四能级原子系统中的电磁诱导吸收

以三个电偶极跃迁(中间跃迁作为探测跃迁、两边分别是耦合跃迁和控制跃迁)构成N型四能级系统为例,研究介质对探测光的吸收.揭示了在N型四能级系统中,既可产生电磁诱导吸收又可产生电磁诱导透明.这不仅取决于非相干转移率的大小,而且还取决于耦合场、控制场的强度和第四个简并能级的衰减速率大小.关键词：电磁诱导吸收电磁诱导透明原子相干的自发转移能级的衰减速率     

Y型四能级系统中Doppler展宽对真空诱导相干性相关的探测场吸收的影响

利用数值计算结果,讨论了在Y型四能级原子系统中Doppler展宽对与真空诱导相干性(VIC) 相关的探测场吸收性质的影响.研究结果表明: 当无Doppler展宽时,只有不存在VIC时才可能产生电磁感应透明(EIT)现象; VIC将导致探测场吸收的明显改变和增益产生;在VIC存在和不存在两种情况中,吸收曲线都具有关于探测场失谐对称的双峰结构. 当有Doppler展宽时,在VIC存在和不存在两种情况中都能产生EIT现象; VIC仍将导致探测场吸收的明显改变和增益产生;不管是否存在VIC,探测场吸收都具有以下特征:吸收曲线不再具有关于探测场失谐的对称性且随Doppler展宽宽度(D)值的增大而逐渐从双峰结构变为单峰结构,探测场吸收不随D值的增大而单调增大或减小,在探测场和驱动场的传播方向相反时可获得比传播方向相同时更小的探测场吸收.     

耦合场失谐对闭合Λ型四能级系统中电磁诱导透明和电磁诱导吸收的影响

电磁诱导透明(EIT)和电磁诱导吸收(EIA)是光与物质相互作用中表现出来的奇特的非线性效应,对其形成机理及非线性特性的研究具有重要的理论意义和巨大的潜在应用价值.构建一个闭合Λ型四能级系统包括两个基态精细结构能级和两个激发态精细结构能级,除耦合场和探测场外,还附加了两个射频场分别作用于激发态精细结构能级和基态精细结构...     

Y型四能级系统中Doppler展宽对VIC相关的双光子吸收的影响

利用数值计算结果讨论了Doppler展宽对Y型四能级原子系统中真空诱导相干 性(VIC)相关的双光子吸收的影响. 研究结果表明: 1)在无Doppler展宽的情况中, 不存在VIC时, 吸收曲线具有双峰结构并产生电磁感应透明(EIT)现象, 存在VIC时吸收曲线具有单峰结构而EIT现象不再发生; 2)在有Doppler展宽的情况中, 不管是否存在VIC, EIT现象都能发生; 不存在VIC时, 不管探测场和驱动场传播方向相同还是相反, 随Doppler展宽宽度D值的增大, 吸收先增大后减小, 吸收曲线逐渐从双峰结构变为单峰结构; 存在VIC时, 若探测场和驱动场传播方向相同, 随D值的增大, 吸收先增大后减小, 吸收曲线逐渐从单峰结构变为双峰结构; 若探测场和驱动场传播方向相反, 随D值的增大, 吸收单调减小, 但吸收曲线仍保持单峰结构.     

真空场诱导相干对梯形四能级原子系统中单光子和双光子透明的影响

当一个梯形四能级原子系统的中间两个能级分别与真空辐射场相互作用耦合到基态和激发态时,自发衰变路径间的量子干涉效应导致了V和Λ型的真空场诱导相干(VIC)。利用半经典理论,分别讨论了这两种类型的VIC对单光子和双光子电磁诱导透明的影响,并发现Λ型的真空场诱导相干增强双光子的吸收,而对单光子的吸收几乎无影响;V型的真空场诱导相干抑制单光子和双光子的吸收。     

倒Y型四能级原子系统中电磁诱导透明的相干控制

研究了倒Y型四能级原子系统中相干控制电磁诱导透明.应用微扰理论给出一阶近似条件下,不同控制场原子系统对探测光场响应的解析式及电磁诱导透明窗宽度的解析式.在探测场为弱场时,分析了系统中控制光场强度、耦合光场强度及其失谐量对电磁诱导透明窗的影响.研究发现电磁诱导透明窗随控制光场强度的增强变宽,而随耦合光场强度的增强变窄,当探测光场与耦合光场偏离双光子共振时,透明窗外的吸收增加,透明窗变宽.在弱探测场、弱控制场条件下,分析了初始时刻原子处在相干叠加态时的相对相位、相对强度与探测场和控制场的相对相位等对系统吸收特性及透明窗的影响.结果表明探测场与控制场的相对相位对吸收的影响与相干叠加态中两能级之间几率幅的相对相位对吸收的影响作用相反,系统在两下能级干涉极大时,存在一个很宽的透明带.应用缀饰态理论和量子相干理论对所得结果进行了解释.     

闭合Λ型4能级系统中的电磁诱导透明和电磁诱导吸收

准Λ型4能级系统具有电磁诱导吸收(EIA)和电磁诱导透明(EIT)两种特性.准Λ型4能级系统包括两个基态精细结构能级和两个激发态精细结构能级,除光学耦合场和探测场外,附加了一个射频场作用于两个激发态精细结构能级之间.若对此系统进行拓展,在两个基态精细结构能级之间引入一个驱动场,则构成4场作用下的闭合Λ型4能级系统.本文对新引进的驱动场的作用规律进行了重点研究.研究结果表明,当驱动场和射频场的Rabi频率满足不同关系时,系统呈现EIA或EIT两种不同特性,探测吸收曲线的整体轮廓也随之改变.     

四能级系统中相位控制电磁诱导透明研究

提出了一种利用微波场的相对相位调控电磁诱导透明(EIT)光谱特性的方法. 在外加双微波驱动场的准Λ型四能级原子系统中,通过求解系统的密度矩阵方程得到探测场的吸收谱,分析了电磁诱导透明窗口的位置随微波驱动场相位的变化规律,并借助缀饰态理论给出了准确解释. 结果表明,对于确定的作用场强度,调节微波驱动场的相位可实现电磁诱导透明的频率位置及间隔的准确控制.关键词：四能级原子系统电磁诱导透明(EIT)相位控制微波场     

Y型四能级原子系统对探测场的吸收和色散

运用数值模拟的方法计算了Y型四能级原子系统在弱场条件下对探测场的吸收和色散.结果发 现,通过调制能级间附加的外场强度,该系统呈现出电磁感应透明特性,出现增益区并伴有 较大负折射率的色散效应.同时还发现,当外加场的拉比频率相位发生改变时,系统对探测 光场的吸收和色散将随之变化.关键词：电磁感应透明自发辐射量子干涉     

单光子和双光子电磁诱导透明谱的相干调制

采用一束相干外场作用在倒Y模型原子的基态与另外状态构成的跃迁上,实现对单光子和双光子电磁诱导透明谱的调制.经研究发现相干外场对单光子和双光子的吸收性质有类似的影响效果.由于相干外场的作用,吸收谱的共振点附近出现吸收峰将原单重透明谱分裂为双重透明谱.诱导的吸收峰的高度和透明谱的频谱宽度与相干外场的强度有密切关系.并用缀饰态理论解释了这些物理现象.这些研究对多通道光通信以及对原子光学性质的调控方面有积极意义.     

Double dark resonances and the dispersion properties in a four-level inverted-Y atomic system

The electromagnetically induced transparency (EIT) and its dispersion properties in a four-level inverted-Y atomic system are investigated. The absorption spectrum of a weak probe field shows two EIT windows (dark resonances) whose location, width, and depth can be controlled by manipulating the parameters of the coupling fields; the corresponding dispersion properties are also measured by using a Mach-Zehnder interferometer. The experimental measurements agree well with the theoretical calculations. This kind of system can find important applications in two-channel quantum communication and information storage.     

Enhancement of Kerr nonlinearity via spontaneously generated coherence in a four-level N-type atomic system

A theoretical investigation is carried out into the effect of spontaneously generated coherence (SGC) on Kerr nonlinearity of a four-level N-type system. It’s found that the Kerr nonlinearity can be obviously enhanced with SGC present. We attribute the enhancement of Kerr nonlinearity mainly to the generation of extra coherences induced by the superposition of the two SGC channels, and when the superposition is controlled by the interference between two SGC channels properly, the maximal Kerr nonlinearity does not only enter the electromagnetically induced transparency window as the spontaneous generated coherences intensify, but also gets enhanced about 10 times with very large SGC coefficients than that with no SGC effect.     

Precise measurement of optical frequency with the help of electromagnetically induced transparency

We have studied electromagnetically induced transparency (EIT) spectra in a frequency span as wide as 300 MHz. This tunability of EIT spectra provides an opportunity to utilize the sub-natural spectra in measuring unknown laser frequency very accurately. EIT is observed when control and probe laser frequency detunings are equal. This correlation has been used to identify and measure unknown probe frequency with a very high degree of accuracy, subject to the condition that control laser frequency is known.     

Controllable Kerr nonlinearity with vanishing absorption in a four-level inverted-Y atomic system

The giant enhancement of Kerr nonlinearity in a four-level inverted-Y atomic system is investigated theoretically. Compared with that generated in a generic three-level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. The physical mechanism leading to the giant enhancement of Kerr nonlinearity is also discussed.     

Electromagnetically induced transparency in five-level cascade scheme of Rb atoms: An analytical approach

Electromagnetically induced transparency (EIT) in the five-level cascade scheme of ⁸⁵Rb atoms is investigated by analytical method. In the weak field limit of the probe light, the linear susceptibility, absorption, and dispersion coefficients have been derived in analytical forms. Unusual EIT signatures of the system are studied in details.     

Squeezing and entanglement of a two-mode field in a four-level tripod atomic system

The interaction of a collection of N four-level tripod configuration atoms with two orthogonally polarized probe fields is investigated. Under the condition of electromagnetically induced transparency (EIT), we calculate the squeezing and entanglement spectra of the output probe fields. By analyzing the output spectrum, we find that the squeezing and entanglement of the probe fields can be well-preserved after passing through the optically thick medium. Additionally, the effects of the ground state dephasing rates of the atoms on the entanglement and squeezing of the output two-mode squeezed fields are investigated. It is shown that the dephasing rates will degrade the entanglement and squeezing, and these quantum properties can be lost when the dephasing rates increase up to a certain value. This will be useful in the quantum computation and quantum communication.     

基于Rb原子电磁诱导透明的量子干涉实验研究

报道了基于85RbD2线电磁诱导透明(EIT)的量子干涉现象,发现当一耦合光和探测光之间满足拉曼共振条件时出现电磁诱导透明现象,在某些条件下也观察到电磁诱导吸收(EIA).而当用一束耦合光和一束泵浦光共同作用于5S1/2,F=3→5P3/2,F′=3和5S1/2,F=3→5P3/2,F′=4能级上时,探测光的吸收谱表现出三峰结构,并且峰强弱与两耦合光之间的相对强度有关.     

非相干泵浦对原子系统位相相关吸收性质的影响

研究发现在具有真空诱导相干性的开放和封闭ladder 型原子系统中,探测场和驱动场之间相对位相对吸收性质有重要的调制作用,同时非相干泵浦对位相相关的吸收性质有显著的影响.在这两种系统中,通过调节非相干泵浦,可以实现从吸收到增益和从粒子数反转激光到无粒子数反转激光的转化,并可获得最大的无反转激光增益.但是,当非相干泵浦不存在时,对相对位相的任意值,在封闭系统中只出现吸收而不能得到无反转激光增益;然而在开放系统中,对于适当的相对位相值甚至可以产生比有非相干泵浦时更大的无反转激光增益.