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Resonant Auger Scattering by Attosecond X-Ray Pulses
Quan-Wei Nan, Chao Wang, Xin-Yue Yu, Xi Zhao, Yongjun Cheng, Maomao Gong, Xiao-Jing Liu, Victor Kimberg, and Song-Bin Zhang
Chin. Phys. Lett.    2023, 40 (9): 093201 .   DOI: 10.1088/0256-307X/40/9/093201
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As x-ray probe pulses approach the subfemtosecond range, conventional x-ray photoelectron spectroscopy (XPS) is expected to experience a reduction in spectral resolution due to the effects of the pulse broadening. However, in the case of resonant x-ray photoemission, also known as resonant Auger scattering (RAS), the spectroscopic technique maintains spectral resolution when an x-ray pulse is precisely tuned to a core-excited state. We present theoretical simulations of XPS and RAS spectra on a showcased CO molecule using ultrashort x-ray pulses, revealing significantly enhanced resolution in the RAS spectra compared to XPS, even in the sub-femtosecond regime. These findings provide a novel perspective on potential utilization of attosecond x-ray pulses, capitalizing on the well-established advantages of detecting electron signals for tracking electronic and molecular dynamics.
Enhanced Extreme Ultraviolet Free Induction Decay Emission Assisted by Attosecond Pulses
Wenkai Tao, Li Wang, Pan Song, Fan Xiao, Jiacan Wang, Zhigang Zheng, Jing Zhao, Xiaowei Wang, and Zengxiu Zhao
Chin. Phys. Lett.    2023, 40 (6): 063201 .   DOI: 10.1088/0256-307X/40/6/063201
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We demonstrate the extreme ultraviolet free induction decay emission that can be significantly enhanced by employing isolated attosecond pulses. The near infrared pulses are applied to excite the neon atoms into Rydberg states coherently, and isolated attosecond pulses are used to manipulate populations of the Rydberg states and the subsequent free induction decay process. The time resolved experimental measurement of dependence of the resonance emission yield would help to understand the buildup dynamics of population of excited states. The enhancement assisted by attosecond pulses can serve as a mechanism to develop high-flux extreme ultraviolet light sources.
Twin-Capture Rydberg State Excitation Enhanced with Few-Cycle Laser Pulses
Jing Zhao, Jinlei Liu, Xiaowei Wang, and Zengxiu Zhao
Chin. Phys. Lett.    2024, 41 (1): 013201 .   DOI: 10.1088/0256-307X/41/1/013201
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Quantum excitation is usually regarded as a transient process occurring instantaneously, leaving the underlying physics shrouded in mystery. Recent research shows that Rydberg-state excitation with ultrashort laser pulses can be investigated and manipulated with state-of-the-art few-cycle pulses. We theoretically find that the efficiency of Rydberg state excitation can be enhanced with a short laser pulse and modulated by varying the laser intensities. We also uncover new facets of the excitation dynamics, including the launching of an electron wave packet through strong-field ionization, the re-entry of the electron into the atomic potential and the crucial step where the electron makes a U-turn, resulting in twin captures into Rydberg orbitals. By tuning the laser intensity, we show that the excitation of the Rydberg state can be coherently controlled on a sub-optical-cycle timescale. Our work paves the way toward ultrafast control and coherent manipulation of Rydberg states, thus benefiting Rydberg-state-based quantum technology.
Transporting Cold Atoms towards a GaN-on-Sapphire Chip via an Optical Conveyor Belt
Lei Xu, Ling-Xiao Wang, Guang-Jie Chen, Liang Chen, Yuan-Hao Yang, Xin-Biao Xu, Aiping Liu, Chuan-Feng Li, Guang-Can Guo, Chang-Ling Zou, and Guo-Yong Xiang
Chin. Phys. Lett.    2023, 40 (9): 093701 .   DOI: 10.1088/0256-307X/40/9/093701
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Trapped atoms on photonic structures inspire many novel quantum devices for quantum information processing and quantum sensing. Here, we demonstrate a hybrid photonic-atom chip platform based on a GaN-on-sapphire chip and the transport of an ensemble of atoms from free space towards the chip with an optical conveyor belts. Due to our platform's complete optical accessibility and careful control of atomic motion near the chip with a conveyor belt, successful atomic transport towards the chip is made possible. The maximum transport efficiency of atoms is about $50\%$ with a transport distance of $500\,\mathrm{µ m}$. Our results open up a new route toward the efficient loading of cold atoms into the evanescent-field trap formed by the photonic integrated circuits, which promises strong and controllable interactions between single atoms and single photons.
Energy Levels and Transition Rates for Laser Cooling Os$^{-}$ and a General Approach to Produce Cold Atoms and Molecules
Yuzhu Lu, Rui Zhang, Changxian Song, Chongyang Chen, Ran Si, and Chuangang Ning
Chin. Phys. Lett.    2023, 40 (9): 093101 .   DOI: 10.1088/0256-307X/40/9/093101
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High-resolution photoelectron energy spectra of osmium anions are obtained using the slow-electron velocity-map imaging method. The energy levels of excited states $^{4}\!F_{7/2}$, $^{4}\!F_{5/2}$ and $^{4}\!F_{3/2}$ of Os$^{-}$ are determined to be 148.730(13), 155.69(15), and 176.76(13) THz [or 4961.09(41), 5193.4(49), and 5896.1(42) cm$^{-1}$], respectively. The lifetime of the opposite-parity excited state $^{6}\!D_{9/2}^{\rm o}$ is determined to be 201(10) µs using a cold ion trap, about 15 times shorter than the previous result 3(1) ms. Our high-level multi-configuration Dirac–Hartree–Fock calculations yield a theoretical lifetime 527 µs. Our work shows that the laser cooling rate of Os$^{-}$ is as fast as that of Th$^{-}$. The advantages of Os$^{-}$ are its near-IR range cooling transition and simple electronic structure, which make Os$^{-}$ a promising candidate for laser cooling of negative ions. We propose a general approach to produce cold atoms and molecules based on the sympathetic cooling of negative ions in combination with a threshold photodetachment.
Enhanced THz Radiation from Spatially Inhomogeneous Fields
Guang-Rui Jia, Deng-Xin Zhao, Song-Song Zhang, Zi-Wei Yue, Chao-Chao Qin, Zhao-Yong Jiao, and Xue-Bin Bian
Chin. Phys. Lett.    2023, 40 (10): 103202 .   DOI: 10.1088/0256-307X/40/10/103202
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Nonlinear terahertz (THz) radiation from gas media usually relies on the asymmetric laser-induced current produced by ultra-intense two-color laser fields with a specific phase delay. Here a new scheme is proposed and theoretically investigated, in which the radiation is generated by spatially inhomogeneous fields induced by relatively low-intensity monochromatic lasers and an array of single triangular metallic nanostructures. Our simulations are based on the classical photocurrent model and the time-dependent Schrödinger equations separately. It is found that the collective motion of the ionized electrons can be efficiently controlled by the inhomogeneous field, resulting in strong residual currents. The intensity of the THz radiation could be enhanced by about two orders of magnitude by increasing the spatial inhomogeneity of the field.
Observation of Two-Dimensional Mott Insulator and $\pi$-Superfluid Quantum Phase Transition in Shaking Optical Lattice
Jingxin Sun, Pengju Zhao, Zhongshu Hu, Shengjie Jin, Ren Liao, Xiong-Jun Liu, and Xuzong Chen
Chin. Phys. Lett.    2023, 40 (8): 083701 .   DOI: 10.1088/0256-307X/40/8/083701
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The Mott insulator and superfluid phase transition is one of the most prominent phenomena in ultracold atoms. We report the observation of a novel 2D quantum phase transition between the Mott insulator and $\pi$ superfluid in a shaking optical lattice. In the deep optical lattice regime, the lowest $S$ band can be tuned to Mott phase, while the higher $P_{x,y}$ bands are itinerant for having larger bandwidth. Through a shaking technique coupling the $s$-orbital to $p_{x,y}$-orbital states, we experimentally observe the transition between the states of the $S$ and $P_{x,y}$ bands, leading to a quantum phase transition from two-dimensional $s$-orbital Mott phase to the $p_{x,y}$-orbital superfluid which condensed at $(\pi,\pi)$ momentum. Using the band-mapping method, we also observe the changes of atomic population in different energy bands during the transition, and the experimental results are well consistent with theoretical expectations.
Chirp Compensation for Generating Ultrashort Attosecond Pulses with 800-nm Few-Cycle Pulses
Li Wang, Xiaowei Wang, Fan Xiao, Jiacan Wang, Wenkai Tao, Dongwen Zhang, and Zengxiu Zhao
Chin. Phys. Lett.    2023, 40 (11): 113201 .   DOI: 10.1088/0256-307X/40/11/113201
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We show that it is feasible to generate sub-40-attosecond pulses with near-infrared few-cycle pulses centered at 800 nm. With proper gating technique, super-broadband continuum spectrum extending from 50 eV to above 200 eV can be obtained, and the intrinsic atto-chirp can be satisfactorily compensated with C filter, producing isolated attosecond pulses with duration of 33 as. According to the wavelength scaling law of high-order harmonic generation, the proposed scheme is of great significance to develop high-flux ultrashort attosecond sources.
Isotope-Shift Measurement of Bosonic Yb$^{+}$ Ions
Hong-Ling Yue, Hu Shao, Zheng Chen, Peng-Cheng Fang, Meng-Yan Zeng, Bao-Lin Zhang, Yao Huang, Ji-Guang Li, Qun-Feng Chen, Hua Guan, and Ke-Lin Gao
Chin. Phys. Lett.    2023, 40 (9): 093202 .   DOI: 10.1088/0256-307X/40/9/093202
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We present a method that the atomic transition frequency measurement relies on the accurate wavemeter, optical frequency comb and stable Fabry–Pérot cavity to precise determination of stable even isotope shift on single Yb$^{+}$ ion ($A=168$, 170, 172, 174, 176). The $6s$ ${}^{2}\!S_{1/2} \leftrightarrow 6p\,{}^{2}\!P_{1/2}$   and $5d\,{}^{2}\!D_{3/2} \leftrightarrow 6s\,{}^{3}[3/2]_{1/2}$   resonance dipole transition frequencies are preliminarily measured by using a wavemeter which is calibrated by the 729 nm clock laser of ${}^{40}$Ca$^{+}$. Meanwhile, those frequencies are double checked by using optical frequency comb for correction of deviation. Ultimately, by changing frequency locking points at an ultralow expansion cavity more slightly and monitoring the corresponding atomic fluorescence changing with 17%, we finally improve the resonant frequency uncertainty to $\pm 6$ MHz, which is one order of improvement in precision higher than previously published measurements on the same transitions. A King-plot analysis with sensitivity to coupling between electrons and neutrons is carried out to determine the field and mass shift constants. Our measurement combined with existing or future isotope shift measurements can be used to determine basic properties of atomic nuclei, and to test new forces beyond the Standard Model.
Wavelength Dependence of Atomic Excitation for Ar Subject to Intense Midinfrared Laser Pulses
Yang-Ni Liu, Song-Po Xu, Mu-Feng Zhu, Zheng-Rong Xiao, Shao-Gang Yu, Lin-Qiang Hua, Xuan-Yang Lai, Wei Quan, Wen-Xing Yang, and Xiao-Jun Liu
Chin. Phys. Lett.    2023, 40 (10): 103201 .   DOI: 10.1088/0256-307X/40/10/103201
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We report experimental and theoretical investigations of wavelength dependence of Rydberg state excitation (RSE) process of Ar subject to intense laser fields. By simultaneously measuring ionization and RSE yields of Ar atoms subject to strong laser fields at a series of wavelengths, we obtain the wavelength scaling law of the ratio of Ar$^{*}$ over Ar$^{+}$ with respect to the laser intensity, and this result can be well reproduced by a nonadiabatic model, but not by the classical-trajectory Monte Carlo model. Our results indicate that the nonadiabatic corrections of the photoelectron tunneling exit and tunneling probability play a significant role at shorter wavelengths. Analysis shows that the wavelength dependence phenomenon is due to the interplay of the nonadiabatic effect, wave-packet diffusion and Coulomb focusing effect of the liberated electron.
Generation of Ultrafast Attosecond Magnetic Field from Ne Dimer in Circularly Polarized Laser Pulses
Shujuan Yan, Qingyun Xu, Xinyu Hao, Ying Guo, and Jing Guo
Chin. Phys. Lett.    2023, 40 (11): 113101 .   DOI: 10.1088/0256-307X/40/11/113101
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By numerically solving time-dependent Schrödinger equations, we investigate the generation of electron currents, ultrafast magnetic fields and photoelectron momentum distributions (PMD) when circularly polarized laser pulses interact with a Ne dimer in the charge migration (CM) process. By adjusting the laser wavelength, we consider two cases: (i) coherent resonance excitation ($\lambda=76$ nm) and (ii) direct ionization ($\lambda=38$ nm). The results show that the current and magnetic field generated by the Ne dimer under resonance excitation are stronger than under direct ionization. This phenomenon is due to the quantum interference between the initial state $2p\sigma_{\rm g}$ and the excited state $3s\sigma_{\rm g}$ under resonance excitation, so the CM efficiency of the dimer can be improved and the strength of the PMD under different ionization conditions is opposite to the strength of the electron current and induced magnetic field. In addition, we also find that both $2p\pi_{\rm g}$ and $2p\pi_{\rm u}$ have coherent resonance excitation with $3s\sigma_{\rm g}$ state and generate periodic oscillating currents for the Ne dimer. The study of the dynamics of the Ne dimer under different ionization conditions lays a foundation for research of ultrafast magnetism in complex molecular systems.
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