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Quantum connectivity optimization algorithms for entanglement source deployment in a quantum multi-hop network
Zhen-Zhen Zou, Xu-Tao Yu, Zai-Chen Zhang
Frontiers of Physics. 2018, 13 (2 ): 130202-.
https://doi.org/10.1007/s11467-017-0721-7
At first, the entanglement source deployment problem is studied in a quantum multi-hop network, which has a significant influence on quantum connectivity. Two optimization algorithms are introduced with limited entanglement sources in this paper. A deployment algorithm based on node position (DNP) improves connectivity by guaranteeing that all overlapping areas of the distribution ranges of the entanglement sources contain nodes. In addition, a deployment algorithm based on an improved genetic algorithm (DIGA) is implemented by dividing the region into grids. From the simulation results, DNP and DIGA improve quantum connectivity by 213.73% and 248.83% compared to random deployment, respectively, and the latter performs better in terms of connectivity. However, DNP is more flexible and adaptive to change, as it stops running when all nodes are covered.
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Robust general N user authentication scheme in a centralized quantum communication network via generalized GHZ states
Ahmed Farouk, J. Batle, M. Elhoseny, Mosayeb Naseri, Muzaffar Lone, Alex Fedorov, Majid Alkhambashi, Syed Hassan Ahmed, M. Abdel-Aty
Frontiers of Physics. 2018, 13 (2 ): 130306-.
https://doi.org/10.1007/s11467-017-0717-3
Quantum communication provides an enormous advantage over its classical counterpart: security of communications based on the very principles of quantum mechanics. Researchers have proposed several approaches for user identity authentication via entanglement. Unfortunately, these protocols fail because an attacker can capture some of the particles in a transmitted sequence and send what is left to the receiver through a quantum channel. Subsequently, the attacker can restore some of the confidential messages, giving rise to the possibility of information leakage. Here we present a new robust General N user authentication protocol based on N -particle Greenberger–Horne–Zeilinger (GHZ) states, which makes eavesdropping detection more effective and secure, as compared to some current authentication protocols. The security analysis of our protocol for various kinds of attacks verifies that it is unconditionally secure, and that an attacker will not obtain any information about the transmitted key. Moreover, as the number of transferred key bits N becomes larger, while the number of users for transmitting the information is increased, the probability of effectively obtaining the transmitted authentication keys is reduced to zero.
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Chimera states in bipartite networks of FitzHugh–Nagumo oscillators
Zhi-Min Wu, Hong-Yan Cheng, Yuee Feng, Hai-Hong Li, Qiong-Lin Dai, Jun-Zhong Yang
Frontiers of Physics. 2018, 13 (2 ): 130503-.
https://doi.org/10.1007/s11467-017-0737-z
Chimera states consisting of spatially coherent and incoherent domains have been observed in different topologies such as rings, spheres, and complex networks. In this paper, we investigate bipartite networks of nonlocally coupled FitzHugh–Nagumo (FHN) oscillators in which the units are allocated evenly to two layers, and FHN units interact with each other only when they are in different layers. We report the existence of chimera states in bipartite networks. Owing to the interplay between chimera states in the two layers, many types of chimera states such as in-phase chimera states, antiphase chimera states, and out-of-phase chimera states are classified. Stability diagrams of several typical chimera states in the coupling strength–coupling radius plane, which show strong multistability of chimera states, are explored.
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A versatile electrostatic trap with open optical access
Sheng-Qiang Li(李胜强), Jian-Ping Yin (印建平)
Frontiers of Physics. 2018, 13 (2 ): 133701-.
https://doi.org/10.1007/s11467-017-0727-1
A versatile electrostatic trap with open optical access for cold polar molecules in weak-field-seeking state is proposed in this paper. The trap is composed of a pair of disk electrodes and a hexapole. With the help of a finite element software, the spatial distribution of the electrostatic field is calculated. The results indicate that a three-dimensional closed electrostatic trap is formed. Taking ND3 molecules as an example, the dynamic process of loading and trapping is simulated. The results show that when the velocity of the molecular beam is 10 m/s and the loading time is 0.9964 ms, the maximum loading efficiency reaches 94.25% and the temperature of the trapped molecules reaches about 30.3 mK. A single well can be split into two wells, which is of significant importance to the precision measurement and interference of matter waves. This scheme, in addition, can be further miniaturized to construct one-dimensional, two-dimensional, and three-dimensional spatial electrostatic lattices.
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Slow light effect with high group index and wideband by saddle-like mode in PC-CROW
Yong Wan, Li-Jun Jiang, Sheng Xu, Meng-Xue Li, Meng-Nan Liu, Cheng-Yi Jiang, Feng Yuan
Frontiers of Physics. 2018, 13 (2 ): 134202-.
https://doi.org/10.1007/s11467-017-0719-1
Slow light with high group index and wideband is achieved in photonic crystal coupled-resonator optical waveguides (PC-CROWs). According to the eye-shaped scatterers and various microcavities, saddlelike curves between the normalized frequency f and wave number k can be obtained by adjusting the parameters of the scatterers, parameters of the coupling microcavities, and positions of the scatterers. Slow light with decent flat band and group index can then be achieved by optimizing the parameters. Simulations prove that the maximal value of the group index is>104 , and the normalized delay bandwidth product within a new varying range of ng >102 or ng >103 can be a new and effective criterion of evaluation for the slow light in PC-CROWs.
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On the improvement of signal repeatability in laser-induced air plasmas
Shuai Zhang, Sahar Sheta, Zong-Yu Hou, Zhe Wang
Frontiers of Physics. 2018, 13 (2 ): 135201-.
https://doi.org/10.1007/s11467-017-0735-1
The relatively low repeatability of laser-induced breakdown spectroscopy (LIBS) severely hinders its wide commercialization. In the present work, we investigate the optimization of LIBS system for repeatability improvement for both signal generation (plasma evolution) and signal collection. Timeintegrated spectra and images were obtained under different laser energies and focal lengths to investigate the optimum configuration for stable plasmas and repeatable signals. Using our experimental setup, the optimum conditions were found to be a laser energy of 250 mJ and a focus length of 100 mm. A stable and homogeneous plasma with the largest hot core area in the optimum condition yielded the most stable LIBS signal. Time-resolved images showed that the rebounding processes through the air plasma evolution caused the relative standard deviation (RSD) to increase with laser energies of>250 mJ. In addition, the emission collection was improved by using a concave spherical mirror. The line intensities doubled as their RSDs decreased by approximately 25%. When the signal generation and collection were optimized simultaneously, the pulse-to-pulse RSDs were reduced to approximately 3% for O(I), N(I), and H(I) lines, which are better than the RSDs reported for solid samples and showed great potential for LIBS quantitative analysis by gasifying the solid or liquid samples.
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Structural, optical, and thermal properties of MAX-phase Cr2 AlB2
Xiao-Hong Li, Hong-Ling Cui, Rui-Zhou Zhang
Frontiers of Physics. 2018, 13 (2 ): 136501-.
https://doi.org/10.1007/s11467-017-0743-1
First-principles calculations of the structural, optical, and thermal properties of Cr2 AlB2 are performed using the pseudopotential plane-wave method within the generalized gradient approximation (GGA). Calculation of the elastic constant and phonon dispersion indicates that Cr2 AlB2 is mechanically and thermodynamically stable. Analysis of the band structure and density of states indicates that Cr2 AlB2 is metallic. The thermal properties under increasing temperature and pressure are investigated using the quasi-harmonic Debye model. The results show that anharmonic effects on Cr2 AlB2 are important at low temperature and high pressure. The calculated equilibrium primitive cell volume is 95.91 Å3 at T = 300 K, P = 0 GPa. The ability of Cr2 AlB2 to resist volume changes becomes weaker with increasing temperature and stronger with increasing pressure. Analysis of optical properties of Cr2 AlB2 shows that the static dielectric function of Cr2 AlB2 is 53.1, and the refractive index n 0 is 7.3. If the incident light has a frequency exceeding 16.09 eV, which is the plasma frequency of Cr2 AlB2 , Cr2 AlB2 changes from metallic to dielectric material.
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Elastic, dynamical, and electronic properties of LiHg and Li3 Hg: First-principles study
Yan Wang (王研), Chun-Mei Hao (郝春梅), Hong-Mei Huang (黄红梅), Yan-Ling Li (李延龄)
Frontiers of Physics. 2018, 13 (2 ): 137102-.
https://doi.org/10.1007/s11467-017-0723-5
The elastic, dynamical, and electronic properties of cubic LiHg and Li3 Hg were investigated based on first-principles methods. The elastic constants and phonon spectral calculations confirmed the mechanical and dynamical stability of the materials at ambient conditions. The obtained elastic moduli of LiHg are slightly larger than those of Li3 Hg. Both LiHg and Li3 Hg are ductile materials with strong shear anisotropy as metals with mixed ionic, covalent, and metallic interactions. The calculated Debye temperatures are 223.5 K and 230.6 K for LiHg and Li3 Hg, respectively. The calculated phonon frequency of the T2 g mode in Li3 Hg is 326.8 cm−1 . The p states from the Hg and Li atoms dominate the electronic structure near the Fermi level. These findings may inspire further experimental and theoretical study on the potential technical and engineering applications of similar alkali metal-based intermetallic compounds.
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Exotic ferromagnetism in the two-dimensional quantum material C3 N
Wen-Cheng Huang, Wei Li, Xiaosong Liu
Frontiers of Physics. 2018, 13 (2 ): 137104-.
https://doi.org/10.1007/s11467-017-0741-3
The search for and study of exotic quantum states in novel low-dimensional quantum materials have triggered extensive research in recent years. Here, we systematically study the electronic and magnetic structures in the newly discovered two-dimensional quantum material C3 N within the framework of density functional theory. The calculations demonstrate that C3 N is an indirect-band semiconductor with an energy gap of 0.38 eV, which is in good agreement with experimental observations. Interestingly, we find van Hove singularities located at energies near the Fermi level, which is half that of graphene. Thus, the Fermi energy easily approaches that of the singularities, driving the system to ferromagnetism, under charge carrier injection, such as electric field gating or hydrogen doping. These findings not only demonstrate that the emergence of magnetism stems from the itinerant electron mechanism rather than the effects of local magnetic impurities, but also open a new avenue to designing field-effect transistor devices for possible realization of an insulator–ferromagnet transition by tuning an external electric field.
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Dynamic conductivity modified by impurity resonant states in doping three-dimensional Dirac semimetals
Shuai Li, Chen Wang, Shi-Han Zheng, Rui-Qiang Wang, Jun Li, Mou Yang
Frontiers of Physics. 2018, 13 (2 ): 137303-.
https://doi.org/10.1007/s11467-017-0742-2
The impurity effect is studied in three-dimensional Dirac semimetals in the framework of a T-matrix method to consider the multiple scattering events of Dirac electrons off impurities. It has been found that a strong impurity potential can significantly restructure the energy dispersion and the density of states of Dirac electrons. An impurity-induced resonant state emerges and significantly modifies the pristine optical response. It is shown that the impurity state disturbs the common longitudinal optical conductivity by creating either an optical conductivity peak or double absorption jumps, depending on the relative position of the impurity band and the Fermi level. More importantly, these conductivity features appear in the forbidden region between the Drude and interband transition, completely or partially filling the Pauli block region of optical response. The underlying physics is that the appearance of resonance states as well as the broadening of the bands leads to a more complicated selection rule for the optical transitions, making it possible to excite new electron-hole pairs in the forbidden region. These features in optical conductivity provide valuable information to understand the impurity behaviors in 3D Dirac materials.
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Topological Fulde–Ferrell and Larkin–Ovchinnikov states in spin-orbit-coupled lattice system
Yao-Wu Guo, Yan Chen
Frontiers of Physics. 2018, 13 (2 ): 137402-.
https://doi.org/10.1007/s11467-017-0728-0
The spin-orbit coupled lattice system under Zeeman fields provides an ideal platform to realize exotic pairing states. Notable examples range from the topological superfluid/superconducting (tSC) state, which is gapped in the bulk but metallic at the edge, to the Fulde–Ferrell (FF) state (having a phase-modulated order parameter with a uniform amplitude) and the Larkin–Ovchinnikov (LO) state (having a spatially varying order parameter amplitude). Here, we show that the topological FF state with Chern number (C =−1) (tFF1 ) and topological LO state with C = 2 (tLO2 ) can be stabilized in Rashba spin-orbit coupled lattice systems in the presence of both in-plane and out-of-plane Zeeman fields. Besides the inhomogeneous tSC states, in the presence of a weak in-plane Zeeman field, two topological BCS phases may emerge with C =−1 (tBCS1 ) far from half filling and C = 2 (tBCS2 ) near half filling. We show intriguing effects such as different spatial profiles of order parameters for FF and LO states, the topological evolution among inhomogeneous tSC states, and different non-trivial Chern numbers for the tFF1 and tLO1,2 states, which are peculiar to the lattice system. Global phase diagrams for various topological phases are presented for both half-filling and doped cases. The edge states as well as local density of states spectra are calculated for tSC states in a 2D strip.
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Analytical assessment of some characteristic ratios for s -wave superconductors
Ryszard Gonczarek, Mateusz Krzyzosiak, Adam Gonczarek, Lucjan Jacak
Frontiers of Physics. 2018, 13 (2 ): 137403-.
https://doi.org/10.1007/s11467-017-0739-x
We evaluate some thermodynamic quantities and characteristic ratios that describe low- and hightemperature s-wave superconducting systems. Based on a set of fundamental equations derived within the conformal transformation method, a simple model is proposed and studied analytically. After including a one-parameter class of fluctuations in the density of states, the mathematical structure of the s-wave superconducting gap, the free energy difference, and the specific heat difference is found and discussed in an analytic manner. Both the zero-temperature limit T = 0 and the subcritical temperature range T ≤T c are discussed using the method of successive approximations. The equation for the ratio R 1 , relating the zero-temperature energy gap and the critical temperature, is formulated and solved numerically for various values of the model parameter. Other thermodynamic quantities are analyzed, including a characteristic ratio R 2 , quantifying the dynamics of the specific heat jump at the critical temperature. It is shown that the obtained model results coincide with experimental data for low-T c superconductors. The prospect of application of the presented model in studies of high-T c superconductors and other superconducting systems of the new generation is also discussed.
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AC-current-induced magnetization switching in amorphous microwires
V. Zhukova, J. M. Blanco, A. Chizhik, M. Ipatov, A. Zhukov
Frontiers of Physics. 2018, 13 (2 ): 137501-.
https://doi.org/10.1007/s11467-017-0722-6
We studied the influence of AC current flowing through microwires, on magnetization dynamics. We used a previously developed Sixtus-Tonks modified setup to evaluate the domain wall (DW) velocity within the microwire. However, instead of a magnetizing solenoid, we used a current flowing through the microwire. We observed that the AC current flowing through the annealed Co-rich microwire leads to remagnetization by fast domain wall propagation. The estimated DW velocity was approximately 4.5 km/s, which is similar to and even higher than that reported for the magnetic-field-driven domain wall propagation in Fe- and Co-rich microwires. We measured the DW velocity under tensile stress, and found that the DW velocity decreases under applied stress. An observed DW propagation induced by the current flowing through the microwire is explained considering the influence of an Oersted magnetic field on the outer domain shell. This field has a circular easy magnetization direction and magnetostatic interaction between the outer circumferentially magnetized shell and the inner axially magnetized core.
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