Two different regimes in a V-type three-level atom trapped in an optical cavity

In this paper two different behaviors of a V-type three-level atom which is driven by a classical field in an optical cavity are shown. We show that the behavior of an atom depends on the values of the critical photon number. The system treatment for large enough values of the critical photon number is described by the semiclassical laser theory. In contrast, for small enough values of the critical photon number, the system shows new quantum properties. In the former case, it is shown that the system performs like a conventional laser and in the latter one, the system acts as an effective two-level model. The behaviors of the system are investigated both in the semiclassical approximation and full quantum theory. For comparing the results, computer simulations are implemented.     

The nonlinear effects over time evolution of a three-level atom confined in a single mode optical cavity

A single atom is trapped in an optical cavity in the presence and absence of a nonlinear mirror corresponding to the nonlinear and linear regimes, respectively. The time evolutions of both systems are derived. The resultant equations are numerically solved by a fourth-order Runge–Kutta method. The effect of the nonlinear mirror over time evolution of the population inversion, the mean photon number and the second-order coherence function is investigated. It is shown that in the presence of the nonlinear effects, the time average of the population inversion is increased. As the time evolution proceeds, the mean photon number is decreased as well as the light exhibiting sub-Poissonian photon distributions. Under specific conditions and in a weak-driving limit, these systems can be well approximated by an effective two-level atom. The result of the calculations confirms the predictions of the two-level model.     

State transfer and entanglement of two mechanical oscillators in coupled cavity optomechanical system

We investigate coupled two-cavity optomechanical systems to show their potential usages by revealing the physical processes. Under two conditions, we deduce the correspondingly effective Hamiltonian with beam splitter type and nondegenerate parametric-down conversion type, respectively. Including the whole interactions, we show that the state transfer and the stationary entanglement between the two mechanical resonators can be achieved.     

Enhancement of discord and entanglement with detuning for two coupled quantum dots in a driven cavity

We study the quantum discord for a system of two identical coupled quantum dots interacting with quantized cavity field in the presence of cavity as well as dot decay and detuning. The cavity is externally driven by a coherent light. These results are compared with the entanglement of the quantum dots in various parameter regimes in which system may or may not show bistability. We show that the discord in the steady state is nonzero for any nonzero cavity field amplitude. The system has higher discord in the upper branch of the bistability curve where the entanglement is zero. We also find many other interesting results including high discord and entanglement in the presence of detuning, a phenomenon which we further examine by approximating the density matrix in the appropriate limit.     

Time evolution of entanglement and bistability of two coupled quantum dots in a driven cavity

Abstract

The time evolution of entanglement between two quantum dots (QDs) trapped inside a cavity driven by a coherent quantized field is studied. In the presence of dissipation, entanglement shows many interesting features such as sudden death and revival, and finite steady state value after sudden death. We also investigate dependence of entanglement on dot variables and its relation to bistability. It is found that entanglement vanishes when the cavity field intensity approaches the upper branch of the bistability curve. When the cavity is driven by a modulated field in the presence of dissipation, it can periodically generate entanglement, which is much larger than the maximum value attained in the steady-state for this system but the dots are never fully entangled.     

Optical force and friction of a V-type three-level atom in a driven high-Q cavity

A model is presented to calculate the optical force and friction for a three-level atom in a V-type configuration in a weakly driven high-finesse cavity. Analytical expressions for the force and friction are derived using Heisenberg equations. It is demonstrated that the cooling rate can be increased by one order of magnitude over that of a two-level atomic system, which would stimulate further experimental investigations.     

Two-color bright solitons in a three-level atomic system in the cascade configuration

We investigate two-component spatial optical solitons in a cascaded three-level atomic system. We derive an existence curve in the parameter space of power and spatial widths that reveals the existence of a plethora of coupled solitons. These solitons can exist with two different frequencies and also with two different widths. Our analytical results have been verified by direct numerical simulations. Stability analysis confirms that these solitons are stable.     

Effect of the Stark shift on entanglement in a double two-photon JC model

Considering a double two-photon JC model, we investigate the entanglement between the two two-level atoms and that between the two cavity fields, and study the effect of the Stark shift on entanglement. The results show that, on the one hand the atom–atom and cavity–cavity concurrences evolve periodically with time and the periods are affected by the Stark shift; on the other hand, the two atoms are not disentangled at any time when the Stark shift is considered, and for large values of the Stark shift parameter, the two atoms can remain in a stationary entangled state. In addition, we find that the so-called entanglement sudden death can occur under appropriate conditions on the dynamic Stark shift for a certain initial state of the system.     

Focusing and defocusing dynamics of weak-light beam in a resonant three-level atomic system

Focusing and defocusing dynamics of weak-light ring-shaped beams in a Λ-type atomic system are investigated. It is found that focusing of weak light is possible due to the quantum interference effect. The focusing or defocusing regime with vanishing absorption can be manipulated by adjusting detunings from the resonant transition. When the fields are tuned appropriately larger than resonant frequencies, the beam propagates in the defocusing regime and diffraction of the beam takes place. Conversely, the beam focuses in the medium when the laser frequencies are tuned smaller than the resonant frequencies.     

冷轧变形对TiNi合金阻尼特性的影响

为了探讨冷轧变形对TiNi合金阻尼特性的影响,及TiNi合金马氏体的阻尼特性与组织结构之间的关系,采用示差扫描量热分析、透射电镜分析、动态机械分析和音频阻尼测试方法,系统研究了冷轧变形后Ti50Ni50合金马氏体的阻尼特性.研究结果表明:低频和音频时,Ti50Ni50合金马氏体的阻尼值随着冷轧变形量的增加呈现先增加而后降低的趋势,且音频时热马氏体和冷轧变形后马氏体的阻尼值较低频时的阻尼值均有大幅度地下降;冷轧后马氏体的高阻尼不仅与界面运动有关,也与马氏体中的缺陷有关.     

分析部分环状覆盖PCLD圆锥壳自由振动与阻尼特性的半解析法

基于Donnell薄壳和线粘弹性理论,对于粘弹性层仅考虑剪切变形,并采用复常量模型模拟粘性层的能耗特性,导出了PCLD圆锥层合壳的整合一阶常微分矩阵方程,由于周向曲率是纵向坐标的函数,系数矩阵比圆柱层合壳复杂。然后借助精细积分和传递矩阵法,提出了一种分析部分覆盖PCLD圆锥层合壳自由振动和阻尼特性的半解析方法。通过数值算例证明了本文方法的有效性,文中还讨论了覆盖率等参数对PCLD圆锥层合壳固有频率和损耗因子的影响,影响程度和PCLD圆柱层合壳也不同。     

热声斯特林发动机系统起消振过程研究

在自行研制的1台行波型热声斯特林发动机上考察其起振和消振行为。针对不同的加热功率和充气压力，系统地研究了起消振过程中的温度、压力变化特性，着重分析了滞后回路形成的过程和影响热声系统滞后回路的因素，指出滞后回路存在的条件，对深入理解热声系统的起消振行为具有参考意义。     

基于大型振动台试验的SSI阻尼体系判别研究

阻尼体系表征着结构体系的整体耗能特征,阻尼体系类型的判别是结构动力分析方法择取的前提,亦是保证结构抗震分析结果准确的基础.动力作用下土-结构相互作用(soil-structure interaction,SSI)阻尼体系的鉴别,传统上常简单地依材性为判据,缺乏深入实际的基础性科学研究.基于阻尼体系最基本的判定方法,藉大...     

激光陀螺捷联惯导系统减振功率谱分析

应用多体系统传递矩阵法,推导了激光陀螺捷联惯导减振系统各元件的传递方程和传递矩阵,建立了相应的多体系统动力学模型,获得了系统总传递方程、总传递矩阵和响应的功率谱密度.分别应用文中方法和通常振动分析方法,获得了随机输入条件下激光陀螺捷联惯导减振系统动态响应的功率谱密度,仿真结果对比表明了文中方法的有效性.文中方法无需建立系统总体动力学方程,计算速度快、建模灵活,为激光陀螺捷联惯导系统减振设计提供了新的技术手段.     

安装预紧量对金属橡胶构件干摩擦阻尼的影响

为了研究安装预紧量对金属橡胶构件的干摩擦阻尼性能及寿命的影响,分别对预紧量为Q=1.11mm和Q=2.2mm的金属橡胶隔振器进行了静态及振动实验研究.结果表明:改变金属橡胶隔振器的预紧量,其承载能力及能量耗散性能均将发生变化,具有较小预紧量(Q=1.1 mm)的金属橡胶隔振器的承载能力及耗散振动能量的能力优于具有较大预紧量(Q=2.2 mm)的金属橡胶隔振器的相应指标,且使用寿命比较长.实验证明,适当控制金属橡胶构件的预紧量,可以实现对金属橡胶隔振器的干摩擦阻尼性能的有效控制.     

传感器固有频率和阻尼对冲击加速度检测的影响

研究了硅微机械高g(g为重力加速度)加速度传感器的固有频率和阻尼特性对冲击响应的影响。传感器固有频率低,阻尼小时,冲击加速度的响应波形包含传感器共振波,造成测量干扰。采用有适当阻尼,固有频率高的双质量块结构高g加速度传感器,进行接近2万g加速度峰值的一系列落杆冲击实验,都未见共振响应。同样的传感器制作成欠阻尼,进行实验时,发现共振干扰。该实验所用的传感器芯片面积小,固有频率高,调整该结构的弹性梁厚度,可制作量程为2×103g～2×105g的加速度传感器。     

超导HWR腔垂直测试低温系统试验研究

中国科学院先导科技专项ADS(Accelerator Driven Suberitical,ADS)嬗变系统中超导HWR(half-wave resonator,HWR)腔垂直测试需低温系统维持4.2 K(液氦)的低温环境,低温系统降温过程包括氮气置换、液氮预冷、氦气置换和液氦冷却。通过实验建立了低温系统降温4个阶段不同测点温度随时间的变化规律,在此基础上,计算了液氦的消耗速率和杜瓦的静态热负荷,分析了低温系统在稳定工作状态时最佳的液氦补液时间间隔。结果表明:该低温系统满足超导HWR腔垂直测试需求,消耗液氮约175 kg、液氦约2 048 L,低温系统稳定工作时液氦体积消耗速率为32 L/h,杜瓦静态热负荷为21.36 W,液氦合理补液时间间隔为4 h,为后续超导HWR腔垂直测试提供了保障。     

MMA/EMA/EA胶乳型互穿网络聚合物阻尼特性研究

用乳液聚合的方法制备了MMA/EMA/EA的LIPN ,对其阻尼特性进行了研究 ,并研究了增塑剂和填料对其阻尼性能的影响。结果发现 ,此LIPN具有良好的阻尼特性 ,增塑剂的加入对其阻尼特性影响很小。而不同的填料对其阻尼特性的影响不同。其中具有球状立体结构的富勒烯的加入会使其阻尼性能得到大幅度提高     

环形倍频腔系统稳定性的分析

为了实现通过腔外倍频钛宝石可调谐激光(851．1m)而得到所需波长(425．6nm)的光。首先根据二次谐波产生理论讨论了针对利用LBO晶体倍频851．1nm光时有关晶体参数的选择，然后在此基础上利用矩阵光学的方法分析了环型外谐振倍频腔的几何参数，包括腔的尺寸，反射镜的曲率半径等对系统稳定性的影响及倍频光输出功率稳定性的影响，并作了数值计算和分析。