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A Realization of the $W_{1+\infty}$ Algebra and Its $n$-Algebra
Chun-Hong Zhang, Rui Wang, Ke Wu, Wei-Zhong Zhao
Chin. Phys. Lett. 2017, 34 (8):
080202
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DOI: 10.1088/0256-307X/34/8/080202
We consider a realization of the $W_{1+\infty}$ algebra and investigate its $n$-algebra, which is different from the $n$-algebra of Zhang et al. [ 2016 arXiv:1606.07570v2] It is found that the generators $W_m^{s}$ with any fixed superindex $s\geqslant 1$ yield the null sub-$2s$-algebra. The nontrivial sub-$4$-algebra and Virasoro–Witt $3$-algebra are presented. Moreover, we extend the generators to the multi-variables case. These generators also yield the $W_{1+\infty}$ algebra and null $n$-algebras.
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Asymmetric Decoy State Measurement-Device-Independent Quantum Cryptographic Conferencing
Rui-Ke Chen, Wan-Su Bao, Hai-Ze Bao, Chun Zhou, Mu-Sheng Jiang, Hong-Wei Li
Chin. Phys. Lett. 2017, 34 (8):
080301
.
DOI: 10.1088/0256-307X/34/8/080301
Measurement-device-independent quantum cryptographic conferencing (MDI-QCC) protocol suggests an important scheme for practical multiparty quantum communication. As far as we know, MDI-QCC or MDI-quantum key distribution protocols always assume that the decoy state strategies used at each user's side are the same. In this study, to mitigate the system complexity and to improve the performance of MDI-QCC protocol in the finite-key case, we propose an asymmetric decoy state method for MDI-QCC protocol, and present security analysis and numerical simulations. From numerical simulations, our protocol can achieve better performance in the finite-key case. That is, with a finite data size of $10^{11}$, it can achieve nonzero secret key rate over 43.6 km.
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Application of a Discrete Phase-Randomized Coherent State Source in Round-Robin Differential Phase-Shift Quantum Key Distribution
Ying-Ying Zhang, Wan-Su Bao, Hong-Wei Li, Chun Zhou, Yang Wang, Mu-Sheng Jiang
Chin. Phys. Lett. 2017, 34 (8):
080302
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DOI: 10.1088/0256-307X/34/8/080302
Recently, a novel kind of quantum key distribution called the round-robin differential phase-shift (RRDPS) protocol was proposed, which bounds the amount of leakage without monitoring signal disturbance. The protocol can be implemented by a weak coherent source. The security of this protocol with a simply characterized source has been proved. The application of a common phase shift can improve the secret key rate of the protocol. In practice, the randomized phase is discrete and the secret key rate is deviated from the continuous case. In this study, we analyze security of the RRDPS protocol with discrete-phase-randomized coherent state source and bound the secret key rate. We fix the length of each packet at 32 and 64, then simulate the secret key rates of the RRDPS protocol with discrete-phase randomization and continuous-phase randomization. Our simulation results show that the performance of the discrete-phase randomization case is close to the continuous counterpart with only a small number of discrete phases. The research is practically valuable for experimental implementation.
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Progress of the Inertial Mass Measurement Project at NIM
Zhuang Fu, Zhong-Hua Zhang, Zheng-Kun Li, Wei Zhao, Lu-Shuai Qian, Shi-Song Li
Chin. Phys. Lett. 2017, 34 (8):
080601
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DOI: 10.1088/0256-307X/34/8/080601
An experiment is proposed to precisely measure the Planck constant. In this experiment, the Planck constant is measured based on the inertial mass measurement rather than the gravitational mass determinations in some other well-known experiments, e.g., the Kibble balance and counting atoms. We link the mechanical force to a quantum-traceable electrostatic force by a beam balance oscillator. After a 5-year continuous effort, the principle of the proposal is verified by a preliminary measurement with a relative uncertainty of $5.4\times 10^{-5}$. The proposal has the potential to achieve much higher measurement accuracy with further improvements.
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Pygmy and Giant Dipole Resonances in Proton-Rich Nuclei $^{17,18}$Ne
Hong Lv, Shi-Sheng Zhang, Zhen-Hua Zhang, Yu-Qian Wu, Li-Gang Cao
Chin. Phys. Lett. 2017, 34 (8):
082101
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DOI: 10.1088/0256-307X/34/8/082101
The pygmy and giant dipole resonances in proton-rich nuclei $^{17,18}$Ne are investigated with a fully self-consistent approach. The properties of ground states are calculated in the Skyrme Hartree–Fock with the Bardeen–Cooper–Schrieffer approximation to take into account the pairing correlation. The quasiparticle random phase approximation (QRPA) method is used to explore the properties of excited dipole states. In the calculations the SLy5 Skyrme interaction is employed. In addition to the giant dipole resonances, pygmy dipole resonances (PDR) are found to be located in the energy region below 10 MeV in both $^{17,18}$Ne. The strength and transition density show that the low-lying states are typical PDR states. However, analyzing the QRPA amplitudes of proton and neutron 2 quasiparticle (2qp) configurations for a given low-lying state in $^{17,18}$Ne, we find that the PDR state is less collective, more like a single 2qp excitation.
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Coherent Features of Resonance-Mediated Two-Photon Absorption Enhancement by Varying the Energy Level Structure, Laser Spectrum Bandwidth and Central Frequency
Wen-Jing Cheng, Guo Liang, Ping Wu, Tian-Qing Jia, Zhen-Rong Sun, Shi-An Zhang
Chin. Phys. Lett. 2017, 34 (8):
083201
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DOI: 10.1088/0256-307X/34/8/083201
The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited (TL)-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.
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Carpet Cloak Design for Rough Surfaces
Mohammad Hosein Fakheri, Hooman Barati, Ali Abdolali
Chin. Phys. Lett. 2017, 34 (8):
084101
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DOI: 10.1088/0256-307X/34/8/084101
Conventional carpet cloak structures have been utilized to conceal the objects located on a planar perfect electric conductor surface. We systematically investigate hiding arbitrarily shaped objects on a rough surface, as a more general and practical scenario. In addition, the required cloak is designed considering different boundary conditions for the surface beneath the object, despite the previous studies. To achieve an invisibility cloak, taking advantage of linear coordinate transformation, a simple homogeneous material is obtained to realize the cloak structure, facilitating the fabrication processes. Numerical simulations validate the performance of the proposed cloaking method. Therefore, the proposed structure is capable of cloaking in more general and complicated scenarios.
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Pressure Dependence of the Small-Signal Gain and Saturation Intensity of a Copper Bromide Laser
M. E. Aeinehvand, S. Behrouzinia, M. K. Salem, M. Elahei, K. Khorasani
Chin. Phys. Lett. 2017, 34 (8):
084201
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DOI: 10.1088/0256-307X/34/8/084201
A pair of copper bromide lasers in an oscillator–amplifier configuration is used to investigate the small signal gain and saturation intensity as amplifying parameters and output power of lasers, versus pressure of buffer gas. It is shown that the amplifying parameters and laser output power have a maximum value at optimum buffer gas pressure of 11 Torr. The challenge between microscopic parameters such as stimulated emission cross section, laser upper level lifetime, and population inversion, which determine the values of laser characteristics respective to the operational pressure of buffer gas, are investigated. Thus an optimum delay time of about 10 ns is determined, and a maximum output power equivalent to about 12 W is extracted. The amplifying parameters and measured output power of laser versus delay times show some local maxima and minima at the delay time interval of 6–43 ns.
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High-Yield High-Efficiency Positron Generation in High-$Z$ Metal Targets Irradiated by Laser Produced Electrons from Near-Critical Density Plasmas
Wei Song, Rong-Hao Hu, Yin-Ren Shou, Zheng Gong, Jin-Qing Yu, Chen Lin, Wen-Jun Ma, Yan-Yin Zhao, Hai-Yang Lu, Xue-Qing Yan
Chin. Phys. Lett. 2017, 34 (8):
085201
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DOI: 10.1088/0256-307X/34/8/085201
An improved indirect scheme for laser positron generation is proposed. The positron yields in high-$Z$ metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically. It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV. Using near-critical density targets for electron acceleration, the number of high energy electrons can be increased dramatically. Through start-to-end simulations, it is shown that up to $6.78\times10^{10}$ positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.
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A Method of Using a Carbon Fiber Spiral-Contact Electrode to Achieve Atmospheric Pressure Glow Discharge in Air
Wen-Zheng Liu, Shuai Zhao, Mao-Lin Chai, Jiang-Qi Niu
Chin. Phys. Lett. 2017, 34 (8):
085203
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DOI: 10.1088/0256-307X/34/8/085203
During discharge, appropriately changing the development paths of electron avalanches and increasing the number of initial electrons can effectively inhibit the formation of filamentary discharge. Based on the aforementioned phenomenon, we propose a method of using microdischarge electrodes to produce a macroscopic discharge phenomenon. In the form of an asymmetric structure composed of a carbon fiber electrode, an electrode structure of carbon fiber spiral-contact type is designed to achieve an atmospheric pressure glow discharge in air, which is characterized by low discharge voltage, low energy consumption, good diffusion and less ozone generation.
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Charge Density Wave States and Structural Transition in Layered Chalcogenide TaSe$_{2-x}$Te$_{x}$
Lin-Lin Wei, Shuai-Shuai Sun, Kai Sun, Yu Liu, Ding-Fu Shao, Wen-Jian Lu, Yu-Ping Sun, Huan-Fang Tian, Huai-Xin Yang
Chin. Phys. Lett. 2017, 34 (8):
086101
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DOI: 10.1088/0256-307X/34/8/086101
The structural features and three-dimensional nature of the charge density wave (CDW) state of the layered chalcogenide 1T-TaSe$_{2-x}$Te$_{x}$ ($0\le x\le 2.0$) are characterized by Cs-corrected transmission electron microscopy measurements. Notable changes of both average structure and the CDW state arising from Te substitution for Se are clearly demonstrated in samples with $x>0.3$. The commensurate CDW state characterized by the known star-of-David clustering in the 1T-TaSe$_{2}$ crystal becomes visibly unstable with Te substitution and vanishes when $x=0.3$. The 1T-TaSe$_{2-x}$Te$_{x}$ ($0.3\le x\le 1.3$) samples generally adopt a remarkable incommensurate CDW state with monoclinic distortion, which could be fundamentally in correlation with the strong $q$-dependent electron–phonon coupling-induced period-lattice-distortion as identified in TaTe$_{2}$. Systematic analysis demonstrates that the occurrence of superconductivity is related to the suppression of the commensurate CDW phase and the presence of discommensuration is an evident structural feature observed in the superconducting samples.
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Pressure-Induced Charge-Order Melting and Reentrant Charge Carrier Localization in the Mixed-Valent Pb$_{3}$Rh$_{7}$O$_{15}$
Yan Li, Zhao Sun, Jia-Wei Cai, Jian-Ping Sun, Bo-Sen Wang, Zhi-Ying Zhao, Y. Uwatoko, Jia-Qiang Yan, Jin-Guang Cheng
Chin. Phys. Lett. 2017, 34 (8):
087201
.
DOI: 10.1088/0256-307X/34/8/087201
The mixed-valent Pb$_{3}$Rh$_{7}$O$_{15}$ undergoes a Verwey-type transition at $T_{\rm v} \approx 180$ K, below which the development of Rh$^{3+}$/Rh$^{4+}$ charge order induces an abrupt conductor-to-insulator transition in resistivity. Here we investigate the effect of pressure on the Verwey-type transition of Pb$_{3}$Rh$_{7}$O$_{15}$ by measuring its electrical resistivity under hydrostatic pressures up to 8 GPa with a cubic anvil cell apparatus. We find that the application of high pressure can suppress the Verwey-type transition around 3 GPa, above which a metallic state is realized at temperatures below $\sim $70 K, suggesting the melting of charge order by pressure. Interestingly, the low-temperature metallic region shrinks gradually upon further increasing pressure and disappears completely at $P >7$ GPa, which indicates that the charge carriers in Pb$_{3}$Rh$_{7}$O$_{15}$ undergo a reentrant localization under higher pressures. We have constructed a temperature-pressure phase diagram for Pb$_{3}$Rh$_{7}$O$_{15}$ and compared to that of Fe$_{3}$O$_{4}$, showing an archetype Verwey transition.
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Molecular Beam Epitaxy Growth of Tetragonal FeS Films on SrTiO$_{3}$(001) Substrates
Kun Zhao, Hai-Cheng Lin, Wan-Tong Huang, Xiao-Peng Hu, Xi Chen, Qi-Kun Xue, Shuai-Hua Ji
Chin. Phys. Lett. 2017, 34 (8):
087401
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DOI: 10.1088/0256-307X/34/8/087401
We report the successful growth of the tetragonal FeS film with one or two unit-cell (UC) thickness on SrTiO$_{3}$(001) substrates by molecular beam epitaxy. Large lattice constant mismatch with the substrate leads to high density of defects in single-UC FeS, while it has been significantly reduced in the double-UC thick film due to the lattice relaxation. The scanning tunneling spectra on the surface of the FeS thin film reveal the electronic doping effect of single-UC FeS from the substrate. In addition, at the Fermi level, the energy gaps of approximately 1.5 meV are observed in the films of both thicknesses at 4.6 K and below. The absence of coherence peaks of gap spectra may be related to the preformed Cooper-pairs without phase coherence.
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Electronic, Elastic and Piezoelectric Properties of Two-Dimensional Group-IV Buckled Monolayers
Jing Shi, Yong Gao, Xiao-Li Wang, Si-Ning Yun
Chin. Phys. Lett. 2017, 34 (8):
087701
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DOI: 10.1088/0256-307X/34/8/087701
Electronic, elastic and piezoelectric properties of two-dimensional (2D) group-IV buckled monolayers (GeSi, SnSi and SnGe) are studied by first principle calculations. According to our calculations, SnSi and SnGe are good 2D piezoelectric materials with large piezoelectric coefficients. The values of $d_{11}$ of SnSi and SnGe are 5.04 pm/V and 5.42 pm/V, respectively, which are much larger than 2D MoS$_{2}$ (3.6 pm/V) and are comparable with some frequently used bulk materials (e.g., wurtzite AlN 5.1 pm/V). Charge transfer is calculated by the Löwdin analysis and we find that the piezoelectric coefficients ($d_{11}$ and $d_{31}$) are highly dependent on the polarizabilities of the anions and cations in group-IV monolayers.
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Ionoluminescence Spectra of a ZnO Single Crystal Irradiated with 2.5MeV H$^{+}$ Ions
Li Zheng, Guang-Fu Wang, Meng-Lin Qiu, Ying-Jie Chu, Mi Xu, Peng Yin
Chin. Phys. Lett. 2017, 34 (8):
087801
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DOI: 10.1088/0256-307X/34/8/087801
The ionoluminescence (IL) spectra of a ZnO single crystal irradiated with 2.5 MeV H$^{+}$ ions reveal that its intensity decreases with increasing the ion fluence, which indicates that the concentration of luminescence centers decreases with irradiation. The Gaussian decomposition results of the ZnO IL spectrum with a fluence of 1.77$\times$10$^{11}$ ions/cm$^{2}$ show that the spectrum is a superposition of energy levels centered at 1.75 eV, 2.10 eV, 3.12 eV and 3.20 eV. The four peaks are associated with electronic transitions from CB to V$_{\rm Zn}$, CB to O$_{\rm i}$, Zn$_{\rm i}$ to VB and the decay of self-trapped excitons, respectively. The results of single-exponential fitting demonstrate that different luminescent centers have different radiation resistance, which may explain why the emission decreases more slowly in the NBE band than in the DBE band. The agglomeration of larger point clusters accounts for the decrease in the concentration of luminescence centers and the increase in the concentration of non-luminescence centers, which indicates that the defect clusters induced by ion implantation act as nonradiative recombination centers and suppress light emission. The results of the photoluminescence spectra of a virgin ZnO single crystal and a ZnO single crystal irradiated with a fluence of 3.4$\times$10$^{14}$ ions/cm$^{2}$ show that compared with the virgin ZnO, the emission intensity of irradiated ZnO decreases by nearly two orders of magnitude, which demonstrates that the irradiation effect reduces radiative recombination and enhances nonradiative recombination. The conclusions of photoluminescence are consistent with the IL results.
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High Refractive Index Ti$_3$O$_5$ Films for Dielectric Metasurfaces
Sohail Abdul Jalil, Mahreen Akram, Gwanho Yoon, Ayesha Khalid, Dasol Lee, Niloufar Raeis-Hosseini, Sunae So, Inki Kim, Qazi Salman Ahmed, Junsuk Rho, Muhammad Qasim Mehmood
Chin. Phys. Lett. 2017, 34 (8):
088102
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DOI: 10.1088/0256-307X/34/8/088102
Ti$_3$O$_5$ films are deposited with the help of an electron beam evaporator for their applications in metasurfaces. The film of subwavelength (632 nm) thickness is deposited on a silicon substrate and annealed at 400$^{\circ}\!$C. The ellipsometry result shows a high refractive index above 2.5 with the minimum absorption coefficient in the visible region, which is necessary for high efficiency of transparent metasurfaces. Atomic force microscopy analysis is employed to measure the roughness of the as-deposited films. It is seen from micrographs that the deposited films are very smooth with the minimum roughness to prevent scattering and absorption losses for metasurface devices. The absence of grains and cracks can be seen by scanning electron microscope analysis, which is favorable for electron beam lithography. Fourier transform infrared spectroscopy reveals the transmission and reflection obtained from the film deposited on glass substrates. The as-deposited film shows high transmission above 60%, which is in good agreement with metasurfaces.
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37 articles
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