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Volume 37 Issue 3
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Energy Variance in Decoherence
Zi-Gang Yuan, Xin-Yu Zhang, He Zhao, Yan-Chao Li
Chin. Phys. Lett. 2020, 37 (3): 030301 .   DOI: 10.1088/0256-307X/37/3/030301
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We study the effect of the initial-state energy variance to the short-time behavior of the Loschmidt echo (LE) in a purely dephasing model. We find that the short-time LE behaves as a Gaussian function with the width determined by the initial-state energy variance of the interaction Hamiltonian, while it is a quartic decaying function with the width determined by the initial-state energy variance of the commutator between the interaction Hamiltonian and the environmental Hamiltonian when the initial state is an eigenstate of the interaction Hamiltonian. Furthermore, the Gaussian envelope in the temporal evolution of LE in strong coupling regime is determined by the inband variance. We will also verify the above conclusion in the XY spin model (as environment).
Quantized Superfluid Vortex Filaments Induced by the Axial Flow Effect
Hao Li, Chong Liu, Zhan-Ying Yang, Wen-Li Yang
Chin. Phys. Lett. 2020, 37 (3): 030302 .   DOI: 10.1088/0256-307X/37/3/030302
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We report the quantized superfluid vortex filaments induced by the axial flow effect, which exhibit intriguing loop structures on helical vortexes. Such new vortex filaments correspond to a series of soliton excitations including the multipeak soliton, W-shaped soliton, and anti-dark soliton, which have no analogue when the axial flow effect is absent. In particular, we show that the vortex filaments induced by the multipeak soliton and W-shaped soliton arise from the dual action of bending and twisting of the vortex, while the vortex filament induced by the anti-dark soliton is caused only by the bending action, which is consistent with the case of the standard bright soliton. These results will deepen our understanding of breather-induced vortex filaments and will be helpful for controllable ring-like excitations on vortices.
Soliton Molecules and Some Hybrid Solutions for the Nonlinear Schrödinger Equation
Bao Wang, Zhao Zhang, Biao Li
Chin. Phys. Lett. 2020, 37 (3): 030501 .   DOI: 10.1088/0256-307X/37/3/030501
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Based on velocity resonance and Darboux transformation, soliton molecules and hybrid solutions consisting of soliton molecules and smooth positons are derived. Two new interesting results are obtained: the first is that the relationship between soliton molecules and smooth positons is clearly pointed out, and the second is that we find two different interactions between smooth positons called strong interaction and weak interaction, respectively. The strong interaction will only disappear when $t \to \infty$. This strong interaction can also excite some periodic phenomena.
Visualization of Fiber Moving in Air Tunnel with Velocity Gradient
Yang Miao, Xiang Guo, Xiao-Jun Zhang
Chin. Phys. Lett. 2020, 37 (3): 034201 .   DOI: 10.1088/0256-307X/37/3/034201
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To measure the parameters of fiber and to visualize the reshaping process of fiber in air tunnel, an experimental approach is developed in the present work. The tunnel is designed with gradient flow velocity, and the fiber reshaping images as well as the fiber length value are obtained experimentally. An analytical expression of velocity distribution in the tunnel is theoretically derived and the simulated results are obtained. Automatic fiber reshaping including stretch and rotation is verified using the dynamical equation and the multi-spherical chain model. It is shown that pull force by air flow makes a chain of balls become straight and Stokes moment makes the ball chain rotate. Finally, reshaping criterion related with flow velocity is formulated.
High-Efficiency Broadband Near-Infrared Single-Photon Frequency Upconversion and Detection
Jian-Hui Ma, Hui-Qin Hu, Yu Chen, Guang-Jian Xu, Hai-Feng Pan, E Wu
Chin. Phys. Lett. 2020, 37 (3): 034202 .   DOI: 10.1088/0256-307X/37/3/034202
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We propose and demonstrate a high efficiency broadband near infrared single-photon upconversion and detection with a broadband pump laser based on sum frequency conversion in the PPLN crystal. By using a pump laser centered at 1040 nm with a spectral bandwidth of 10 nm, the signal single-photons centered at 1562 nm with a broadband bandwidth up to 7.2 nm are frequency-converted from the near infrared to the visible regime. A maximum conversion efficiency of 18.8% is achieved, while the background noise is measured to be only $1.2\times 10^{-3}$ counts/pulse. The corresponding spectral linewidth of the upconverted photons is 0.2 nm. This scheme of broadband infrared single-photon upconversion and detection provides potential solutions in infrared laser ranging, broadband infrared imaging and quantum key distribution.
Diode Pumped Rubidium Laser Based on Etalon Effects of Alkali Cell Windows
Fang-Jin Ning, Zhi-Yong Li, Rong-Qing Tan, Lie-Mao Hu, Song-Yang Liu
Chin. Phys. Lett. 2020, 37 (3): 034203 .   DOI: 10.1088/0256-307X/37/3/034203
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We demonstrate that the etalon effects of alkali cells can be used as the output coupler of an alkali laser. Based on a rubidium cell with highly parallelized windows, a 2.7 W rubidium laser with optical efficiency of 20.9% and slope efficiency of 31.8% is obtained by adopting unconventional output couplers. Since it has compact configuration and the inner surface of the rubidium cell is uncoated, this may be used in high power laser systems with long lifetimes.
Asymptotical Locking Tomography of High-Dimensional Entanglement
Ling-Jun Kong, Rui Liu, Wen-Rong Qi, Zhou-Xiang Wang, Shuang-Yin Huang, Chenghou Tu, Yongnan Li, Hui-Tian Wang
Chin. Phys. Lett. 2020, 37 (3): 034204 .   DOI: 10.1088/0256-307X/37/3/034204
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High-dimensional (HD) entanglement provides a very promising way of transcending the limitations of the two-dimensional entanglement between qubits for increasing channel capacity in many quantum protocols. In the pursuit of capitalizing on the HD entangled states, one of the central issues is to unambiguously and comprehensively quantify and reconstruct them. The full quantum state tomography is a unique solution, but it is undesirable and even impractical because the measurements increase rapidly in $d^4$ for a bipartite $d$-dimensional quantum state. Here we present a very efficient and practical tomography method—asymptotical locking tomography (ALT), which can harvest full information of bipartite $d$-dimensional entangled states by very few measurements less than $2d^2$ only. To showcase the validity and reasonableness of our ALT, we carry out the test with the two-photon spin-orbital angular momentum hyperentangled states in a four-dimensional subspace. Besides high-efficiency and practicality, our ALT is also universal and can be generalized into multipartite HD entanglement and other quantum systems.
Effect of Mean Flow on Acoustic Wave Propagation in a Duct with a Periodic Array of Helmholtz Resonators
Jiang-Wei Liu, Dian-Long Yu, Hai-Bin Yang, Hui-Jie Shen, Ji-Hong Wen
Chin. Phys. Lett. 2020, 37 (3): 034301 .   DOI: 10.1088/0256-307X/37/3/034301
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Sound propagation properties of a duct system with Helmholtz resonators (HRs) are affected by mean flow. Previous studies have tended to focus on the effects of mean flows on acoustic response of a duct system with a finite number of HRs. Employing an empirical impedance model, we present a modified transfer matrix method for studying the effect of mean flow on the complex band structure of an air duct system with an infinite periodic array of HRs. The efficiency of the modified transfer matrix is demonstrated by comparison between an example of transmission response calculation for a finite single HR loaded duct and the finite element simulation result calculated using the COMSOL software. Numerical results are presented to analyze the effect of mean flow on the band structure and transmission loss of the sound wave in the duct system. It is hoped that this study will provide theoretical guidance for acoustic wave propagation of HR silencer in the presence of mean flow.
Atomic Mixing Induced by Ion Irradiation of V/Cu Multilayers
Yan-Bin Sheng, Hong-Peng Zhang, Tie-Long Shen, Kong-Fang Wei, Long Kang, Rui Liu, Tong-Min Zhang, Bing-Sheng Li
Chin. Phys. Lett. 2020, 37 (3): 036101 .   DOI: 10.1088/0256-307X/37/3/036101
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Bulk Cu/V multilayers simultaneously possess high strength and excellent radiation resistance thanks to their high density of interfaces. Irradiation-induced atomic mixing of Cu/V multilayers has been less investigated. Here, we investigate the ion irradiation of bulk Cu/V multilayers exposed to H$_{2}^{+}$ or He$^{+}$ ions at 350$^\circ\!$C. The microstructure and elemental distribution are investigated by transmission electron microscopy and energy dispersive x-ray spectroscopy. Facetted bubbles and atomic mixing are observed after ion irradiation. The possible mechanisms of irradiation-induced atomic mixing are discussed.
Fe–Al Phase Formation Studied by Internal Friction during Heating Process
Gang-Ling Hao, Yu-Chuan Li, Xing-Fu Wang, Wei-Guo Wang, Xin-Fu Wang, Dan Wang, Xian-Yu Li
Chin. Phys. Lett. 2020, 37 (3): 036102 .   DOI: 10.1088/0256-307X/37/3/036102
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We systematically investigate the internal friction properties of a Fe–(43 at.%)Al powder mixture compact during the heating process with the expectation to understand the phase formation and transition process. Three internal friction peaks are successively observed during the heating process from room temperature to 750$^{\circ}\!$C, but almost completely disappear in the subsequent cooling process. Three internal friction peaks exhibit obvious measuring frequency dependence, which increases with decreasing the frequency. The first internal friction peak originates from the micro-sliding of weak bonding interface between Al particles corresponding to a recrystallization process of deformed Al particles. The second internal friction peak is attributed to a phase formation process associated with the formation of the intermediate phase Fe$_{2}$Al$_{5}$. The third internal friction peak is considered to result from the formation of the FeAl intermetallic compound owing to the reaction of Fe$_{2}$Al$_{5}$ and residual Fe initiated by a dramatic thermal explosion reaction.
Production of $^{87}$Rb Bose–Einstein Condensate with a Simple Evaporative Cooling Method
Rehman Fazal, Jia-Zhen Li, Zhi-Wen Chen, Yuan Qin, Ya-Yi Lin, Zuan-Xian Zhang, Shan-Chao Zhang, Wei Huang, Hui Yan, Shi-Liang Zhu
Chin. Phys. Lett. 2020, 37 (3): 036701 .   DOI: 10.1088/0256-307X/37/3/036701
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A Bose–Einstein condensate with a large atom number is an important experimental platform for quantum simulation and quantum information research. An optical dipole trap is the a conventional way to hold the ultracold atoms, where an atomic cloud is evaporatively cooled down before reaching the Bose–Einstein condensate. A carefully designed trap depth controlling curve is typically required to realize the optimal evaporation cooling. We present and demonstrate a simple way to optimize the evaporation cooling in a crossed optical dipole trap. A polyline shape optical power control profile is easily obtained with our method, by which a pure Bose–Einstein condensate with atom number $1.73\times10^5 $ is produced. Theoretically, we numerically simulate the optimal evaporation cooling using the parameters of our apparatus based on a kinetic theory. Compared to the simulation results, our evaporation cooling shows a good performance. We believe that our simple method can be used to quickly realize evaporation cooling in optical dipole traps.
Bright-Dark Mode Coupling Model of Plasmons
Jing Zhang, Yong-Gang Xu, Jian-Xin Zhang, Lu-Lu Guan, Yong-Fang Li
Chin. Phys. Lett. 2020, 37 (3): 037101 .   DOI: 10.1088/0256-307X/37/3/037101
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We propose a coupling model to describe the interaction between the bright and dark modes of the plasmons of a dimer composed of two orthogonal gold nano-rods (GNRs), referred to as the BDMC model. This model shows that the eigen-frequencies of the coupled plasmons are governed by Coulomb potential and electrostatic potential. With the BDMC model, the behaviors of the coupling coefficient and the frequency offset, which is a new parameter introduced here, are revealed. Meanwhile, the asymmetric behavior of two eigen-frequencies related to gap of two GNRs is explained. Using the harmonic oscillator model and the coupled parameters obtained by the BDMC model, the bright mode absorption spectra of the dimer are calculated and the results agree with the numerical simulation.
Improvement of Thermoelectric Performance in BiCuSeO Oxide by Ho Doping and Band Modulation
Bo Feng, Guang-Qiang Li, Xiao-Ming Hu, Pei-Hai Liu, Ru-Song Li, Yang-Lin Zhang, Ya-Wei Li, Zhu He, Xi-An Fan
Chin. Phys. Lett. 2020, 37 (3): 037201 .   DOI: 10.1088/0256-307X/37/3/037201
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We try to use Ho doping combined with band modulation to adjust the thermoelectric properties for BiCuSeO. The results show that Ho doping can increase the carrier concentration and increase the electrical conductivity in the whole temperature range. Although Seebeck coefficient decreases due to the increase of carrier concentration, it still keeps relatively high values, especially in the middle and high temperature range. On this basis, the band-modulation sample can maintain relatively higher carrier concentration while maintaining relatively higher mobility, and further improve the electrical transporting performance. In addition, due to the introduction of a large number of interfaces in the band-modulation samples, the phonon scattering is enhanced effectively and the lattice thermal conductivity is reduced. Finally, the maximal power factor (PF) of 5.18 $\mu$W$\cdot$cm$^{-1}$K$^{-2}$ and the dimensionless thermoelectric figure of merits (ZT) of 0.81 are obtained from the 10% Ho modulation doped sample at 873 K.
Growth Control of High-Performance InAs/GaSb Type-II Superlattices via Optimizing the In/Ga Beam-Equivalent Pressure Ratio
Da-Hong Su, Yun Xu, Wen-Xin Wang, Guo-Feng Song
Chin. Phys. Lett. 2020, 37 (3): 037301 .   DOI: 10.1088/0256-307X/37/3/037301
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The performance of type-II superlattice (T2SL) long-wavelength infrared devices is limited by crystalline quality of T2SLs. We optimize the process of growing molecular beam epitaxy deposition T2SL epi-layers on GaSb (100) to improve the material properties. Samples with identical structure but diverse In/Ga beam-equivalent pressure (BEP) ratio are studied by various methods, including high-resolution x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy. We find that appropriately increasing the In/Ga BEP ratio contributes to improving the quality of T2SLs, but too large In BEP will much more easily cause a local strain, which can lead to more InSb islands in the InSb interfaces. The InSb islands melt in the InSb interfaces caused by the change of chemical potential of In atoms may result in the "nail" defects covering the whole T2SLs, especially the interfaces of GaSb-on-InAs. When the In/Ga BEP ratio is about 1, the T2SL material possesses a lower full width at half maximum of $+$1 first-order satellite peak, much smoother surface and excellently larger area uniformity.
MBE Growth and Characterization of Strained HgTe (111) Films on CdTe/GaAs
Jian Zhang, Shengxi Zhang, Xiaofang Qiu, Yan Wu, Qiang Sun, Jin Zou, Tianxin Li, Pingping Chen
Chin. Phys. Lett. 2020, 37 (3): 038101 .   DOI: 10.1088/0256-307X/37/3/038101
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Strained HgTe thin films are typical three-dimensional topological insulator materials. Most works have focused on HgTe (100) films due to the topological properties resulting from uniaxial strain. In this study, strained HgTe (111) thin films are grown on GaAs (100) substrates with CdTe (111) buffer layers using molecular beam epitaxy (MBE). The optimal growth conditions for HgTe films are determined to be a growth temperature of 160$^{\circ}\!$C and an Hg/Te flux ratio of 200. The strains of HgTe films with different thicknesses are investigated by high-resolution x-ray diffraction, including reciprocal space mapping measurements. The critical thickness of HgTe (111) film on CdTe/GaAs is estimated to be approximately 284 nm by Matthews' equations, consistent with the experimental results. Reflection high-energy electron diffraction and high-resolution transmission electron microscopy investigations indicate that high-quality HgTe films are obtained. This exploration of the MBE growth of HgTe (111) films provides valuable information for further studies of HgTe-based topological insulators.
Surface Morphology Improvement of Non-Polar a-Plane GaN Using a Low-Temperature GaN Insertion Layer
Shen Yan, Xiao-Tao Hu, Jun-Hui Die, Cai-Wei Wang, Wei Hu, Wen-Liang Wang, Zi-Guang Ma, Zhen Deng, Chun-Hua Du, Lu Wang, Hai-Qiang Jia, Wen-Xin Wang, Yang Jiang, Guoqiang Li, Hong Chen
Chin. Phys. Lett. 2020, 37 (3): 038102 .   DOI: 10.1088/0256-307X/37/3/038102
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We demonstrate that a low-temperature GaN insertion layer could significantly improve the surface morphology of non-polar a-plane GaN.The two key factors in improving the surface morphology of non-polar a-plane GaN are growth temperature and growth time of the GaN insertion layer. The root-mean-square roughness of a-plane GaN is reduced by 75% compared to the sample without the GaN insertion layer. Meanwhile, the GaN insertion layer is also beneficial for improving crystal quality. This work provides a simple and effective method to improve the surface morphology of non-polar a-plane GaN.
Performance Analyses of Planar Schottky Barrier MOSFETs with Dual Silicide Layers at Source/Drain on Bulk Substrates and Material Studies of ErSi$_{x}$/CoSi$_{2}$/Si Stack Interface
Bin Wang, Hao-Yu Kong, Lei Sun
Chin. Phys. Lett. 2020, 37 (3): 038501 .   DOI: 10.1088/0256-307X/37/3/038501
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A dual silicide layer structure is proposed for Schottky barrier metal-oxide-semiconductor field effect transistors (MOSFETs) on bulk substrates. The source/drain regions are designed to be composed with dual stacked silicide layers, forming different barrier heights to silicon channel. Performance comparisons between the dual barrier structure and the single barrier structure are carried out with numerical simulations. It is found that the dual barrier structure has significant advantages over the single barrier structure because the drive current and leakage current of the dual barrier structure can be modulated. Furthermore, the dual barrier structure's performance is nearly insensitive to the total silicide thickness, which can relax the fabrication requirements and even make an SOI substrate unnecessary for planar device design. The formation of ErSi$_{x}$/CoSi$_{2}$ stacked multilayers has been proved by experiments.
Effect of Barrier Temperature on Photoelectric Properties of GaN-Based Yellow LEDs
Jia-Ming Zeng, Xiao-Lan Wang, Chun-Lan Mo, Chang-Da Zheng, Jian-Li Zhang, Shuan Pan, Feng-Yi Jiang
Chin. Phys. Lett. 2020, 37 (3): 038502 .   DOI: 10.1088/0256-307X/37/3/038502
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The effect of growth temperature of barriers on photoelectric properties of GaN-based yellow light emitting diodes (LEDs) is investigated. It is found that as the barrier temperature increases, the crystal quality of multi-quantum wells (MQWs) and the quality of well/barrier interface are improved, and the quantum well is thermally annealed, so that the indium atoms in the quantum well migrate to the equilibrium position, reducing the phase separation of the quantum well and improving the crystal quality of quantum wells (QWs). However, the external quantum efficiency (EQE) of the samples begins to decrease when raising the barrier temperature even further. One explanation may be that the higher barrier temperature destroys the local state in the quantum well and reduces the well/barrier interface quality. Therefore, a suitable barrier temperature is proposed, contributing to the improvement of the luminous efficiency of the yellow LEDs.
High-Performance Germanium Waveguide Photodetectors on Silicon
Xiu-Li Li, Zhi Liu, Lin-Zhi Peng, Xiang-Quan Liu, Nan Wang, Yue Zhao, Jun Zheng, Yu-Hua Zuo, Chun-Lai Xue, Bu-Wen Cheng
Chin. Phys. Lett. 2020, 37 (3): 038503 .   DOI: 10.1088/0256-307X/37/3/038503
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Germanium waveguide photodetectors with 4 μm widths and various lengths are fabricated on silicon-on-insulator substrates by selective epitaxial growth. The dependence of the germanium layer length on the responsivity and bandwidth of the photodetectors is studied. The optimal length of the germanium layer to achieve high bandwidth is found to be approximately 8 μm. For the $4 \times 8$ ${\mu}$m$^{2}$ photodetector, the dark current density is as low as 5 mA/cm$^{2}$ at $-1$ V. At a bias of $-1$ V, the 1550 nm optical responsivity is as high as 0.82 A/W. Bandwidth as high as 29 GHz is obtained at $-4$ V. Clear opened eye diagrams at 50 Gbits/s are demonstrated at 1550 nm.
Effect of Lattice Distortion on the Magnetic Tunnel Junctions Consisting of Periodic Grating Barrier and Half-Metallic Electrodes
He-Nan Fang, Yuan-Yuan Zhong, Ming-Wen Xiao, Xuan Zang, Zhi-Kuo Tao
Chin. Phys. Lett. 2020, 37 (3): 038504 .   DOI: 10.1088/0256-307X/37/3/038504
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A spintronic theory is developed to study the effect of lattice distortion on the magnetic tunnel junctions (MTJs) consisting of single-crystal barrier and half-metallic electrodes. In the theory, the lattice distortion is described by strain, defect concentration and recovery temperature. All three parameters will modify the periodic scattering potential, and further alter the tunneling magnetoresistance (TMR). The theoretical results show that: (1) the TMR oscillates with all the three parameters; (2) the strain can change the TMR about 30%; (3) the defect concentration will strongly modify the periodic scattering potential, and further change the TMR about 50%; and (4) the recovery temperature has little effect on the periodic scattering potential, and only can change the TMR about 10%. The present work may provide a theoretical foundation to the application of lattice distortion for MTJs consisting of single-crystal barrier and half-metallic electrodes.
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