不同原子的选择电离和测量产生腔场压缩的比较

研究了一个慢的二能级里德伯原子和一个快的三能级里德伯原子与腔场发生相互作用后腔场的压缩性质。结果表明, 对快原子进行选择电离和测量, 腔场不存在压缩; 而对慢原子进行选择性电离和测量, 腔场存在压缩, 最大压缩处压缩参量可达２５％ 。     

原子的选择电离和测量对腔场压缩性质的影响

研究了里德伯原子与腔场发生相互作用后腔场的压缩性质.结果表明,对不同的原子进行选择电离和测量腔场的压缩性质不同.且最大压缩处压缩参量可达25%.     

里德伯原子向超冷等离子体的自发转化

在铯原子MOT中,利用三光子激发冷原子获得超冷里德伯原子,改变里德伯原子间的相互作用时间,获得超冷等离子体的信号.研究了里德伯原子向超冷等离子体的自发转化过程和里德伯原子的初始电离机理. 关键词： 里德伯原子 相互作用 等离子体 电离机理     

腔增强热里德伯原子光谱

高精度里德伯原子光谱在研究里德伯原子间的相互作用、里德伯能级结构、电磁场的精密测量等方面具有重要的应用价值,里德伯原子光谱对比度、信噪比的提高和线宽的压窄是获得高灵敏测量的基础.本文通过理论和实验研究了腔增强的里德伯原子光谱,与自由空间的光谱相比实现了在光谱线宽不变情况下11.5倍的光谱对比度和信噪比的提高.其原因是在双光子共振处产生的电磁诱导透明和光泵浦效应会导致腔内原子对探测光吸收的减弱,提高了光学腔的阻抗匹配效率,从而使进入腔内的光强增大,因此提高了里德伯原子光谱的对比度和信噪比,提高的倍数取决于探测光穿过原子的透射率.预期通过优化铯原子温度,光谱的对比度和信噪比能够提高23倍.本工作为提高里德伯原子光谱的对比度和基于里德伯原子的精密测量灵敏度提供了参考.     

选择原子测量对原子偶极压缩效应的影响

考虑两个初始处于纠缠态的A型三能级原子,将其中一原子注入双模腔中与光场发生共振相互作用的情况.采用数值计算方法,研究了对腔外原子的选择测量对腔内原子偶极压缩效应的影响.研究结果表明:采用选择原子测量方法,通过对腔外原子进行选择性测量,可增强腔内原子的偶极压缩效应.     

远程控制纠缠原子的偶极压缩

考虑初始处于EPR态的两个二能级原子A、B,将B原子注入处于真空态和单光子态的叠加态的腔中,演化一段时间后,对B原子进行选择性测量,通过选择合适的腔场初始叠加状态和演化时间,可控制原子A的偶极矩压缩效应.     

用相干态腔场控制纠缠原子的偶极压缩

考虑初始处于EPR态的两个二能级原子A、B,将B原子注入处于相干态的腔中,演化一段时问后,对B原子进行选择性测量.当相干态腔场的平均光子数足够大时,原子A可呈现偶极矩压缩效应.     

原子-腔-光纤复合系统中的纠缠特性

采用Negativity熵来描述两子系统间的纠缠,研究了由两个二能级原子与光纤联接的单模腔构成的系统的纠缠特性.利用数值计算方法讨论了原子与腔场的耦合强度和原子选择性测量对纠缠特性的影响.研究结果表明:对一个原子的选择性测量,可增强原子间与腔场间和腔场与腔场间的纠缠.     

双模腔场与一个V型三能级原子共振相互作用的压缩特性

采用全量子理论和数值计算方法,研究了初始处于相干态的双模腔场与一个V型三能级原子共振相互作用的压缩特性,讨论了在没有对原子进行态选择测量、直接对原子进行态选择测量和应用经典微波场并对原子进行态选择测量的三种情况下,腔模平均光子数、耦合系数以及相互作用时间对压缩特性的影响。证明了压缩随着两个腔模光子数的增加而增加,而且通过对原子进行态选择性测量可以使压缩大大地增强,即使少光子数也一样。综合所有情形,发现最大压缩可以接近75%。     

原子-腔-光纤复合系统中的纠缠特性

采用Negativity熵来描述两子系统间的纠缠,研究了由两个二能级原子与光纤联接的单模腔构成的系统的纠缠特性.利用数值计算方法讨论了原子与腔场的耦合强度和原子选择性测量对纠缠特性的影响.研究结果表明:对一个原子的选择性测量,可增强原子间与腔场间和腔场与腔场间的纠缠.     

Displacing Rydberg electrons: the mono-cycle nature of half-cycle pulses

A THz "half-cycle" pulse is a fast ( <1 ps) unipolar pulse, followed by a slow unipolar pulse of opposite polarity. We found that the interaction of such THz pulses with very high Rydberg states results in a displacement of the electron within the atom, while the ionization is strongly suppressed. In classical terms: the first fast unipolar feature corresponds to a start kick of the Rydberg electron, while the second unipolar feature acts as a stop kick. A semiclassical model is presented which qualitatively reproduces the ionization suppression and redistribution.     

Collision of Rydberg atom A** with ground-state atom B: Optical potential

The method of optical potential was used to calculate the slow collision of Rydberg atom A** with ground-state atom B. As an example, calculations were carried out for the Na**(nl)+He system.     

Entanglement dynamics and quasiprobability distribution for the degenerate Raman process

In this paper, we consider the model which consists of a degenerate Raman process involving two degenerate Rydberg energy levels of an atom interacting with a single-mode cavity field. The influence of the atomic coherence on the von Neumann entropy of the atom and the atomic inversion is investigated. It is shown that the atomic coherence decreases the amount of atom-field entanglement. It is also found that the collapse and revival times are independent of the atomic coherence, while the amplitude of the revivals is sensitive to this coherence. Moreover, the Q function and the entropy squeezing of the field are examined. Some new conclusions can be obtained.     

压缩真空中的电磁诱导透明

从主方程出发,通过解析求解密度矩阵非对角元,研究了压缩真空中Λ型三能级原子的电磁诱导透明现象(EIT).研究结果表明:EIT显著地依赖于相干光场的相位、压缩真空的压缩强度和压缩相位.Λ型三能级原子不但有电磁诱导透明和慢光速现象,而且还会表现出对探测光的增益、快光速和反向光速效应;且Λ型三能级原子对探测光场的吸收和增益与探测光强度有关,这与普通真空中不同. 关键词： 压缩真空 电磁诱导透明 增益     

Perturbation of highly excited states of an atom by the field of a neutral particle

Rydberg atom A** states perturbed by the force field of a neutral atom B are examined. The problem is reduced to studying the wave functions of the composite system and elucidating their fundamental differences from the Rydberg wave functions. The wave function of the Rydberg atom A**-atom B system is constructed using the finite-radius potential method with consideration for the short- and long-range interactions of the weakly bound Rydberg electron with the perturbing particle. The Na**-He system is considered as an example.     

原子间相互作用对双模原子激光压缩性质的影响

研究了由单模压缩相干态光场与Ξ型三能级原子玻色爱因斯坦凝聚体(BEC)相互作用系统中耦合输出的双模原子激光的压缩特性,重点讨论了玻色爱因斯坦凝聚体原子间相互作用对原子激光压缩性质的影响,并讨论了原子激光压缩对光场初始压缩因子的依赖关系。结果表明:由光场诱导的双模原子激光呈现周期性的压缩,原子间的相互作用和光场初始压缩因子对原子的压缩性质具有重要影响。原子间的相互作用影响原子激光压缩的振荡频率而不会影响其压缩深度,而初始光场的压缩因子则对原子激光压缩深度产生调制作用,且初始光场的压缩因子越大,则原子激光压缩的时间越短。     

An experimental approach for investigating many-body phenomena in Rydberg-interacting quantum systems

Recent developments in the study of ultracold Rydberg gases demand an adwanced level of experimental sophistication, in which high atomic and optical densities must be combined with excellent control of external fields and sensitive Rydberg atom detection. We describe a tailored experimental system used to produce and study Rydberg-interacting atoms excited from dense ultracold atomic gases. The experiment has been optimized for fast duty cycles using a high flux cold atom source and a three beam optical dipole trap. The latter enables tuning of the atomic density and temperature over several orders of magnitude, all the way to the Bose--Einstein condensation transition. An elec- trode structure surrounding the atoms allows for precise control over electric fields and single-particle sensitive field ionization detection of Rydberg atoms. We review two experiments which highlight the influence of strong Rydberg---Rydberg interactions on different many-body systems. First, the Rydberg blockade effect is used to pre-structure an atomic gas prior to its spontaneous evolution into an ultracold plasma. Second, hybrid states of photons and atoms called dark-state polaritons are studied. By looking at the statistical distribution of Rydberg excited atoms we reveal correlations between dark-state polaritons. These experiments will ultimately provide a deeper understanding of many-body phenomena in strongly-interacting regimes, including the study of strongly-coupled plasmas and interfaces between atoms and light at the quantum level.     

High-precision three-dimensional Rydberg atom localization in a four-level atomic system

Rydberg atoms have been widely investigated due to their large size, long radiative lifetime, huge polarizability and strong dipole-dipole interactions. The position information of Rydberg atoms provides more possibilities for quantum optics research, which can be obtained under the localization method. We study the behavior of three-dimensional(3 D)Rydberg atom localization in a four-level configuration with the measurement of the spatial optical absorption. The atomic localization precision depends strongly on the detuning and Rabi frequency of the involved laser fields. A 100% probability of finding the Rydberg atom at a specific 3 D position is achieved with precision of ～0.031λ. This work demonstrates the possibility for achieving the 3 D atom localization of the Rydberg atom in the experiment.