原子相干态中的压缩现象

计算表明,与场的相干态类似的原子相干态,具有不同于场的相干态的压缩行为;进一步证明:直接类比于(?)(ξ)不能得到“原子压缩算符”.     

原子间相互作用对V型三能级原子激光压缩性质的影响

研究了V型三能级原子玻色-爱因斯坦凝聚体与双模压缩相干态光场相互作用系统中原子激光的两个正交分量的压缩性质,并与三型三能级原子玻色-爱因斯坦凝聚体和双摸压缩相干态相互作用系中原子激光的压缩作了比较.结果表明:压缩相干态光场的初始压缩因子和凝聚体中原子间的相互作用强度对原子激光的两个正交分量的压缩有明显的影响,随光场压缩因子增大原子激光的压缩深度增加,而随原子间相互作用变强,对原子激光的正交分量的压缩的影响变浅.     

原子玻色-爱因斯坦凝聚体对V型三能级原子激光压缩性质的影响

利用格子液体方法对V型三能级原子玻色-爱因斯坦凝聚体与双模压缩相干态光场相互作用系统的哈密顿量进行分析,发现文献中对原子间相互作用部分的处理有不合理之处,从而对该哈密顿量作出了改进并研究了V型三能级原子玻色-爱因斯坦凝聚体与双模压缩相干态光场相互作用系统中原子激光的两个正交分量的压缩性质.研究表明:V型三能级原子玻色-爱因斯坦凝聚体中光场-原子相互作用强度对原子激光的两正交分量的涨落有明显的影响. 关键词： 玻色-爱因斯坦凝聚 V型三能级原子 压缩相干态 压缩原子激光     

双模SU(1,1)相干态场与V型三能级原子相互作用的动力学

研究了关联双模SU(1,1)相干态场与V型三能级原子的相互作用对原子动力学行为的影响及双模场的量子统计性质随时间的演化,证明了在双模SU(1,1)相干态光场作用下,原子的拉比振荡表现出与光场初态为双模压缩真空态或SU(2)相干态时的完全不同的特征。 关键词：     

原子薛定谔猫态中角动量的压缩及其时间演化

在低Q值腔内，原子相干态在一些特定时刻可以演化为原子薛定谔猫态.讨论了在这种原子薛定谔猫态中原子角动量的涨落和高阶涨落.根据不确定性原理，进一步研究了原子角动量的压缩和高阶压缩性质及其演化.研究表明，原子薛定谔猫态可以被压缩到二阶和六阶，但不能被压缩到四阶.当原子薛定谔猫态中被叠加的原子相干态数为无限多项时，其压缩特性与原子相干态相同. 关键词： 原子相干态 薛定谔猫态 角动量压缩 Bloch态     

光场诱导的原子激光的量子相干性

基于伞量子理论,分别研究了几种重要的光场作用下,从原子玻色-爱因斯坦凝聚(BEC)体耦合输出的原子激光的量子相干特性.结果表明,粒子数态光场诱导的原子激光总是反聚束的,相干态光场诱导的原子激光是任意阶相干的,而压缩相干态光场诱导的原子激光总是聚束的.表明用光场诱导产生的原子激光具有与初始光场完全相间的量子相干性质.     

原子间相互作用对原子激光压缩性质的影响

研究了原子间相互作用对光场与原子玻色-爱因斯坦凝聚体相互作用系统中耦合输出的相干原子束压缩性质的影响．结果表明：原子激光的两正交分量的涨落均可压缩，玻色-爱因斯坦凝聚体中原子间的相互作用不利于原子激光的压缩． 关键词： 玻色-爱因斯坦凝聚 压缩相干态光场 压缩原子激光     

可控制权重因子的原子纠缠态的制备

提出了一种利用二能原子与相干态腔场的非共振相互作用制备原子纠缠态的方案。在一定条件下,获得了可控制权重因子的原子纠缠态以及纠缠两原子的4个贝尔基。     

原子相干态中角动量的高阶涨落及高阶压缩

利用SU(2)李代数讨论了原子相干态中角动量的二阶、四阶和六阶涨落,并在高阶不确定关系基础上提出了角动量高阶压缩的定义.研究了原子相干态中角动量涨落的二阶、四阶和六阶压缩情况.运用这里的定义和方法可进一步研究更高阶的压缩情况,从而把高阶压缩推广到原子算符的涨落上. 关键词： 原子相干态 Bloch态 SU(2)压缩     

外场引起的原子相干与无反转激光:V型系统

利用密度矩阵方法在裸态和缀饰态中研究了在外场引起原子相干的v型寿命自加宽能级系统中产生无反转激光的条件。发现适当选择抽运概率,该系统可以产生无反转激光。 关键词：     

Mathematical modeling of the population dynamics of “dark” states of a three-level system

Mathematical modeling of the population dynamics is performed for states of a three-level system (atom) with a V-type configuration transforming a light pulse. It is assumed that the excited eigenstates of the atom are degenerate and coupled by coherent interaction, one of the states being radiating (radiative), while the other state is nonradiating (??dark??). The population dynamics of atomic states is described on the basis of numerical solutions of equations for the matrix elements of the density operator. The dependence of the efficiency of population of the atomic dark state from the values of the parameters of an irradiation pulse and from the ratio of the period of population oscillations of excited atomic states (caused by their coherent interaction) to the lifetime of the atomic radiating state is determined. Typical examples of the time dependence of the population of states of the atom considered are presented for the cases of irradiation by a short (as compared to the lifetime of the radiating state) sinusoidal light pulse and by a long rectangular light pulse with the resonance carrier frequency.     

Dark-line in optically-thick vapors: inversion phenomena and line width narrowing

An analysis of the phenomenon of coherent population trapping as observed by means of the dark state in the case of optically thick vapors in alkali metal atoms is presented. Very different behaviors are predicted for the observation of the dark state in the fluorescence and transmission spectra of the same atomic sample when the optical length is not negligible. Among other effects, the dark line observed in the fluorescence signal may look inverted appearing as a bright line, while in the transmission signal a narrowing of the line width resonance line is observed for an increase of the atomic density. In the pure three-level scheme a subnatural width is predicted. These effects, related to the electromagnetically induced transparency phenomenon, are readily observed in experiments, which are found to be in excellent agreement with the theory developed. Received 28 March 2001 and Received in final form 3 October 2001     

双通道离化系统的相干控制

研究了中间态为准连续态的双通道离化系统中激光的相对相位对稳态光电子谱的影响,给出了系统发生相干俘获的条件及相应的系统状态,讨论了俘获率对激光强度、频差及准连续态能级间隔的依赖关系 关键词： 准连续态 相干控制     

COHERENT POPULATION TRAPPING IN MULTILEVEL LASER-INDUCED CONTINUUM STRUCTURE SYSTEM INCLUDING CASCADE TWO-PHOTON PROCESSES

We have investigated the atomic coherent population trapping in a mul tilevel laser-induced continuum structure system including cascade two-photon processes, in which two sets of quasicontinua of excited levels to be modeled as the Bixon-Jortner quasicontinuum are laser-embedded into a previously structu reless atomic continuum.The condition leading to the atomic coherent population trapping and the coherent population trapping state are given explicitly. And th e effects of the Fano factors, the laser intensities and the detunings on the am ount of population trapped in the atomic bound states and the populations distri buted in the two sets of quasicontinua are also examined.     

三能级原子与少周期脉冲串作用中的相干布居捕获

研究了少周期脉冲串作用下三能级原子中的布居转移和相干布居捕获现象.在非旋波近似的情况下求解了密度矩阵方程.研究结果表明在等时间间隔的锁相脉冲作用下,系统能级的布居逐步转移并积累,系统基态相干也逐步积累.在满足脉冲重复频率为基态能级频差的整数分之一倍时,三能级系统和频率梳中两梳齿频率成分作用形成相干布居捕获现象,原子暗态布居值达到最大,介质对脉冲透明.在适当选取少周期脉冲参量的情况下,在0.5个ns的时间内三能级系统相干性演化到最大后到达稳态,相干布居捕获发生.与脉宽为100个fs的多周期脉冲相比,少周期脉冲串在介质中建立相干布居捕获的时间缩短两个数量级.由于频率梳中与三能级系统发生作用的梳频成份有相同的频移,相干布居捕获的条件双光子共振仍然满足.因而,当两基态能级频率差较大时,如果选取少周期脉冲载波频率为系统能级1至2和1至3的传输频率之和的一半ω=(ω₁+ω₂)/2,室温下原子热运动的引起的多普勒频移并不会破坏相干布居捕获.     

Six-Fold Degenerate Dark States in a Four-Level Atomic System

With all driving fields on Raman resonance, a tripod-type atomic system quickly evolves into a dark state decoupled from the lossy excited level. The dark state depends strongly on field Rabi frequencies, spontaneous decay rates, and the initial atomic population in a complicated way. Analytical results reveal that it is a sixfold degenerate dark state with its three components superposed both coherently and incoherently due to population redistribution from spontaneous emission.     

Macroscopic atom-molecule dark state and its collective excitations in fermionic systems

We show that a robust macroscopic atom-molecule dark state can exist in fermionic systems, which represents a coherent superposition between the ground molecular Bose-Einstein condensates and the atomic BCS paired state. We take advantage of the tunability offered by external laser fields, and explore this superposition for demonstrating coherent oscillations between ground molecules and atom pairs. We interpret the oscillation frequencies in terms of the collective excitations of the dark state.     

ATOMIC COHERENT POPULATION TRAPPING AND ITS APPLICATION IN A RAMAN-TYPE PHOTOIONIZATION SYSTEM WITH THREE BOUND STATES

We have studied the atomic coherent population trapping in a Raman-type, photoionization system with three bound states. The conditions for the system having two or one stable eigenstate are given. The influences of Fano asymmetric factors on the coberent population transfer are also analyzed.It is found that the property of the system having on]y one population trapping state consisting of the ground state, and one excited state, can be utilized to transfer the atomic initial population into one excited state.     

High contrast Ramsey fringes with coherent-population-trapping pulses in a double lambda atomic system

We report the observation of Raman-Ramsey fringes using a double lambda scheme creating coherent population trapping in an atomic ensemble combined with pulsed optical radiations. The observation was made in a Cs vapor mixed with N2 buffer gas in a closed cell. The double lambda scheme is created with lin perpendicular lin polarized laser beams leading to higher contrast than the usual simple lambda scheme. The pulsed trapping technique leads to narrow fringe widths scaling as 1/(2T) with high contrasts which are no longer limited by the saturation effect. This technique operates in a different way from the classical Ramsey sequence: the signal is done by applying a long trapping pulse to prepare the atomic state superposition, and fringe detection is accomplished by optical transmission during a short second trapping pulse without any perturbation of the dark state.