激光惯性约束聚变中光学汤姆逊散射研究进展

当前,激光惯性约束聚变在越来越接近点火的极端能量密度条件下,实验与模拟的偏离逐渐增大,一个关键原因是缺乏对黑腔等离子体状态及其影响黑腔能量学和内爆对称性的细致研究和判断。光学汤姆逊散射主动式、诊断精确、参数完备的优点,使之成为激光惯性约束聚变黑腔等离子体状态参数精密诊断的标准方法。中国面向激光惯性约束聚变研究的光学汤姆逊散射实验技术的发展与神光系列激光装置的建设和在其上开展的物理实验紧密相关。近年来,四倍频汤姆逊散射实验技术在神光III原型和100 kJ激光装置上相继建立,部分实验结果不仅加深了对激光惯性约束聚变靶物理的认识,还反映了实验条件对汤姆逊散射诊断的影响,促进了实验技术的精密化发展。在未来,还需要进一步发展多支路汤姆逊散射、五倍频汤姆逊散射和超热相干汤姆逊散射等新技术,面向点火黑腔条件,大幅提升激光等离子体状态参数的诊断精度,开展新物理机制的探索和研究,在激光惯性约束聚变和其他高能量密度物理科学领域发挥更重要的作用。     

THz波的产生及探测技术

THz技术是20世纪90年代发展起来的一门新兴学科,本文较为详细地介绍了目前产生THz波的主要方法、原理以及探测THz波的主要手段和机理.     

Optical properties in a two-dimensional quantum ring: Confinement potential and Aharonov-Bohm effect

Optical properties of a two-dimensional quantum ring with pseudopotential in the presence of an external magnetic field and magnetic flux have been theoretically investigated. Our results show that both of the pseudopotential and magnetic field can affect the third non-linear susceptibility and oscillator strength. In addition, we found that the oscillator strength and the absolute value of the resonant peak of the linear, non-linear and total absorption coefficient demonstrates the Aharonov-Bohm oscillation with magnetic flux, moreover, changes in confinement potential can influence the Aharonov-Bohm oscillation in peak while the resonant peak value of the linear, non-linear and total refractive index changes decreases as magnetic flux increases.     

用于生物单分子操纵的磁镊技术

镊是近年发展起来的一种用于生命科学研究领域的微操纵技术.简要介绍了所搭建的磁镊装置及利用2.8μm直径的磁珠进行的操纵实验;利用一种搜索算法分析所记录的磁珠运动视频,得出磁珠的运动轨迹和运动速度,并与理论分析相验证.研究结果表明该磁镊装置具有一定的实用性.     

High-pressure phases of hydrogen cyanide: formation of hydrogenated carbon nitride polymers and layers and their electronic properties

We have performed a set of first-principles simulations to consider the possible phase transitions in molecular crystals of HCN under high pressure. Our calculations reveal several transition paths from the orthorhombic phase to tetragonal and then to triclinic phases. The transitions from the orthorhombic to the tetragonal phases are of the second order, whereas those from the tetragonal to the triclinic phases turn out to be of the first-order type and characterized by an abrupt decrease in volume. Our calculations show that, by adjustment of the temperature and pressure of the HCN molecular crystal, novel layered and polymeric crystals with insulating, semiconducting or metallic properties can be found. Based on our simulation results, two different crystal formation mechanisms are deduced. The stabilities of the predicted structures at ambient pressure are further assessed by performing phonon or MD simulations. In addition, the electron transport properties of the predicted polymers are obtained using the non-equilibrium Green's function technique combined with density functional theory. The results show that the polymers have metallic-like I-V characteristics.     

Experimental implementation of a fixed-point duality quantum search algorithm in the nuclear magnetic resonance quantum system

In this work, we demonstrated a fixed-point quantum search algorithm in the nuclear magnetic resonance (NMR) system. We constructed the pulse sequences for the pivotal operations in the quantum search protocol. The experimental results agree well with the theoretical predictions. The generalization of the scheme to the arbitrary number of qubits has also been given.     

Digital pulse shape discrimination methods for n-γ separation in an EJ-301 liquid scintillation detector

A digital pulse shape discrimination system based on a programmable module NI-5772 has been established and tested with an EJ-301 liquid scintillation detector. The module was operated by running programs developed in Lab VIEW, with a sampling frequency up to 1.6 GS/s. Standard gamma sources22 Na,137Cs and60 Co were used to calibrate the EJ-301 liquid scintillation detector, and the gamma response function was obtained. Digital algorithms for the charge comparison method and zero-crossing method have been developed. The experimental results show that both digital signal processing(DSP) algorithms can discriminate neutrons from γ-rays. Moreover,the zero-crossing method shows better n-γ discrimination at 80 ke Vee and lower, whereas the charge comparison method gives better results at higher thresholds. In addition, the figure-of-merit(FOM) for detectors of two different dimensions were extracted at 9 energy thresholds, and it was found that the smaller detector presented better n-γseparation for fission neutrons.     

The geometric phase of the quantum systems with slow but finite rate of the external time-dependent field

With the help of the time-dependent gauge transformation technique, we have studied the geometric phase of a spin-half particle in a rotating magnetic field. We have found that the slow but finite frequency of the rotating magnetic field will make the difference between the adiabatic geometric phase and the exact geometric phase. When the frequency is much smaller than the energy space and the adiabatic condition is perfectly guaranteed, the adiabatic approximation geometric phase is exactly consistent with the adiabatic geometric phase. A simple relation for the accuracy of the adiabatic approximation is given in terms of the changing rate of the frequency of the rotating magnetic field and the energy level space.     

Tunable supercurrent through a double Aharonov–Bohm interferometer

The supercurrent through a double Aharonov–Bohm interferometer formed by parallel-coupled four quantum dots is investigated theoretically. The possibility of controlling the supercurrent of the system is explored by tuning the interdot coupling, dot energy levels, and magnetic flux treading the ring connecting dots and leads. Whether the supercurrent sign can be changed depends not only on the magnetic flux but also on the quantum dot energy levels. By tuning the quantum dot energy levels, the behavior of the supercurrent shows swap effects, which might be used to design a qubit. It is also found that the oscillation period of the supercurrent with respect to the magnetic flux depends on the ratio of the two parts fluxes.     

Construction of the elliptic Gaudin system based on Lie algebra

Gaudin model is a very important integrable model in both quantum field theory and condensed matter physics. The integrability of Gaudin models is related to classical r-matrices of simple Lie algebras and semi-simple Lie algebra. Since most of the constructions of Gaudin models works concerned mainly on rational and trigonometric Gaudin algebras or just in a particular Lie algebra as an alternative to the matrix entry calculations often presented, in this paper we give our calculations in terms of a basis of the typical Lie algebra, A _n , B _n , C _n , D _n , and we calculate a classical r-matrix for the elliptic Gaudin system with spin.