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Validity of Lamb-Dicke Approximations in Ion-Trap Systems
LAN Hai-Jiang, ZHANG Miao, WEI Lian-Fu
Chin. Phys. Lett. 2010, 27 (1):
010304
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DOI: 10.1088/0256-307X/27/1/010304
The Lamb-Dicke (LD) approximation (LDA) is usually utilized to simplify the treatments for the dynamics of ion-trap systems, where the so-called LD parameters should be sufficiently small. In this Letter, based on the quantum dynamics of a single trapped ion beyond the LDA, we discuss the fidelities of the control-NOT (CNOT) gate generated by performing the usual LDA. It is shown that the fidelity of the generated CNOT gate under the LDA is sufficiently high for the current LD experiments, e.g., it reaches 99.9% for η=0.20. The validity of the LDA is also discussed by calculating these fidelities for slightly larger LD parameters, e.g., η=0.4, etc.
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Yrast Properties of Dysprosium Isotopes in the Double Mid-Shell Region
ZOU Wen-Hua, GU Jian-Zhong,
Chin. Phys. Lett. 2010, 27 (1):
012101
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DOI: 10.1088/0256-307X/27/1/012101
The yrast bands of the even-even dysprosium isotopes 164-174Dy are calculated up to high angular momentum 34h based on the projected shell model. Our calculations are in good agreement with the experiments quantitatively. They predict that an energy minimum of the first 2+ state in these isotopes exists around the neutron mid-shell N=104, implying the maximum collectivity in 66170Dy104, however, the energy ratio R4=E(4+1)/E(2+1) reaches a saturation at N=102. Meanwhile, the back-bending plots of these yrast bands are examined carefully. It is found that the sharpness of the back-bending has a gradual shift along the dysprosium isotopic chain, namely, the slope of the back-bending becomes steeper as the neutron number increases except for an irregularity of a decreasing dip angle in the double mid-shell nucleus 170Dy. We suggest that 170Dy undergoes a dual alignment with midshell high-j protons and neutrons aligning simultaneously at spin I≈16h, which probably results in the distinctive back-bending behavior.
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Measurement of Secular Motion Frequency in Miniature Paul Trap to Ascertain the Stability Parameters
GUO Bin, , GUAN Hua, LIU Qu, , HUANG Yao, , HUANG Xue-Ren, GAO Ke-Lin,
Chin. Phys. Lett. 2010, 27 (1):
013202
.
DOI: 10.1088/0256-307X/27/1/013202
40Ca+ ions are trapped and laser cooled in a miniature Paul trap. The secular motion was observed by the radio-frequency resonance of the ion cloud and Zeeman profile sidebands of a single ion experimentally. The trap stability parameters a and q are determined with an uncertainty under 1% by the secular motion frequency measurement. The trap efficiency is 0.75. A practicable suggestion is given for the benefits of a new trap design.
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Positron-Impact Excitation of Hydrogen Atoms in Debye Plasmas
ZHANG Song-Bin, QI Yue-Ying, QU Yi-Zhi, CHEN Xiang-Jun, WANG Jian-Guo
Chin. Phys. Lett. 2010, 27 (1):
013401
.
DOI: 10.1088/0256-307X/27/1/013401
The positron-impact excitation of hydrogen atoms embedded in plasma environments is investigated using the close-coupling approximation from the low to intermediate energy region without including any positronium formation channel, and the excitation cross sections for 1s→2s, 1s→2p and 2s→2p processes are calculated in a wide Debye parameter range. The screening interactions, described by the Debye-Hückel model, decrease the coupling matrix elements, resulting in the reduction of the excitation cross sections from a few percent to one magnitude of ten. This will alter remarkably the spectroscopy of hydrogen in intensity and position, which should be considered in the simulation and diagnostics under some specific plasma conditions.
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Spatial Dispersion Induced by Cross-Phase Modulation
SHI Mei-Zhen, LI Chuang-She, ZUO Cui-Cui, ZHANG Yan-Peng, NIE Zhi-Qiang, ZHENG Huai-Bin, LI Chang-Biao, SONG Jian-Ping, GAN Chen-Li
Chin. Phys. Lett. 2010, 27 (1):
014205
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DOI: 10.1088/0256-307X/27/1/014205
We demonstrate our experiment of controlling spatial displacements of the probe beam induced by the cross-Kerr effect in a three-level V-type atomic system. By increasing the atomic density or the intensity of strong control laser beams, spatial displacements are enhanced. We further study the difference of effects from the atomic density and the laser intensity. In addition, the spatial displacement efficiencies of the probe beam in different energy level atomic systems are compared. Such studies of controlling spatial displacements can have potential applications in soliton deflection, spatial optical switch and generating spatially correlated (entangled) laser beams in multi-level EIT systems.
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Period Continuous Tuning of an Efficient Mid-Infrared Optical Parametric Oscillator Based on a Fan-out Periodically Poled MgO-Doped Lithium Niobate
XIONG Bo, ZHANG Shu-Bao, GUO Lin, ZHANG Ling, LIN Xue-Chun, LI Jin-Min
Chin. Phys. Lett. 2010, 27 (1):
014206
.
DOI: 10.1088/0256-307X/27/1/014206
We report a period continuously tunable, efficient, mid-infrared optical parametric oscillator (OPO) based on a fan-out periodically poled MgO-doped congruent lithium niobate (PPMgLN). The OPO is pumped by a Nd:YAG laser and a maximum idler output average power of 1.65W at 3.93μm is obtained with a pump average power of 10.5W, corresponding to the conversion efficiency of about 16% from the pump to the idler. The output spectral properties of the OPO with the fan-out crystal are analyzed. The OPO is continuously tuned over 3.78-4.58μm (idler) when fan-out periods are changed from 27.0 to 29.4μm. Compared with temperature tuning, fan-out period continuous tuning has faster tuning rate and wider tuning range.
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A Modified LBM Model for Simulating Gas Seepage in Fissured Coal Considering Klinkenberg Effects and Adsorbability-Desorbability
TAN Yun-Liang, TENG Gui-Rong, ZHANG Ze
Chin. Phys. Lett. 2010, 27 (1):
014701
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DOI: 10.1088/0256-307X/27/1/014701
A modified Lattice-Boltzmann method is proposed by considering the Klinkenberg effect and adsorbability-desorbability for the purpose of simulating methane gas seepage in fissured coal. The results show that the Klinkenberg effect has a little influence on methane gas seepage in fissured coal, so it can be neglected in engineering computations for simplicity. If both the Klinkenberg effect and the adsorbability-desorbability are considered, the Klinkenberg influence on gas pressure decreases as the Darcy coefficient increases. It is found by gas drainage simulations that near a drainage hole, the effect of adsorption and desorption cannot be neglected, and the location of the drainage hole has a great influence on drainage efficient λ when the hole is just located at the mid-zone of the coal seam, λ is 0.691808; when the hole is excursion down to 1.0m from the mid-zone of coal seam, λ decreases to 0.668631; when the hole is excursion up or down to 2.0m from the mid-zone of coal seam, λ decreases to 0.632917. The simulations supply an effective approach for optimizing the gas drainage hole location.
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Effect of Different Substrate Temperature on Sb-Doped ZnO Thin Films Prepared by Pulsed Laser Deposition on Sapphire Substrates
ZHAO Zi-Wen, HU Li-Zhong, ZHANG He-Qiu, SUN Jing-Chang, BIAN Ji-Ming, SUN Kai-Tong, CHEN Xi, ZHAO Jian-Ze, LI Xue, ZHU Jin-Xia,
Chin. Phys. Lett. 2010, 27 (1):
017301
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DOI: 10.1088/0256-307X/27/1/017301
Sb-doped ZnO thin films are deposited on c-plane sapphire substrates by pulsed laser deposition. Hall results indicate that the conductivity of the Sb-doped ZnO thin films is strongly dependent on the substrate temperature. The sample deposited at the temperature of 550°C exhibits p-type conductivity. It gives a resistivity of 15.25Ω・cm, with a Hall mobility of 1.79cm2V-1s-1 and a carrier concentration of 2.290×1017cm-3 at room temperature. The x-ray diffraction indicates that the Sb-doped ZnO thin films deposited in the range of 450-650°C are high c-axis oriented. Low-temperature photoluminescence spectra indicate that the sample deposited at 550°C shows the strong acceptor-bound exciton (A0X) emission.
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Cap Layer Influence on Impurity-Free Vacancy Disordering of InGaAs/InP Quantum Well Structure
AN Yu-Peng, YANG Hua, MEI Ting, WANG Yi-Ding, TENG Jing-Hua, XU Cheng-Dong
Chin. Phys. Lett. 2010, 27 (1):
017302
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DOI: 10.1088/0256-307X/27/1/017302
Quantum well intermixing (QWI) by the impurity-free vacancy disordering (IFVD) technique is an important and effective approach for the monolithic integration of optoelectronic devices based on InGaAs/InP quantum well structures. We experimentally investigate the influence of the capping layer SiO2 and Si3N4 on the QWI by IFVD. The results show that for all the samples with three-types differently doped (P, N and I) top InP layers, Si3N4 can always induce a larger photoluminescence blueshift than SiO2 in the IFVD QWI process, which attributes more to the group III and V vacancies point defects created in the interface of Si3N4-InP than that of SiO2-InP, proved by the SIMS measurements. The inherent mechanisms for explaining these properties are further discussed.
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Fabrication and Characterization of C60-Based Organic Schottky Diodes
CHENG Xiao-Man, , HU Zi-Yang, , WU Ren-Lei, , WANG Zhong-Qiang, , YIN Shou-Gen,
Chin. Phys. Lett. 2010, 27 (1):
017303
.
DOI: 10.1088/0256-307X/27/1/017303
We have fabricated organic Schottky barrier diodes with Cu/LiF/C60/Al andwiched construction. Cu and Al are selected as the cathode and the anode, respectively. C60 is used as the organic layer and LiF as the buffer layer inserted between the cathode and C60. After the annealing process, Schottky contact is well formed at the Al/C60 interface and Ohmic contact is formed at the (Cu/LiF)/C60 interface. The current density-voltage (J-V) measurements of the diodes present nonlinear behavior. As a result, the rectification ratio reaches 1×03. The characteristics of the diodes have been analyzed using the energy band diagram. The values of Schottky barrier height ΦB, ideality factor n and reverse saturation current density Js are extracted according to the standard thermionic emission model.
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Electronic, Vibrational, and Superconducting Properties of High-Pressure Metallic SiH4: ab initio Calculations
YAN Yan, GONG Jie, ZONG Zhan-Guo,
Chin. Phys. Lett. 2010, 27 (1):
017401
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DOI: 10.1088/0256-307X/27/1/017401
We extensively explore the experimentally proposed metallic structure of hcp P63 for the hydrogen rich compound, SiH4. It is found that the lattice dynamic of this structure is severely unstable. By freezing the soften mode, an orthorhombic Pbcn structure is discovered to be dynamically stable up to 226GPa. Within the conventional BCS theory, the calculated critical temperature Tc within the proposed Pbcn structure is 16.5K at 188GPa, in good agreement with the experimental result (17.5K). Thus, we propose that the current predicted orthorhombic phase is a better candidate for the metallic phase of SiH4.
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Fabrication and Characterization of Mn0.5Zn0.5Fe2O4 Magnetic Nanofibers
XIANG Jun, SHEN Xiang-Qian, SONG Fu-Zhan, MENG Xian-Feng
Chin. Phys. Lett. 2010, 27 (1):
017502
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DOI: 10.1088/0256-307X/27/1/017502
Mn0.5Zn0.5Fe2O4 Magnetic nanofibers were fabricated by calcining electrospun polymer/inorganic composite nanofibers and characterized by thermogravimetric and differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and a vibrating sample magnetometer. The experimental results show that the pure spinel structure is basically formed when the composite nanofibers are calcined at 450°C for 2h. With the increasing calcination temperature, both the saturation magnetization and coercivity of nanofiber samples increase initially along with the growth of Mn0.5Zn0.5Fe2O4 nanocrystals contained in the nanofibers. However, when the calcination temperature reaches 550°C, the saturation magnetization of nanofibers starts to dramatically decrease owing to the formation of the α-Fe2O3 phase at this temperature. The prepared Mn0.5Zn0.5Fe2O4 nanofibers calcined at 500°C for 2h have diameters ranging from 100 to 200nm. Their saturation magnetization and coercivity are 12.37emu/g and 4.81kA/m at room temperature, respectively.
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Electron Paramagnetic Resonance and Optical Absorption of VO2+ Doped Bis (glycinato) Mg (II) Monohydrate Single Crystals
Prashant Dwivedi, Ram Kripal, Santwana Shukla
Chin. Phys. Lett. 2010, 27 (1):
017601
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DOI: 10.1088/0256-307X/27/1/017601
We investigate the electron paramagnetic resonance (EPR) of VO2+ ions in bis (glycinato) Mg (II) monohydrate single crystals at room temperature. Detailed EPR analysis indicates the presence of only one VO2+ site. The vanadyl complexes are found to take up the substitutional position. The angular variation of the EPR spectra in three planes a*b, bc and ca* are used to determine principal g and A tensors. The values of spin Hamiltonian parameters are gx= 2.1447× 10-4, gy= 1.9974×10-4, gz= 1.9131×10-4, Ax= 49×10-4, Ay= 60×10-4, Az= 82×10-4 cm-1. The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental data. By correlating EPR and optical data, different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.
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Effects of Depolarization Field and Interfacial Coupling on the Polarization of Ferroelectric Bilayers
ZHENG Chao-Dan, , ZHANG Duan-Ming, LIU Xin-Ming, YANG Bin, LIU Chao-Jun, YU Jun
Chin. Phys. Lett. 2010, 27 (1):
017702
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DOI: 10.1088/0256-307X/27/1/017702
A ferroelectric bilayer model considering depolarization field and interfacial coupling is proposed and the expression of the depolarization field is derived. The spatial profiles of spontaneous polarization and hysteresis loops are calculated using the numerical method with and without considering the depolarization field. The effects of the depolarization field and interfacial coupling on the polarization of second-order ferroelectric bilayers are studied systematically. When interfacial coupling is ferroelectric coupling, the interface spontaneous polarization increases and the area of hysteresis loop becomes larger with increasing coupling. When interfacial coupling is antiferroelectric coupling, the depolarization field makes the central loop become smaller and the shape of the hysteresis loop becomes steep. Meanwhile, as interfacial coupling increases, the outer loops stretch further out horizontally and the size of the central loop widens.
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Dielectric Properties of GaN in THz Frequencies
FANG He-Nan, ZHANG Rong, LIU Bin, LU Hai, DING Jian-Ping, XIE Zi-Li, XIU Xiang-Qian, ZHENG You-Dou, XIAO Ming-Wen, ZHANG Cai-Hong, CHEN Jian, WU Pei-Heng
Chin. Phys. Lett. 2010, 27 (1):
017802
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DOI: 10.1088/0256-307X/27/1/017802
The complex refractive indices and the dielectric function of GaN for frequencies ranging from 0.25 to 1.22THz are obtained using THz time-domain spectroscopy. The real part of the dielectric function first decreases from 0.25 to 0.42THz and then oscillates from 0.42 to 1.22THz, whereas the imaginary part of the dielectric function is oscillating within the whole range of frequency. The simple Drude model is extended to take into account the effect of defects on the dielectric function. The extended model is in agreement with the experimental data.
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Giant Temperature Coefficient of Resistance in ZnO/Si (111) Thin Films
ZHOU Xiao-Fang, ZHANG Hui, LI Yong, TANG Xiao-Dong, CHEN Qing-Ming, ZHANG Peng-Xiang
Chin. Phys. Lett. 2010, 27 (1):
018101
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DOI: 10.1088/0256-307X/27/1/018101
Giant negative temperature coefficient of resistance (TCR) was observed in ZnO/Si (111) thin films. The films were grown using the pulsed laser deposition (PLD) technique, taking Si (111) wafer as substrates, with a substrate at the temperature below 450°C in the PLD. It is found that both TCR-temperature behavior and TCR value are strongly affected by deposition temperature. The maximal TCR value over -10.9%K-1 can be observed at the deposition temperature from 20°C to 350°C and reaches to -13%K-1 at deposition temperature 20°C where the film shows X-ray diffraction amorphous. The results suggest that the ZnO/Si films demonstrate great potentials when used in a low-cost, high-performance, non-cooling and highly sensitive bolometer.
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Preparation and Characteristics of GaN Films on Freestanding CVD Thick Diamond Films
ZHANG Dong, BAI Yi-Zhen, QIN Fu-Wen, BIAN Ji-Ming, JIA Fu-Chao, WU Zhan-Ling, ZHAO Ji-Jun, JIANG Xin,
Chin. Phys. Lett. 2010, 27 (1):
018102
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DOI: 10.1088/0256-307X/27/1/018102
Prefer-oriented and fine grained polycrystalline GaN films are prepared by plasma enhanced metal organic chemical vapour deposition on nucleation surfaces of freestanding thick diamond films. The characteristics of the GaN films are characterized by x-ray diffraction, reflection high energy electron diffraction and atomic force microscopy. The results indicate that the structure and morphology of the films are strongly dependent on the deposition temperature. The most significant improvements in morphological and structural properties of GaN films are obtained under the proper deposition temperature of 400°C.
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Application of Small-World Measures to Multichannel Event-Related Potential Activity during Generation of Global and Local Imagery
SUI Dan-Ni, ZHAO Qing-Bai, TANG Yi-Yuan,
Chin. Phys. Lett. 2010, 27 (1):
018702
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DOI: 10.1088/0256-307X/27/1/018702
The Small world model has been successfully used to explore the abnormal pattern of brain information processing in some neuropsychiatric diseases, but not engaged in the study of cognitive functions. We apply the small-world measures: the clustering coefficient and average path length, to evaluate multi-channel event-related potential activity during the generation of global and local imagery. Results show that the brain functional networks of the global and local imagery generation are both small-world ones. In addition, the local imagery generation has a larger clustering coefficient, while the global imagery generation has a shorter average path length. These results support the global precedence in the global-local imagery generation, and reflect the different processing modes in which global imagery emphasizes particularly on global integration, while local imagery on local specialization. Our results indicate that small-world measures could be applied to quantify the difference of brain activities in different cognitive tasks, and further provide some explanations for cognitive behavior.
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78 articles
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