bluuebunny/crossref_metadata_2025 huggingface dataset:
Exchange bias tuning of metal ions doped in CuO nanocomposites
Authors: Liu Kui-Li  , Zhou Si-Hua  , Chen Song-Ling  ,   Laboratory & Equipment Management Department, Zhoukou Normal University, Zhoukou 466001, China
Published: December 2020

In this paper, the nanocomposites are synthesized by the non-equal precipitation method to study the effect of the metal ions doped in antiferromagnetic matrix on the exchange bias. XRD patterns and SEM images reveal that the as-synthesized CuO nanocomposites have uniform size (～80 nm), and the ferrimagnetic particles MFe2O4 (M=Cu, Ni) are embedded in the antiferromagnetic (AFM) CuO matrix by doping of magnetic metal ions Ni and Fe. And the ferrimagnetic phase MFe2O4 (M=Cu, Ni) is formed through the addition of a small amount of Fe that reacts with Cu and Ni ions. Effects of different doping amount of Ni on exchange bias are different. A small doping amount of Ni can induce magnetic disorder at the interface of both phases, then the spin-glass-like phase may be formed. The spin-glass-like phases enhance the pinning effect on the magnetic moments of ferrimagnetic phase. Meanwhile, during field cooling process the antiferromagnetic phase splits into domains, which are aligned either with cooling field or in the original antiferromagnetic configuration. The domain wall serves as pinning sites for the magnetic moments of ferromagnetic phase, and the exchange bias effect is increased. The AFM NiO grains with high anisotropic energy are generated, this also increases the exchange bias effect when continuous doping of Ni ions. In the process of field cooling (FC), upward shift occurs in all hysteresis loops, which is perpendicular to the exchange bias. As x=0.08 (x is the concentration of Ni) the perpendicular displacement is 3.6%, this behavior also proves that under FC measurements, the spin-glass-like phase can be formed between the antiferromagnetic nanopaticles. It is the magnetic exchange coupling at the interface between the ferrimagnetic phase and the spin-glass-like phase that result in an upward shift in the entire measurement range. The plot of M versus T under zero field cooling (ZFC) and field cooling (FC) indicates that the exchange bias effect in these composites is ascribed to the exchange coupling at the interface between the ferrimagnetic particles and the spin-glass-like phase. With continuous introduction of magnetic Ni ions, the exchange bias field first increases slowly, then at x=0.08 it increases sharply. The existence of AFM NiO with high anisotropic energy and the domain structure in AFM matrix are the causes of the result.
A study of the middle time-scale periodic behavior of light curve of BL Lac object OJ287
Authors: Ding Nan  , Zhang Hao-Jing  , Zhang Xiong  , Ou Jian-Wen  , Luo Dan  ,   School of Physics and Electronic Information Technology, Yunnan Normal University, Kunming 650500, China
Published: December 2020

In this paper, we collect the 37 years' data observed for BL Lac object OJ287 in the optical band, and construct its light curve from 1972 to 2009. Using the method of Lomb-Scargle Fourier transform, we analyze the middle time-scale periodic behavior and discover the primary periodic compositions of 52.0±1.1 day and 255±23 day. Then, we simulate the quasi-periodic signal of period doubling bifurcations and compare it with the observation data at different time-interval in their phase diagram and correlation dimension. Result indicates that OJ287 has multi-period scale features. At different time-intervals, there are different harmonic period components in the quasi-periodic light curve. Variation of harmonic period component is related with the disturbance of accretion flow which is from the secondary black hole to the primary black hole, and the periodicity variability may bifurcate the harmonic period component when the primary accretion flow is influenced by a strong disturbance.
Entangled W state of multi degree of freedom system based on orbital angular momentum
Authors: Fan Rong-Hua  , Guo Bang-Hong  , Guo Jian-Jun  , Zhang Cheng-Xian  , Zhang Wen-Jie  , Du Ge  ,   Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510631, China;,   Guangdong Cable TV Network Co., LTD, Guangzhou 510066, China
Published: December 2020

We propose a method of generating the three-photon W state. The method uses parametric down-conversion process and hybrid entanglement swapping from multiphoton spin-entangled states to multiphoton orbital angular momentum (OAM) entangled states, with the aid of a pair of polarization photons. They generate W state entangled in different degrees of freedom of polarization and OAM with a high-dimensional Hilbert space. By simply changing the methods of generating a polarization-OAM-linear momentum entangled W state. Our method produces two mutually symmetric W states with strong entanglement and high dimension, which is expected to realize the secure communication of extending quantum bits.
Non-Markovianity of open two-level system by means of quantum coherence
Authors: He Zhi  , Li Li  , Yao Chun-Mei  , Li Yan  ,   College of Physics and Electronics, Hunan University of Arts and Science, Changde 415000, China
Published: December 2020

We propose an approach to measuring non-Markovianity of an open two-level system from quantum coherence perspective including l1 norm of coherence and quantum relative entropy of coherence, and derive corresponding non-Markovian conditions. Further, as a particular application, non-Markovian conditions of an open two-level system undergoing phase damping channel, random unitary channel and amplitude damping channel, respectively are investigated. Specifically speaking, for the three channels we obtain non-Markovian conditions based on l1 norm of coherence at any initial state of system, and find that non-Markovian conditions are the same as the conditions of other measurements, i.e., information back-flow, divisibility and quantum mutual entropy for the phase damping channel and amplitude damping channel, but non-Markovian conditions new and different from the conditions of other measurements for random unitary channel. On the other hand, for phase damping channel we obtain non-Markovian conditions based on quantum relative entropy of coherence at any initial state of system, which are the same as the conditions of other measures, i.e., information back-flow, divisibility and quantum mutual entropy. However, for the random unitary channel and amplitude damping channel we obtain non-Markovian conditions at maximally coherent state of system.
Long distance measurement device independent quantum key distribution with quantum memories
Authors: Sun Ying  , Zhao Shang-Hong  , Dong Chen  ,   School of Information and Navigation, Air Force Engineering University, Xi'an 710077, China;,   Department of Information Security, Xi'an Communication College, Xi'an 710006, China
Published: December 2020

We propose a long distance measurement-device-independent (MDI) quantum-key-distribution (QKD) with quantum memory, and analyze the relationship between the key generation rate and the storage efficiency of quantum memory. Our protocol is considered and compared with MDI-QKD without quantum memory. We present general formulas for our protocol with three-intensity decoy states. The simulation results show that the maximum secure distance supported by MDI-QKD with quantum memory is about 500 km, while the maximum secure distance of MDI-QKD without quantum memory is only 216 km. With certain limits, prolonging the time of maintaining the necessary quantum fidelity can increase security key transmission distance. Furthermore, the protocol is robust against device imperfection such as quantum memory decoherence effects, which can be easily applied to practical QKD system.
Resonance-like enhancement in high-order above-threshold ionzation of argon at different wavelengths
Authors: Wang Pin-Yi  , Jia Xin-Yan  , Fan Dai-He  , Chen Jing  ,   Southwest Jiaotong University, Quantum Optoelectronic Laboratory, Chengdu 610031, China;,   Beijing Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

Quantum S-matrix theory and “uniform approximation” method are used to study the resonance-like enhancement (RLE) structures in photoelectron spectrum of high-order above-threshold ionization (HATI) for argon atoms subjected to strong laser fields at different wavelengths. Our results show that both in the near infrared and mid-infrared fields, the RLE structures in the photoelectron spectra will appear, which manifests as a group of adjacent HATI peaks that show a significant enhancement when the laser intensity increases only a few percent. The RLE occurs precisely when the laser intensity satisfies the channel-closing (CC) condition, and this further confirms the explanation of CC mechanism of the RLE. More importantly, we find that with increasing laser wavelength, the resonance-like enhancement and suppression will appear alternately in the photoelectron energy spectrum, and this alternation phenomenon will be more pronounced as the intensity increases. This phenomenon may be attributed to the interference of “quantum orbital” of electrons which collide with the core at different return time. Since in the condition of long wavelength, the alternation phenomenon of the RLE is more pronounced, the RLE is distributed from the low-energy regime to the cutoff-regime in the photoelectron energy spectrum, thus making the RLE broader than that in the case of short wavelength. This may be used to explain the experimentally observed extension of the RLE energy region at longer wavelength. In addition, it is also shown that similar to the case of the near infrared laser fields, two types of RLE structures are also found in strong mid-infrared laser fields, where type-Ⅰ enhancement occurs in the region 5%-10% below even CC for Ar atom whose ground state has an odd parity, and its intensity dependence is comparatively smooth; and type-Ⅱ enhancement appears exactly at the channel closing and has a particularly sharp intensity dependence. And both types of enhancements are due to the constructive interference of a large amount of quantum orbits.
A model for phonon thermal conductivity of multi-constrained nanostructures
Authors: Hua Yu-Chao  , Cao Bing-Yang  ,   Department of Engineering Mechanics, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China
Published: December 2020

The rapid development of nanotechnology makes it possible to further understand nanoscale heat conduction. Theoretical analysis and experimental measurement have demonstrated the size-dependence of thermal conductivity on a nanoscale. As dielectric material (such as silicon), phonons are the predominant carriers of heat transport. Phonon ballistic transport and boundary scattering lead to the significant reduction of thermal conductivity. Various models, in which only one geometrical constraint of phonon transport is considered, have been proposed. In engineering situations the phonon transport can be influenced by multiple geometrical constraints, especially for material with long intrinsic phonon mean free path. However, at present a phonon thermal conductivity model in which the multiple geometrical constraints of phonon transport are taken into account, is still lacking. In the present paper, a multi-constrained phonon thermal conductivity model is obtained by using the phonon Boltzmann transport equation and modifying the phonon mean free path. The geometrical constraints are dealt with separately, and the effects of these constraints on thermal conductivity are then combined by the Matthiessen's rules. Different boundary conditions can lead to different influences on the phonon transport, so different methods should be used for different boundary constraints. The differential approximation method is utilized for the constraint in the direction of heat flux, while phonon scatterings on side surfaces are characterized by modifying the phonon mean free path. The model which characterizes various nanostructures including nanofilms(in-plane and cross-plane) and finite length rectangular nanowires, can well agree with the Monte Carlo simulations of different Knudsen numbers. The model with the Knudsen number Knx equal to 0 can well predict the experimental data for the in-plane thermal conductivity of nanofilm. When the Knudsen numbers Kny and Knz vanish, the model corresponds to the cross-plane thermal conductivity of nanofilm. Moreover, with Knx=0 and Kny=Knz, the model corresponds to the square nanowires of infinite length, and the similar slopes between the model and the experimental data of nanowires can be achieved.
Co-phasing detecting method based on grating dispersed fringe for Fizeau optical interferometric telescope
Authors: Yan Zhao-Jun  , Chen Xin-Yang  , Yang Peng-Qian  , Zhou Dan  , Zheng Li-Xin  , Zhu Neng-Hong  ,   The Astronomical Optical Instrument Group, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China;,   Joint Laboratory for High Power Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy Sciences, Shanghai 201800, China
Published: December 2020

For the Fizeau optical interferometric telescope system, the co-phasing detection of piston errors between sub-apertures plays an important role in realizing the high resolution of system. In this paper, the relationship between piston error and the main peak displacement of monochromatic interferogram of two sub-aperture system is analyzed based on physical principles, then the piston error detecting method is developed and clarified based on their linear relationship in the range of one wavelength. Furthermore, an innovative co-phasing detecting method based on grating dispersed interferogram with bandwidth light source is proposed, and its feasibility, detecting precision and dynamic range are analyzed in theory and studied in simulation. The results prove that with this method, the piston error between the two sub-apertures of the system can be soundly detected and its measuring error is less than 20 nm while the piston error is not more than 50 μm. In addition, the novel method solves the problems of 2π ambiguity and direction determination that might exist within some other detecting methods. Besides its millimeter level dynamic range, this new co-phasing detecting method provides a new way and an effective reference for in-depth research of co-phasing detecting techniques.
Impact of metal target’s atom lattice structure on its quantum radar cross-section
Authors: Xu Shi-Long  , Hu Yi-Hua  , Zhao Nan-Xiang  , Wang Yang-Yang  , Li Le  , Guo Li-Ren  ,   State Key Laboratory of Pulsed Power Laser Technology(Electronic Engineering Institute), Hefei 230037, China;,   Key Laboratory of Electronic Restriction of Anhui Province Hefei 230037 China
Published: December 2020

With the development of quantum radar technology, the interaction of photons and targets has gradually become a new hotspot. Quantum radar cross section (QRCS) is an important parameter fon describing the visibility of the target illuminated by light quantum. #br#According to the conservation of energy and the finite element method, the expression of QRCS derived by Marco Lanzagorta is extended, which can be applied to QRCS calculations of non-planar convex targets. As the surface elements of the target have different incident and scattering angles, the integral equation can give a higher calculation accuracy and is suitable for bistatic or multistatic situations. #br#The distribution pattern of the target’s atoms is varied. Using the interatomic distance as the only parameter to describe the atomic distribution is inaccurate. In this paper the metal atomic lattice is considered. Simulation of the QRCS that is composed of three kinds of metal atomic lattices (face-centered cubic, body-centered cubic and hexagonal close-packed lattices) with different atomic distributions has been made. The hexagonal close-packed lattice with asymmetrical distribution for different azimuth angles is discussed. Simulation result shows that with different arrangement of atoms, the main lobe of the target QRCS is basically unchanged, while the quantum side-lobes of the target with sparsely arranged atoms are much more significant. This reveals a different characteristic of QRCS, and provides theoretic basis for quantum radar and stealth technique researches.
Electromagnetically induced transparency in a near-resonance coupling field
Authors: Wang Meng  , Bai Jin-Hai  , Pei Li-Ya  , Lu Xiao-Gang  , Gao Yan-Lei  , Wang Ru-Quan  , Wu Ling-An  , Yang Shi-Ping  , Pang Zhao-Guang  , Fu Pan-Ming  , Zuo Zhan-Chun  ,   Institute of Physics, Chinese Academy of Sciences, Beijing National Laboratory for Condensed Matter Physics, Beijing 100190, China;,   College of Physics and Information Engineering, Hebei Normal University, Shijiazhuang 050000, China
Published: December 2020

The phenomenon of electromagnetically induced transparency (EIT) in 85Rb atomic vapor is studied in a -type of four-level system with the coupling laser frequency detuned from the atomic resonance frequency. We find that the EIT intensity grows weaker as the coupling laser frequency is detuned from resonance, but the relative depth of the transparency window increases. The maximum depth appears when the coupling frequency is detuned at about +180 MHz, not at the resonance frequency. We demonstrate that this is a result of the combined effect of the two excited states, and present a theoretical analysis based on the four-level system, which agrees quite well with the experimental results.
Third-order optical nonlinearity at communication wavelength and spectral characteristics of Ge-Se based chalcogenide glasses
Authors: Qiao Bei-Jing  , Chen Fei-Fei  , Huang Yi-Cong  , Dai Shi-Xun  , Nie Qiu-Hua  , Xu Tie-Feng  ,   Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies, Ningbo University, Ningbo 315211, China
Published: December 2020

A series of Ge-Se chalcogenide glasses incorporated with same molar percentage of Ga, Sn, Sb and Te are synthesized by melt-quenching method. The variations of optical band gaps doped with different elements are investigated by absorption spectra, and the relationship of optical band gap with glass network structure is studied by Raman spectra The results show that the doping of heavy metallic elements (except Ga) could reduce the optical band gap of the Ge-Se glass due to the decrease of the number of Se-Se chains or ring bonds. Third-order optical nonlinearities of the glasses are studied by femtosecond Z-scan method at a telecom wavelength of 1550nm. The results show that the performance of third-order optical nonlinearity of the Ge-Se glass could be improved by doping the above-mentioned elements. By comparison, the Sn-doped Ge-Se glass has a maximum nonlinear refraction index (n2) of 6.36× 10-17 m2/W and a figure of merit of over 23. By combining the experimental results from Raman spectra, the enhancement of third-order optical nonlinearity after the introduction of Sn can be ascribed to the formation of Sn(Se1/2)4 tetrahedra that enters into the main frame of Ge-Se glass and results in a stable Ge-Sn-Se network. Te doping could also remarkably enhance the n2 value of the Ge-Se glass, however, it could cause large two-photon absorption, leading to a poor value of figure of merit. The research result shows that chalcogenide glass in Ge-Sn-Se ternary system is an ideal candidate material for designing and fabricating infrared devices with high performance and environmental friendness.
Source ranging based on frequency band decomposition and distance weighting using a single acoustic vector sensor in shallow water
Authors: Zhu Liang-Ming  , Li Feng-Hua  , Sun Mei  , Chen De-Sheng  ,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China;,   College of Physics, University of Chinese Academy of Sciences, Beijing 100049, China;,   School of Physics and Electronic Engineering, Taishan University, Taian 271021, China
Published: December 2020

A novel method is proposed for the passive source range estimation based on union processing of pressure and particle horizontal velocity. Autocorrelation functions’ warping spectra of pressure and particle velocities have frequency invariability. The spectra of the warped autocorrelation functions of pressure and particle horizontal velocity have the same line spectrum feature, while the spectrum of the warped autocorrelation function of particle vertical velocity possesses both line and broadband spectrum features. Moreover, the warped autocorrelation function’s spectrum of particle vertical velocity has more peaks, and the peak width is broader than those of pressure and particle horizontal velocity. In this paper, source ranges are estimated based on frequency band decomposition and distance weighting, and a guided source with a known range is employed to provide the crucial frequency invariant features. Experimental data in shallow water with an iso-speed profile are used to verify the approach which can reasonably estimate source ranges with the relative errors of the source ranging basically less than 7%. This method can effectively reduce the mainlobe width and background level of the cost function, and can significantly improve the resolution of source range estimation, compared with the results of conventional source ranging approach that uses a single pressure hydrophone.
Viscoelastic focusing of microparticles in circular cross-sectional microchannels
Authors: Dai Qing  , Xiang Nan  , Cheng Jie  , Ni Zhong-Hua  ,   School of Mechanical Engineering, Southeast University, Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Nanjing 211189, China
Published: December 2020

Particle focusing induced by viscoelasticity of fluids has attracted increasing interest in recent years. However, the regulation mechanisms of critical parameters affecting the particle focusing behaviors are still unclear. This paper systematically characterized the dynamics of particle migration in non-Newtonian fluid flows, and analyzed the effects of flow rate and channel length on particle focusing behaviors. Först, the lateral migration behaviors of particles suspended in Newtonian fluids (e.g., pure water and 22 wt% glycerol aqueous solution) are compared with those in non-Newtonian fluids (8 wt% polyvinylpyrrolidone aqueous solution). It is found that the particles suspended in non-Newtonian fluids would migrate towards the channel centerline and form a single-line particle array under the action of elastic force while the particles suspended in Newtonian fluids would migrate to form a famous Segré-Silberberg particle annular ring due to the effects of inertial lift forces. Second, the effects of particle size and driving flow rate on particle viscoelastic focusing are quantitatively analyzed. Results show that with increasing flow rate the focusing degree increases and finally stabilize at a certain value, and the large particles have better focusing quality than the small ones. Finally, the dynamic focusing process of particles along the channel length is investigated. A mathematical model of safe channel length for achieving particle focusing is derived and validated by experiments. It is found that the safe channel length for large particles is significantly shorter than that for small ones. The obtained results would improve the understanding of particle focusing processes and mechanisms, and help realize the flexible control of particle migration behaviors in non-Newtonian fluids.
Spreading dynamics of liquid droplet on gradient micro-structured surfaces
Authors: Lin Lin  , Yuan Ru-Qiang  , Zhang Xin-Xin  , Wang Xiao-Dong  ,   Department of Thermal Engineering, School of Mechanical Engineering, University of Science and Technology, Beijing 100083, China;,   State Key Laboratory of Alternative Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
Published: December 2020

Designed microtextured surfaces have shown promising applications in tuning the wettability of a liquid droplet on the surfaces and attracted great attention over the past decade; unfortunately, the effect of surface geometry on wetting properties is still poorly understood. In this work, two- and multi-stage pillar microtextures are designed to construct gradient surfaces by altering pillar width and spacing. Then, the multi-phase lattice-Boltzmann method (LBM) is used to investigate the wetting dynamics of a liquid droplet on the gradient surface. Results show that for the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis is found to be proportional to the roughness gradient when droplet/surface system is in the Cassie-Baxter state. However, this proportional relation is no longer correct when the system is in the transition state between the Wenzel and Cassie-Baxter states. For the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis always increases linearly with increasing roughness gradient. Results also show that when a larger droplet is placed on the multi-stage gradient surface, stronger droplet motion is observed due to the smaller contact angle hysteresis. The present LBM simulations provide a guideline for the design and manufacture of the microtextured surfaces to tune the droplet wettability and motion.
Influence of iron impurity interaction in copper-iron dilute magnetic alloy at low temperatures
Authors: Zhang Yu-Sheng  , Li Jing-Dong  , Liu Meng-Yu  , Yang Bin  , Chen Huan-Xin  , Wang Hui-Ling  ,   Huazhong University of Science and Technology, School of Energy and Power Engineering, Wuhan 430074, china;,   Huazhong University of Science and Technology, School of Electrical and Electronic Engineering, Wuhan 430074, china
Published: December 2020

In the paper the coupling impurities theory is used, and both s-d interaction effect and phonon effect in dilute magnetic alloys are discussed . The Green’s function is used to analyse the Hamiltonian of the system. In copper-iron dilute magnetic alloy the magnetic impurities interaction has a huge impact on thermoelectric power in the condition of high concentration of iron. Theoretic value of thermoelectric power of dilute magnetic copper-iron alloy with high concentration of iron changing with temperature is given. We have chosen three typical copper-iron dilute magnetic alloys and calculated the thermoelectric power under the effect of impurities and the effect of impurities interaction. Their atomic percentage concentrations are 0.1%, 0.13% and 0.15% respectively. Theoretical value of the thermoelectric power under the effect of impurities interaction in copper-iron alloy complies with experimental value. This paper provides the basic theoretical analysis for promoting the application of low-temperature copper-iron dilute magnetic thermocouple.
A new Stckelberg holographic superconductor model
Authors: Peng Yan  , Deng Fang-An  , Liu Guo-Hua  , Yang Kai-Fan  ,   School of Mathematics and Computer Science, Shaanxi University of Technology, Hanzhong 723000, China
Published: December 2020

The AdS/CFT correspondence has provided us a useful approach to describe strongly interacting systems holographically through weakly coupled gravitational duals. One of the mostly studied gravity duals is the holographic superconductor, which is constructed by a scalar field coupled to a Maxwell field in an AdS black hole background. It is shown that when the Hawking temperature of a black hole drops below a critical value, the black hole becomes unstable and this instability in the (d+1) dimensional AdS black hole corresponds to a d-dimensional phase transition at the boundary, called holographic superconductor model. Generally speaking, the instability of the gravity systems belongs to the second-order phase transition. Lately, it was stated that the holographic superconductor with the spontaneous breaking of a global U(1) symmetry via the Stckelberg mechanism allows the first-order phase transition to occur. Some further studies are carried out by considering new forms of the Stckelberg mechanism. So it is very interesting to extend the discussion to other new forms of Stckelberg mechanism to explore the rich properties of holographic superconductors. By considering new higher correction terms of the scalar fields, we investigate a general class of holographic superconductors via Stckelberg mechanism in the background of four-dimensional AdS black hole. We obtain richer structures in the metal/superconductor phase transitions. We study the condensation of the scalar operator and find that when the model parameter is above a threshold value, this new model allows first-order phase transition to occur. We also examine the effects of the backreaction on the threshold model parameter and find that backreaction makes the first-order phase transitions easier to happen (or smaller threshold parameters above which the phase transition changes from second to first order). We may conclude that the model parameter coupled with the backreaction can determine the order of phase transitions.
Planar quantum squeezing and atom interferometry
Authors: Huang Xin-Yao  , Xiang Yu  , Sun Feng-Xiao  , He Qiong-Yi  , Gong Qi-Huang  ,   State Key Laboratory of Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
Published: December 2020

Reduction of quantum noise in one spin component is a significant tool for enhancing the sensitivities of interferometers and atomic clocks. It has been recently implemented for ultra-cold atomic Bose-Einstein condensate (BEC) interferometer. This type of quantum noise reduction reduces the measurement noise near some predetermined phase. However, if the phase is completely unknown prior to measurement, then it is not known which phase quadrature should be in a squeezed state. We introduce a novel planar squeezing uncertainty relation for spin variance in a plane, and analyze how to obtain such a planar quantum squeezed (PQS) state by using a double-well single component BEC, through the use of local nonlinear S-wave scattering interaction between trapped atoms. Here, we consider the PQS that is generated by using two hyperfine states in a two components BEC system, which is useful for quantum metrology. By comparison with the case of two spatial wells, the Hamiltonian parameters can be controlled in a more efficient way. The spin component can be measured by detecting the occupation number difference between the two internal modes, while one needs to observe a spatial interference pattern in the double well BEC case. This is the major difference between the internal and external cases. Another difference is that one can use the Rabi frequency Ω instead of the Josephson parameters to switch the Hamiltonian parameters through using a diabatic technique. Therefore the coupling could be switched off or on to study the different evolutions. PQS simultaneously reduces the quantum noises of two orthogonal spin projections below the standard quantum limit, while increases the noise in the third dimension. This allows the improvement in phase measurement at any phase-angle. PQS states that reductions of fluctuations everywhere in a plane have potential utility in "one-shot" phase measurement, where iterative or repeated measurement strategies cannot be utilized. The improved interferometric phase measurements and planar uncertainty relations are useful for detecting the entanglement in mesoscopic system between two distinguished modes regardless of the third component.
Progress towards primary frequency standard
Authors: Ruan Jun  , Wang Ye-Bing  , Chang Hong  , Jiang Hai-Feng  , Liu Tao  , Dong Rui-Fang  , Zhang Shou-Gang  ,   National Time Service Center, Chinese Academy of Sciences, Xi'an 710600, China;,   Key Laboratory of Time and Frequency Primary Standard, Chinese Academy of Sciences, Xi'an 710600, China
Published: December 2020

The cesium fountain clock as primary frequency standard is widely used in the areas, such as time-keeping system, satellite navigation, fundamental physics research, etc. The principle of operation of cesium fountain clock is introduced. The noise source and frequency shift term are ananlyzed. The major noise source influencing frequency stability are cold atom loading time, microwave phase noise related to Dick effect, and detection laser frequency noise. The major frequency bias influencing frequency uncertainty is blackbody radiation frequency shift,cold atom collision frequency shift,distributed cavity phase frequency shift and microwave leakage frequency shift.The key technique to achieve highperformance cesium fountain clock is sumerized. The application of cesium fountain clock is presented. The status of space cesium clock and future primary frequency standard of optical clock are shown.
Equivalent-measurement evaluation method of minimum resolvable gas concentration
Authors: Li Jia-Kun  , Wang Xia  , Jin Wei-Qi  , Zhang Xu  ,   Key Laboratory of Photoelectronic Imaging Technology and System of the Ministry of Education, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Currently, there is no standard method of evaluating the performance of the gas leak infrared imaging detection system. The evaluating criterions vary greatly and are deficient in aspects of completeness and accuracy, such as noise equivalent temperature difference, noise equivalent concentration path length, and minimum detectable leak rates. Minimum resolvable gas concentration (MRGC) is a latest proposed parameter for evaluating the performance of a passive gas leak infrared imaging detection system, which takes full advantage of the comprehensive evaluation capability of the temperature resolution and spatial resolution of the minimum resolvable temperature difference (MRTD) model. The MRGC takes into account the environmental and gas state parameters, the size of the gas plume and other factors which influence the MRGC measurement. However, the MRGC measurement system is complicated and many state parameters need to be controlled, especially the wide range and dedicated gas concentration meters are required. Therefore, the mathematical model of MRGC is derived and established. By comparing the principles and measurement methods of the performance parameters, MRGC and MRTD, a novel MRGC equivalent measurement evaluation method is proposed, on condition that the minimum resolvable radiation differences are equal. Using ethylene and ammonia as the target, the equivalently measured results of MRGC are obtained. The results show that the MRGC increases with the spatial frequency increasing and the smaller the temperature difference is between the gas and the background blackbody, the faster the MRGC increases. What is more, when the spatial frequency is fixed, MRGC increases with the gas temperature approaching to the background temperature. The background temperature varies asymptotically, which means that if the gas temperature equals the background temperature, the system cannot detect the gas four-bar pattern, no matter what the gas concentration is (here, the maximum gas concentration is 1 million ppm under normal pressure.). The directly measured and equivalently measured results of ethylene are in good agreement within errors of less than ±20%, and the maximum error is 18.26% at a spatial frequency of 0.214f0, which demonstrates the feasibility and effectiveness of the method. Because the equivalent measurement method only needs the traditional MRTD measurement results and the gas infrared spectrum database, it is simple and reliable, which is very significant for the study and application of the gas leak infrared imaging detection systems.
Femtosecond fiber laser for high-stability and high-quality pulse compression
Authors: Lian Fu-Qiang  , Fan Zhong-Wei  , Bai Zhen-Ao  , Liu Yi-Zhou  , Lin Wei-Ran  , Zhang Xiao-Lei  , Zhao Tian-Zhuo  ,   Academy of Opto-electronics, Chinese Academy of Sciences, Beijing 100094, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Peking University, Beijing 100871, China;,   Beijing GK Laser Technology Co., Ltd, Beijing 100190, China
Published: December 2020

We demonstrate a femtosecond fiber master oscillator power amplifier system of high-stability and high-quality pulse compression, which is applied to corneal refractive surgery. The nonlinear-polarization-evolution mode-locking in a hybrid-cavity Yb-fiber oscillator consisting of both polarization-maintaining (PM) and non-PM fibers is demonstrated. In this paper, the PM-fibers introduced into the mode-locked fiber oscillator partially replace non-PM fibers. This alternative approach is conducive to reducing the adverse effect of uncontrolled fiber birefringence, which originates from the on-PM fiber suffering environmental temperature fluctuation and mechanical vibration. Once the length of non-PM fiber is comparable to the fiber beat length, the uncontrolled fiber birefringence caused by environment starts to abate the laser robustness, repeatability, and reliability of mode-locking. The stability becomes notoriously worse for long-cavity Yb-fiber oscillators. The PM-fibers adopted in the mode-locked fiber oscillator could improve the mode-locked stability of nonlinear-polarization-evolution self-started with long-cavity Yb-fiber oscillators. We study the dependence of the compressed pulse quality on the parameters of input pulse pre-chirp injected into the Yb-doped fiber amplifier. Due to the nonlinear-chirp and third order dispersion, the mode-locked pulse shape in time-domain will produce distortion during power being amplified in the Yb-doped fiber amplifier. A diffraction grating to adjust the pre-chirp of the input pulse from positive value to negative value launched into the Yb-doped fiber amplifier is placed between mode-locked Yb-fiber oscillator and Yb-doped fiber amplifier. We vary the pre-chirp by changing the distance between the diffraction grating and triangular prism and then adjust the second grating pair to compress the amplified pulses into its shortest pulse duration of full-width at half maximum measured by an autocorrelator. The experimental results show that the best compression quality of mode-locked pulse occurs at the negative pre-chirp with a measured pulse width of 183 fs. Deviation from this optimum pre-chirp degrades the compressed-pulse quality and features an increased temporal pedestal. The fiber laser produces self-started mode-locking at a repetition rate of 19.4 MHz, an average power of 1.2 W, a pulse width of 183 fs. The homemade femtosecond fiber laser is used to perform surgery on ex vivo pig corneas. The surgey shows that the light burst of femtosecond laser in corneal tissues could cut pig corneas, which proves that the femtosecond fiber laser satisfies the surgical operation requirements of animal corneas.
Quantum measurement with cavity optomechanical systems
Authors: Chen Xue  , Liu Xiao-Wei  , Zhang Ke-Ye  , Yuan Chun-Hua  , Zhang Wei-Ping  ,   Quantum Institute for Light and Atoms, Department of Physics, East China Normal University, Shanghai 200062, China;,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

Cavity optomechanics originated from the research of interferometric detection of gravitational waves, and later became a fast-growing area of techniques and approaches ranging from the fields of atomic, molecular, and optical physics to nano-science and condensed matter physics as well. Recently, it focused on the exploration of operating mechanical oscillators deep in the quantum regime, with an interest ranging from quantum-classical interface tests to high-precision quantum metrology. In this paper, recent theoretical work of our group in the field of quantum measurement with cavity optomechanical systems is reviewed. We explore the quantum measurement theory and its applications with several unconventional cavity optomechanical schemes working in the quantum regime. This review covers the basics of quantum noises in the cavity optomechanical setups and the resulting standard quantum limit of precision displacement and force measurement. Three novel quantum measurement proposals based on the hybrid optomechanical system are introduced. First, we describe a quantum back-action insulated weak force sensor. It is realized by forming a quantum-mechanics-free subsystem with two optomechanical oscillators of reversed effective mass. Then we introduce a role-reversed atomic optomechanical system which enables the preparation and the quantum tomography of a variety of non-classical states of atoms. In this system, the cavity field acts as a mechanical oscillator driven by the radiation pressure force from an ultracold atomic field. In the end, we recommend a multimode optomechanical transducer that can detect intensities significantly below the single-photon level via adiabatic transfer of the microwave signal to the optical frequency domain. These proposals demonstrate the possible applications of optomechanical devices in understanding of quantum-classical crossover and in achieving quantum measurement limit.
Measurement of space charges in air based on sound pulse method
Authors: Liu Kang-Lin  , Liao Rui-Jin  , Zhao Xue-Tong  ,   State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electrical Engineering, Chongqing University, Chongqing 400044, China
Published: December 2020

The space charge in air is closely related to the mechanism of corona discharge. In order to study the onset and sustainability of corona discharge, acquiring the distribution of space charge is necessary but there still exists a puzzle which has not been settled. According to the sound pulse method, in this paper we present a kind of signal processing algorithm to analyze the electric field which is generated by modulating the space charge in the sound field. The electric filed is dependent on the form of sound emission and space charge density. The waveform of electric field is related to space charge density. Through the proposed algorithm, the space charge density can be obtained by analyzing electric field signal. The area in which the space charges need to be measured, is divided into elements. Each element is small enough so that the space charge quantity in each element is assumed to be the same. The following assumption is accepted during numerical simulation: space charge densities in the wave fronts are the same. The curve of electric field produced, received by electric field antenna, is the vector sum of electric filed produced by each element, and then calculated by numerical simulation. In order to satisfy the assumption in each measurement case, the requirements for sound emission system under different cases are discussed. In different cases, different sound emission systems are required. For space charges which are distributed uniformly, plane wave or spherical wave is suitable; for one-dimensional space charge distribution, plane wave is necessary; for space charge two-dimensional or three-dimensional space charge distribution, plane wave array is availed. What is more, a corresponding measuring system is developed which can be used for measuring the space charge density. This system mainly contains the producing of sound pulse, producing of space charges and the receiving of electric field signal. The producing of sound pulse is designed according to the measurement requirement for multi-needle-to-plate geometry which is assumed that space charge is distributed uniformly in the gap. With the experimental model, the space charge density in multi-needle-to-plate geometry is calculated according to the algorithm proposed in this paper. The result is compared with the calculated one by the method of corona currents, verifying the proposed method.
Study on the photodetachment wave packet dynamics of H- ion in a gradient electric field
Authors: Chen Zhao-Hang  , Wang De-Hua  , Cheng Shao-Hao  ,   School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, China
Published: December 2020

Using the combination of the time-dependent perturbation theory and the closed-orbit theory, we put forward a calculation formula for the autocorrelation function of H ion in a gradient electric field, and then calculate and analyze the autocorrelation function of the system. Especially, we discuss the effect of laser pulse width, electric field strength and the electric field gradient on the autocorrelation function of H ion in a gradient electric field. It is demonstrated that when the laser pulse width is very narrow, far less than the period of the detached electron, the quantum wave packet revival phenomenon is significant. A series of sharp reviving peaks appear in the autocorrelation function, which are caused by the interference between the returning electron wave packets travelling along the closed orbit and the outgoing electron wave packets. However, with the increase of laser pulse width, the quantum wave packet revival phenomenon becomes weakened. When the difference between the pulse width and the period of the closed orbit is not very large, the reviving peaks in the autocorrelation function become widely spread gradually and the oscillatory structures get flattened. This correspondence will vanish finally due to the interference between the adjacent peaks. In addition, our study also suggests that the background electric field strength and the electric field gradient in the gradient electric field can also have significant effects on the autocorrelation function. With the increase of background electric field strength and electric field gradient, the period of the detached electron's closed orbit gets shorter, the number of the revival peaks in the autocorrelation function is increased gradually, and the quantum wave packet revival phenomenon will be enhanced. Therefore, we can control the autocorrelation function of the hydrogen negative ion by changing the laser pulse width and the external electric field strength. Our results will provide some reference values for the experimental research on the wave packet dynamic property of atoms or ions in external fields.