点间隧穿耦合对四能级三量子点电磁感应透明介质孤子动力学的影响

利用概率幅变分近似结合多重尺度法,研究了探测光在两边产生点间隧道耦合的非对称阵列型三量子点电磁诱导透明介质的传播性质.结果表明,由于系统的色散效应和点间隧穿耦合产生的非线性效应相平衡,系统能形成稳定传播的超低速时间光孤子.有趣的是,仅开启一边的点间隧穿耦合(即另一边关闭),随着点间隧穿耦合强度的增加,光孤子的速度呈现出先增大后减小的变化趋势,但光孤子的幅度却一直增大.两边两个点间隧穿耦合强度均开启后,随着点间隧穿强度逐渐的增大,光孤子的幅度随着点间隧穿强度的增大会出现逐渐减小,直到出现一个拐点后才迅速增大;而光孤子的速度相比较于单个隧穿强度的影响会明显降低,且出现停滞的现象.这些结果不但揭示出点间隧道耦合对三量子点电磁感应透明介质光孤子的动力学有着重要影响,而且还预言在半导体量子点器件中可利用点间隧道耦合调节其光孤子传输的幅度.     

半导体三量子点电磁感应透明介质中的非线性法拉第偏转

利用一束弱线性π偏振探测光在与其平行的磁场作用下所形成的两偏振分量,然后结合量子点间的隧穿耦合,构建了五能级M型半导体三量子点分子电磁感应透明介质.通过研究该体系的线性光学性质发现,操控量子点间隧穿耦合强度可有效调节系统中隧穿诱导透明窗口的宽度,并实现对介质的反常色散与正常色散的"开关"调节效应.随后,对体系非线性法拉第效应的研究发现,在相同的外加磁场下探测光的非线性法拉第偏转方向与线性法拉第偏转相反且非线性法拉第偏转角更大.     

点间隧穿调控五能级M型三量子点电磁感应透明介质中的孤子碰撞性质

基于现有实验,本文构建一束弱线性偏振光在平行于传播方向的磁场作用下分裂为两正交偏振光,当其与三角形三量子点相互作用后形成五能级M型三量子点电磁感应透明介质模型.随后,利用多重尺度结合傅里叶积分方法研究体系中的光孤子传播及两孤子间的碰撞特性,结果发现孤子间的碰撞方式是由其初始相位差所决定.当孤子间初相位差为0时,孤子间的碰撞为周期性弹性碰撞;当初相位差为π/4,π/2和π时,孤子间会产生排斥作用力而使两孤子分离.有趣的是,孤子间的碰撞特征受量子点间的隧穿强度的调控.当点间隧穿强度的增加,初相位差为0的孤子间的碰撞周期减小;而初相位差为π/4,π/2和π时孤子间的排斥力增大.这为实验上如何操控半导体量子点器件中的孤子动力学提供了一定的理论依据.     

纵波光学声子耦合对级联型电磁感应透明半导体量子阱中暗-亮光孤子类型的调控

利用多重尺度法,解析地研究了计及纵波光学声子耦合弛豫效应下级联型三能级电磁诱导透明半导体量子阱介质中时间光孤子的动力学特征.结果表明:纵波光学声子耦合强度的大小能有效调控体系时间光孤子的类型;发现孤子的群速度也可通过纵波光学声子耦合强度和控制光来调控.这为实验上如何操控半导体量子阱的孤子动力学提供了一定的理论依据.     

量子点中两耦合时间矢量光孤子的碰撞特性

构建一个由一束弱线性偏振探测光场在与其平行的磁场作用下形成的两正交偏振分量,联合两束强耦合控制光场与半导体单量子点相互作用所形成的四能级半导体量子点电磁感应透明介质模型,利用多重尺度法,解析地研究了该半导体量子点电磁感应透明介质中的两耦合时间矢量光孤子的稳定性及其碰撞特性。结果发现,该体系中两耦合时间矢量光孤子的碰撞特性与其初始相位差有关;当两孤子分量为同相或反相时,孤子间会呈现出近弹性碰撞且无能量转移;而当孤子分量间初始相位差为π2时,两孤子则会在融合之后再彼此分离且出现能量转移。     

计及激子-双激子相干下半导体单量子点中的空间光孤子对

考虑激子-双激子的相干效应, 解析地研究了半导体单量子点中探测光和信号光的吸收特性和非线性传播特性.结果发现, 在线性条件下, 单量子点中出现电磁感应透明现象; 进一步分析可得, 电磁感应透明所呈现的是单窗口或双窗口或光学增益均可通过调节控制光强加以控制.在非线性条件下, 弱信号光诱导弱探测光产生两个分量, 这两个分量在系统中所激发的自克尔和交叉克尔 非线性效应与系统的衍射效应相平衡从而形成稳定的亮-亮, 亮-暗, 暗-暗等空间光孤子对. 关键词： 半导体量子点 电磁感应透明 空间光孤子对     

能级构型对InAs/GaAs量子点电磁感应透明介质中光孤子存储的影响

基于现有的实验,利用不同频率的光脉冲耦合到InAs/GaAs量子点的不同能级之间可形成梯形、Λ形和V形等3类量子点电磁诱导透明介质.继而研究这三类能级构型InAs/GaAs量子点电磁诱导透明介质中的光孤子形成和存储性质,结果表明,梯形和Λ形InAs/GaAs量子点体系不但可形成光孤子还可以实现光孤子的存储与读取,且其所存储光孤子的保真度比光存储的保真度高;但V形InAs/GaAs量子点体系却不能形成光孤子,这是由于体系的非线性效应非常弱.有趣的是在相同的实验参数下,Λ形InAs/GaAs量子点体系所存储的光孤子幅度比梯形所存储的光孤子幅度大.这为半导体量子点器件对所存储光孤子进行调幅操作提供了理论依据.     

多层结构双自旋过滤隧道结中的电子输运特性

在转移矩阵方法及Mireles和Kirczenow的量子相干输运理论的基础上,研究了正常金属层/磁性半导体层/非磁绝缘层/磁性半导体层/正常金属层型双自旋过滤隧道结中Rashba自旋轨道耦合效应和自旋过滤效应对自旋相关输运的影响.讨论了隧穿磁电阻（TMR）、隧穿电导与各材料层厚度、Rashba自旋轨道耦合强度以及两磁性半导体中磁矩的相对夹角θ之间的关系.研究表明：含磁性半导体层的双自旋过滤隧道结由于磁性半导体层的自旋过滤效应和Rashba自旋轨道耦合作用可获得极大的TMR值.另外TMR和隧穿电导随着Rashba自旋轨道耦合强度的变化而振荡,振荡周期随Rashba自旋轨道耦合强度的增大逐渐减小. 关键词： 双自旋过滤隧道结 Rashba自旋轨道耦合 隧穿磁电阻 隧穿电导     

极性半导体超晶格中的等离激元与纵光学声子的耦合模

在无规相近似下,计入相邻量子阱间的电子隧穿效应,研究了极性半导体超晶格中的等离激元与纵光学声子的耦合,得到了它们耦合模的色散关系,并表明外磁场存在时,电子隧穿使体系出现了一支新的耦合模.     

混合原子光机械系统中的量子相干控制

研究了原子相干及量子相干对混合原子光机械系统输出特性的影响。应用微扰方法及光腔的输入输出理论求解Langevin方程,得到了混合原子光机械系统对弱探测场的响应函数。分析了腔模与原子系统的耦合强度、量子干涉效应对混合原子光机械系统输出特性的影响。研究发现,控制原子系统的量子干涉效应,即可控制混合原子光机械系统的输出特性;改变原子系统的控制场强度,便可改变混合原子光机械系统的透明窗口宽度,从而得到由原子吸收谱调制的光机械系统的吸收谱;在光机械系统透明窗口中心区域可实现探测场的放大;改变原子系统中控制场或耦合场的失谐量,可以控制混合原子光机械系统的透明窗口位置。     

Steady-state linear optical properties and Kerr nonlinear optical response of a four-level quantum dot with phonon-assisted transition

The linear optical properties and Kerr nonlinear optical response in a four-level loop configuration Ga As/Al Ga As semiconductor quantum dot are analytically studied with the phonon-assisted transition(PAT). It is shown that the changes among a single electromagnetically induced transparency(EIT) window, a double EIT window and the amplification of the probe field in the absorption curves can be controlled by varying the strength of PAT κ. Meanwhile, double switching from the anomalous dispersion regime to the normal dispersion regime can likely be achieved by increasing the Rabi energy of the external optical control field. Furthermore, we demonstrate that the group velocity of the probe field can be practically regulated by varying the PAT and the intensity of the optical control field. In the nonlinear case, it is shown that the large SPM and XPM can be achieved as linear absorption vanishes simultaneously, and the PAT can suppress both third-order self-Kerr and the cross-Kerr nonlinear effect of the QD. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength, and may provide some new possibilities for technological applications.     

DNA adsorption on graphene

We study analytically the properties of the optical absorption and the spatial weak-light solitons in a quantum dot molecule system with the interdot tunneling coupling (ITC). It is shown that, for the linear case, there exists tunneling induced transparency (TIT) in the context of a weak ITC, while the TIT can be replaced by Autler-Townes splitting in the presence of a strong ITC. For the nonlinear case, it is probable to realize the spatial optical solitons even under weak light intensity. Interestingly, we find that there appears transformation behavior between the bright and dark solitons by properly turning both the ITC strength and the detuning of the probe field. Meanwhile, the transformation condition of the bright and dark solitons is obtained. Additionally it is also found that the amplitude of the solitons first descends and then rises with the increasing of ITC strength. Our results may have potential applications for nonlinear optical experiments and optical telecommunication engineering in solid systems.     

Ultraslow optical solitons in a four-level tripod atomic system

We investigate possible formation and propagation of localized, shape-preserving nonlinear optical pulse in a resonant, lifetime-broadened four-level tripod atomic system via electromagnetically induced transparency (EIT). We prove both analytically and numerically that although in anomalous dispersion regimes near resonance a superluminal optical soliton may appear, such soliton suffers serious absorption. However, by choosing appropriate parameters to make the system work in normal dispersion regimes and within an EIT transparency window, ultraslow optical solitons with very low light intensity can form and propagate stably in the system.     

Monte Carlo simulations of electromagnetically induced transparency in a square lattice of Rydberg atoms

We study the steady optical response of a square lattice in which all trapped atoms are driven by a probe and a coupling fields into the ladder configuration of electromagnetically induced transparency(EIT). It turns out to be a manybody problem in the presence of van der Waals(vd W) interaction among atoms in the upmost Rydberg state, so Monte Carlo(MC) calculation based on density matrix equations have been done after introducing a sufficiently large cut-off radius. It is found that the absorption and dispersion of EIT spectra depends critically on a few key parameters like lattice dimension, unitary vd W shift, probe Rabi frequency, and coupling detuning. Through modulating these parameters, it is viable to change symmetries of the absorption and dispersion spectra and control on demand depth and position of the transparency window. Our MC calculation is expected to be instructive in understanding many-body quantum coherence effects and in manipulating non-equilibrium quantum phenomena by utilizing vd W interactions of Rydberg atoms.     

Tunneling-induced ultraslow solitons in triangular quantum dot molecules

We theoretically investigate the propagation of a weak probe laser pulse in a triangular quantum dot molecules scheme based on the tunneling induced transparency. We find that the ultraslow optical solitons can be realized due to the destructive quantum interference induced by the interdot tunneling coupling which can be adjusted by the gate voltage appropriately. This work may provide practical applications such as electro-optic modulated devices and other information processes in semiconductor quantum dots structure.     

光学-射频双光子耦合作用下的电磁诱导透明和电磁诱导吸收

在通常的Λ型三能级系统中,光学耦合场和探测场分别激发两个不同的光学跃迁,探测吸收谱呈现电磁诱导透明(EIT)特性.若将此系统拓展为光学-射频双光子耦合场和探测场共同作用下的准Λ型四能级系统,探测吸收谱呈现电磁诱导吸收(EIA)和EIT两种特性.通过求解系统的密度矩阵方程,分析了EIA和EIT的产生条件,并给出了相应的缀饰态解释.研究结果表明,在准Λ型四能级系统中,光学耦合场对EIA和EIT的形成起决定作用,共振时出现EIA,非共振时出现EIT,而且EIA和EIT的线宽随着光学耦合场拉比频率的增大而增加. 关键词： 电磁诱导透明 电磁诱导吸收 射频场 光学耦合场     

Enhancement of charge and spin Seebeck effect in triple quantum dots coupling to ferromagnetic and superconducting electrodes

We theoretically study the thermoelectric transport properties through a triple quantum dots (QDs) device with the central QD coupled to a ferromagnetic lead, a superconducting one, and two side QDs with spin-dependent interdot tunneling coupling. The thermoelectric coefficients are calculated in the linear response regime by means of nonequilibrium Green's function method. The thermopower is determined by the single-electron tunneling processes at the edge of superconducting gap. Near the outside of the gap edge the thermopower is enhanced while thermal conductance is suppressed, as a result, the charge figure of merit can be greatly improved as the gap appropriately increases. In the same way, charge figure of merit also can be greatly improved near the outside of the gap edge by adjusting interdot tunneling coupling and asymmetry coupling of the side QDs to central QD. Moreover, the appropriate increase of the interdot tunneling splitting and spin polarization of ferromagnetic lead not only can improve charge thermopower and charge figure of merit, but also can enhance spin thermopower and spin figure of merit. Especially, the interdot tunneling splitting scheme provides a method of controlling charge (spin) figure merit by external magnetic field.     

∧型四能级系统中的多重电磁诱导光透明研究

运用密度矩阵理论,研究了在外加相干耦合场作用下∧型四能级系统的吸收和色散特性。数值模拟表明：通过调节外加相干场的拉比频率强度,该系统可以单重、双重电磁诱导光透明现象,并在缀饰态表象中给出了定性解释。在双重电磁诱导透明现象中,透明窗的位置和吸收峰值可以通过调节外加相干场的失谐量来进行控制,而且透明点的位置可以连续变化。每个透明窗口在吸收最低时都伴随着高折射率,因此可以在此介质中实现超光速传播。     

五能级原子系统中的多重电磁感应透明

利用半经典理论,研究了在相干外场驱动下的倒三脚架型原子系统的吸收性质.数值计算结果表明:通过调节相干场的Rabi频率,该系统可以呈现出三重、双重、单重电磁感应透明;在三重电磁感应透明中,透明窗的位置可以通过调节相干场的失谐量来进行控制,而且透明点的位置可连续地变化,即在一定范围内存在一系列连续频率的探测光无吸收地通过介质.最后,在缀饰态表象中对上述现象给出了解释.     

调谐耦合场作用下的电磁诱导透明和增益

在通常的A型三能级系统中,耦合场和探测场分别与一对光学跃迁能级发生相互作用,使探测吸收曲线上出现线宽极窄的电磁诱导透明(Electromagnetically Induced Transparency,EIT)特性.本文采用调谐耦合场同时激励两个基态精细结构能级与激发态能级之间的跃迁,使系统同时呈现EIT和自发诱导相干...