SGC Switching Between Subluminal to Superluminal Propagation in V-Type Atom

For a V-type three-level atomic system with two closely spaced upper levels, we investigate the light pulse propagation properties with only one laser field. Due to spontaneously generated coherence, the group velocity of the light pulse can be changed from subluminal to superluminal. The effects of the field intensity and the two-upper level splitting on the group velocity are also shown. At last, an analytical expression for the group velocity is given in the case of a weak field.     

SGC Switching Between Subluminal to Superluminal Propagation in V-Type Atom

For a V-type three-level atomic system with two closely spaced upper levels, we investigate the light pulse propagation properties with only one laser field. Due to spontaneously generated coherence, the group velocity of the light pulse can be changed from subluminal to superluminal. The effects of the field intensity and the two-upper level splitting on the group velocity are also shown. At last, an analytical expression for the group velocity is given in the case of a weak field.     

准Λ型四能级中用非匹配高斯脉冲实现相干布居转移

文章研究用非匹配高斯脉冲实现四能级准Λ型系统中的相干布居转移.从密度矩阵方程出发,对四个态的布居数随时间的演化进行了数值模拟.模拟结果表明,泵浦光场的拉比频率强度和失谐量对布居转移率的影响和探测光场、耦合光场的拉比频率强度及失谐量对布居转移率的影响不同;自发辐射诱导相干(SGC)对布居转移率的影响不大.但当它们选取适当参数的时候,基态的布居几乎可以全部被转移到目标态能级.     

Subluminal and Superluminal Phenomena in a Four-Level Atom

In a four-level atomic system, we investigate the light pulse propagation properties interacting with only one laser field. It is shown that in the steady state, the group velocity of the light pulse can be changed from subluminal to superluminal by varying the field detuning. Meanwhile, the effects of the field intensity on the group velocity are also shown. At last, with special parameters, the analytical solution for the group index is also obtained.     

Subluminal and Superluminal Phenomena in a Four-Level Atom

In a four-level atomic system, we investigate the light pulse propagation properties interacting with only one laser field. It is shown that in the steady state, the group velocity of the light pulse can be changed from subluminal to superluminal by varying the field detuning. Meanwhile, the effects of the field intensity on the group velocity are also shown. At last, with special parameters, the analytical solution for the group index is also obtained.     

Absorption-Amplification Response with or Without Spontaneously Generated Coherence in a Coherent Four-Level Atomic Medium

We discuss and analyze the absorption-amplification properties of a weak probe field in a typical four-level atomic system in the presence of an additional coherence term, the spontaneously generated coherence term. Theinfluences of the spontaneously generated coherence and a coherent pump field on the probe absorption (amplification)are investigated in detail. We show that the absorption of such a weak probe field can be dramatically enhanced dueto the presence of the spontaneously generated coherence. At the same time, the probe-absorption profile exhibitsthe double-peak structure and the probe-absorption peak gradually decreases as the pump intensity increases. On thecontrary, the amplification of such a weak probe field near the line center of the probe transition can be achieved byadjusting the coherent pump field intensity in the absence of the spontaneously generated coherence.     

Amplification mechanism and effects of spontaneously generated coherence on the probe gain in a four-level system

We investigate the amplification mechanism in a four-level system by both the density-matrix and quantum-jump approaches. We show that the asymmetry between three-photon stimulated emission and one-photon absorption process is responsible for the inversionless amplification of the probe field. We also investigate the effects of spontaneously generated coherence (SGC) on the probe gain, and find that due to the SGC, the probe gain can be greatly enhanced and can be modulated by changing the relative phase between the applied fields.     

N型四能级系统的原子吸收

研究了在较强光低饱和限制下相干光场与N型四能级原子相互作用系统中原子的吸收性质。借助于数值计算,讨论了较强光失谐、探针光强、激发能级向低能级衰减的分配系数对原子吸收的影响。结果表明,抽运场失谐使原子吸收发生横向变化,信号场失谐使原子吸收发生纵向变化;探针光强影响非线性吸收,并通过它影响原子吸收,当探针光强远小于抽运和信号光强时,原子吸收与线性吸收一致,均表现为电磁感应透明特征,当信号光强增大,非线性吸收产生了增益,原子吸收也由透明变为增益;激发能级同时向两个低能级衰减,当对应探针光的原子衰减通道的衰减分配系数趋近零时,原子吸收随该系数变化非常强烈,当该分配系数等于零时,其增益在探针场共振处趋于无穷大。     

Effects of Spontaneously Generated Coherence on Intensity-Intensity Correlation in a Driven Y-Type Atom

In this paper, we investigate the spontaneously generated coherence (SGC) effects on the fluorescence fields intensity-intensity correlation in a resonant driven four-level Y-type atomic system. By using a strong control field, in the absense of SGC effects, strong correlation and anticorrelation
fluorescence photons can be produced from two ladder transitions in this system respectively. However, in the presence of SGC effects, the fluorescence fields correlation properties are reversed for the two transitions. The above phenomena can be traced to the quantum destructive or constructive interference in terms of dressed states.     

Sub- and Super-Luminal Phenomena in a Doubly Driven Four-Level System

With the occurrence of an adding driving field, the properties of the dispersion and the absorption of a four-level system are changed greatly. The system can produce the normal and anomalous dispersion regions with proper parameters. Here, the driving fields can be seemed as knobs to manipulate the groupvelocity of a weak probe field between subluminal and superluminal.     

N-型四能级系统的EIT和MOLLOW谱分析

构建双耦合场作用下的N-型四能级系统,详细讨论系统的探测吸收特性随两个耦合场Rabi频率取不同值时的变化规律,得到EIT、Mollow和Autler-Townes双峰效应及其它们之间的相互转化规律。通过找出N-型四能级系统中的多个跃迁通道,将系统按跃迁通道拆分成多个子系统,不同的拆分方法实现了不同跃迁通道之间的量子干涉,从而使系统呈现出三种产生条件和物理本质不同的非线性效应。     

Comparative Study of Light Manipulation in Three-Level Systems Via Spontaneously Generated Coherence and Relative Phase of Laser Fields *

We present a comparative study of the control of-group velocity in three-level atomic systems including $\Lambda{}$-, Ladder-, and-V-types via spontaneously generated coherence (SGC) and relative phase of laser-fields. In the steady regime, expressions of group index are derived as an-analytical function of controllable parameters related to SGC and relative phase.-It is shown that the group velocity can be further slowed down or speeded up-under SGC in which modifications of group velocity due to the SGC in $\Lambda{}$--and V-systems are stronger than that in Ladder-system. In particular, when-interference strength of SGC p increases from 0.7 to 1.0, the light-propagation is switched from superluminal to subluminal modes (for $\Lambda{}$--and Ladder-systems) or from subluminal to superluminal modes (for V-system). In-the presence of relative phase, the group velocity changes between subluminal and-superluminal modes with a period of 2$\pi{}$. In resonant region, the largest-positive value of group index reaches at the relative phase $\varphi{}$ = $\pi{}$-while the largest negative value of group index reaches at $\varphi{}$ = 0 and-2$\pi{}$ for the $\Lambda{}$- and Ladder-systems, otherwise, for the V-system the-largest positive group index occurs at $\varphi{}$ = 0 and 2$\pi{}$, and the largest-negative group index occurs at $\varphi{}$ = $\pi{}$.     

在梯形四能级原子系统中的慢光和超光速传播

研究了梯形四能级冷原子系统的非线性光学行为,在一微波场耦合两上简并能级时双暗态共振将会出现。在合适的参数条件下,系统将表现出正常色散与反常色散之间的转变。改变耦合场和微波场的大小能够调控慢光和超光速间的转变。     

Doppler展宽的封闭原子系统中无反转增益的相位控制

研究了在具有自发辐射诱导相干性的Doppler展宽的封闭Λ型三能级系统中探测场和驱动场之间的相对位相对探测场无反转增益的控制作用. 研究结果表明: 1) 不管探测场和驱动场是同向传播还是反向传播, 驱动场是失谐还是共振,无反转增益总是随相对位相的改变而作周期性变化,周期为2π. 2) 驱动场共振时,无反转增益极大值随Doppler展宽值的增大而单调减小,且反向传播时比同向传播时减小的速度更快;驱动场失谐时,无反转增益的极大值随Doppler展宽值的增大不再单调地减小或增大. 在以上两种情况下,均可以通过调 关键词： 自发辐射诱导相干 相位控制 Doppler展宽 无反转增益     

Doppler展宽的封闭原子系统中无反转增益的相位控制

研究了在具有自发辐射诱导相干性的Doppler展宽的封闭Λ型三能级系统中探测场和驱动场之间的相对位相对探测场无反转增益的控制作用. 研究结果表明: 1) 不管探测场和驱动场是同向传播还是反向传播, 驱动场是失谐还是共振，无反转增益总是随相对位相的改变而作周期性变化，周期为2π. 2) 驱动场共振时，无反转增益极大值随Doppler展宽值的增大而单调减小，且反向传播时比同向传播时减小的速度更快；驱动场失谐时，无反转增益的极大值随Doppler展宽值的增大不再单调地减小或增大. 在以上两种情况下，均可以通过调     

Theoretical Study of Light Propagation in an Open Four-Level Quantum System

International Journal of Theoretical Physics - In this paper, theoretically the light propagation and dynamical control of weak probe pulse in an open four-level N-type atomic medium are...     

Storage and Retrieval of a Weak Optical Signal Improved by Spontaneously Generated Coherence in an Atomic Assemble

We investigate the reversible storage of a weak single-mode light signal in a Λ-type three-level atomic system with spontaneously generated coherence (SGC) and pumped by an incoherent field.The scheme is phase-dependent.If the phase of the controlling field is set oppositely to that of the signal field,the combination of SGC with weak pump overcomes the drawback of incompletely retrieval in the conventional scheme,leading to 100% retrieval fidelity or even to the amplification of the retrieved signal with respect to its initial one.     

Absorption-Dispersion Properties in a Four-Level Atomic System with Vacuum-Induced Coherence

We discuss and analyze absorption-dispersion response for the probe field in a typical four-level atomic system with vacuum-induced coherence (VIC) arising from the cross coupling pathways associated with a pair of upper excited hyperfine levels. We find that VIC effect can preserve electromagnetically induced transparency (EIT) by using the detailed numerical simulations based on the density-matrix equations and analytical calculations in the dressed-state picture. We also show that the atomic hyperfine structure cannot be a hindrance to obtaining EIT.     

Phase control in an open Λ-type system with spontaneously generated coherence

This paper investigates the control role of the relative phase between the probe and driving fields on the gain, dispersion and populations in an open A system with spontaneously generated coherence （SGC）. It shows that by adjusting the value of the relative phase, a change from lasing with inversion to lasing without inversion can be realized; the values and frequency spectrum regions of the inversionless gain and dispersion can be obviously varied; high refractive index with zero absorption and electromagnetically induced transparency can be achieved. It is also found that when the driving field is resonant, the shapes of the dispersion and the gain curves versus the probe detuning are very similar if the relative phase of the dispersion lags π/2 than that of the gain, however for the off-resonant driving field the similarity will disappear; the gain, dispersion and populations are periodical functions of the relative phase, the modulation period is always 2π; the contribution of SGC to the inversionless gain and dispersion is much larger than that of the dynamically induced coherence.