SPECIAL TOPIC—The 70th anniversary of National University of Defense Technology
国防科技大学物理学科起源于哈军工时期的物理教授会和原子工程系, 专业积淀深厚、军事特色鲜明. 七十年传承, 始终面向国家重大战略特别是国防科技战略, 为我国相关领域培养了一大批优秀人才. 围绕国防高科技武器基础原理和新概念武器开展特色研究, 在极端条件物态物性、强场超快、聚变能源、量子技术、武器物理等方面形成优势, 孵化了核科学与技术、光学工程一级学科和量子信息、高能量密度物理等交叉学科, 形成了基础研究与军事应用紧密结合、前沿探索与高水平人才培养有机统一、自主创新与开放合作相得益彰的鲜明特色, 建成了一流的拔尖人才培养基地和前沿创新科研平台. 在国防科技大学 70年校庆之际, 在国内对基础学科发展前所未有重视之时, 国防科技大学对物理学科的支持力度也进入了全新时期, 学科发展进入快车道, 高水平成果不断涌现.
在《物理学报》编辑部的大力支持下, 我们组织了“国防科技大学建校 70周年专题”, 主要集中展示了极端条件和量子信息技术两个方向的部分成果. 在极端条件物理方面, 赵增秀等利用符合测量技术, 展示了强飞秒激光场下二氧化碳二聚体的多体解离过程; 康冬冬和戴佳钰等发展机器学习结合的大尺度精确原子尺度计算方法, 研究了类地行星内部铁流体的离子输运性质; 高城和吴建华等利用精确的多组态 Dirac-Fock方法, 计算了局域热平衡 Sn等离子体 EUV辐射不透明度, 有助于 EUV光刻光源的设计和研究; 李永强等综述了近年来利用动力学平均场方法, 开展光晶格超冷原子量子模拟的进展; 王伟权和银燕等利用粒子模拟方法, 结合机器学习, 获得了钻孔辐射压加速机制下离子峰值能量; 邹德滨等利用粒子模拟方法和蒙特卡罗方法, 研究了强激光作用超薄氘靶产生中子的过程. 在量子信息方面, 邹宏新等综述了中国空间站冷原子光钟激光系统研究进展, 该系统已于 2022年 10月 31日随“梦天”实验舱成功发射; 刘伟涛等综述了在室外环境中开展的关联成像中关于成像系统、信噪甄别技术和成像算法等方面的研究进展, 并浅析了未来发展方向; 江天等综述了典型的本征磁性拓扑绝缘体 MnBi2Te4的研究进展, 着重阐述了量子反常霍尔效应、轴子绝缘体态和马约拉纳零能模等拓扑量子态, 并展望了下一步研究方向; 杨俊波等归纳了几种目前最常用的片上光互连器件的智能设计方法, 并详细分析了智能化设计的片上光互连器件的几个重大研究进展与趋势; 刘肯和朱志宏等综述总结了近年来在异质集成二维材料光子器件中进行非线性光学特性研究的最新进展 (2023年第 17期已发表), 阐述了基于转移方法和直接生长法制备的优势和技术难点, 指明了发展趋势.
国防科技大学物理学科的发展始终与国防科技发展紧密相连, 始终秉持“面向国防科技前沿基础, 建设特色一流物理学科”的建设理念, 坚持前沿创新, 在培养一流人才的道路上继续前进.
2023, 72 (18): 184103.
doi: 10.7498/aps.72.20230702
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Laser-driven ion acceleration has potential applications in high energy density matter, ion beam-driven fast ignition, beam target neutron source, warm dense matter heating, etc. Ultrashort relativistic laser interacting with solid target can generate ion beam with several hundreds of MeV in energy, and the quality of the ion beam depends strongly on the interaction parameters between the laser and the target. Development in deep learning can provide new method of analyzing the relationship between parameters in physics system, which can significantly reduce the computational and experimental cost. In this paper, a continuous mapping model of ion peak and cutoff energy is developed based on a fully connected neural network (FCNN). In the model, the dataset is composed of nearly 400 sets of particle simulations of laser-driven solid targets, and the input parameters are laser intensity, target density, target thickness, and ion mass. The model uses sparse parameter values to obtain the analysis results in a large range of parameters, which greatly reduces the computational amount of multi-dimensional parameters sweeping in a wide range. Based on the results of this model mapping, the correction formula for the ion peak energy is obtained. Furthermore, the ratio of ion cutoff energy to peak energy of each set of particle simulation is calculated. Repeating the same training process of ion peak energy and cutoff energy, the continuous mapping model of energy ratio is developed. According to the energy ratio model mapping results, the quantitative description of the relationship between ion cutoff energy and peak energy is realized, and the fitting formula for the cutoff energy of the hole-boring radiation pressure acceleration (HB-RPA) mechanism is obtained, which can provide an important reference for designing the laser-driven ion acceleration experiments.
2023, 72 (18): 185201.
doi: 10.7498/aps.72.20230706
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Neutron production via D(d, n)3He nuclear reaction during the interaction of two counter-propagating circularly polarized laser pulses with ultra-thin deuterium target is investigated by particle-in-cell simulation and Monte Carlo method. It is found that the rotation direction and initial relative phase difference of laser electric field vector have important effects on deuterium foil compression and neutron characteristics. The reason is attributed to the net light pressure and the difference in transverse instability development. The highest neutron yield can be obtained by choosing two laser pulses with a relative phase difference of 0 and the same rotation direction of the electric field vector. When the relative phase difference is 0.5π or 1.5π and the rotation direction of electric field vector is different, the neutrons have a directional spatial distribution and the neutron yield only slightly decreases. For left-handed circularly polarized laser pulse and right-handed circularly polarized laser pulse, each with an intensity of 1.23 × 1021 W/cm2, a pulse width of 33 fs and a relative phase difference of 0.5π, it is possible to produce a pulsed neutron source with a yield of 8.5 × 104 n, production rate of 1.2 × 1019 n/s, pulse width of 23 fs and good forward direction as well as tunable spatial distribution. Comparing with photonuclear neutron source and beam target neutron source driven by ultraintense laser pulses, the duration of neutron source in our scheme decreases significantly, thereby possessing many potential applications such as neutron nuclear data measurement. Our scheme offers a possible method to obtain a compact neutron source with short pulse width, high production rate and good forward direction.
2023, 72 (18): 187101.
doi: 10.7498/aps.72.20230704
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The interaction between non-trivial topological states and the magnetic order of intrinsic magnetic topological insulators gives rise to various exotic physical properties, including the quantum anomalous Hall effect and axion insulator. These materials possess great potential applications in low-power topological spintronic devices and topological quantum computation. Since the first intrinsic magnetic topological insulator, MnBi2Te4, was discovered in 2019, this material system has received significant attention from researchers and sparked a research boom. This paper begins with discussing the fundamental properties of MnBi2Te4 and then turns to important research findings related to this intrinsic magnetic topological insulator. Specifically, it focuses on the quantum anomalous Hall effect, axion insulating state, and Majorana zero energy mode exhibited by the MnBi2Te4 series. Furthermore, this paper highlights other research directions and current challenges associated with this material system. Finally, this paper provides a summary and outlook for future research on MnBi2Te4, aiming to offer valuable references for researchers in related fields.
2023, 72 (18): 183701.
doi: 10.7498/aps.72.20230701
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With the development of atomic cooling technology and optical lattice technology, the quantum system composed of optical lattice and ultracold atomic gas has become a powerful tool for quantum simulation. The purity and highly controllable nature of the optical lattice give it a strong regulatory capability. Therefore, more complex and interesting physical phenomena can be simulated, which deepens the understanding of quantum many-body physics. In recent years, we have studied different Bose systems with strong correlations in optical lattice based on the bosonic dynamical mean-field theory, including multi-component system, high- orbit bosonic system, and long-range interaction system. In this review, we introduce the research progress of the above mentioned. Through the calculation by using bosonic dynamical mean-field theory which has been generalized to multi-component and real space versions, a variety of physical phenomena of optical crystal lattice Bose system in weak interaction intervals to strong interaction intervals can be simulated. The phase diagram of spin-1 ultracold bosons in a cubic optical lattice at zero temperature and finite temperature are drawn. A spin-singlet condensate phase is found, and it is observed that the superfluid can be heated into a Mott insulator with even (odd) filling through the first (second) phase transition. In the presence of a magnetic field, the ground state degeneracy is broken, and there are very rich quantum phases in the system, such as nematic phase, ferromagnetic phase, spin-singlet insulating phase, polar superfluid, and broken-axisymmetry superfluid. In addition, multistep condensations are also observed. Further, we calculate the zero-temperature phase diagram of the mixed system of spin-1 alkali metal atoms and spin-0 alkali earth metal atoms, and find that the system exhibits a non-zero magnetic ordering, which shows a second-order Mott insulation-superfluid phase transition when the filling number is $n=1$ , and a first-order Mott insulation-superfluid phase transition when the filling number is $n=2$ . The two-step Mott-insulating-superfluid phase transition due to mass imbalance is also observed. In the study of long-range interactions, we first use Rydberg atoms to find two distinctive types of supersolids, and then realize the superradiant phase coupled to different orbits by controlling the reflection of the pump laser in the system coupled to the high-finesse cavity. Finally, we study the high-orbit Bose system. We propose a new mechanism of spin angular-momentum coupling with spinor atomic Bosons based on many-body correlation and spontaneous symmetry breaking in a two-dimensional optical lattice, and then study the orbital frustration in a hexagonal lattice. We find that the interaction between orbital frustration and the strong interaction results in exotic Mott and superfluid phases with spin-orbital intertwined orders.
2023, 72 (18): 183301.
doi: 10.7498/aps.72.20231245
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Image, as a method of information acquisition, is indispensable for human beings, and it plays an irreplaceable role in military and civilian fields, such as detection and scouting, precision guidance, transportation, and industrial production. In the outdoor environment, the resolution, signal-to-noise ratio, and working distance of optical imaging are limited as result of the influence of background light, stray light, and atmospheric medium. In recent years, with the development of muti-discipline such as optics, physics, information theory, and computer science, the new optical imaging technologies continue to emerge, thus bringing new opportunities for outdoor optical imaging towards long-distance, large field of view and high information flux. As one of the new active imaging technologies, correlation imaging has the potential applications of robustness against turbulence and noise, and the possibility of beating the Rayleigh limit. It can deal with the problems better, such as sharp attenuation of optical power caused by long distances, detection of interference signals from environmental noise, and influence of turbulence. Based on the principle of optical imaging, this paper analyzes the factors affecting optical imaging, in terms of resolution, signal-to-noise ratio, spatial bandwidth product, and imaging distance under outdoor environment, focusing on the research progress of outdoor correlation imaging including imaging systems, signal-to-noise screening technology and imaging algorithm. In addition, we analyze the requirements of optical imaging for longer distances and broader field of view, and consider the fundamental problems and the key technologies.
2023, 72 (18): 187901.
doi: 10.7498/aps.72.20230699
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We study experimentally the three-body Coulomb explosion dynamics of carbon dioxide dimer ${\rm{(CO_2)}}_{2}^{4+}$ ions produced by intense femtosecond laser field. The three-dimensional momentum vectors as well as kinetic energy are measured for the correlated fragmental ions in a cold-target recoil-ion momentum spectrometer (COLTRIMS). Carbon dioxide dimer is produced during the supersonic expansion of ${\rm{(CO_2)_2}}$ gas from a 30 μm nozzle with 10 bar backing pressure. The linearly polarized laser pulses with a pulse duration (full width at half maximum of the peak intensity) of 25 fs, a central wavelength of 790 nm, a repetition rate of 10 kHz, and peak laser intensities on the order of ${\rm{8 \times10^{14}}}\;{\rm{W/cm^2}}$ are produced by a femtosecond Ti:sapphire multipass amplification system. We concentrate on the three-particle breakup channel ${\rm{(CO_2)_2^{4+}}} \rightarrow {\rm{CO}}_{2}^{2+}+{\rm{CO^+}}+ {\rm{O^+}}$ . The two-particle breakup channels, ${\rm{(CO_2)_2^{4+}}} \rightarrow {\rm{CO}}_{2}^{2+}+ {\rm{CO_{2}}^{2+}}$ and ${\rm{CO_2^{2+}}\rightarrow CO^++O^+}$ , are selected as well for reference. The fragmental ions are guided by a homogenous electric field of 60 V/cm toward microchannel plates position-sensitive detector. The time of flight (TOF) and position of the fragmental ions are recorded to reconstruct their three-dimensional momenta. By designing some constraints to filter the experimental data, we select the data from different dissociative channels. The results demonstrate that the three-body Coulomb explosion of ${\rm{(CO_2)}}_{2}^{4+}$ ions break into ${\rm{CO}}_{2}^{2+}+{\rm{CO}}^++{\rm{O}}^+$ through two mechanisms: sequential fragmentation and non-sequential fragmentation, in which the sequential fragmentation channel is dominant. These three fragmental ions are produced almost instantaneously in a single dynamic process for the non-sequential fragmentation channel but stepwise for the sequential fragmentation. In the first step, the weak van der Waals bond breaks, ${\rm{(CO_2)}}_{2}^{4+}$ dissociates into two ${\rm{CO}}_{2}^{2+}$ ions; and then one of the C=O covalent bonds of ${\rm{CO}}_{2}^{2+}$ breaks up, the ${\rm{CO}}_{2}^{2+}$ ion breaks into ${\rm{CO^+}}$ and ${\rm{O^+}}$ . The time interval between the two steps is longer than the rotational period of the intermediate ${\rm{CO}}_{2}^{2+}$ ions, which is demonstrated by the circle structure exhibited in the Newton diagram. We find that the sequential fragmentation channel plays a dominant role in the three-body Coulomb explosion of ${\rm{(CO_2)}}_{2}^{4+}$ ions in comparison of the event ratio of the two fragmentation channels.
2023, 72 (18): 184202.
doi: 10.7498/aps.72.20230412
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The world's first space optical clock (SOC) developed in China, which is composed of five subsystems, i.e. an optical unit, a physics unit, an electronic control unit, a space optical frequency comb, and an ultrastable laser, was successfully launched with the Mengtian space laboratory on October 31, 2022, and entered into the China Space Station (CSS). Compact and stable laser is a key element for the operation of the SOC. The optical unit consists of 5 lasers with wavelengths of 461, 679, 689, 707 and 813 nm, respectively. With a synchronous-tuning-like scheme, high-quality external cavity diode lasers (ECDLs) are developed as the seeds. The linewidths of the lasers are all reduced to approximately 100 kHz, and their tuning ranges, free from mode hopping, are capable of reaching 20 GHz, satisfying the requirements for the SOC. With careful mechanical and thermal design, the stability of the laser against vibration and temperature fluctuation is sufficiently promoted to confront the challenge of rocket launching. While the power from the ECDL is sufficient for 679-nm repump laser and 707-nm repump laser, additional injection lock is utilized for the 461-nm laser and 689-nm laser to amplify the power of the seeds to more than 600 mW, so that effective first and second stage Doppler cooling can be achieved. To generate an optical lattice with deep enough potential well, over 800-mW 813-nm lasers are required. Therefore, a semiconductor tapered amplifier is adopted to amplify the seed to more than 2 W, so as to cope with various losses of the coupling optics. The wavelengths and output power values of the 5 lasers are monitored and feedback is controlled by the electronic control unit. All the modules are designed and prepared as orbital replaceable units, which can be easily replaced by astronauts in case failure occurs. Now the lasers are all turned on and operate normally in CSS. More data of the SOC will be obtained in the near future. At present stage, according to our evaluation, the continuous operation time of the SOC is limited by the injection locked lasers, which are relatively vulnerable to mode hopping. Hopefully, this problem can be solved by improving the laser diode preparing technology, or developing fiber lasers with compact frequency conversion modules.
2023, 72 (18): 184204.
doi: 10.7498/aps.72.20230705
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2023, 72 (18): 187102.
doi: 10.7498/aps.72.20231258
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Liquid iron is the major component of planetary cores. Its structure and dynamics under high pressure and temperature is of great significance in studying geophysics and planetary science. However, for experimental techniques, it is still difficult to generate and probe such a state of matter under extreme conditions, while for theoretical method like molecular dynamics simulation, the reliable estimation of dynamic properties requires both large simulation size and ab initio accuracy, resulting in unaffordable computational costs for traditional method. Owing to the technical limitation, the understanding of such matters remains limited. In this work, combining molecular dynamics simulation, we establish a neural network potential energy surface model to study the static and dynamic properties of liquid iron at its extreme thermodynamic state close to core-mantle boundary. The implementation of deep neural network extends the simulation scales from one hundred atoms to millions of atoms within quantum accuracy. The estimated static and dynamic structure factor show good consistency with all available X-ray diffraction and inelastic X-ray scattering experimental observations, while the empirical potential based on embedding-atom-method fails to give a unified description of liquid iron across a wide range of thermodynamic conditions. We also demonstrate that the transport property like diffusion coefficient exhibits a strong size effect, which requires more than at least ten thousands of atoms to give a converged value. Our results show that the combination of deep learning technology and molecular modelling provides a way to describe matter realistically under extreme conditions.
2023, 72 (18): 183101.
doi: 10.7498/aps.72.20230455
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Sn is the material for an extreme ultraviolet (EUV) light source working at 13.5 nm, therefore the radiative properties of Sn plasma are of great importance in designing light source. The radiative opacity and emissivity of Sn plasma at local thermodynamic equilibrium are investigated by using a detailed-level-accounting model. In order to obtain precise atomic data, a multi-configuration Dirac-Fock method is used to calculate energy levels and oscillator strengths of ${\rm{Sn}}^{6+}$ -${\rm{Sn}}^{14+}$ . The electronic correlation effects of $4{\rm d}^m\text{-}4{\rm f}^m$ ($m=1, 2, 3, 4$ ) and $ 4\mathrm{p}^n\text{-}4\mathrm{d}^n $ ($n=1, 2, 3$ ) are mainly considered, which dominate the radiation near 13.5 nm. The number of fine-structure levels reaches about 200000 for each ionization stage in the present large-scale configuration interaction calculations. For the large oscillator strengths (> 0.01), the length form is in accord with the velocity form and their relative difference is about 20%–30%. The calculated transmission spectra of Sn plasma at 30 eV and 0.01 g/cm3 are compared with the experimental result, respectively, showing that they have both good consistency. The radiative opacity and emissivity of Sn plasma at the temperature in a range of 16–30 eV and density in a scope of of 0.0001–0.1 g/cm3 are investigated systematically. The effects of the plasma temperature and plasma density on radiation characteristics are studied. The results show that the radiative properties near 13.5 nm are broadened with the increase of density at a specific temperature, while it is narrowed with the increase of temperature for a specific density. The present investigation should be helpful in designing and studying EUV light source in the future.
2023, 72 (17): 174202.
doi: 10.7498/aps.72.20230729
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Photonic platforms with excellent nonlinear optical characteristics are very important to improve the devices' performance parameters such as integration, modulation speeds and working bandwidths for all-optical signal processing. The traditional processing technology of photonic platforms based on silicon, silicon nitride and silicon oxide is mature, but the nonlinear function of these optical platforms is limited due to the characteristics of materials; Although two-dimensional (2D) materials possess excellent nonlinear optical properties, their nonlinear potentials cannot be fully utilized because of their atomic layer thickness. Integrating 2D materials with mature photonic platforms can significantly improve the interaction between light and matter, give full play to the potentials of 2D materials in the field of nonlinear optics, and improve the nonlinear optical performances of the integrated platforms on the basis of fully utilizing the mature processing technology of the photonic platforms. Based on the above ideas, starting from the basic principle of nonlinear optics (Section 2), this review combs the research progress of various nonlinear photonic platforms (resonators, metasurfaces, optical fibers, on-chip waveguides, etc.) heterogeneously integrated with 2D materials, realized by traditional transfer methods (Section 3) and emerging direct-growth methods (Section 4) in recent years, and the introduction is divided into second-order and third-order nonlinearity. Comparing with the transfer methods, the advantages of using direct-growth methods to realize the heterogeneous integration of 2D materials and photonic platforms for the study of nonlinear optics are expounded, and the technical difficulties to be overcome in preparing the actual devices are also pointed. In the future, we can try to grow 2D materials directly onto the surfaces of various cavities to study the enhancement of second-order nonlinearity; we can also try to grow 2D materials directly onto the on-chip waveguides or microrings to study the enhancement of third-order nonlinearity. Generally speaking, the research on integrated nonlinearity by directly growing 2D materials onto various photonic structures has aroused great interest of researchers in this field. As time goes on, breakthrough progress will be made in this field, and technical problems such as continuous growth of high-quality 2D materials onto photonic structures and wafer-level large-scale preparation will be broken through, further improving the performance parameters of chips and laying a good foundation for optical communication, signal processing, optical sensing, all-optical computing, quantum technology and so on.
2023, 72 (21): 214207.
doi: 10.7498/aps.72.20231242
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As a kind of quantum phenomenon, Hong-Ou-Mandel (HOM) interference is more robust against phase noise. Because of this feature, robust quantum holography emerges, through which wave function of interested photon can be retrieved according to HOM interference pattern. For better understanding and developing this method, we derive a theoretical framework of robust HOM holography. In the quantum holography scheme, test state and reference state interfere at beam splitter (BS). Then, degree of freedom (DOF) resolved detections (such as spatial resolved detection, temporal resolved detection or spectrum resolved detection) are used at the BS output ports, respectively. Based on the single photon detection results, the DOF resolved coincidence counts are postselected, producing interference patterns. The information of the test states is retrieved from the patterns. According to different test states and reference states, four combinations are analysed, including measuring the wave function of single photon state by using standard single photon state or coherent state and measuring the wave function of coherent state through using standard single photon state or coherent state. In all cases, information of the test states is reflected in normalized second-order correlation function or interference patterns in similar forms. Specially, the wave function of test states can be directly retrieved from the interference patterns, with no complex algorithm required. Besides, phase noise from environment has no influence on this kind quantum holography. Comparison between traditional holography and quantum holography is made and analysed.
