纯消相干对量子点-微腔激射性质的影响

应用量子主方程理论研究量子点-微腔耦合系统的激射性质.分别探索了不同类型的微腔耦合系统("好的系统"、"中等系统")在外加泵浦场的作用下表现出的激射现象.分析比较了失谐大小及环境纯消相干对这两种微腔耦合系统的内部特性(光场分布、腔内光子数等)产生的影响.数值仿真表明:对于"好的系统",在失谐量不大的情况下,引入适当的纯消相干有利于提高耦合系统的激射性能;对于"中等系统",由于失谐条件下光子在腔内集聚困难,因而很难达到激射,但是通过引入适量的纯消相干可以对腔内光场分布和光子数产生剧烈调制作用.该结果对于研究单量子点激光器,以及探索光与物质相互作用等方面具有指导作用.     

耗散耦合腔阵列耦合量子化腔场驱动三能级体系中的单光子输运

基于准玻色方法,解析求解了环境作用下一维耦合腔阵列耦合一个量子化腔场驱动的级联能级原子系统中单光子输运的反射率、透射率和相应等效势的表达式,并详细讨论了耗散情况下控制参数对单光子输运的影响.研究结果表明:在实验范围内选择合适的参数时,原子耗散和腔场耗散都能使反射率峰值降低,但原子耗散影响反射率较大,同等参数取值条件下反射率峰值减小更为显著;更为重要的是对于在环境作用下的体系,通过调节原子和腔场之间的失谐以及驱动量子化腔场的光子数仍可使单光子接近达到全反射.     

等效零折射率材料微腔中均匀化腔场作用下的简正模劈裂现象

研究了零折射率材料微腔中人造原子与腔模的相干耦合现象.首先通过数值模拟的方法研究了在二维光子晶体微腔中填充阻抗匹配的零折射率材料后腔模的场分布.结果表明零折射率材料的引入使得原本以驻波场形式存在的腔模分布在整个微腔中变得近似均匀且值最大.其次,将人造原子放入腔中的不同位置并与腔模耦合,结果从频谱上观察到腔模的劈裂与人造原子在腔中的位置无关.最后,利用微波实验,通过开口谐振环等效的人造原子与一维复合左右手传输线等效的零折射率材料微腔之间的耦合验证了仿真结果的准确性.该结果为腔量子电动力学中量子点对位难的问题提供了新的方案,同时零折射率材料微腔也为今后研究原子与光子之间的相互作用提供了一个新的平台.     

含克尔介质微波激射器的原子辐射率

建立了含克尔介质微波激射器(micromaser with Kerr medium)的基本量子原理,分析计算了处于不同方式(热原子和超冷原子状态)下的二能级原子沿z轴穿过处于相干态的含克尔介质微腔的原子辐射率,并着重讨论了克尔介质与单模辐射场作用的耦合强度χ、失谐量Δ和原子注入速率r对原子辐射概率的影响. 关键词： 含克尔介质微波激射器 热原子和超冷原子 原子辐射率     

强度相关耦合双Jaynes-Cummings模型中的纠缠和量子失谐

研究强度相关耦合双Jaynes-Cummings模型中, 两运动原子初始处于最大纠缠态、光场初始处于单模热态时, 强度相关耦合、热光场平均光子数以及原子运动对两原子的纠缠和量子失谐的影响. 结果表明: 考虑强度相关耦合时, 纠缠和量子失谐均出现周期性地消失和回复现象, 并且, 回复以后的纠缠和量子失谐能达到初始值. 腔场温度的升高会加速纠缠和量子失谐的消失. 此外, 原子运动的场模结构参数对该模型中的纠缠和量子失谐影响很大, 其值选择合适时, 两个原子能够自始至终地保持纠缠或量子失谐状态. 关键词： 强度相关耦合 双Jaynes-Cummings模型 纠缠 量子失谐     

单模光腔中N个二能级原子系统的有限温度特性和相变

本文研究单模光场中N个二能级原子Dicke模型的有限温度特性和相变. 把原子赝自旋转换为双模费米算符, 用虚时路径积分方法推导出系统的配分函数, 对作用量变分求极值得到系统的热力学平衡方程, 及原子布居数期待值和平均光子数随原子-光场耦合强度变化的解析表达式. 重点研究了在量子涨落起主导作用的低温区, 由耦合强度变化产生的从正常相到超辐射相的相变, 指出该相变遵从Landau连续相变理论, 平均光子数可作为序参数, 零值表示正常相, 大于零则为超辐射相. 在零温极限下本文的结果和量子相变理论完全符合. 另外, 本文也讨论了系统的热力学性质, 比较有限温度相变和量子相变的异同. 发现, 在强耦合区低温稳定态的光子数和平均能量都和绝对零度的值趋于一致, 而超辐射相的熵则随耦合强度的增强迅速衰减为零.     

光腔中两组分玻色-爱因斯坦凝聚体的受激辐射特性和量子相变

研究了单模光腔中两组分玻色-爱因斯坦凝聚的基态性质和相关的量子相变.通过利用自旋相干态变换将等效赝自旋哈密顿算符对角化并求得基态能量泛函.基态能量泛函对其经典场变量进行变分并取极小值,得到光子数解和相边界曲线.通过稳定性讨论发现系统除了出现正常相和超辐射相之外,还得到了多稳的宏观量子态;受激辐射来自于原子数反转的集体态,单组分的Dicke系统中并没有此现象;受激辐射只能从一组分的原子中产生,而另外的仍保持在普通超辐射状态.通过调整相关的原子-场耦合强度和频率失谐,超辐射和受激辐射态的顺序可以在原子的两个组分之间互换.     

劣腔情况失谐双光子光学双稳系统的原子压缩效应

本文采用广义Wigner分布函数的Fokker-Planck方程的方法,讨论了劣腔极限下失谐双光子光学双稳系统的原子压缩效应,得到压缩区在失谐参数△-θ平面的分布,发现在足够大的原子失谐条件下,原子算符R₂也可能出现压缩效应。 关键词：     

量子点腔系统中抽运诱导受激辐射与非谐振腔量子电动力学特性的研究

从量子点和腔相互作用的哈密顿量出发,利用包括非相干抽运,退相干项主方程,并结合量子回归定理,考虑相关初始条件,理论推导和数值计算相结合得出量子点多光子发射光谱精确数值结果.分析多光子发射光谱(费米子统计)和相应单光子情况(玻色子统计)时,得到依据费米子统计,退相干和热浴模型的多光子发射光谱同最近文献[22]量子点——微柱腔实验结果符合得非常好.结合理论和当前实验,显示了量子点腔系统中抽运诱导受激辐射和非谐振腔量子电动力学. 关键词： 量子点 微腔 受激辐射 发射光谱     

基于腔衰减的未知原子纠缠态的浓缩方案

基于具有两个近似简并基态(|g〉,|e〉)和一个激发态(|r〉)的三能级原子的两基态为静态量子比特,光子数态为飞行量子比特.两对非最大原子纠缠对中各有一个原子被分别囚禁在两个泄露腔中,在大失谐极限和激发态自发辐射系数γ远小于失谐量Δ的情况下,利用经典激光脉冲激发和与量子化腔场耦合作用后,通过对从腔中泄露出来的光子进行探测,可以将两对未知非最大原子纠缠态以一定的概率浓缩成最大纠缠态.充分考虑并且利用了腔的衰减,增强了实验的可行性和进行远距离的纠缠态浓缩的实现.     

Effect of Cavity Decay on Entanglement of Ladder-Type Three-Level Atoms and a Two-Mode Cavity Field

Considering the adiabatical approximation and the large detuning condition, we give the effective Hamiltonian of a ladder-type three levels atom interacting with a bimodal cavity field. If two identical three-level atoms are sent through the cavity one by one, a two-atom entangled state can be generated. With the choice of the appropriate interaction time, a maximally entangled state of two atoms can be obtained if decoherence effect is ignored. Moreover, we discuss the effect of cavity decay on four physical quantities including atomic population probability, residual entanglement of the first atom and the cavity field, concurrence between the two atoms, and fidelity for generating atomic EPR state, all of which decrease with the increase of cavity decay when the other parameters are fixed.     

利用三平面腔镜共焦腔产生多模压缩光束

设计了一种阈值下的简并光学参量振荡腔用于产生多模压缩光束,并且利用"薄晶体近似"的方法分析了这个光学参量振荡腔,得到了输出多模压缩光束的噪声谱.数值模拟了多模压缩光束的压缩度和抽运光场或者振荡腔的失谐量之间的关系,得出只有适当选择本底光的相位,抽运光的幅度以及共焦腔的失谐量时,才可以探测到好的信号场噪声谱压缩度.     

Parametric instability and Hamiltonian chaos in cavity semiclassical electrodynamics

We study the nonlinear dynamics of the interaction of two-level atoms and a selected mode of a high-Q cavity with frequency modulation analytically and numerically. In the absence of modulation, the corresponding semiclassical Heisenberg equations for the expectation values of the collective atomic observables and the field-mode amplitudes allow, in the rotating wave approximation and in the strong-coupling limit, an exact solution with arbitrary detuning. Using this solution, we detect the coherent effect of trapping of the population of atomic levels and of trapping of the number of photons in the cavity. The explanation for this effect lies in the destructive interference of the atomic dipoles and the field mode. The integrable version of the system of equations exhibits a separatrix near which a stochastic layer is formed when modulation is introduced. The width of the layer is found to gradually increase with degree of modulation, and finally it fills the entire energy-permissible volume of the phase space. We show that the rotating wave approximation does not hinder the formation of Hamiltonian chaos in cavity semiclassical electrodynamics. The calculation of the maximum Lyapunov indices of nonlinear (in this approximation) equations of motion as functions of the modulation frequency δ and the frequency of natural Rabi oscillations of the atom-field system, Ω, suggests that Hamiltonian chaos appears first in the area of the fundamental parametric resonance, δ/2Ω≃1. Parametric instability increases with increasing modulation and decreasing detuning from the atom-field resonance, generating at exact resonance new areas of chaos corresponding to multiple parametric resonances. The results of numerical experiments and estimates of the characteristic parameters show that Rydberg atoms placed in a high-Q microwave cavity are possible objects for observing parametric instability and dynamical chaos. Zh. éksp. Teor. Fiz. 115, 740–753 (February 1999)     

Influence of an External Classical Field on the Interaction Between a Field and an Atom in Presence of Intrinsic Damping

The effect of intrinsic damping on the interaction between a two-level atom and a multi-photon cavity field in the presence of an external classical field is studied. Under certain conditions and use of a transformation, the system is transformed to a generalized Jaynes Cummings model, with the influence of classical field included in the detuning parameter. The temporal evolution of some statistical aspects such as, the atomic inversion, the squeezing phenomena and linear entropy are obtained. In addition, we present the effects of the intrinsic damping and detuning parameters on the above mentioned quantities, for one and two photons. The entropy is used as a measure of the degree of entanglement, and consequently discussed.     

Quantum phase properties of the field in a two-photon micromaser

In this paper, we study the quantum phase properties of the field in a two-photon micromaser, including the effects of the finite detuning of the intermediate level. For initial coherent state of the cavity field and atoms initially in their excited state multipeak phase structure appears which eventually leads to the randomization of the cavity field phase. However, the approach towards the randomization depends upon the detuning. If the atoms are injected in a coherent superposition of their upper and lower atomic states then the phase distribution evolves into two-peak structure. For initial thermal state and atoms in polarized state, cavity field acquires some phase. We also consider the effect of finite Q of the cavity, random injection of the atoms and fluctuations in the interaction time.     

Bistability of material waves in an atomic Bose-Einstein condensate in a magnetic interferometer

It is shown theoretically that, upon filling a ring cavity (a loop magnetic waveguide) with an atomic Bose-Einstein condensate (BEC), a hysteresis dependence of the atomic number density inside the cavity on the atomic flux introduced into the cavity from the outside appears. Main parameters of the measuring system being proposed are determined: the reflectance of the magnetic mirror through which the condensate is introduced, the length of the ring cavity, and the strength of the constant magnetic field governing the BEC velocity in the cavity.     

Geometric Phase and Entanglement of a Three-Level Atom With and Without Rotating Wave Approximation

In this paper, we study the dynamics of entanglement between three-level atom and optical field, initially prepared in the squeezed coherent state. We discuss the dynamical behavior of the geometric phase and entanglement, measured by the von Neumann entropy, with and without rotating wave approximation during the time of evolution. The effect of the squeezing and detuning parameters on the evolution of entanglement and geometric phase will be examined. We find that the squeezing and detuning parameters play a central role on the evolution of the geometric phase and nonlocal correlation between the field and the three-level atom. Moreover, we show that the dynamics of the system in the presence of rotating wave approximation has a richer structure compared with the absence of rotating wave approximation.     

非锁相Lorenz-Haken方程动力学研究

考虑原子的相干性和经典注入光场，利用随机微分方程给出非锁相条件下的Lorenz-Haken方程，研究失谐量、注入经典光场和原子相干性对非锁相Lorenz-Haken方程动力学特性的影响．在激光运转情形，失谐量造成光场位相的混沌，系统在不同条件下，出现四吸引子、双吸引子及单吸引子混沌状态，且体系的分数维维数较锁相条件下增加．光场失谐量、注入光场和原子相干性可抑制混沌．在双稳态运转下，光场位相为π的偶数倍或奇数倍，使光场稳定于正值和负值，故体系出现对称双稳态对，但无混沌状态． 关键词： 非锁相Lorenz-Haken方程 混沌 原子相干性 注入光场     

Interaction of nonlinear resonances in cavity QED

Strong coupling of the internal and external degrees of freedom of a cold atom to each other and to the spatially periodic field of the standing light wave in a high-finesse cavity is responsible for the dynamic instability of the atomic center-of-mass motion. Due to a weak interaction of the internal nonlinear resonances in the standard model of cavity QED, a stochastic layer appears, whose width in the semiclassical approximation is estimated in terms of the main parameters of the system: atomic recoil frequency, mean number of excitations, and detuning from the resonance. As a result, the atomic motion in the absolutely regular potential has the fractal character, with long Lévy flights alternating with small chaotic oscillations in potential wells.