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Quantum Correlations in a Family of Bipartite Qubit-Qutrit Separable States
YE Biao-Liang, LIU Yi-Min, LIU Xian-Song, ZHANG Zhan-Jun
Chin. Phys. Lett. 2013, 30 (2):
020302
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DOI: 10.1088/0256-307X/30/2/020302
Quantum correlations in a family of bipartite separable qubit-qutrit quantum-classical correlated states are investigated by using two popular measures, i.e., the original quantum discord (OQD) method by Ollivier and Zurek [ Phys. Rev. Lett. 88 (2001) 017901] and the measurement-induced disturbance (MID) method by Luo [ Phys. Rev. A 77 (2008) 022301]. It is found that both of them are functions of a parameter partially characterizing the concerned states, however, quantum correlations evaluated via the convenient MID method are somewhat overestimated.
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Quantum Random Walk in Periodic Potential on a Line
LI Min, ZHANG Yong-Sheng, GUO Gunag-Can
Chin. Phys. Lett. 2013, 30 (2):
020304
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DOI: 10.1088/0256-307X/30/2/020304
We investigate the discrete-time quantum random walks on a line in periodic potential. The probability distribution with periodic potential is more complex compared to the normal quantum walks, and the standard deviation σ has interesting behaviors for different period q and parameter θ. We study the behavior of standard deviation with variation in walk steps, period, and θ. The standard deviation increases approximately linearly with θ and decreases with 1/q for θ∈(0,π/4), and increases approximately linearly with 1/q for θ∈[π/4,π/2). For θ∈(π/4, 3π/4), the transmission is larger than the reflection, with sensibility the diffussion will be accelerated. However, when q=2, the standard deviations are nearly the same, and when q>2, the standard deviation will decrease.
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Synthesis and Improved Acetone Sensing Properties of Porous α-Fe2O3 Nanowires
LIU Li, CHI Xiao, WANG Guo-Guang, LIU Chang-Bai, SHAN Hao, ZHANG Xiao-Bo, WANG Lian-Yuan, GUAN Hong-Yu
Chin. Phys. Lett. 2013, 30 (2):
020701
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DOI: 10.1088/0256-307X/30/2/020701
Porous α-Fe2O3 nanowires are synthesized by a simple wet chemical method with a precursor of peroxyacetyl nitrate (PAN), and α-Fe2O3 nanoparticles are also synthesized in the same way except for the addition of PAN. Gas sensors are fabricated by coating the samples on ceramic tubes with Au signal electrodes and Ni-Cr heaters. A sensing investigation reveals that the porous α-Fe2O3 nanowires have a higher sensitivity compared to α-Fe2O3 nanoparticles at 260°C. The corresponding sensor response (Ra/Rg) is 18.2 at the maximum to 100 ppm acetone, and the response and recovery times are about 8 and 12 s, respectively. The porous and one-dimensional nanostructures of the porous α-Fe2O3 nanowires benefit for the gas-absorption and electrical-signal-transfer, and thus improve the sensor sensitivity consequentially.
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Alpha-Decay Study of Unfavored Transitions in Bismuth Isotopes
NI Dong-Dong, REN Zhong-Zhou
Chin. Phys. Lett. 2013, 30 (2):
022101
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DOI: 10.1088/0256-307X/30/2/022101
The unfavored α transitions of bismuth isotopes, including the newly observed α-decay fine structure in 209Bi [Beeman et al., Phys. Rev. Lett. 108 (2012) 062501] are investigated by the generalized density-dependent cluster model (GDDCM). Instead of the Wentzel–Kramers–Brillouin barrier penetration probability, the exact solution of the Schr?dinger equation under outgoing Coulomb wave boundary conditions is presented. The calculated α-decay half-lives are found to be in good agreement with the experimental data for both odd- A and odd-odd nuclei. This indicates that the GDDCM has good applicability for unfavored α transitions in addition to favored ones. Some predictions on α-decay half-lives are also made for reference in future experiments.
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First Application of Single-Shot Cross-Correlator for Characterizing Nd:glass Petawatt Pulses
WANG Yong-Zhi, OUYANG Xiao-Ping, MA Jin-Gui, YUAN Peng, XU Guang, QIAN Lie-Jia
Chin. Phys. Lett. 2013, 30 (2):
024201
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DOI: 10.1088/0256-307X/30/2/024201
We report the first application of a single-shot cross-correlator for pulse duration and pulse contrast diagnostics in Nd:glass petawatt laser. The information of pulse duration, measured in the single-shot, guides the fine adjustment of the pulse compressor in real time. By integrating several shots of measurements at different time delays together, the petawatt pulse profile is obtained within an overall temporal window of ~100 ps, indicating a contrast of ~104. The measurements suggest that the additional contrast improvement is necessary for the Nd:glass petawatt laser system, which should be different from conventional Ti:sapphire lasers and is also discussed.
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Stable Single Polarization, Single Frequency, and Linear Cavity Er-Doped Fiber Laser Using a Saturable Absorber
LI Qi, YAN Feng-Ping, PENG Wan-Jing, FENG Su-Chun, FENG Ting, TAN Si-Yu, LIU Peng
Chin. Phys. Lett. 2013, 30 (2):
024202
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DOI: 10.1088/0256-307X/30/2/024202
A simple approach for stable single polarization, single frequency, and linear cavity erbium doped fiber laser is proposed and demonstrated. A Fabry–Pérot filter, polarizer and saturable absorber are used together to ensure stable single frequency, single polarization operation. The optical signal-to-noise ratio of the laser is approximately 57 dB, and the Lorentz linewidth is 13.9 kHz. The polarization state of the laser with good stability is confirmed and the degree of polarization is >99%.
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High Intensity Single-Mode Peak Observed in the Lasing Spectrum of InAs/GaAs Quantum Dot Laser
YUE Li, GONG Qian, YAN Jin-Yi, CAO Chun-Fang, LIU Qing-Bo, WANG Yang, CHENG Ruo-Hai, WANG Hai-Long, LI Shi-Guo
Chin. Phys. Lett. 2013, 30 (2):
024209
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DOI: 10.1088/0256-307X/30/2/024209
We report on abnormal lasing spectra of InAs/GaAs quantum dot lasers, where a single-mode peak exists with optical intensity several times larger than that of other modes. The maximum side mode suppression ratio of the single-mode peak is measured to be 10.11 dB at 29°C with injection current of 413 mA. It is found that the emergence of this abnormal lasing spectrum happens in a certain range of operation temperature and current. The sharp increase in optical intensity of the single-mode peak is closely related to the disappearance of optical lasing modes located at the higher energy side of the enhanced mode.
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High Energy Terahertz Parametric Oscillator Based on Surface-Emitted Configuration
XU De-Gang, ZHANG Hao, JIANG Hao, WANG Yu-Ye, LIU Chang-Ming, YU Hong, LI Zhong-Yang, SHI Wei, YAO Jian-Quan
Chin. Phys. Lett. 2013, 30 (2):
024212
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DOI: 10.1088/0256-307X/30/2/024212
We experimentally demonstrate a high power nanosecond pulsed terahertz (THz)-wave parametric oscillator (TPO) by using a wide pump beam. A surface emitted cavity configuration is employed to reduce the THz absorption in MgO:LiNbO3 crystal. The THz wave can be tuned from 1 THz to 3 THz. A maximum THz output energy of 438 nJ/pulse is achieved at 1.56 Hz using a 4.5-mm-diameter pump beam with a pulse energy of 226 mJ pump energy with the repetition of 10 Hz, corresponding to the energy conversion efficiency of 1.94×10?6.
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Estimating the Radial Profile of Edge Plasma Electrical Fluctuations in the IR-T1 Tokamak
K. Mikaili Agah, M. Ghoranneviss, M. K. Salem, A. Salar Elahi, S. Mohammadi, R. Arvin
Chin. Phys. Lett. 2013, 30 (2):
025202
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DOI: 10.1088/0256-307X/30/2/025202
The radial dependence of edge plasma turbulence is investigated in the IR-T1 tokamak. The radial profile of the fluctuation level and spectra are measured using an array of Langmuir probes (rake probe) in the r/a=0.75–1.2 region. In all radial positions the edge plasma is turbulently unstable, with a broad band fluctuation spectrum in the frequency range f= 10–1000 kHz. The relative fluctuation level, as monitored by the ion saturation current J+, is always highest near the wall and decreases monotonically toward the plasma center, while the shape of the fluctuation power spectra is almost unchanged. The result of this experiment shows that in contrast to the more inner regions, the plasma near the wall does not simply have a small density fluctuation about a mean, but rather a shredded structure in which one can imagine that discrete shreds of plasma interact with one another rather than with the average background.
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AlGaN/GaN MISHEMTs with Sodium-Beta-Alumina as the Gate Dielectrics
TIAN Ben-Lang, CHEN Chao, ZHANG Ji-Hua, ZHANG Wan-Li, LIU Xing-Zhao
Chin. Phys. Lett. 2013, 30 (2):
026101
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DOI: 10.1088/0256-307X/30/2/026101
AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) with sodium beta-alumina (SBA) thin films as the gate dielectrics are studied. AlGaN/GaN metal-semiconductor high-electron-mobility transistors (MESHEMTs) and MISHEMTs with Al2O3 thin-film gate dielectrics are also fabricated for comparative study. The MISHEMTs with SBA gate dielectrics show nearly four orders of magnitude lower gate leakage current and an approximately 60% increase in maximum transconductance, indicating that SBA can serve as an effective dielectric for AlGaN/GaN MISHEMTs. However, SBA gate dielectrics result in threshold voltage modulation of AlGaN/GaN MISHEMTs. Compared with those of AlGaN/GaN MESHEMTs, the threshold voltages of AlGaN/GaN MISHEMTs with Al2O3 gate dielectrics shift negatively from ?5.5 V to ?7.5 V. In contrast with the normally used gate dielectrics, the threshold voltages of MISHEMTs with SBA gate dielectrics shift positively from ?5.5 V to ?3.5 V. Based on an x-ray photoelectron spectrum study and energy band spectrum calculation, the primary mechanism of the threshold voltage modulation is attributed to the decrease in the surface valence-band maximum and the increase in the barrier height by SBA gate dielectrics.
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A Single Cluster Covering for Dodecagonal Quasiperiodic Ship Tiling
LIAO Long-Guang, ZHANG Wen-Bin, YU Tong-Xu, CAO Ze-Xian
Chin. Phys. Lett. 2013, 30 (2):
026102
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DOI: 10.1088/0256-307X/30/2/026102
The single cluster covering approach provides a plausible mechanism for the formation and stability of octagonal and decagonal quasiperiodic structures. For dodecagonal quasiperiodic patterns, such a single cluster covering scheme is still unavailable. We demonstrate that ship tiling, one of the dodecagonal quasiperiodic structures, can be completely covered by a single cluster. A deflation procedure is devised by assigning proper orientations to different tiles, and nine types of vertex configurations, if the mirror patterns are considered to be identical, have been identified, which fulfill the closure condition under deflation and all result in a T-cluster centered at the vertex.
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Plasmon-Enhanced Upconversion Fluorescence in Er3+:Ag Phosphate Glass: the Effect of Heat Treatment
Raja J. Amjad, M. R. Sahar, S. K. Ghoshal, M. R. Dousti, S. Riaz, A. R. Samavati, M. N. A Jamaludin, S. Naseem
Chin. Phys. Lett. 2013, 30 (2):
027301
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DOI: 10.1088/0256-307X/30/2/027301
The melt quenching method is used to prepare erbium-doped silver nanoparticle (NP) embedded phosphate glass. The effect of annealing on the glass on the formation of silver NPs produced by the reduction of silver (Ag+→Ago) is studied. The glass samples are characterized by x-ray diffraction, UV-vis-NIR absorption, photoluminescence spectroscopy and transmission electron microscopy (TEM) imaging. The absorption spectra reveal not only the peaks due to Er3+ ions, but also the surface plasmon resonance band of silver NPs located around ~442 nm. The TEM imaging shows the homogeneous distribution of silver NPs of almost spherical shape with an average diameter of ~5 nm. Upconversion luminescence spectra show two major emissions at 550 and 638 nm, originating from the 4S3/2 and 4F9/2 energy levels of the Er3+ ions, respectively. The enhancement in the luminescence intensity of both the green and red bands is found to be due to the effective local field of the silver NPs as well as the energy transfer from the nanoclusters, comprised of centers with silver ions bound to silver atoms in dimers or trimers to Er3+ ions, whereas quenching occurred due to the energy transfer from erbium ions to silver NPs (Er3+→Ago).
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Research with KNbO3 Bulk and Surface Properties Based on Density Functional Theory
SUN Hong-Guo, ZHOU Zhong-Xiang, YUAN Cheng-Xun, YANG Xiao-Niu
Chin. Phys. Lett. 2013, 30 (2):
027302
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DOI: 10.1088/0256-307X/30/2/027302
The geometrical structure optimization, band structure, density of states, and charge density contour of potassium niobate (KNbO3) in the bulk [100] direction and (100) surface are calculated and analyzed using density functional theory. The elastic constants, which can describe the bonding characteristics and structural stability, are also computed, and the dielectric function, which can be used to calculate all the other optical properties of the material, is evaluated. Local density approximation functional analysis using CASTEP software is also employed. Several similarities and differences are observed in the properties of the KNbO3 bulk and surface. Almost all of the calculated results for the bulk sample are twice those of the surface sample. The results are consistent with the experiment.
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The Predicted fcc Superconducting Phase for Compressed Se and Te
ZHOU Da-Wei, PU Chun-Ying, Szczęániak Dominik, ZHANG Guo-Fang, LU Cheng, LI Gen-Quan, SONG Jin-Fan
Chin. Phys. Lett. 2013, 30 (2):
027401
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DOI: 10.1088/0256-307X/30/2/027401
In the framework of the ab initio random structure search method, we show that elemental Se and Te undergo pressure-induced structural transition from the bcc to fcc phase, in agreement with the theoretical results previously reported. By means of the pseudopotential plane-wave method based on density functional perturbation theory, the fcc structure for both elements is found to be another phonon-mediated superconducting phase of these materials. With a reasonable value for the Coulomb pseudopotential μ?=0.12, the maximum superconducting transition temperature Tc in the fcc phase of Se and Te is estimated to be about 5.7 K and 4.6 K, respectively. Furthermore, we show that in the entire fcc phase for Se and Te, the superconducting transition temperature decreases together with the increase in pressure, leading to the final suppression of the superconductivity. It is suggested that such behavior is mainly caused by the rapid increase in the mean-square phonon frequency ?ω2? with pressure. Finally, a very strong electron-phonon coupling value, for both Se and Te in the fcc phase, is found along the G–K high symmetry lines.
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Superconductivity Tuned by the Iron Vacancy Order in KxFe2?ySe2
BAO Wei, LI Guan-Nan, HUANG Qing-Zhen, CHEN Gen-Fu, HE Jun-Bao, WANG Du-Ming, M. A. Green, QIU Yi-Ming, LUO Jian-Lin, WU Mei-Mei
Chin. Phys. Lett. 2013, 30 (2):
027402
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DOI: 10.1088/0256-307X/30/2/027402
Combining in-depth neutron diffraction and systematic bulk studies, we discover that the √5×√5 Fe vacancy order, with its associated block antiferromagnetic order, is the ground state with varying occupancy ratios of the iron 16#em/em# and vacancy 4d sites across the phase-diagram of KxFe2?ySe2. The orthorhombic order, with one of the four Fe sites vacant, appears only at intermediate temperatures as a competing phase. The material experiences an insulator to metal crossover when the √5×√5 order is highly developed. Superconductivity occurs in such a metallic phase.
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The Luminescence of a CuI Film Scintillator Controlled by a Distributed Bragg Reflector
TONG Fei, ZHU Zhi-Chao, LIU Bo, YI Ya-Sha, GU Mu, CHEN Hong
Chin. Phys. Lett. 2013, 30 (2):
027803
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DOI: 10.1088/0256-307X/30/2/027803
We investigate the emission properties of CuI film scintillators and the effect of distributed Bragg reflectors. The free-exciton emission and the donor-acceptor pair emission from the CuI thin film with the peak wavelengths of 410 nm and 420 nm are observed. However, for the two emission bands, the distributed Bragg reflector reflection results in different enhancements, which is interpreted by the varying transmittance with wavelength. Angle-dependence of emission profile is decided by the transmittance and DBR reflection, which may be useful in scintillation detection applications.
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The Influence of Graded AlGaN Buffer Thickness for Crack-Free GaN on Si(111) Substrates by using MOCVD
XU Pei-Qiang, JIANG Yang, MA Zi-Guang, DENG Zhen, LU Tai-Ping, DU Chun-Hua, FANG Yu-Tao, ZUO Peng, CHEN Hong
Chin. Phys. Lett. 2013, 30 (2):
028101
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DOI: 10.1088/0256-307X/30/2/028101
GaN films with different thicknesses of Al composition graded AlGaN buffer are grown on substrates of Si(111) by metal-organic chemical vapor deposition (MOCVD). The thicknesses of graded AlGaN buffer are fixed at 200 nm, 300 nm, and 450 nm, respectively. Optical microscopy, atomic force microscopy, x-ray diffraction, and Raman spectroscopy are employed to characterize these samples. We find that the thickness of the graded AlGaN buffer layer plays a key role on the following growth of GaN films. The optimized thickness of the graded AlGaN buffer layer is 300 nm. Under such conditions, the GaN epitaxial film is crack-free, and its dislocation density is the lowest.
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Sparse Transform Matrices and Their Application in the Calculation of Electromagnetic Scattering Problems
CAO Xin-Yuan, CHEN Ming-Sheng, WU Xian-Liang
Chin. Phys. Lett. 2013, 30 (2):
028401
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DOI: 10.1088/0256-307X/30/2/028401
When compressed sensing is introduced into the moment method, a 3D electromagnetic scattering problem over a wide angle can be solved rapidly, and the selection of sparse basis has a direct influence on the performance of this algorithm, especially the number of measurements. We set up five sparse transform matrices by discretization of five types of classical orthogonal polynomials, i.e., Legendre, Chebyshev, the second kind of Chebyshev, Laguerre, and Hermite polynomials. Performances of the algorithm using these matrices are compared via numerical experiments, and the results show that some of them obviously work excellently and can accelerate wide angle scattering analysis greatly.
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The Effects of a Low-Temperature GaN Interlayer on the Performance of InGaN/GaN Solar Cells
LI Liang, ZHAO De-Gang, JIANG De-Sheng, LIU Zong-Shun, CHEN Ping, WU Liang-Liang, LE Ling-Cong, WANG Hui, YANG Hui
Chin. Phys. Lett. 2013, 30 (2):
028801
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DOI: 10.1088/0256-307X/30/2/028801
An InGaN/GaN p-i-n solar cell inserted with a 5-nm low-temperature (LT) GaN interlayer between the p-GaN cap layer and the InGaN i-layer is grown on a c-plane sapphire substrate by metal organic chemical vapor deposition. The effects of the LT GaN interlayer on the performance of the InGaN/GaN solar cells are investigated. It is found that the LT-GaN interlayer prevents the extension of threading dislocations from the InGaN layer to the p-GaN layer and improves the crystal quality of both the p-GaN cap layer and the InGaN i-layer, ultimately leading to an increasing external quantum efficiency and photocurrent density of the InGaN/GaN solar cells.
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63 articles
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