v1 submitted 4 October, 2021; originally announced October 2021.

Comments: 14 pages, 21 figures

Quality assurance test and Failure Analysis of SiPM Arrays of GECAM Satellites

Authors: D. L. Zhang, M. Gao, X. L. Sun, X. Q. Li, Z. H. An, X. Y. Wen, C. Cai, Z. Chang, G. Chen, C. Chen, Y. Y. Du, R. Gao, K. Gong, D. Y. Guo, J. J. He, D. J. Hou, Y. G. Li, C. Y. Li, G. Li, L. Li, X. F. Li, M. S. Li, X. H. Liang, X. J. Liu, Y. Q. Liu , et al. (23 additional authors not shown)

Abstract: The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) satellite consists of two small satellites. Each GECAM payload contains 25 gamma ray detectors (GRD) and 8 charged particle detectors (CPD). GRD is the main detector which can detect gamma-rays and particles and localize the Gamma-Ray Bursts (GRB),while CPD is used to help GRD to discriminate gamma-ray bursts an… ▽ More The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) satellite consists of two small satellites. Each GECAM payload contains 25 gamma ray detectors (GRD) and 8 charged particle detectors (CPD). GRD is the main detector which can detect gamma-rays and particles and localize the Gamma-Ray Bursts (GRB),while CPD is used to help GRD to discriminate gamma-ray bursts and charged particle bursts. The GRD makes use of lanthanum bromide (LaBr3) crystal readout by SiPM. As the all available SiPM devices belong to commercial grade, quality assurance tests need to be performed in accordance with the aerospace specifications. In this paper, we present the results of quality assurance tests, especially a detailed mechanism analysis of failed devices during the development of GECAM. This paper also summarizes the application experience of commercial-grade SiPM devices in aerospace payloads, and provides suggestions for forthcoming SiPM space applications. △ Less

Submitted 9 December, 2021; v1 submitted 1 September, 2021; originally announced September 2021.

Comments: 13 pages, 23 figures

Journal ref: RDTM-D-21-00057R4.2021.9.1

Performance Prediction of InP/GaAsSb Double Heterojunction Bipolar Transistors for THz applications

Authors: Xin Wen, Akshay Arabhavi, Wei Quan, Olivier Ostinelli, Chhandak Mukherjee, Marina Deng, Sébastien Frégonèse, Thomas Zimmer, Cristell Maneux, Colombo R. Bolognesi, Mathieu Luisier

Abstract: The intrinsic performance of "type-II" InP/GaAsSb double heterojunction bipolar transistors (DHBTs) towards and beyond THz is predicted and analyzed based on a multi-scale technology computer aided design (TCAD) modeling platform calibrated against experimental measurements. Two-dimensional hydrodynamic simulations are combined with 1-D full-band, atomistic quantum transport calculations to shed l… ▽ More The intrinsic performance of "type-II" InP/GaAsSb double heterojunction bipolar transistors (DHBTs) towards and beyond THz is predicted and analyzed based on a multi-scale technology computer aided design (TCAD) modeling platform calibrated against experimental measurements. Two-dimensional hydrodynamic simulations are combined with 1-D full-band, atomistic quantum transport calculations to shed light on future DHBT generations whose dimensions are decreased step-by-step, starting from the current device configuration. Simulations predict that a peak transit frequency $f_{T,peak}$ of around 1.6 THz could be reached in aggressively scaled type-II DHBTs with a total thickness of 256 nm and an emitter width $W_E$ of 37.5 nm. The corresponding breakdown voltage $BV_{CEO}$ is estimated to be 2.2 V. The investigations are put in perspective with two DHBT performance limiting factors, self-heating and breakdown characteristics. △ Less

Submitted 18 July, 2021; originally announced July 2021.

Comments: 10 pages, 11 figures

Journal ref: Journal of Applied Physics 130, 034502, 2021

Design and test of a portable Gamma-Ray Burst simulator for GECAM

Authors: Can Chen, Shuo Xiao, Shaolin Xiong, Nian Yu, Xiangyang Wen, Ke Gong, Xinqiao Li, Chaoyang Li, Dongjie Hou, Xiongtao Yang, Zijian Zhao, Yuxuan Zhu, Dali Zhang, Zhenghua An, Xiaoyun Zhao, Yupeng Xu, Yusa Wang

Abstract: The main scientific goal of the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is to monitor various types of Gamma-Ray Bursts (GRB) originated from merger of binary compact stars, which could also produce gravitational wave, and collapse of massive stars. In order to study the response of GECAM Gamma-Ray Detectors (GRDs) to high-energy bursts and test the in-fl… ▽ More The main scientific goal of the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is to monitor various types of Gamma-Ray Bursts (GRB) originated from merger of binary compact stars, which could also produce gravitational wave, and collapse of massive stars. In order to study the response of GECAM Gamma-Ray Detectors (GRDs) to high-energy bursts and test the in-flight trigger and localization software of GECAM before the launch, a portable GRB simulator device is designed and implemented based on grid controlled X-ray tube (GCXT) and direct digital synthesis (DDS) technologies. The design of this GRB simulator which modulates X-ray flux powered by high voltage up to 20 kV is demonstrated, and the time jitter (FWHM) of the device is about 0.9 $μ$s. Before the launch in December, 2020, both two GECAM satellites were irradiated by different types of GRBs (including short and long bursts in duration) generated by this GRB simulator. The light curves detected with GECAM/GRDs are consistent with the programmed input functions within statistical uncertainties, indicating the good performance of both the GRDs and the GRB simulator. △ Less

Submitted 10 July, 2021; v1 submitted 26 June, 2021; originally announced June 2021.

Comments: 15 pages, 12 figures, accepted to be published in Experimental Astronomy on 09 July 2021

Realizing spatiotemporal effective media for acoustic metamaterials

Authors: Xinhua Wen, Xinghong Zhu, Hong Wei Wu, Jensen Li

Abstract: The effective medium representation is fundamental in providing a performance-to-design approach for many devices based on metamaterials. While there are recent works in extending the effective medium concept into the temporal domain, a direct implementation is still missing. Here, we construct an acoustic metamaterial dynamically switching between two different configurations with a time-varying… ▽ More The effective medium representation is fundamental in providing a performance-to-design approach for many devices based on metamaterials. While there are recent works in extending the effective medium concept into the temporal domain, a direct implementation is still missing. Here, we construct an acoustic metamaterial dynamically switching between two different configurations with a time-varying convolution kernel, which can now incorporate both frequency dispersion of metamaterials and temporal modulation. We establish the effective medium formula in temporally averaging the compressibilities, densities and even Willis coupling parameters of the two configurations. A phase disorder between the modulation of different atoms is found negligible on the effective medium. Our realization enables a high-level description of metamaterials in the spatiotemporal domain, making many recent proposals, such as magnet-free non-reciprocity, broadband slow-light and Fresnel drag using spatiotemporal metamaterials possible for implementations in future. △ Less

Submitted 9 April, 2021; originally announced April 2021.

Comments: 17 pages, 4 figures

Journal ref: Phys. Rev. B 104, 060304 (2021)