高激发态原子的相干效应

本文以高激发态原子为研究对象, 由基态、激发态和高激发态能级形成阶梯型三能级系统, 理论上求解阶梯型三能级系统的密度矩阵方程, 研究了高激发态原子的相干效应, 计算获得探测光的吸收和色散曲线. 并研究了高激发态原子间相互作用以及外加电场对相干效应的影响. 结果表明, 外加场可以使吸收和色散曲线产生频移.     

Electromagnetically induced transparency of single Λ-type three-level atom in high-finesse optical cavity

We study the features of the electromagnetically induced transparency (EIT) in a single Λ-type three-level atom placed in a high finesse cavity under the action of a coupling laser and a probe laser. Our calculations show that three transparency windows appear when the pump strength is big enough. It can be explained by the residual pump in the cavity resulting mostly in the energy splitting. Level |3〉is split into four slightly different energy levels. An interference takes place between excitation pathways. Furthermore, it is also shown that the frequencies of the EIT windows can be tuned by changing the coupling field detuning Δ₂ and the reflection profile is very sensitive to the cavity field detuning Δ_c.     

Mechanical effects of light on the Ξ-type three-level atom in a high-finesse optical cavity

A theoretical study is carried out for the modification and implication of the effect on the Ξ-type three level atom in a high-finesse optical cavity driven by light field including spontaneous emission and the cavity decay. Analytic expressions for the dipole force, the friction force, the optical potentials and the friction coefficient are obtained. Then the numerical and graphical methods are used to investigate the friction coefficient with the controlling parameters. It is shown that the friction coefficient is strongly dependent on the controlling parameters. The cooling rate can increase by one order of magnitude more than that of a two-level atomic system. The reason can be given using the dressed states and the Sisyphus cooling mechanism, which would stimulate further experimental investigations.     

压缩真空中梯形三能级原子的辐射压力

研究了压缩真空中梯形三能级原子在单色行波场中的辐射压力。从系统的哈密顿量出发,利用玻因-马尔可夫近似,推导出了原子的光学布洛赫方程。此时用数值方法求得布洛赫方程的稳态解,然后用图示法考察了原子的辐射压力随双光子失谐、拉比频率、自发发射率等参量的依赖关系。结果表明：单光子跃迁和双光子跃迁可导致辐射压力出现各自的多普勒位移共振峰;辐射压力表现出较宽的失谐范围且强烈依赖于压缩参量以及压缩真空和相干光之间的相位关系。当相位满足匹配条件时,辐射压力减小。     

Ladder π‐Conjugated Materials Containing Main‐Group Elements

Ladder π‐conjugated compounds, which have fully ring‐fused polycyclic skeletons, are an important class of materials possessing significant potentials for application in organic electronics. The incorporation of main‐group elements, such as B, Si, P, S, and Se, into the ladder skeletons as bridging moieties is a powerful strategy to endow unusual electronic structures as well as suitable molecular arrangements in the solid state, giving rise to attractive photophysical and electronic properties. Recent efforts have produced a number of fascinating ladder materials, some of which indeed showed high performance as light‐emitting materials and charge carrier transporting materials. This Focus Review is an overview of the progress in this chemistry, focusing on several important π‐conjugated skeletons.     

Interplay between spin frustration and magnetism in the exactly solved two-leg mixed spin ladder

We study a mixed spin-(3/2,1) ladder system with antiferromagnetic rung coupling and next-nearest-neighbor interaction.The exactly solved Ising-chain model is employed to investigate the ground-state properties and thermodynamics of the low-dimensional ladder system.Our results show that the competition between different exchange couplings brings in a large variety of ground states characterized by various values of normalized magnetization equal to 0,1/5,2/5,3/5,1.Moreover,an interesting double-peak structure is also detected in the thermal dependence of magnetic susceptibility and specific heat when the frustration comes into play.It is shown that the double-peak phenomenon at zero-field for the case of AF_2 ground-state arises from the very strong antiferromagnetic rung coupling,while other cases are attributed to the excitations induced by temperature and external field around the phase boundary.     

超冷铯Rydberg原子的Autler-Townes分裂

主要研究超冷铯Rydberg原子阶梯型三能级系统的Autler-Townes(A-T)分裂.铯原子基态6S_(1/2)、第一激发态6P_(3/2)和Rydberg态形成阶梯型三能级系统,强耦合光共振作用于6P_(3/2)(F′=5)→34D_(5/2)的跃迁,探测光由偏振光谱锁定在6S_(1/2)(F=4)→6P_(3/2)(F′=5)的跃迁,并由双通的声光调制器在其共振跃迁附近扫描,形成的Rydberg原子A-T分裂谱由单光子计数器探测.A-T光谱的双峰间距与耦合光的拉比频率成正比,实验结果与理论计算在耦合光拉比频率Ω_c2π×9 MHz时符合得很好,在拉比频率Ω_c2π×9 MHz时,测量的A-T分裂比理论计算值小13%.产生偏差的主要原因是由于较大的耦合光拉比频率Ω_c增加了激发的Rydberg原子数,Rydberg原子间的相互作用产生了较大的退相干率所致.     

双波段多级低噪放的匹配设计与仿真

针对双波段低噪声放大电路设计存在的多级匹配问题,提出一种解决双波段多级低噪放匹配的方法.首先根据每一级低噪放指标要求设置优化参数,找到输入输出最佳阻抗值,然后用串联微带线和并联微带枝节将双波段LNA的每一级输入输出阻抗值匹配到50,最后将其级联,从而实现了双波段三级LNA的设计.仿真结果表明:该低噪声放大器在2.69 GHz和3.5 GHz频点处匹配良好,噪声系数小于1 d B,S11和S22都小于-20 d B,增益大于40 d B,从而能同时传输2个非同步信号,提高了频谱利用率,并减少了带外噪声干扰.     

磁性和非磁性元素掺杂的自旋梯状化合物Sr_(14)(Cu_(0.97)M_(0.03))_(24)O_(41)(M=Zn,Ni,Co)的结构和电输运性质

利用固相反应法制备了Sr14Cu24O41及其系列B位掺杂Sr14(Cu0.97M0.03)24O41(M=Zn,Ni,Co)的样品.X射线衍射分析显示,所有样品均为纯相,晶格常数a与c没有明显的变化;Zn掺杂样品晶格常数b没有明显变化,而Ni,Co掺杂样品晶格常数b分别稍有增加.选区电子衍射研究揭示:磁性元素Ni,Co及非磁性元素Zn掺杂,可能主要替代了Sr14Cu24O41结构中自旋链上的Cu原子,从而影响了自旋链上的dimer排列,破坏电荷有序超结构.电输运测量显示:Zn2+,Ni2+,Co3+离子掺杂样品的电阻率降低,但仍体现半导体行为,所有的掺杂样品都存在一个渡越温度Tρ,当TTρ时,其导电机理是以单空穴热激发导电占主要地位,在TTρ时,配对的局域化空穴的一维变程跳跃导电占主要优势;在相同的掺杂量下,非磁性元素Zn掺杂对电阻率值的影响大于磁性元素Ni,Co掺杂的影响,而磁性元素Ni,Co掺杂对渡越温度Tρ的影响大于非磁性元素Zn掺杂的影响.     

双模SU(2)相干态场与一个A型三能级原子共振相互作用的光场非经典性质

采用全量子理论和数值计算方法,研究了初始处于SU(2)相干态的双模腔场与一个A型三能级原子共振相互作用的光场非经典性质,讨论了在没有对原子进行态选择测量、直接对原子进行态选择测量和应用经典微波场并对原子进行态选择测量的三种情况下,两个腔模总光子数、配分参量和耦合系数对光场非经典性质的影响.结果表明,增加两个腔模的总光子数M或对原子进行态选择测量,双模差压缩明显增强;减小配分参量和应用经典场并对原子进行态选择测量,α模光子的亚Poisson统计分布的平均程度变浅,而b模变深;两模间的反相关特征保持不变,增加M或直接对原子进行态选择测量,反相关平均程度变浅;直接对原子进行态选择测量,违背CauchySchwartz不等式.

Abstract：

Nonclassical properties of a two-mode field initially in an SU(2)coherent state resonantly interacting with a threelevel A-type atom are investigated by means of the quantum theory and numerical calculations.The dependence of the nonclassical properties on the total photon number of the two-mode,the partition parameter and the coupling constant is discussed for three cases:(1)no state-selective atomic measurement;(2)direct state-selective atomic measurement;and (3)state-selective atomic measurement after the application of a classical field.The results indicate that when the total photon number of the two-mode is increased or the state-selective measurement is performed on the atom,the difference squeezing of two-mode is distinctly enhanced;and when the partition parameter is decreased or the state-selective measurement is performed on the atom after the application of a classical field,the average intensity of the sub-Poisson statistic distribution of mode a is reduced and that of mode b is enhanced;when the total photon number of the two modes is increased or the direct state-selective measurement is performed on the atom,the anti-correlation character between the two modes is preserved,but the average intensity of the anti-correlation is reduced;and when the direct state-selective measurement is performed on the atom,the Cauchy-Schwartz inequality is violated.