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Finite-Key Analysis for a Practical High-Dimensional Quantum Key Distribution System Based on Time-Phase States
Ya-Hui Gan, Yang Wang, Wan-Su Bao, Ru-Shi He, Chun Zhou, Mu-Sheng Jiang
Chin. Phys. Lett. 2019, 36 (4):
040301
.
DOI: 10.1088/0256-307X/36/4/040301
High-dimensional quantum states key distribution (HD-QKD) can enable more than one bit per photon and tolerate more noise. Recently, a practical HD-QKD system based on time-phase states has provided a secret key at Mbps over metropolitan distances. For the purposes of further improving the secret key rate of a practical HD-QKD system, we make two main contributions in this work. Firstly, we present an improved parameter estimation for this system in the finite-key scenario based on the Chernoff bound and the improved Chernoff bound. Secondly, we analyze how the dimension $d$ affects the performance of the practical HD-QKD system. We present numerical simulations about the secret key rate of the practical HD-QKD system based on different parameter estimation methods. It is found that using the improved Chernoff bound can improve the secret key rate and maximum channel loss of the practical HD-QKD system. In addition, a mixture of the 4-level and 8-level practical HD-QKD system can provide better performance in terms of the key generation rate over metropolitan distances.
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Variational Approach to Study $\mathcal{PT}$-Symmetric Solitons in a Bose–Einstein Condensate with Non-locality of Interactions
Wei Qi, Hai-Feng Li, Zhao-Xin Liang
Chin. Phys. Lett. 2019, 36 (4):
040501
.
DOI: 10.1088/0256-307X/36/4/040501
Considering the non-locality of interactions in a Bose–Einstein condensate, the existence and stability of solitons subject to a $\mathcal{PT}$-symmetric potential are discussed. In the framework of the variational approach, we investigate how the non-locality of interactions affects the self-localization and stability of a condensate with attractive two-body interactions. The results reveal that the non-locality of interactions dramatically influences the shape, width, and chemical potential of the condensate. Analytically variational computation also predicts that there exists a critical negative non-local interaction strength ($p_{\rm c} < 0$) with each fixed two-body interaction ($g_{0} < 0$), and there exists no bright soliton solution for $p_{0} < p_{\rm c}$. Furthermore, we study the effect of the non-locality interactions on the stability of the solitons using the Vakhitov–Kolokolov stability criterion. It is shown that for a positive non-local interaction ($p_{0}>0$), there always exist stable bright solitons in some appropriate parameter regimes.
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A Gain-Switched Fe:ZnSe Laser Pumped by a Pulsed Ho,Pr:LLF Laser
Ying-Yi Li, You-Lun Ju, Tong-Yu Dai, Xiao-Ming Duan, Chun-Fa Guo, Li-Wei Xu
Chin. Phys. Lett. 2019, 36 (4):
044201
.
DOI: 10.1088/0256-307X/36/4/044201
We demonstrate a gain-switched Fe:ZnSe laser pumped by a 2958 nm pulsed Ho,Pr:LLF laser. The maximum single pulse energy is 16.4 $\mu$J with a minimum pulse duration of 13.9 ns at the pulse repetition frequency of 1 Hz when the Fe:ZnSe crystal is cooled to 77 K by liquid nitrogen, corresponding to a slope efficiency of 22.9%. The central wavelength and FWHM linewidth are 3957.4 nm and 23.2 nm, respectively. The output energy monotonically decreases as the crystal temperature increases in the range 77–293 K.
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A High Conversion Efficiency Q-Switched Intracavity Nd:YVO$_{4}$/KTA Optical Parametric Oscillator under Direct Diode Pumping at 880nm
Li-Jiao He, Ke Liu, Nan Zong, Zhao Liu, Zhi-Min Wang, Yong Bo, Xiao-Jun Wang, Qin-Jun Peng, Da-Fu Cui, Zu-Yan Xu
Chin. Phys. Lett. 2019, 36 (4):
044202
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DOI: 10.1088/0256-307X/36/4/044202
We report a high conversion efficiency Q-switched Nd:YVO$_{4}$/KTiOAsO$_{4}$ (KTA) intracavity optical parametric oscillator (IOPO) operating near 3.5 μm based on direct 880 nm laser diode (LD) pumping. A maximum average idler output power of 2.6 W with a pulse width of about 7.9 ns is achieved under an absorbed LD power of 45.4 W at a pulse repetition rate (PRR) of 10 kHz. The maximum optical-optical conversion efficiency from LD power to OPO mid-infrared (MIR) output of 6.74% is achieved. To our knowledge, this is the highest conversion efficiency for a KTA-IOPO by exploiting a Q-switched laser as the parent fundamental pump source. The beam quality factors $M^{2}$ of the MIR beam at the full output power with a PRR of 10 kHz are within 2.12 in both the horizontal and vertical directions, indicating a near Gaussian mode.
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Temperature-Dependent Dielectric Characterization of Magneto-Optical Tb$_{3}$Sc$_{2}$Al$_{3}$O$_{12}$ Crystal Investigated by Terahertz Time-Domain Spectroscopy
Ju-Geng Li, Sen-Miao Yang, Xin Chen, Nai-Feng Zhuang, Qi-Biao Zhu, An-Hua Wu, Xian Lin, Guo-Hong Ma, Zuan-Ming Jin, Jian-Quan Yao
Chin. Phys. Lett. 2019, 36 (4):
044203
.
DOI: 10.1088/0256-307X/36/4/044203
Terbium scandium aluminum garnet (TSAG) crystals have been widely used in magneto-optical systems. We investigate the complex refractive index of the TSAG crystal in the terahertz frequency range using terahertz (THz) time-domain spectroscopy in the temperature range 100–300 K. It is observed that the refractive index and the absorption coefficient increase with the THz frequency. The refractive index increases with the temperature. We measure the temperature coefficient of the refractive index of the TSAG crystal in the frequency range 0.4–1.4 THz. Furthermore, the loss tangent, i.e., the ratio of experimental values of the imaginary and real part of the dielectric permittivity, is found to be almost independent of frequency. TSAG is very promising for applications in THz optoelectronics because it has a high dielectric constant, low loss, and low thermal coefficient of the dielectric constant.
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The 10kW Level High Brightness Face-Pumped Slab Nd:YAG Amplifier with a Hybrid Cooling System
Shuai Li, Ya-Ding Guo, Zhong-Zheng Chen, Lin Zhang, Ke-Ling Gong, Zhi-Feng Zhang, Bao-Shan Wang, Jian Xu, Yi-Ting Xu, Lei Yuan, Yang Kou, Yang Liu, Yan-Yong Lin, Qin-Jun Peng, Zu-Yan Xu
Chin. Phys. Lett. 2019, 36 (4):
044204
.
DOI: 10.1088/0256-307X/36/4/044204
We demonstrate a high power, high brightness, slab amplifier based on face-pumped Nd:YAG slab gain modules, having a high efficient hybrid cooling system of the conduction cooling and forced convection cooling. Using a single gain module, a laser output power up to 4.5 kW with a remarkable optical-optical conversion efficiency of 51% is realized, indicating an excellent lasing performance of the Nd:YAG slab module. The amplifier operates at a repetition rate of 700 Hz and delivers a maximum average output power exceeding 10.5 kW with pulse duration of 150 μs. A good beam quality factor is measured to be $\beta=1.9$. To the best of our knowledge, this is the highest brightness for a 10 kW level Nd:YAG slab amplifier.
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Multi-Path Ghost Imaging by Means of an Additional Time Correlation
Rui Liu, Ling-Jun Kong, Yu Si, Zhou-Xiang Wang, Wen-Rong Qi, Chenghou Tu, Yongnan Li, Hui-Tian Wang
Chin. Phys. Lett. 2019, 36 (4):
044205
.
DOI: 10.1088/0256-307X/36/4/044205
Ghost imaging functions achieved by means of the spatial correlations between two photons is a new modality in imaging systems. With a small number of photons, ghost imaging is usually realized based on the position correlation of photon pairs produced from the spontaneous parametric down-conversion process. Here we demonstrate a way to realize multi-path ghost imaging by introducing an additional time correlation. Different delays of paths will induce the shift of the coincidence peak, which carries the information about objects. By choosing the suitable coincidence window, we obtain images of three objects simultaneously, with a visibility of 87.2%. This method provides insights and techniques into multi-parameter ghost imaging. It can be applied to other correlated imaging systems, for example, quantum spiral imaging.
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Synthesis and Characteristics of Type Ib Diamond Doped with NiS as an Additive
Jian-Kang Wang, Shang-Sheng Li, Ning Wang, Hui-Jie Liu, Tai-Chao Su, Mei-Hua Hu, Fei Han, Kun-Peng Yu, Hong-An Ma
Chin. Phys. Lett. 2019, 36 (4):
046101
.
DOI: 10.1088/0256-307X/36/4/046101
Large diamond single crystals doped with NiS are synthesized under high pressure and high temperature. It is found that the effects on the surface and shape of the synthesized diamond crystals are gradually enhanced by increasing the NiS additive amount. It is noted that the synthesis temperature is necessarily raised to 1280$^{\circ}\!$C to realize the diamond growth when the additive amount reaches 3.5% in the synthesis system. The results of Fourier transform infrared spectroscopy (FTIR) demonstrate that S is incorporated into the diamond lattice and exists in the form of C–S bond. Based on the FTIR results, it is found that N concentration in diamond is significantly increased, which are ascribed to the NiS additive. The analysis of x-ray photoelectron spectroscopy shows that S is present in states of C–S, S–O and C–S–O bonds. The relative concentration of S compared to C continuously increases in the synthesized diamonds as the amount of additive NiS increases. Additionally, the electrical properties can be used to characterize the obtained diamond crystals and the results show that diamonds doped with NiS crystals behave as n-type semiconductors.
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Strain Induced Nanopillars and Variation of Magnetic Properties in La$_{0.825}$Sr$_{0.175}$MnO$_{3}$/LaAlO$_{3}$ Films
Xin Li, Jing-Zhi Han, Xiong-Zuo Zhang, Yin-Feng Zhang, Hai-Dong Tian, Ming-Zhu Xue, Kun Li, Xin Wen, Wen-Yun Yang, Shun-Quan Liu, Chang-Sheng Wang, Hong-Lin Du, Xiao-Dong Zhang, Xin-An Wang, Ying-Chang Yang, Jin-Bo Yang
Chin. Phys. Lett. 2019, 36 (4):
046102
.
DOI: 10.1088/0256-307X/36/4/046102
To investigate the process of strain relaxation and resultant variation of microstructure and magnetic properties, low-doped La$_{0.825}$Sr$_{0.175}$MnO$_{3}$ epitaxial films with different thicknesses are deposited on LaAlO$_{3}$ substrates and strain induced nanopillars are discovered inside the La$_{0.825}$Sr$_{0.175}$MnO$_{3}$ film. Perpendicular oriented nanopillars mainly exist below 30 nm and tend to disappear above 30 nm. The distribution of nanopillars not only induce the variation of lattice parameters and local structural distortion but also lead to the deviation of easy magnetization axis from the perpendicular direction. Specifically, the out-of-plane lattice parameters of the film decrease quickly with the increase of the thickness but tend to be constant when the thickness is above 30 nm. Meanwhile, the variations of magnetic properties along in-plane and out-of-plane directions would also decline at first and they then remain nearly unchanged. Our work constructs the relationship between nanopillars and magnetic properties inside films. We are able to clearly reveal the effects of inhomogeneous strain relaxation.
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High-Pressure Phase Transitions of Cubic Y$_{2}$O$_{3}$ under High Pressures by In-situ Synchrotron X-Ray Diffraction
Sheng Jiang, Jing Liu, Xiao-Dong Li, Yan-Chun Li, Shang-Ming He, Ji-Chao Zhang
Chin. Phys. Lett. 2019, 36 (4):
046103
.
DOI: 10.1088/0256-307X/36/4/046103
High-pressure phase transitions of cubic Y$_{2}$O$_{3}$ are investigated using in situ synchrotron x-ray diffraction in a diamond anvil cell up to 36.3 GPa. The pressure-induced phase transitions of cubic Y$_{2}$O$_{3}$, which display apparent inconsistencies in previous studies, are verified to be from a cubic phase to a monoclinic phase and further to a hexagonal phase at 11.7 and 21.6 GPa, respectively. The hexagonal Y$_{2}$O$_{3}$ displays noticeable anisotropic compressibility due to its layered structure and it is stable up to the highest pressure in the present study. A third-order Birch–Murnaghan fit based on the observed pressure-volume data yields zero pressure bulk moduli of 180(3), 196(7) and 177(7) GPa for cubic, monoclinic and hexagonal phases, respectively.
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Effect of Post-Annealing on Structural and Electrical Properties of ZnO:In Films
Guo-Ping Qin, Hong Zhang, Hai-Bo Ruan, Jiang Wang, Dong Wang, Chun-Yang Kong
Chin. Phys. Lett. 2019, 36 (4):
047301
.
DOI: 10.1088/0256-307X/36/4/047301
Indium-doped ZnO (ZnO:In) films are deposited on quartz substrates by rf magnetron sputtering. The effects of post-annealing on structural, electrical, optical and Raman properties are investigated by x-ray diffraction, Raman scattering, Hall measurement and first-principles calculation. The results indicate that all of the ZnO:In films have excellent crystallinity with a preferred ZnO (002) orientation. It is found that the incorporation of In can dramatically increase the intensity of the 274 cm$^{-1}$ Raman mode. However, both post-annealing treatment and increasing O$_{2}$ partial pressure in the process of preparing thin films can reduce the intensity of the 274 cm$^{-1}$ mode or even eliminate it, and relax compressive stress of the ZnO:In film judged by analyzing the shifts of the (002) Bragg peaks and $E_{2}$ (high) mode. Finally, the origin of the 274 cm$^{-1}$ mode is inferred to be the vibration of Zn interstitial (Zn$_{\rm i}$) defects, which play a crucial role in the high electron concentration and low resistivity of ZnO:In films annealed in an appropriate temperature range (450–600$^{\circ}\!$C).
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Neutrino Emission and Cooling of Dark-Matter-Admixed Neutron Stars
Wen-Bo Ding, Zi Yu, Yan Xu, Chun-Jian Liu, Tmurbagan Bao
Chin. Phys. Lett. 2019, 36 (4):
049701
.
DOI: 10.1088/0256-307X/36/4/049701
The GW170817 binary neutron star merger event in 2017 has raised great interest in the theoretical research f neutron stars. The structure and cooling properties of dark-matter-admixed neutron stars are studied here using relativistic mean field theory and cooling theories. The non-self-annihilating dark matter (DM) component is assumed to be ideal fermions, among which the weak interaction is considered. The results show that pulsars J1614-2230, J0348+0432 and EXO 0748-676 may all contain DM with the particle mass of 0.2–0.4 GeV. However, it is found that the effect of DM on neutron star cooling is complicated. Light DM particles favor the fast cooling of neutron stars, and the case is converse for middle massive DM. However, high massive DM particles, around 1.0 GeV, make the low mass (around solar mass) neutron star still undergo direct Urca process of nucleons at the core, which leads the DM-admixed stars cool much more quickly than the normal neutron star, and cannot support the direct Urca process with a mass lower than 1.1 times solar mass. Thus, we may conjecture that if small (around solar mass) and super cold (at least surface temperature 5–10 times lower than that of the usual observed data) pulsars are observed, then the star may contain fermionic DM with weak self-interaction.
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21 articles
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