Y型四能级中的双电磁感应透明和超窄吸收

采用密度矩阵方程．对双光场耦合的分子Y型四能级系统的粒子数分布和吸收特性进行了计算和分析,在此能级系统中得到了双暗态共振和双电磁感应透明．并讨论了相应的物理机制。同时,我们讨论了Y型四能级两个上能级的自发辐射产生的量子干涉效应对电磁感应透明的影响,发现自发辐射干涉相消可以产生超窄线宽和导致探测光的吸收增强,自发辐射干涉相长可以展宽谱线和减弱探测光的吸收,并运用缀饰态理论对以上计算结果进行分析,与采用密度矩阵方程的计算结果一致。     

基于碰撞产生的频域和时域内的量子干涉效应研究

从理论和实验两方面对以往较少涉及的原子-分子混合体系中基于碰撞而产生间距较大多能级间的相干和两延时波包间的相干及量子干涉效应进行研究,揭示通过碰撞这种非相干过程可产生在频域内具有较大能级间距多能级间的相干和时域内两延时波包间的相干.运用半经典密度矩阵理论及缀释态理论对碰撞产生的多能级系统量子干涉效应进行计算和分析;同时实验上用ns脉冲染料激光器观察到钠原子-分子混合体系中基于等频双光子两步激发及钠原子-分子混合激发而产生的钠原子3S-3P(1/2,3/2)-5S(或4D)系统基于碰撞产生的频域和时域内的量子干涉效应.本工作为进一步运用非相干碰撞过程研究较大间距多能级间和两延时波包间的相干提供了一种新的有效的方法,可望在高灵敏高精度激光光谱、原子分子激发态结构信息及物理化学过程的控制等方面具有广泛的应用.     

准Λ型四能级系统中的超窄谱线的研究

在一般Λ型三能级模型的基础上提出准Λ型四能级系统,并对准Λ型四能级模型的共振荧光谱作了详尽的研究.从上能级向两边下能级辐射的自发辐射谱中产生了三个超窄谱线,且在很大参数范围内光谱具有这一特性.三个超窄谱线的产生是和两个相干驱动场的Rabi频率密切相关,在较大的Rabi频率作用下谱线会变得更窄,而当只有一个驱动场作用时是不会产生谱线变窄效应的.能级间的碰撞弛豫和非相干激发严重地破坏了谱线变窄.这种超窄谱线效应是多通道量子干涉的结果 关键词： 准Λ型四能级系统 超窄谱线 多通道量子干涉     

压缩真空中的三能级原子的自发辐射

对压缩真空与Ｖ型三能级原子的相互作用作了理论分析,探讨了量子干涉效应对压缩真空中原子自发辐射的影响。当原子的上能级简并时强的量子干涉效应影响原子的定态和定态出射光谱,使它们对原子的初态敏感。这种情况下,压缩使谱线趋于关于压缩真空中心频率对称,量子干涉使谱线趋于不对称。     

基于腔QED系统的几何量子失谐及其传送

研究了基于腔量子电动力学（腔QED）系统的几何量子失谐及其传送。该系统包括两个独立的子系统，每个子系统由两个二能级原子与单模腔共振相互作用。结果表明，所有初始存储在原子A1A2中的几何量子失谐最终被转移到原子B1B2和腔C1C2。同时，原子A1A2 ，B1B2和腔C1C2的几何量子失谐在该量子系统中可以发生猝死（DSD）以及纠缠突然死亡（ESD）。但是，在该量子系统中几何量子失谐不能完全由于原子的自发辐射和腔衰减而复活。此外，原子A1A2 ，B1B2和腔C1C2几何量子失谐的量，取决于其纯度p，并与其成比例，p的值越小，几何失谐越小。它也表明，在原子自发辐射和腔衰减的情况下，原子A1A2 ，B1B2和腔C1C2的几何量子失谐将经历振荡衰减并最终衰减到零。不过，在没有原子自发辐射和腔衰减的情况下，原子A1A2 ，B1B2和腔C1C2的几何量子失谐却没有衰减。     

基于腔QED系统的几何量子失谐及其传送

研究了基于腔量子电动力学（腔QED）系统的几何量子失谐及其传送。该系统包括两个独立的子系统，每个子系统由两个二能级原子与单模腔共振相互作用。结果表明，所有初始存储在原子A1A2中的几何量子失谐最终被转移到原子B1B2和腔C1C2。同时，原子A1A2 ，B1B2和腔C1C2的几何量子失谐在该量子系统中可以发生猝死（DSD）以及纠缠突然死亡（ESD）。但是，在该量子系统中几何量子失谐不能完全由于原子的自发辐射和腔衰减而复活。此外，原子A1A2 ，B1B2和腔C1C2几何量子失谐的量，取决于其纯度p，并与其成比例，p的值越小，几何失谐越小。它也表明，在原子自发辐射和腔衰减的情况下，原子A1A2 ，B1B2和腔C1C2的几何量子失谐将经历振荡衰减并最终衰减到零。不过，在没有原子自发辐射和腔衰减的情况下，原子A1A2 ，B1B2和腔C1C2的几何量子失谐却没有衰减。     

低频强场作用下三维光子晶体中单个二能级原子的自发辐射

控制受激原子的自发辐射是当前量子光学领域的一个重要课题.现有的研究表明,原子不同跃迁通道之间的量子干涉导致了新的光学现象,如无粒子数反转光放大,光谱变化,自发辐射相消等.Evers和Keitel提出了一种非常有效的方法,相当大地降低了一个二能级系统中上能态布居数的衰减;在他们的方法中,一个相干的强的低频场作用于单个二能级原子,此场的频率低于原子跃迁的整个衰减宽度,产生了由上能级到下能级原子态的不同衰减通道,从而导致自发辐射的量子干涉,显著地抑制了自发辐射.另一方面:在光学和固体物理领域,光子晶体引起了人们很大的兴趣.     

基于自发辐射相干控制的电磁感应透明诱导无反转光放大效应

建立微波驱动基态精细结构跃迁的Λ型三能级系统,研究基于自发辐射相干控制的电磁感应透明诱导无反转光放大效应.微波场作用于基态精细结构能级之间,产生3个透明窗口,利用适当角度的自发辐射相干效应与电磁感应透明耦合,实现透明向光放大的转化.结果表明,透明转化为光放大时,激发态与基态能级之间以及两个基态能级之间均不出现粒子数反转,但在产生光放大的过程中必须经历两个基态能级出现粒子数反转的状态.调节微波场的频率失谐量可以改变基态能级上的粒子数分布,有利于无反转光放大的产生.     

空场诱导相干性对倒转Y型四能级原子系统中单光子和双光子吸收性质的影响

当倒转Y-型四能级原子的两基态能级邻近简并时，连接基态的两个跃迁路径与同一个真空场辐射场相互作用导致的量子干涉效应便产生了空场诱导相干性.空场诱导相干性能使倒转Y-型四能级原子在共振点的单光子和双光子电磁诱导透明现象减弱，而在其他失谐量处产生单光子增益现象。同时，外加相干光场的相对相位对原子的吸收性质有重要的影响.     

被三个耦合场驱动的四能级原子的电磁感应透明

研究了被三个耦合场驱动的四能级原子系统的自发辐射，通过计算自发辐射场对应的原子极化率，发现在某些特定参数下系统具有电磁感应透明的特性，同时发现电磁感应透明效应产生时，驱动场强度与自发辐射场处于相同量级. 关键词： 电磁感应透明 自发辐射 量子干涉     

Level structure of 159Lu

The high-spin states of 159Lu were populated by fusion-evaporation reaction 144Sm (19F, 4n) with beam energy 106 MeV. A new level scheme was established, which consists of the yrast band with negative parity, the octupole vibration band based on the states and quasipartical band with positive parity. The high spin states of 159Lu were discussed by systemic characteristics.     

Level structure of 146Tb

The level structure of the doubly odd nucleus ¹⁴⁶Tb has been studied via the ¹¹⁸Sn(³²S, 1p3n) reaction using techniques of in-beam -ray spectroscopy. Measurements of -ray anisotropies, X- and - -t coincidences were performed with 12 BGO(AC)HPGe detectors. Based on the measured results, the level scheme of ¹⁴⁶Tb has been revised significantly and extended up to an excitation energy of 8.39 MeV. The level structure has been interpreted qualitatively by coupling an h _11/2 proton-particle and an h _11/2 neutron-hole to the excited states in the ¹⁴⁶Gd core.Received: 3 July 2003, Published online: 26 November 2003PACS: 23.20.Lv transitions and level energies - 27.60. + j      

Level structure of 76As

The energy-level structure of ⁷⁶As has been studied by the ⁷⁵As(d, p) reaction with 12.0 MeV incident deuterons. Eighty-seven excited energy levels up to 2.5 MeV have been identified. The angular distributions for thirty-nine of the observed transitions are compared with distorted-wave Born approximation calculations. Angular momentum transfers are determined and spectroscopic strengths are deduced from the data. The results are compared with shell-model sum rules and with (d, p) results on N = 42 isotones. Possible spin values are assigned for some of the levels based on the present results, (n, γ), (p, n) and (p, nγ) studies.     

Level structure of106Mo

The level scheme of the very neutron rich nucleus ₁₀₆ ⁴² Mo₆₄ has been studied for the first time through theβ decay of¹⁰⁶Nb. Six new excited states were observed inγ singles andγ-γ coincidence experiments in addition to the 2⁺, 4⁺ and 6⁺ members of the ground state band. The excitation energies and the deexcitation pattern suggest the interpretation of the levels at 710, 885 and 956 keV as the 2 ₂ ⁺ , 3 ₁ ⁺ and 0 ₂ ⁺ states, respectively. The data support the assumption of a non-axial deformation of¹⁰⁶Mo. A half-life of (1.02±0.05) s has been determined for theβ decay of¹⁰⁶Nb.     

Level densities of heaviest nuclei

The intrinsic level densities of superheavy nuclei in the α-decay chains of ^296,298,300120 are calculated using the single-particle spectra obtained with the modified two-center shell model. The role of the shell and pairing effects on the level density as well as their quenching with excitation energy are studied. The extracted level density parameter is expressed as a function of mass number, ground-state shell correction, and excitation energy. The results are compared with the phenomenological values of level density parameters used to calculate the survival of excited heavy nuclei.     

Level structure of78Rb

The excited states of⁷⁸Rb have been investigated by means of in-beam andβ-γ spectroscopy. The production of⁷⁸Rb and theβ radioactivity of⁷⁸Sr have been made through the⁵⁴Fe(²⁸Si,3pn) and⁵⁴Fe(²⁸Si,2p2n) reactions, respectively. Four rotational bands have been observed in the high-spin band structure. The signature splitting is large in the two bands, while the other two bands have small splitting. A detailed low-lying level scheme of⁷⁸Rb has been constructed for the first time via theβ decay of⁷⁸Sr in order to search for a linking transition between the high-spin band head and low lying states.     

A Device for Offsetting High Level Electrical Interferences in Low Level Detectors

It is often useful to maintain an analogue output of a signal which has excessive noise. At near D.C. frequencies, this is seldom possible. However, when the noise can be identified, two ways of correcting this situation are immediately available. The first is to eliminate the interference at the source and the second is to supply appropriate offset to this interference. In the case of high-level energy sources, it is virtually impossible to eliminate their interference and it becomes necessary to fabricate electrical offsets to do this. This procedure is well-established in electronics and is used extensively in operational amplifiers.     

Level mixing induced transparency

We discuss level mixing induced transparency (LMIT), which is experimentally found in a thick absorber of FeCO₃ containing the ⁵⁷Fe Mössbauer nuclei. LMIT is observed if two hyperfine levels of the excited state nucleus cross. Absorption of gamma radiation drops by about 25% with respect to the sum of two overlapping absorption lines. The absorption deficit is explained by the mixing of the crossing levels with a symmetry breaking interaction. The level mixing induces a polarization change of the scattered radiation. In such a way, the radiation develops in “normal modes,” which are less absorbed in a thick absorber. We show that, in spite of the absorption drop, the area of the absorption line does not change. This confirms the general knowledge that interference phenomena (destructive or constructive) do not change the lifetime of an excited state particle (atom, nucleus, etc).