Showing 1–42 of 42 results for author: Shen, K

Atom Optics for Multidimensional Raman Interferometry

Authors: Yingpeng Zhao, Yiyang Shao, Wenjian Tong, Shuning Bao, Yuanlong Zhang, Mengnan Yi, Shengzhe Wang, Ke Shen, Bin Wu, Yanying Feng

Abstract: The coherent control of atomic wave packets in multiple momentum dimensions is a central challenge in Raman atom optics and a key requirement for multidimensional atom interferometry. In this paper, a momentum-basis theoretical framework is developed for two-dimensional Raman interactions. We formulate the atom-laser interaction for two-dimensional Raman beams and obtain the effective two-level gr… ▽ More The coherent control of atomic wave packets in multiple momentum dimensions is a central challenge in Raman atom optics and a key requirement for multidimensional atom interferometry. In this paper, a momentum-basis theoretical framework is developed for two-dimensional Raman interactions. We formulate the atom-laser interaction for two-dimensional Raman beams and obtain the effective two-level ground-state Hamiltonian after adiabatic elimination of the excited states. The resulted Hamiltonian is constructed on the reachable momentum-state lattice and includes AC Stark shifts, intra-dimensional Raman couplings, and cross-dimensional Raman coupling terms, thereby describing multidimensional Raman dynamics beyond a simple superposition of independent single-dimensional models. The framework is used to analyze the principles and operating conditions of two-dimensional atom interferometry. Cross-dimensional Raman coupling and sequential reverse Raman transitions are identified as the main mechanisms that redistribute atoms into non-target momentum states and reduce the contrast of atomic interferometer fringe. Experimentally, Ramsey fringes are observed in a cold-atom fountain interferometer, with a contrast of $14.8\%$ at an interrogation time of $T=10~{\rm ms}$, in good agreement with the theoretical calculation. The conditions required for velocity-sensitive multidimensional atom interferometry are further clarified, including detuning control, velocity-class selection, and suppression of undesired inter-dimensional transitions. This work provides a theoretical and experimental basis for multidimensional Raman atom interferometry. △ Less

Submitted 13 June, 2026; originally announced June 2026.

Comments: 17 pages, 6 figures,

Ambiguity-Free Inertial Measurement with Multi-Wavelength Atom Interferometry

Authors: Wei-Chen Jia, Yue Xin, Ke Shen, Yan-Ying Feng

Abstract: White-light interferometry enables ambiguity-free localization by synthesizing interference envelopes from multiple optical wavelengths, but no analogous capability has been realized for coherent matter waves. Here we report the first experimental demonstration of multi-wavelength atom interferometry, establishing the matter-wave counterpart of white-light interferometry. By exploiting counter-pro… ▽ More White-light interferometry enables ambiguity-free localization by synthesizing interference envelopes from multiple optical wavelengths, but no analogous capability has been realized for coherent matter waves. Here we report the first experimental demonstration of multi-wavelength atom interferometry, establishing the matter-wave counterpart of white-light interferometry. By exploiting counter-propagating atomic beams as multi-wavelength matter wave sources and synthesizing interference envelopes from their spectral components, we realize inertial measurements based on envelope localization rather than conventional fringe-phase estimation. The resulting multi-scale interferometric response provides ambiguity-free operation, a well-defined rotational scale factor, and reduced sensitivity to initial phase bias. As a proof of principle, we demonstrate simultaneous dual-axis rotation and acceleration sensing and directly resolve the phase ambiguity that fundamentally limits conventional open-loop atom interferometers. We further measure the Earth's rotation with a relative error of 4.3% and a long-term stability of 93 ppm at an averaging time of 15,000 s. Our results establish multi-wavelength atom interferometry as a new paradigm for coherent matter-wave sensing, extending the principles of white-light interferometry to atom optics and opening new opportunities for inertial sensing, geodesy, precision metrology, and inertial navigation. △ Less

Submitted 10 June, 2026; originally announced June 2026.

Comments: 10 pages,4 figures

Closed-loop dual-channel atomic beam interferometry beyond the half-fringe limit

Authors: Wei-Chen Jia, Yue Xin, Ke Shen, Zhi-Xin Meng, Xiang-Xiang Lu, Yi-Cheng Deng, Yuan-Xing Liu, Yan-Ying Feng

Abstract: Atom interferometric inertial sensors offer exceptional sensitivity but are fundamentally constrained by the periodic phase response of matter-wave interference, which imposes an intrinsic half-fringe dynamic-range limit and prevents continuous inertial tracking. In multi-axis configurations, additional cross coupling between acceleration and rotation further complicates closed-loop operation. Her… ▽ More Atom interferometric inertial sensors offer exceptional sensitivity but are fundamentally constrained by the periodic phase response of matter-wave interference, which imposes an intrinsic half-fringe dynamic-range limit and prevents continuous inertial tracking. In multi-axis configurations, additional cross coupling between acceleration and rotation further complicates closed-loop operation. Here we demonstrate the first dual-channel closed-loop operation of an atomic beam interferometer, realizing decoupled feedback control of acceleration- and rotation-induced phases and overcoming the half-fringe limitation. Using continuous, transversely cooled $^{87}$Rb atomic beams, the interferometric phases associated with rotation and acceleration are independently extracted, tracked across multiple fringes, and actively compensated through Raman frequency modulation. This closed-loop scheme enables unambiguous measurements up to $\pm1\,\mathrm{^{\circ}/s}$ in rotation and $\pm0.17\,\mathrm{g}$ in acceleration while maintaining high fringe contrast, corresponding to nearly two orders-of-magnitude extension beyond the conventional half-fringe limit. The sensor achieves a long-term stability of $4\times10^{-4}\,\mathrm{^{\circ}/h}$ for rotation and $4\,\mathrm{μg}$ for acceleration at an averaging time of $1000\,\mathrm{s}$. By converting the intrinsically periodic interferometric response into stabilized phase-encoded inertial channels, this work establishes a new operating regime for atomic beam interferometry and advances matter-wave sensors toward practical quantum inertial navigation under dynamic conditions. △ Less

Submitted 15 March, 2026; originally announced March 2026.

Comments: 6 pages,4 figures

Electric field switching of altermagnetic spin-splitting in multiferroic skyrmions

Authors: Gui Wang, Yuhang Li, Bin Li, Xianzhe Chen, Jianting Dong, Weizhao Chen, Xiaobing Chen, Naifu Zheng, Maosen Guo, Aomei Tong, Hua Bai, Hongrui Zhang, Yifan Gao, Kaiwen Shen, Jiangyuan Zhu, Jiahao Han, Yingfen Wei, Hao Jiang, Xumeng Zhang, Ming Wang, Kebiao Xu, Wu Shi, Pengfei Wang, Jia Zhang, Qihang Liu , et al. (4 additional authors not shown)

Abstract: Magnetic skyrmions are localized magnetic structures that retain their shape and stability over time, thanks to their topological nature. Recent theoretical and experimental progress has laid the groundwork for understanding magnetic skyrmions characterized by negligible net magnetization and ultrafast dynamics. Notably, skyrmions emerging in materials with altermagnetism, a novel magnetic phase f… ▽ More Magnetic skyrmions are localized magnetic structures that retain their shape and stability over time, thanks to their topological nature. Recent theoretical and experimental progress has laid the groundwork for understanding magnetic skyrmions characterized by negligible net magnetization and ultrafast dynamics. Notably, skyrmions emerging in materials with altermagnetism, a novel magnetic phase featuring lifted Kramers degeneracy-have remained unreported until now. In this study, we demonstrate that BiFeO3, a multiferroic renowned for its strong coupling between ferroelectricity and magnetism, can transit from a spin cycloid to a Neel-type skyrmion under antidamping spin-orbit torque at room temperature. Strikingly, the altermagnetic spin splitting within BiFeO3 skyrmion can be reversed through the application of an electric field, revealed via the Circular photogalvanic effect. This quasiparticle, which possesses a neutral topological charge, holds substantial promise for diverse applications-most notably, enabling the development of unconventional computing systems with low power consumption and magnetoelectric controllability. △ Less

Submitted 10 January, 2026; originally announced January 2026.

Stationary Power-Law Solutions of Kinetic-Alfvénic Turbulence

Authors: Kexun Shen, Zhiwen Cheng, Zhiyong Qiu

Abstract: The wave-kinetic description of weak kinetic-Alfvénic turbulence based on the gyrokinetic theoretical framework is proposed. The wave kinetic equation describing kinetic Alfvén wave spectral cascading via resonant three-wave interactions is derived, and the stationary spectra are analytically obtained using the Zakharov transformation in both the long-wavelength limit and the short-wavelength limi… ▽ More The wave-kinetic description of weak kinetic-Alfvénic turbulence based on the gyrokinetic theoretical framework is proposed. The wave kinetic equation describing kinetic Alfvén wave spectral cascading via resonant three-wave interactions is derived, and the stationary spectra are analytically obtained using the Zakharov transformation in both the long-wavelength limit and the short-wavelength limit, for both counter-propagating and co-propagating cases. The cascade directions of stationary solutions are identified and their existence is further verified by numerical solution of the wave kinetic equation. A brief discussion on the relevance of such predictions to the solar wind turbulence and helical kinetic-Alfvénic turbulence is presented. △ Less

Submitted 5 August, 2025; originally announced August 2025.

Comments: 13 pages, 8 figures

Quantum Geometry of Altermagnetic Magnons Probed by Light

Authors: Rundong Yuan, Wojciech J. Jankowski, Ka Shen, Robert-Jan Slager

Abstract: Magnons with momentum-dependent chirality are a key signature of altermagnets. We identify bicircular light as a smoking-gun optical probe for chiral altermagnetic magnons, selectively targeting their quantum geometry induced by an alteration of magnonic chirality. We show that in $d$-wave altermagnets, under a canting magnetic field, the altermagnetic magnons realize a nontrivial quantum geometry… ▽ More Magnons with momentum-dependent chirality are a key signature of altermagnets. We identify bicircular light as a smoking-gun optical probe for chiral altermagnetic magnons, selectively targeting their quantum geometry induced by an alteration of magnonic chirality. We show that in $d$-wave altermagnets, under a canting magnetic field, the altermagnetic magnons realize a nontrivial quantum geometry, resulting in an enhancement of the nonlinear second-order light-magnon interactions. We find that the scattering of bicircular pulses probes the present magnon quantum geometry, even if the magnonic topology is trivial. Hence, our findings establish bicircular Raman response as an optical effect of choice to identify altermagnetic magnons. As such, we propose a universal experimental protocol to distinguish altermagnets from antiferromagnets by detecting their magnon chirality patterns with light, independently of the underlying magnon topology. △ Less

Submitted 4 August, 2025; originally announced August 2025.

Comments: 9+4 pages, 4+3 figures

Observation of ferron transport in ferroelectrics

Authors: Kaiwen Shen, Ping Tang, Xianzhe Chen, Yifan Gao, Yuanfei Fan, Zejing Guo, Yingfen Wei, Hao Jiang, Xumeng Zhang, Ming Wang, Pan He, Wu Shi, Jiahao Han, Yizheng Wu, Jian Shen, Qi Liu, Gerrit E. W. Bauer, Ming Liu

Abstract: Ferroelectrics feature spontaneous electric dipolar order reconfigurable via electric fields. Recent theoretical studies of the collective excitations of this electric dipolar order give rise to the hope that "ferron" quasiparticles may complement the magnons of magnetic materials in information and heat management technologies. Yet direct experimental evidence of ferron transport remains elusive.… ▽ More Ferroelectrics feature spontaneous electric dipolar order reconfigurable via electric fields. Recent theoretical studies of the collective excitations of this electric dipolar order give rise to the hope that "ferron" quasiparticles may complement the magnons of magnetic materials in information and heat management technologies. Yet direct experimental evidence of ferron transport remains elusive. Here we demonstrate efficient ferron injection and detection enabled by ferromagnetic metal contacts, achieving nonlocal signal transmission over micrometer distances in a prototypical ferroelectric PMN-PT. The transmission efficiency can be switched by external magnetic fields that couple to the contacts and gate electric fields that control the ferron excitations. Ferron-based devices open new power saving strategies that employ ferroelectric materials in a future sustainable information society. △ Less

Submitted 30 May, 2025; originally announced May 2025.

Perturbative Fourier Ptychographic Microscopy for Fast Quantitative Phase Imaging

Authors: Martin Zach, Kuan-Chen Shen, Ruiming Cao, Michael Unser, Laura Waller, Jonathan Dong

Abstract: In computational phase imaging with a microscope equipped with an array of light emitting diodes as illumination unit, conventional Fourier ptychographic microscopy achieves high resolution and wide-field reconstructions but is constrained by a lengthy acquisition time. Conversely, differential phase contrast (DPC) offers fast imaging but is limited in resolution. Here, we introduce perturbative F… ▽ More In computational phase imaging with a microscope equipped with an array of light emitting diodes as illumination unit, conventional Fourier ptychographic microscopy achieves high resolution and wide-field reconstructions but is constrained by a lengthy acquisition time. Conversely, differential phase contrast (DPC) offers fast imaging but is limited in resolution. Here, we introduce perturbative Fourier ptychographic microscopy (pFPM). pFPM is an extension of DPC that incorporates dark-field illumination to enable fast, high-resolution, wide-field quantitative phase imaging with few measurements. We interpret DPC as the initial iteration of a Gauss-Newton algorithm with quadratic regularization and generalize it to multiple iterations and more sophisticated regularizers. This broader framework is not restricted to bright-field measurements and allows us to overcome resolution limitations of DPC. We develop tailored annular dark-field illumination patterns that align with the perturbative interpretation and lead to an improvement in the quality of reconstruction with respect to other common illumination schemes. Consequently, our methodology combines an enhanced phase reconstruction algorithm with a specialized illumination strategy and offers significant advantages in both imaging speed and resolution. △ Less

Submitted 10 March, 2025; v1 submitted 13 January, 2025; originally announced January 2025.

Reflections from the 2024 Large Language Model (LLM) Hackathon for Applications in Materials Science and Chemistry

Authors: Yoel Zimmermann, Adib Bazgir, Zartashia Afzal, Fariha Agbere, Qianxiang Ai, Nawaf Alampara, Alexander Al-Feghali, Mehrad Ansari, Dmytro Antypov, Amro Aswad, Jiaru Bai, Viktoriia Baibakova, Devi Dutta Biswajeet, Erik Bitzek, Joshua D. Bocarsly, Anna Borisova, Andres M Bran, L. Catherine Brinson, Marcel Moran Calderon, Alessandro Canalicchio, Victor Chen, Yuan Chiang, Defne Circi, Benjamin Charmes, Vikrant Chaudhary , et al. (119 additional authors not shown)

Abstract: Here, we present the outcomes from the second Large Language Model (LLM) Hackathon for Applications in Materials Science and Chemistry, which engaged participants across global hybrid locations, resulting in 34 team submissions. The submissions spanned seven key application areas and demonstrated the diverse utility of LLMs for applications in (1) molecular and material property prediction; (2) mo… ▽ More Here, we present the outcomes from the second Large Language Model (LLM) Hackathon for Applications in Materials Science and Chemistry, which engaged participants across global hybrid locations, resulting in 34 team submissions. The submissions spanned seven key application areas and demonstrated the diverse utility of LLMs for applications in (1) molecular and material property prediction; (2) molecular and material design; (3) automation and novel interfaces; (4) scientific communication and education; (5) research data management and automation; (6) hypothesis generation and evaluation; and (7) knowledge extraction and reasoning from scientific literature. Each team submission is presented in a summary table with links to the code and as brief papers in the appendix. Beyond team results, we discuss the hackathon event and its hybrid format, which included physical hubs in Toronto, Montreal, San Francisco, Berlin, Lausanne, and Tokyo, alongside a global online hub to enable local and virtual collaboration. Overall, the event highlighted significant improvements in LLM capabilities since the previous year's hackathon, suggesting continued expansion of LLMs for applications in materials science and chemistry research. These outcomes demonstrate the dual utility of LLMs as both multipurpose models for diverse machine learning tasks and platforms for rapid prototyping custom applications in scientific research. △ Less

Submitted 2 January, 2025; v1 submitted 20 November, 2024; originally announced November 2024.

Comments: Updating author information, the submission remains largely unchanged. 98 pages total

Room temperature spin-layer locking of exciton-polariton nonlinearities

Authors: Jiaxin Zhao, Antonio Fieramosca, Kevin Dini, Qiuyu Shang, Ruiqi Bao, Yuan Luo, Kaijun Shen, Yang Zhao, Rui Su, Jesus Zuniga Perez, Weibo Gao, Vincenzo Ardizzone, Daniele Sanvitto, Qihua Xiong, Timothy C. H. Liew

Abstract: Recent advancements in transition metal dichalcogenides (TMDs) have unveiled exceptional optical and electronic characteristics, opened up new opportunities, and provided a unique platform for exploring light-matter interactions under the strong coupling regime. The exploitation of exciton-polaritons, with their peculiar hybrid light-matter properties, for the development of spintronic customizabl… ▽ More Recent advancements in transition metal dichalcogenides (TMDs) have unveiled exceptional optical and electronic characteristics, opened up new opportunities, and provided a unique platform for exploring light-matter interactions under the strong coupling regime. The exploitation of exciton-polaritons, with their peculiar hybrid light-matter properties, for the development of spintronic customizable devices that enhance both the information capacity and functionality at ambient temperatures is often suggested as a promising route. However, although TMD polaritons have shown promising potential, the microscopic mechanisms leading to nonlinearities in TMD polaritons are complex and their spin-anisotropy, a crucial requirement for many proposed polaritonic devices, has been missing. Here, we demonstrate the absence of spin-anisotropic interaction in a monolayer WS2 microcavity (at room temperature) and show how spin-dependent interactions can be controlled and spin anisotropy recovered by engineering double WS2 layer structures with varied interlayer spacing. We attribute this phenomenon to a distinctive feature in exciton-polariton physics: layer-dependent polariton-phonon coupling. We use theoretical calculations of the phonon electrostatic potentials finding a drastically different coupling strength for single and double monolayer samples and discuss qualitatively how this explains the observed spin-anisotropic response. This is further consistent with experiments on multi WS2 layer samples and the identification of a critical separation distance, above which an effective single monolayer spin-anisotropic response is recovered, both in experiment and theory. Our work lays the groundwork for the development of spin-optronic polaritonic devices at room temperature. △ Less

Submitted 24 October, 2024; originally announced October 2024.

Towards real-world applications of levitated optomechanics

Authors: Yuanbin Jin, Kunhong Shen, Peng Ju, Tongcang Li

Abstract: Levitated optomechanics, a rapidly expanding field that employs light to monitor and manipulate the mechanical motion of levitated objects, is increasingly relevant across physics, engineering, and other fields. This technique, which involves levitating micro- and nano-scale objects in a vacuum where they exhibit high-quality motion, provides an essential platform for precision measurements. Noted… ▽ More Levitated optomechanics, a rapidly expanding field that employs light to monitor and manipulate the mechanical motion of levitated objects, is increasingly relevant across physics, engineering, and other fields. This technique, which involves levitating micro- and nano-scale objects in a vacuum where they exhibit high-quality motion, provides an essential platform for precision measurements. Noted for their ultra-high sensitivity, levitated particles hold potential for a wide range of real-world applications. This perspective article briefly introduces the principle of optical levitation and the dynamics of levitated particles. It then reviews the emerging applications of levitated particles in ultrasensitive force and torque measurements, acceleration and rotation sensing, electric and magnetic field detection, scanning probe microscopy, localized vacuum pressure gauging, acoustic transduction, and chemical and biological sensing. Moreover, we discuss the present challenges and explore opportunities to minimize and integrate levitation systems for broader applications. We also briefly review optomechanics with ion traps and magnetic traps which can levitate particles in high vacuum without laser heating. △ Less

Submitted 17 July, 2024; originally announced July 2024.

Comments: Perspective article, 20 pages, 12 figures

Purcell-enhanced optical refrigeration

Authors: Peng Ju, Kunhong Shen, Stefan Püschel, Yuanbin Jin, Hiroki Tanaka, Tongcang Li

Abstract: Optical refrigeration of solids with anti-Stokes fluorescence has been widely explored as a vibration-free cryogenic cooling technology. A minimum temperature of 87 K has been demonstrated with rare-earth ion doped crystals using optical refrigeration. However, the depletion of the upper-lying energy levels in the ground state manifold hinders further cooling to below the liquid nitrogen (LN$_2$)… ▽ More Optical refrigeration of solids with anti-Stokes fluorescence has been widely explored as a vibration-free cryogenic cooling technology. A minimum temperature of 87 K has been demonstrated with rare-earth ion doped crystals using optical refrigeration. However, the depletion of the upper-lying energy levels in the ground state manifold hinders further cooling to below the liquid nitrogen (LN$_2$) temperatures, restricting its applications. In this work, we introduce a Purcell-enhanced optical refrigeration method to circumvent this limitation. This approach enhances the emission of high-energy photons by coupling the emitters to an optical cavity, blue shifting the mean emission wavelength. Such Purcell-enhanced emission facilitates cooling starting from a lower energy level in the ground state manifold, which exhibits a higher occupation below the LN$_2$ temperatures. Using experimentally measured optical coefficients, our theoretical analysis predicts a minimum achievable internal temperature of about 38 K for a Yb$^{3+}$:YLiF$_{4}$ nanocrystal near a cavity under realistic conditions. The proposed method is applicable to other rare-earth ion doped materials and semiconductors, and will have applications in creating superconducting and other quantum devices through solid-state cooling. △ Less

Submitted 11 May, 2026; v1 submitted 29 April, 2024; originally announced April 2024.

Comments: 11 pages, 9 figures

Journal ref: Phys. Rev. Research 8, 023149 (2026)

Observation of non-contact Casimir friction

Authors: Zhujing Xu, Peng Ju, Kunhong Shen, Yuanbin Jin, Zubin Jacob, Tongcang Li

Abstract: Quantum mechanics predicts the occurrence of random electromagnetic field fluctuations, or virtual photons, in vacuum. The exchange of virtual photons between two bodies in relative motion could lead to non-contact quantum vacuum friction or Casimir friction. Despite its theoretical significance, the non-contact Casimir frictional force has not been observed and its theoretical predictions have va… ▽ More Quantum mechanics predicts the occurrence of random electromagnetic field fluctuations, or virtual photons, in vacuum. The exchange of virtual photons between two bodies in relative motion could lead to non-contact quantum vacuum friction or Casimir friction. Despite its theoretical significance, the non-contact Casimir frictional force has not been observed and its theoretical predictions have varied widely. In this work, we report the first measurement of the non-contact Casimir frictional force between two moving bodies. By employing two mechanical oscillators with resonant frequencies far lower than those in Lorentz models of electrons in dielectric materials, we have amplified the Casimir frictional force at low relative velocities by several orders of magnitude. We directly measure the non-contact Casimir frictional force between the two oscillators and show its linear dependence on velocity, proving the dissipative nature of Casimir friction. This advancement marks a pivotal contribution to the field of dissipative quantum electrodynamics and enhances our understanding of friction at the nanoscale. △ Less

Submitted 9 March, 2024; originally announced March 2024.

Effects of plasma nonuniformity on toroidal Alfvén eigenmode nonlinear decay

Authors: Zhiwen Cheng, Kexun Shen, Zhiyong Qiu

Abstract: The parametric decay of toroidal Alfvén eigenmode (TAE) in nonuniform plasmas is investigated using nonlinear gyrokinetic equation. It is found that, the plasma nonuniformity not only significantly enhances the nonlinear coupling cross-section, but also qualitatively modifies the decay process. Specifically, the condition for spontaneous decay becomes the toroidal mode number of the sideband TAE b… ▽ More The parametric decay of toroidal Alfvén eigenmode (TAE) in nonuniform plasmas is investigated using nonlinear gyrokinetic equation. It is found that, the plasma nonuniformity not only significantly enhances the nonlinear coupling cross-section, but also qualitatively modifies the decay process. Specifically, the condition for spontaneous decay becomes the toroidal mode number of the sideband TAE being higher than that of the pump TAE, instead of the frequency of the sideband TAE being lower than the pump TAE in uniform plasmas. The consequences on TAE saturation and energetic particle transport are also discussed. △ Less

Submitted 15 January, 2024; originally announced January 2024.

Report number: NF-106807

Resonant Decay of Kinetic Alfvén Waves and Implication on Spectral Cascading

Authors: Kexun Shen, Zhiwen Cheng, Zhiyong Qiu

Abstract: A general equation describing the resonant nonlinear mode-coupling among kinetic Alfvén waves (KAWs) is derived using nonlinear gyrokinetic theory, which can be applied to study the potentially strong spectral energy transfer of KAWs. As a first application, the parametric decay of a pump KAW into two sideband KAWs are studied, with particular emphasis on the cascading in perpendicular wavenumber.… ▽ More A general equation describing the resonant nonlinear mode-coupling among kinetic Alfvén waves (KAWs) is derived using nonlinear gyrokinetic theory, which can be applied to study the potentially strong spectral energy transfer of KAWs. As a first application, the parametric decay of a pump KAW into two sideband KAWs are studied, with particular emphasis on the cascading in perpendicular wavenumber. It is found that, for the "co-propagating" cases with all three KAWs propagating in the same direction along the equilibrium magnetic field line, it exhibits a dual cascading character in the perpendicular wavenumber space; while for the "counter-propagating" cases with one sideband propagating in the opposite direction with respect to the pump wave, it instead, can exhibit both dual and inverse cascading behaviors. The implications on SAW instability nonlinear saturation and charged particle transport in fusion plasmas is also discussed. △ Less

Submitted 5 January, 2024; originally announced January 2024.

Spatially-coded Fourier ptychography: flexible and detachable coded thin films for quantitative phase imaging with uniform phase transfer characteristics

Authors: Ruihai Wang, Liming Yang, Yujin Lee, Kevin Sun, Kuangyu Shen, Qianhao Zhao, Tianbo Wang, Xincheng Zhang, Jiayi Liu, Pengming Song, Guoan Zheng

Abstract: Fourier ptychography (FP) is an enabling imaging technique that produces high-resolution complex-valued images with extended field coverages. However, when FP images a phase object with any specific spatial frequency, the captured images contain only constant values, rendering the recovery of the corresponding linear phase ramp impossible. This challenge is not unique to FP but also affects other… ▽ More Fourier ptychography (FP) is an enabling imaging technique that produces high-resolution complex-valued images with extended field coverages. However, when FP images a phase object with any specific spatial frequency, the captured images contain only constant values, rendering the recovery of the corresponding linear phase ramp impossible. This challenge is not unique to FP but also affects other common microscopy techniques -- a rather counterintuitive outcome given their widespread use in phase imaging. The underlying issue originates from the non-uniform phase transfer characteristic inherent in microscope systems, which impedes the conversion of object wavefields into discernible intensity variations. To address this challenge, we present spatially-coded Fourier ptychography (scFP), a new method that synergizes FP with spatial-domain coded detection for true quantitative phase imaging. In scFP, a flexible and detachable coded thin film is attached atop the image sensor in a regular FP setup. The spatial modulation of this thin film ensures a uniform phase response across the entire synthetic bandwidth. It improves reconstruction quality and corrects refractive index underestimation issues prevalent in conventional FP and related tomographic implementations. The inclusion of the coded thin film further adds a new dimension of measurement diversity in the spatial domain. The development of scFP is expected to catalyse new research directions and applications for phase imaging, emphasizing the need for true quantitative accuracy with uniform frequency response. △ Less

Submitted 29 November, 2023; originally announced November 2023.

A Continuous Dual-Axis Atomic Interferometric Inertial Sensor

Authors: Pei-Qiang Yan, Wei-Chen Jia, Ke Shen, Yue Xin, Yan-Ying Feng

Abstract: We present an interferometric inertial sensor that utilizes two counter-propagating atomic beams with transverse two-dimensional cooling. By employing three parallel and spatially aligned Raman laser beams for Doppler-sensitive Raman transitions, we successfully generate inertia-sensitive Mach-Zehnder interference fringes with an interrogation length of $2L=54\,\rm{cm}$. The sensor's capability to… ▽ More We present an interferometric inertial sensor that utilizes two counter-propagating atomic beams with transverse two-dimensional cooling. By employing three parallel and spatially aligned Raman laser beams for Doppler-sensitive Raman transitions, we successfully generate inertia-sensitive Mach-Zehnder interference fringes with an interrogation length of $2L=54\,\rm{cm}$. The sensor's capability to measure rotation and acceleration simultaneously in dynamic environments is validated through comparative analysis with classical sensors under force oscillation in different directions. Additionally, we conduct experiments on a turntable to calibrate the gyroscope's scaling factor and address nonlinearity. The angular random walk (ARW) and velocity random walk (VRW) of the senor are $3\times10^{-4}\,^\circ/\rm{\sqrt{h}}$ and $107\,\mathrmμg/\rm{\sqrt{Hz}}$, respectively, with the long-term stability reaching $9\times10^{-4}\,\rm{^\circ/h}$ for rotation and $10\,\rm{μg}$ for acceleration at an integration time of 1000s. △ Less

Submitted 28 July, 2025; v1 submitted 28 November, 2023; originally announced November 2023.

Comments: 11 pages, 6 figures

Atomically smooth films of CsSb: a chemically robust visible light photocathode

Authors: C. T. Parzyck, C. A. Pennington, W. J. I. DeBenedetti, J. Balajka, E. Echeverria, H. Paik, L. Moreschini, B. D. Faeth, C. Hu, J. K. Nangoi, V. Anil, T. A. Arias, M. A. Hines, D. G. Schlom, A. Galdi, K. M. Shen, J. M. Maxson

Abstract: Alkali antimonide semiconductor photocathodes provide a promising platform for the generation of high brightness electron beams, which are necessary for the development of cutting-edge probes including x-ray free electron lasers and ultrafast electron diffraction. However, to harness the intrinsic brightness limits in these compounds, extrinsic degrading factors, including surface roughness and co… ▽ More Alkali antimonide semiconductor photocathodes provide a promising platform for the generation of high brightness electron beams, which are necessary for the development of cutting-edge probes including x-ray free electron lasers and ultrafast electron diffraction. However, to harness the intrinsic brightness limits in these compounds, extrinsic degrading factors, including surface roughness and contamination, must be overcome. By exploring the growth of CsxSb thin films monitored by in situ electron diffraction, the conditions to reproducibly synthesize atomically smooth films of CsSb on 3C-SiC (100) and graphene coated TiO2 (110) substrates are identified, and detailed structural, morphological, and electronic characterization is presented. These films combine high quantum efficiency in the visible (up to 1.2% at 400 nm), an easily accessible photoemission threshold of 550 nm, low surface roughness (down to 600 pm on a 1 um scale), and a robustness against oxidation up to 15 times greater then Cs3Sb. These properties suggest that CsSb has the potential to operate as an alternative to Cs$_3$Sb in electron source applications where the demands of the vacuum environment might otherwise preclude the use of traditional alkali antimonides. △ Less

Submitted 31 May, 2023; originally announced May 2023.

Comments: 11 pages, 6 figures, 1 table

Journal ref: APL Mater. 11, 101125 (2023)

Observation of spin-wave moiré edge and cavity modes in twisted magnetic lattices

Authors: Hanchen Wang, Marco Madami, Jilei Chen, Hao Jia, Yu Zhang, Rundong Yuan, Yizhan Wang, Wenqing He, Lutong Sheng, Yuelin Zhang, Jinlong Wang, Song Liu, Ka Shen, Guoqiang Yu, Xiufeng Han, Dapeng Yu, Jean-Philippe Ansermet, Gianluca Gubbiotti, Haiming Yu

Abstract: We report the experimental observation of the spin-wave moiré edge and cavity modes using Brillouin light scattering spectro-microscopy in a nanostructured magnetic moiré lattice consisting of two twisted triangle antidot lattices based on an yttrium iron garnet thin film. Spin-wave moiré edge modes are detected at an optimal twist angle and with a selective excitation frequency. At a given twist… ▽ More We report the experimental observation of the spin-wave moiré edge and cavity modes using Brillouin light scattering spectro-microscopy in a nanostructured magnetic moiré lattice consisting of two twisted triangle antidot lattices based on an yttrium iron garnet thin film. Spin-wave moiré edge modes are detected at an optimal twist angle and with a selective excitation frequency. At a given twist angle, the magnetic field acts as an additional degree of freedom for tuning the chiral behavior of the magnon edge modes. Micromagnetic simulations indicate that the edge modes emerge within the original magnonic band gap and at the intersection between a mini-flatband and a propagation magnon branch. Our theoretical estimate for the Berry curvature of the magnon-magnon coupling suggests a non-trivial topology for the chiral edge modes and confirms the key role played by the dipolar interaction. Our findings shed light on the topological nature of the magnon edge mode for emergent moiré magnonics. △ Less

Submitted 3 April, 2023; originally announced April 2023.

Journal ref: Phys. Rev. X 13, 021016 (2023)

An Algorithm for Subtraction of Doublet Emission Lines in Angle-Resolved Photoemission Spectroscopy

Authors: Yaoju Tarn, Mekhola Sinha, Christopher Pasco, Darrell G. Schlom, Tyrel M. McQueen, Kyle M. Shen, Brendan D. Faeth

Abstract: Plasma discharge lamps are widely utilized in the practice of angle-resolved photoemission spectroscopy (ARPES) experiments as narrow-linewidth ultraviolet photon sources. However, many emission lines such as Ar-I, Ne-I, and Ne-II have closely spaced doublet emission lines, which result in superimposed replica on the measured ARPES spectra. Here, we present a simple method for subtracting the cont… ▽ More Plasma discharge lamps are widely utilized in the practice of angle-resolved photoemission spectroscopy (ARPES) experiments as narrow-linewidth ultraviolet photon sources. However, many emission lines such as Ar-I, Ne-I, and Ne-II have closely spaced doublet emission lines, which result in superimposed replica on the measured ARPES spectra. Here, we present a simple method for subtracting the contribution of these doublet emission lines from photoemission spectra. Benchmarking against ARPES spectra of well-characterized 2D materials, we demonstrate that this algorithm manages to subtract the doublet signal and reproduce the key features of the monochromated He-I$α$ spectra in a physically sound manner that reliably reproduces quantifiable dispersion relations and quasiparticle lifetimes. △ Less

Submitted 13 March, 2023; originally announced March 2023.

Comments: 8 pages, 4 main figures, 3 appendix figures

Near-field GHz rotation and sensing with an optically levitated nanodumbbell

Authors: Peng Ju, Yuanbin Jin, Kunhong Shen, Yao Duan, Zhujing Xu, Xingyu Gao, Xinjie Ni, Tongcang Li

Abstract: A levitated non-spherical nanoparticle in a vacuum is ideal for studying quantum rotations and is an extremely sensitive torque and force detector. It has been proposed to probe fundamental particle-surface interactions such as the Casimir torque and the rotational quantum vacuum friction, which require it to be driven to rotate near a surface at sub-micrometer separations. Here, we optically levi… ▽ More A levitated non-spherical nanoparticle in a vacuum is ideal for studying quantum rotations and is an extremely sensitive torque and force detector. It has been proposed to probe fundamental particle-surface interactions such as the Casimir torque and the rotational quantum vacuum friction, which require it to be driven to rotate near a surface at sub-micrometer separations. Here, we optically levitate a silica nanodumbbell in a vacuum at about 430 nm away from a sapphire surface and drive it to rotate at GHz frequencies. The relative linear speed between the tip of the nanodumbbell and the surface reaches 1.4 km/s at a sub-micrometer separation. The rotating nanodumbbell near the surface demonstrates a torque sensitivity of $(5.0 \pm 1.1) \times 10^{-26} {\rm NmHz}^{-1/2}$ at room temperature. Moreover, we levitate a nanodumbbell near a gold nanograting and use it to probe the near-field intensity distribution beyond the optical diffraction limit. Our numerical simulation shows it is promising to detect the Casimir torque between a nanodumbbell and a nanograting. △ Less

Submitted 25 January, 2023; originally announced January 2023.

Comments: 4 figures

Journal ref: Nano Letters 23, 10157 (2023)

Informatics-Driven Selection of Polymers for Fuel-Cell Applications

Authors: Huan Tran, Kuan-Hsuan Shen, Shivank Shukla, Ha-Kyung Kwon, Rampi Ramprasad

Abstract: Modern fuel cell technologies use Nafion as the material of choice for the proton exchange membrane (PEM) and as the binding material (ionomer), used to assemble the catalyst layers of the anode and cathode. These applications demand high proton conductivity as well as other requirements. For example, PEM is expected to block electrons, oxygen, and hydrogen from penetrating and diffusing while the… ▽ More Modern fuel cell technologies use Nafion as the material of choice for the proton exchange membrane (PEM) and as the binding material (ionomer), used to assemble the catalyst layers of the anode and cathode. These applications demand high proton conductivity as well as other requirements. For example, PEM is expected to block electrons, oxygen, and hydrogen from penetrating and diffusing while the anode/cathode ionomer should allow hydrogen/oxygen to move easily, so that they can reach the catalyst nanoparticles. Given some of the well-known limits of Nafion, such as low glass-transition temperature, the community is in the midst of an active search for Nafion replacements. In this work, we present an informatics-based scheme to search large polymer chemical spaces, which includes establishing a list of properties needed for the targeted applications, developing predictive machine-learning models for these properties, defining a search space, and using the developed models to screen the search space. Using the scheme, we have identified 60 new polymer candidates for PEM, anode ionomer, and cathode ionomer that we hope will be advanced to the next step, i.e., validating the designs through synthesis and testing. The proposed informatics scheme is generic, and can be used to select polymers for multiple applications in the future. △ Less

Submitted 26 December, 2022; originally announced December 2022.

Comments: in press, JPCC

Journal ref: The Journal of Physical Chemistry C 127, 977 (2023)

Resonantly Enhanced Electric-Field Sensing of Etchless Thin Film Lithium Niobate via Quasibound Sates in the Continuum

Authors: Zhijin Huang, Junzhong Wang, Lifang Yuan, Kaixiang Shen, Qianqian Li, Juan Wang

Abstract: Electric field detection has been widely utilized in many fields such as scientific research and integrated circuits. To enhance the tuning sensitivity of E-field sensor, in this paper, we theoretically proposed a highly sensitive E-field sensor composed of etchless lithium niobate (LN) material and hybrid coupling-grating systems in the visible near-infrared regime. Such configuration supports hi… ▽ More Electric field detection has been widely utilized in many fields such as scientific research and integrated circuits. To enhance the tuning sensitivity of E-field sensor, in this paper, we theoretically proposed a highly sensitive E-field sensor composed of etchless lithium niobate (LN) material and hybrid coupling-grating systems in the visible near-infrared regime. Such configuration supports high-quality factor quasi-BIC resonance, which generates strong localized field confinement. Due to the large electro-optic coefficient of LN material, one can shift the wavelength and reflection ratio of resonance by tuning the refractive index of LN material. An analytical theory is carried out to explain the relationship between the refractive index variations and the applied voltages, so we successfully obtained a tuning sensitivity of 40.8 nm/V and a minimum detectable electric field amplitude of 24.5 mV with wavelength resolution of 1 nm. Due to the low parasitic capacitance of LN material and high conductivity of gold film and ITO layer which are utilized as the electrodes, the 3dB bandwidth of the devices should exceed 154 GHz. And we believe that such a surface-normal E-field sensor has extensive potential for the extremely weak electric field detection. △ Less

Submitted 20 December, 2022; originally announced December 2022.

Comments: 10 pages, 5 figures,

MSC Class: F.2.2 ACM Class: F.2.2

Can Scale-free Network Growth with Triad Formation Capture Simplicial Complex Distributions in Real Communication Networks?

Authors: Mayank Kejriwal, Ke Shen

Abstract: In recent years, there has been a growing recognition that higher-order structures are important features in real-world networks. A particular class of structures that has gained prominence is known as a simplicial complex. Despite their application to complex processes such as social contagion and novel measures of centrality, not much is currently understood about the distributional properties o… ▽ More In recent years, there has been a growing recognition that higher-order structures are important features in real-world networks. A particular class of structures that has gained prominence is known as a simplicial complex. Despite their application to complex processes such as social contagion and novel measures of centrality, not much is currently understood about the distributional properties of these complexes in communication networks. Furthermore, it is also an open question as to whether an established growth model, such as scale-free network growth with triad formation, is sophisticated enough to capture the distributional properties of simplicial complexes. In this paper, we use empirical data on five real-world communication networks to propose a functional form for the distributions of two important simplicial complex structures. We also show that, while the scale-free network growth model with triad formation captures the form of these distributions in networks evolved using the model, the best-fit parameters are significantly different between the real network and its simulated equivalent. An auxiliary contribution is an empirical profile of the two simplicial complexes in these five real-world networks. △ Less

Submitted 12 March, 2022; originally announced March 2022.

Comments: 4 pages, 2 figures

Switching and amplifying three-body Casimir effects

Authors: Zhujing Xu, Peng Ju, Xingyu Gao, Kunhong Shen, Zubin Jacob, Tongcang Li

Abstract: The dynamics of three interacting objects has been investigated extensively in Newtonian gravitational physics (often termed the three-body problem), and is important for many quantum systems, including nuclei, Efimov states, and frustrated spin systems. However, the dynamics of three macroscopic objects interacting through quantum vacuum fluctuations (virtual photons) is still an unexplored front… ▽ More The dynamics of three interacting objects has been investigated extensively in Newtonian gravitational physics (often termed the three-body problem), and is important for many quantum systems, including nuclei, Efimov states, and frustrated spin systems. However, the dynamics of three macroscopic objects interacting through quantum vacuum fluctuations (virtual photons) is still an unexplored frontier. Here, we report the first observation of Casimir interactions between three isolated macroscopic objects. We propose and demonstrate a three terminal switchable architecture exploiting opto-mechanical Casimir interactions that can lay the foundations of a Casimir transistor. Beyond the paradigm of Casimir forces between two objects in different geometries, our Casimir transistor represents an important development for control of three-body virtual photon interactions and will have potential applications in sensing and information processing with the Casimir effect. △ Less

Submitted 24 February, 2022; originally announced February 2022.

Comments: 7 pages, 4 figures

Journal ref: Nature Communications 13, 6148 (2022)

A single-crystal alkali antimonide photocathode: high efficiency in the ultra-thin limit

Authors: C. T. Parzyck, A. Galdi, J. K. Nangoi, W. J. I. DeBenedetti, J. Balajka, B. D. Faeth, H. Paik, C. Hu, T. A. Arias, M. A. Hines, D. G. Schlom, K. M. Shen, J. M. Maxson

Abstract: The properties of photoemission electron sources determine the ultimate performance of a wide class of electron accelerators and photon detectors. To date, all high-efficiency visible-light photocathode materials are either polycrystalline or exhibit intrinsic surface disorder, both of which limit emitted electron beam brightness. In this letter we demonstrate the synthesis of epitaxial thin films… ▽ More The properties of photoemission electron sources determine the ultimate performance of a wide class of electron accelerators and photon detectors. To date, all high-efficiency visible-light photocathode materials are either polycrystalline or exhibit intrinsic surface disorder, both of which limit emitted electron beam brightness. In this letter we demonstrate the synthesis of epitaxial thin films of Cs$_3$Sb on 3C-SiC (001) using molecular-beam epitaxy. Films as thin as 4 nm have quantum efficiencies exceeding 2\% at 532 nm. We also find that epitaxial films have an order of magnitude larger quantum efficiency at 650 nm than comparable polycrystalline films on Si. Additionally, these films permit angle-resolved photoemission spectroscopy measurements of the electronic structure, which are found to be in good agreement with theory. Epitaxial films open the door to dramatic brightness enhancements via increased efficiency near threshold, reduced surface disorder, and the possibility of engineering new photoemission functionality at the level of single atomic layers. △ Less

Submitted 28 December, 2021; originally announced December 2021.

Comments: Submitted Manuscript: 8 pages, 4 figures

Second Chern crystals in four-dimensional synthetic translation space with inherently nontrivial topology

Authors: Xiao-Dong Chen, Fu-Long Shi, Jian-Wei Liu, Ke Shen, Xin-Tao He, Wen-Jie Chen, Jian-Wen Dong

Abstract: Topological states, first known as quantum Hall effect or Chern insulating crystal, have been generalized to many classical wave systems where potential applications such as robust waveguiding, quantum computing and high-performance lasers are expected. However, a crystal can be either topologically trivial or nontrivial, depending on its detailed configuration, and one needs to carefully design t… ▽ More Topological states, first known as quantum Hall effect or Chern insulating crystal, have been generalized to many classical wave systems where potential applications such as robust waveguiding, quantum computing and high-performance lasers are expected. However, a crystal can be either topologically trivial or nontrivial, depending on its detailed configuration, and one needs to carefully design the structure and calculate its topological invariant before the actual applications. Here, we theoretically study and experimentally demonstrate the second Chern crystal in a four-dimensional space by introducing two extra synthetic translation dimensions. Due to the inherently nontrivial topology of the synthetic translation space, this abstract four-dimensional crystal is guaranteed to be topologically nontrivial regardless of the detailed configuration. The dimensional hierarchy of gapless boundary modes can be deduced by dimension reduction. Remarkably, one-dimensional gapless dislocation modes are observed and their robustness is confirmed in our experiments. This ubiquitous phenomenon in synthetic translation space provides perspectives on the findings of topologically nontrivial crystals and inspires the designs of classical wave devices. △ Less

Submitted 10 December, 2021; originally announced December 2021.

Comments: 10 pages, 4 figures

Journal ref: National Science Review 10, nwac289 (2023)

On-chip optical levitation with a metalens in vacuum

Authors: Kunhong Shen, Yao Duan, Peng Ju, Zhujing Xu, Xi Chen, Lidan Zhang, Jonghoon Ahn, Xingjie Ni, Tongcang Li

Abstract: Optical levitation of dielectric particles in vacuum is a powerful technique for precision measurements, testing fundamental physics, and quantum information science. Conventional optical tweezers require bulky optical components for trapping and detection. Here we design and fabricate an ultrathin dielectric metalens with a high numerical aperture of 0.88 at 1064 nm in vacuum. It consists of 500… ▽ More Optical levitation of dielectric particles in vacuum is a powerful technique for precision measurements, testing fundamental physics, and quantum information science. Conventional optical tweezers require bulky optical components for trapping and detection. Here we design and fabricate an ultrathin dielectric metalens with a high numerical aperture of 0.88 at 1064 nm in vacuum. It consists of 500 nm-thick silicon nano-antennas, which are compatible with ultrahigh vacuum. We demonstrate optical levitation of nanoparticles in vacuum with a single metalens. The trapping frequency can be tuned by changing the laser power and polarization. We also transfer a levitated nanoparticle between two separated optical tweezers. Optical levitation with an ultrathin metalens in vacuum provides opportunities for a wide range of applications including on-chip sensing. Such metalenses will also be useful for trapping ultacold atoms and molecules. △ Less

Submitted 20 July, 2021; originally announced July 2021.

Comments: 5 pages

Journal ref: Optica, 8, 1359-1362 (2021)

Synergistical Electroluminescent Manipulation for Efficient Blue Perovskite Light-Emitting Diodes Through Interfacial Nucleation Seeding

Authors: Hai-Yan Wu, Yang Shen, Yan-Qing Li, Kong-Chao Shen, Jian-Xin Tang

Abstract: The low efficiency of metal halide perovskite light-emitting diodes (PeLEDs) with blue emission block their potential applications in large-area full-color displays and solid-state lighting. A delicate control over the entire electroluminescence process is indispensable to overcome the efficiency limitations of blue PeLEDs. Here, we demonstrate an efficient device architecture to synergistically r… ▽ More The low efficiency of metal halide perovskite light-emitting diodes (PeLEDs) with blue emission block their potential applications in large-area full-color displays and solid-state lighting. A delicate control over the entire electroluminescence process is indispensable to overcome the efficiency limitations of blue PeLEDs. Here, we demonstrate an efficient device architecture to synergistically reduce the energetic losses during electron-photon conversion and boost the extraction of trapped light in the device. An interfacial nucleation seeding scheme is proposed to control the crystallization process of highly emissive perovskite nanocrystals and suppress the trap-mediated non-radiative recombination losses due to interfacial hydrogen bonding interactions. This manipulation results in a record external quantum efficiency (EQE) of 12.8% for blue PeLEDs emitting at 486 nm, along with the improved spectral stability and operation lifetime. Additionally, the maximum EQE reaches 16.8% after combining an internal outcoupling structure without spectral distortion, which can be further raised to 27.5% when using a lens-based structure on top of the device. We anticipate that our work provides an effective method for its application in high-performance PeLEDs. △ Less

Submitted 5 December, 2020; originally announced December 2020.

Quality Assurance Test of Silicon Photomultipliers and Electronic Boards for STAR Event Plane Detector

Authors: Ming Shao, Yitao Wu, Zheng Liang, Kaifeng Shen, Zebo Tang, M. A. Lisa, R. Reed, G. Visser, Yongjie Sun, Yi Zhou, Jian Zhou, Guofeng Song, Dongdong Hu, Xu Wang, Xinjian Wang

Abstract: The event plane detector (EPD), installed in the Solenoid Tracker at the Relativistic Heavy-Ion Collider located at the Brookhaven National Laboratory is a plastic scintillator-based device that measures the reaction centrality and event plane in the forward region of the relativistic heavy-ion collisions. We used silicon photomultiplier (SiPM) arrays to detect the photons produced in the scintill… ▽ More The event plane detector (EPD), installed in the Solenoid Tracker at the Relativistic Heavy-Ion Collider located at the Brookhaven National Laboratory is a plastic scintillator-based device that measures the reaction centrality and event plane in the forward region of the relativistic heavy-ion collisions. We used silicon photomultiplier (SiPM) arrays to detect the photons produced in the scintillator via the fiber connection. Signals from the SiPM arrays were amplified by the front-end electronic (FEE) board, and sent to the analog-to-digital converter (ADC) boards for further processing via the receiver(RX) board. The full EPD system consisted of 24 super-sectors (SSs); each SS was equipped with two SiPM boards, two FEE boards and two RX boards, and they corresponded to 744 readout channels. All these boards were mass produced at the University of Science and Technology of China, with a dedicated quality assurance (QA) procedures applied to identify any problems before deployment. This article describes the details of the QA method and the related test system. The QA test results are presented along with the discussions. △ Less

Submitted 22 November, 2020; originally announced November 2020.

Miniscope3D: optimized single-shot miniature 3D fluorescence microscopy

Authors: Kyrollos Yanny, Nick Antipa, William Liberti, Sam Dehaeck, Kristina Monakhova, Fanglin Linda Liu, Konlin Shen, Ren Ng, Laura Waller

Abstract: Miniature fluorescence microscopes are a standard tool in systems biology. However, widefield miniature microscopes capture only 2D information, and modifications that enable 3D capabilities increase the size and weight and have poor resolution outside a narrow depth range. Here, we achieve the 3D capability by replacing the tube lens of a conventional 2D Miniscope with an optimized multifocal pha… ▽ More Miniature fluorescence microscopes are a standard tool in systems biology. However, widefield miniature microscopes capture only 2D information, and modifications that enable 3D capabilities increase the size and weight and have poor resolution outside a narrow depth range. Here, we achieve the 3D capability by replacing the tube lens of a conventional 2D Miniscope with an optimized multifocal phase mask at the objective's aperture stop. Placing the phase mask at the aperture stop significantly reduces the size of the device, and varying the focal lengths enables a uniform resolution across a wide depth range. The phase mask encodes the 3D fluorescence intensity into a single 2D measurement, and the 3D volume is recovered by solving a sparsity-constrained inverse problem. We provide methods for designing and fabricating the phase mask and an efficient forward model that accounts for the field-varying aberrations in miniature objectives. We demonstrate a prototype that is 17 mm tall and weighs 2.5 grams, achieving 2.76 $μ$m lateral, and 15 $μ$m axial resolution across most of the 900x700x390 $μm^3$ volume at 40 volumes per second. The performance is validated experimentally on resolution targets, dynamic biological samples, and mouse brain tissue. Compared with existing miniature single-shot volume-capture implementations, our system is smaller and lighter and achieves a more than 2x better lateral and axial resolution throughout a 10x larger usable depth range. Our microscope design provides single-shot 3D imaging for applications where a compact platform matters, such as volumetric neural imaging in freely moving animals and 3D motion studies of dynamic samples in incubators and lab-on-a-chip devices. △ Less

Submitted 11 October, 2020; originally announced October 2020.

Comments: Published with Nature Springer in Light: Science and Applications

Journal ref: Light: Science & Applications 9.1 (2020): 1-13

Qualification tests of 997 8-inch photomultiplier tubes for the water Cherenkov detector array of the LHAASO experiment

Authors: Kun Jiang, Zebo Tang, Xin Li, Zehua Cao, Cheng Li, Yang Li, Ziwei Li, Ziyang Li, Zheng Liang, Pengzhong Lu, Kaifeng Shen, Kaiyang Wang, Yan Wang, Xin Wu

Abstract: The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi Mountain, Sichuan province of China at an altitude of 4410 meters. One of its main goals is to survey the northern sky for very-high-energy gamma ray sources via its ground-based water Cherenkov detector array (WCDA). 900 8-inch photomultiplier tubes (PMTs) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP)… ▽ More The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi Mountain, Sichuan province of China at an altitude of 4410 meters. One of its main goals is to survey the northern sky for very-high-energy gamma ray sources via its ground-based water Cherenkov detector array (WCDA). 900 8-inch photomultiplier tubes (PMTs) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP) are installed in the WCDA, collecting Cherenkov photons produced by air shower particles crossing water. The design of the PMT base with a high dynamic range for CR365-02-1, the PMT batch test system, and the test results of 997 PMTs are presented in this paper. △ Less

Submitted 26 March, 2021; v1 submitted 27 September, 2020; originally announced September 2020.

Comments: 23 pages, 17 figures

Journal ref: Nuclear Inst. and Methods in Physics Research, A 995 (2021) 165108

Influence of sensor tilts on bio-inspired polarized skylight orientation determination

Authors: Huaju Liang, Hongyang Bai, Tong Zhou, Kai Shen

Abstract: Inspired by many insects, several polarized skylight orientation determination approaches have been proposed. However, almost all of these approaches always require polarization sensor pointing to the zenith of the sky dome. So, the influence of sensor tilts (not point to the sky zenith) on bio-inspired polarization orientation determination needs to be analyzed urgently. Aiming at this problem, a… ▽ More Inspired by many insects, several polarized skylight orientation determination approaches have been proposed. However, almost all of these approaches always require polarization sensor pointing to the zenith of the sky dome. So, the influence of sensor tilts (not point to the sky zenith) on bio-inspired polarization orientation determination needs to be analyzed urgently. Aiming at this problem, a polarization compass simulation system is designed based upon solar position model, Rayleigh sky model, and hypothetical polarization imager. Then, the error characteristics of four typical orientation determination approaches are investigated in detail under only pitch tilt condition, only roll tilt condition, pitch and roll tilts condition respectively. Finally, simulation and field experiments all show that the orientation errors of four typical approaches are highly consistent when they are subjected to tilt interference, in addition, the errors are affected by not only the degree of inclination, but also the solar altitude angle and the relative position between the Sun and polarization sensor. The results of this paper can be used to estimate the orientation determination error caused by sensor tilts and correct this kind of error. △ Less

Submitted 5 November, 2020; v1 submitted 17 July, 2020; originally announced July 2020.

Observation of terahertz magnon of Kaplan-Kittel exchange resonance in yttrium-iron garnet by Raman spectroscopy

Authors: Wei-Hung Hsu, Ka Shen, Yasuhiro Fujii, Akitoshi Koreeda, Takuya Satoh

Abstract: Backscattering Raman spectroscopic investigations were performed on an yttrium-iron garnet single crystal using linearly and circularly polarized light. A terahertz (THz) magnon of the Kaplan-Kittel (KK) exchange resonance was discovered, which had been regarded as unobservable via optical methods. The KK exchange resonance had a 7.8-THz frequency at 80 K, and the polarization selection rule led t… ▽ More Backscattering Raman spectroscopic investigations were performed on an yttrium-iron garnet single crystal using linearly and circularly polarized light. A terahertz (THz) magnon of the Kaplan-Kittel (KK) exchange resonance was discovered, which had been regarded as unobservable via optical methods. The KK exchange resonance had a 7.8-THz frequency at 80 K, and the polarization selection rule led to an antisymmetric Raman tensor of the $A_{2}$ mode. Moreover, the assignment of all the Raman-active phonon modes, $3A_{1g}$, $8E_{g}$, and $14T_{2g}$, was proposed. This study will stimulate further investigation of the coupling of THz magnons and phonons and pave the way toward THz optomagnonics. △ Less

Submitted 25 November, 2020; v1 submitted 8 May, 2020; originally announced May 2020.

Journal ref: Phys. Rev. B 102 (2020) 174432

Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating

Authors: Jilei Chen, Tao Yu, Chuanpu Liu, Tao Liu, Marco Madami, Ka Shen, Jianyu Zhang, Sa Tu, Md Shah Alam, Ke Xia, Mingzhong Wu, Gianluca Gubbiotti, Yaroslav M. Blanter, Gerrit E. W. Bauer, Haiming Yu

Abstract: Magnon spintronics is a prosperous field that promises beyond-CMOS technology based on elementary excitations of the magnetic order that act as information carriers for future computational architectures. Unidirectional propagation of spin waves is key to the realization of magnonic logic devices. However, previous efforts to enhance the Damon-Eshbach-type nonreciprocity did not realize (let alone… ▽ More Magnon spintronics is a prosperous field that promises beyond-CMOS technology based on elementary excitations of the magnetic order that act as information carriers for future computational architectures. Unidirectional propagation of spin waves is key to the realization of magnonic logic devices. However, previous efforts to enhance the Damon-Eshbach-type nonreciprocity did not realize (let alone control) purely unidirectional propagation. Here we experimentally demonstrate excitations of unidirectional exchange spin waves by a nanoscale magnetic grating consisting of Co nanowires fabricated on an ultrathin yttrium iron garnet film. We explain and model the nearly perfect unidirectional excitation by the chirality of the magneto-dipolar interactions between the Kittel mode of the nanowires and the exchange spin waves of the film. Reversal of the magnetic configurations of film and nanowire array from parallel to antiparallel changes the direction of the excited spin waves. Our results raise the prospect of a chiral magnonic logic without the need for fragile surface states. △ Less

Submitted 2 March, 2019; originally announced March 2019.

Journal ref: Phys. Rev. B 100, 104427 (2019)

A tunable low-energy photon source for high-resolution angle-resolved photoemission spectroscopy

Authors: John W. Harter, Philip D. C. King, Eric J. Monkman, Daniel E. Shai, Yuefeng Nie, Masaki Uchida, Bulat Burganov, Shouvik Chatterjee, Kyle M. Shen

Abstract: We describe a tunable low-energy photon source consisting of a laser-driven xenon plasma lamp coupled to a Czerny-Turner monochromator. The combined tunability, brightness, and narrow spectral bandwidth make this light source useful in laboratory-based high-resolution photoemission spectroscopy experiments. The source supplies photons with energies up to ~7 eV, delivering under typical conditions… ▽ More We describe a tunable low-energy photon source consisting of a laser-driven xenon plasma lamp coupled to a Czerny-Turner monochromator. The combined tunability, brightness, and narrow spectral bandwidth make this light source useful in laboratory-based high-resolution photoemission spectroscopy experiments. The source supplies photons with energies up to ~7 eV, delivering under typical conditions >10^12 ph/s within a 10 meV spectral bandwidth, which is comparable to helium plasma lamps and many synchrotron beamlines. We first describe the lamp and monochromator system and then characterize its output, with attention to those parameters which are of interest for photoemission experiments. Finally, we present angle-resolved photoemission spectroscopy data using the light source and compare its performance to a conventional helium plasma lamp. △ Less

Submitted 11 April, 2017; originally announced April 2017.

Journal ref: Review of Scientific Instruments 83, 113103 (2012)

Different Non-extensive Models for heavy-ion collisions

Authors: Keming Shen, Tamas S. Biro, Enke Wang

Abstract: The transverse momentum ($p_T$) spectra from heavy-ion collisions at intermediate momenta are described by non-extensive statistical models. Assuming a fixed relative variance of the temperature fluctuating event by event or alternatively a fixed mean multiplicity in a negative binomial distribution (NBD), two different linear relations emerge between the temperature, $T$, and the Tsallis paramete… ▽ More The transverse momentum ($p_T$) spectra from heavy-ion collisions at intermediate momenta are described by non-extensive statistical models. Assuming a fixed relative variance of the temperature fluctuating event by event or alternatively a fixed mean multiplicity in a negative binomial distribution (NBD), two different linear relations emerge between the temperature, $T$, and the Tsallis parameter $q-1$. Our results qualitatively agree with that of G.~Wilk. Furthermore we revisit the "Soft+Hard" model, proposed recently by G.~G.~Barnaföldi \textit{et.al.}, by a $T$-independent average $p_T^2$ assumption. Finally we compare results with those predicted by another deformed distribution, using Kaniadakis' $κ$ parametrization. △ Less

Submitted 11 January, 2017; originally announced January 2017.

Comments: 12 pages, 3 figures

Modulus-Pressure Equation for Confined Fluids

Authors: Gennady Y. Gor, Daniel W. Siderius, Vincent K. Shen, Noam Bernstein

Abstract: Ultrasonic experiments allow one to measure the elastic modulus of bulk solid or fluid samples. Recently such experiments have been carried out on fluid-saturated nanoporous glass to probe the modulus of a confined fluid. In our previous work [J. Chem. Phys., (2015) 143, 194506], using Monte Carlo simulations we showed that the elastic modulus $K$ of a fluid confined in a mesopore is a function of… ▽ More Ultrasonic experiments allow one to measure the elastic modulus of bulk solid or fluid samples. Recently such experiments have been carried out on fluid-saturated nanoporous glass to probe the modulus of a confined fluid. In our previous work [J. Chem. Phys., (2015) 143, 194506], using Monte Carlo simulations we showed that the elastic modulus $K$ of a fluid confined in a mesopore is a function of the pore size. Here we focus on modulus-pressure dependence $K(P)$, which is linear for bulk materials, a relation known as the Tait-Murnaghan equation. Using transition-matrix Monte Carlo simulations we calculated the elastic modulus of bulk argon as a function of pressure and argon confined in silica mesopores as a function of Laplace pressure. Our calculations show that while the elastic modulus is strongly affected by confinement and temperature, the slope of the modulus versus pressure is not. Moreover, the calculated slope is in a good agreement with the reference data for bulk argon and experimental data for confined argon derived from ultrasonic experiments. We propose to use the value of the slope of $K(P)$ to estimate the elastic moduli of an unknown porous medium. △ Less

Submitted 23 August, 2016; originally announced August 2016.

Relation Between Pore Size and the Compressibility of a Confined Fluid

Authors: Gennady Y. Gor, Daniel W. Siderius, Christopher J. Rasmussen, William P. Krekelberg, Vincent K. Shen, Noam Bernstein

Abstract: When a fluid is confined to a nanopore, its thermodynamic properties differ from the properties of a bulk fluid, so measuring such properties of the confined fluid can provide information about the pore sizes. Here we report a simple relation between the pore size and isothermal compressibility of argon confined in these pores. Compressibility is calculated from the fluctuations of the number of p… ▽ More When a fluid is confined to a nanopore, its thermodynamic properties differ from the properties of a bulk fluid, so measuring such properties of the confined fluid can provide information about the pore sizes. Here we report a simple relation between the pore size and isothermal compressibility of argon confined in these pores. Compressibility is calculated from the fluctuations of the number of particles in the grand canonical ensemble using two different simulation techniques: conventional grand-canonical Monte Carlo and grand-canonical ensemble transition-matrix Monte Carlo. Our results provide a theoretical framework for extracting the information on the pore sizes of fluid-saturated samples by measuring the compressibility from ultrasonic experiments. △ Less

Submitted 3 November, 2015; originally announced November 2015.

Comments: 6 pages, 2 figures

Journal ref: J. Chem. Phys. 143, 194506 (2015)

Laser-induced spatiotemporal dynamics of magnetic films

Authors: Ka Shen, Gerrit E. W. Bauer

Abstract: We present a theory for the coherent magnetization dynamics induced by a focused ultrafast laser beam in magnetic films, taking into account nonthermal (inverse Faraday effect) and thermal (heating) actuation. The dynamic conversion between spin waves and phonons is induced by the magnetoelastic coupling that allows efficient propagation of angular momentum. The anisotropy of the magnetoelastic co… ▽ More We present a theory for the coherent magnetization dynamics induced by a focused ultrafast laser beam in magnetic films, taking into account nonthermal (inverse Faraday effect) and thermal (heating) actuation. The dynamic conversion between spin waves and phonons is induced by the magnetoelastic coupling that allows efficient propagation of angular momentum. The anisotropy of the magnetoelastic coupling renders characteristic angle dependences of the magnetization propa-gation that are strikingly different for thermal and nonthermal actuation. △ Less

Submitted 5 November, 2015; v1 submitted 9 August, 2015; originally announced August 2015.

Comments: 5+3 pages

Journal ref: Phys. Rev. Lett. 115, 197201 (2015)

An in-vacuum diffractometer for resonant elastic soft x-ray scattering

Authors: D. G. Hawthorn, F. He, L. Venema, H. Davis, A. J. Achkar, J. Zhang, R. Sutarto, H. Wadati, A. Radi, T. Wilson, G. Wright, K. M. Shen, J. Geck, H. Zhang, V. Novak, G. A. Sawatzky

Abstract: We describe the design, construction and performance of a 4-circle in-vacuum diffractometer for resonant elastic soft x-ray scattering and reflectivity. The diffractometer, installed on the REIXS beamline at the Canadian Light Source, includes 9 in-vacuum motions driven by in-vacuum stepper motors and operates in ultra-high vacuum at base pressure of 2 x10^-10 Torr. Cooling to a base temperature o… ▽ More We describe the design, construction and performance of a 4-circle in-vacuum diffractometer for resonant elastic soft x-ray scattering and reflectivity. The diffractometer, installed on the REIXS beamline at the Canadian Light Source, includes 9 in-vacuum motions driven by in-vacuum stepper motors and operates in ultra-high vacuum at base pressure of 2 x10^-10 Torr. Cooling to a base temperature of 18 K is provided with a closed-cycle cryostat. The diffractometer includes a choice of 3 photon detectors: a photodiode, a channeltron and a 2D sensitive channelplate detector. Along with variable slit and filter options, these detectors are suitable for studying a wide range of phenomena having both weak and strong diffraction signals. Example measurements of diffraction and reflectivity in Nd-doped (La,Sr)_2CuO_4 and thin film (Ga,Mn)As are shown. △ Less

Submitted 19 May, 2011; originally announced May 2011.

Comments: 9 pages, 8 figures

Journal ref: Rev. Sci. Instrum. 82, 073104 (2011)

Folksonomy as a Complex Network

Authors: Kaikai Shen, Lide Wu

Abstract: Folksonomy is an emerging technology that works to classify the information over WWW through tagging the bookmarks, photos or other web-based contents. It is understood to be organized by every user while not limited to the authors of the contents and the professional editors. This study surveyed the folksonomy as a complex network. The result indicates that the network, which is composed of the… ▽ More Folksonomy is an emerging technology that works to classify the information over WWW through tagging the bookmarks, photos or other web-based contents. It is understood to be organized by every user while not limited to the authors of the contents and the professional editors. This study surveyed the folksonomy as a complex network. The result indicates that the network, which is composed of the tags from the folksonomy, displays both properties of small world and scale-free. However, the statistics only shows a local and static slice of the vast body of folksonomy which is still evolving. △ Less

Submitted 23 September, 2005; originally announced September 2005.