The dynamical properties of Rydberg hydrogen atom near a metal surface

In recent years much attention is focused on the dynamics of Rydberg atom in exter- nal fields. At the same time Rydberg atom near a metal surface plays an important role as a typical theoretical model and produces measurable experimental response[1]. As an interesting model it covers many dynamical effects: instantaneous van der Waals inter- action[2,3], Zeeman-Stark effects and diamagnetic effects in strong fields[4], and so on. Its classical motion is very complex. When the atom-surface i…     

The dynamical properties of Rydberg hydrogen atom near a metal surface

The dynamical properties of Rydberg hydrogen atom near a metal surface are presented by using the methods of phase space analysis and closed orbit theory. Transforming the coordinates of the Hamiltonian, we find that the phase space of the system is divided into vibrational and rotational region. Both the Poincaré surface of section and the closed orbit theory verify the same conclusion clearly. In this paper we choose the atomic principal quantum number asn=20. The dynamical character of the exited hydrogen atom depends sensitively on the atom-surface distanced. Whend is sufficiently large, the atom-surface potential can be expressed by the traditional van der Waals force and the system is integrable. Whend becomes smaller, there exists a critical valued _c. Ford>d _c, the system is near-integrable and the motion is regular. While chaotic motion appears ford<d _c, and the system tends to be non-integrable. The trajectories become unstable and the electron might be captured onto the metal surface.     

平行电磁场中里德堡氢原子的自相似结构研究

利用半经典方法研究了平行电磁场中里德堡氢原子的分形自相似现象. 通过研究平行电磁场中里德堡氢原子的逃逸时间和初始出射角间的关系, 发现了逃逸时间图的自相似结构, 并通过研究与图中冰柱对应的逃逸轨道, 得到了自相似结构和逃逸轨道之间的关系, 发现了该类自相似逃逸轨道满足的规律. 进一步研究了标度能量和标度磁场对体系动力学的影响, 表明标度能量和标度磁场均控制体系的分形自相似结构. 当标度能量或标度磁场比较小时, 没有自相似现象, 随着标度能量或标度磁场的增大, 自相似出现, 体系变复杂.     

Floquet study of ionization and high-order harmonic generation for a hydrogen atom in high-frequency laser fields

In this paper, we investigate the dynamics of a hydrogen atom in high-frequency (several atomic units) super strong (up to several tens of atomic units) laser fields within the high frequency Floquet theory framework. The ionization rate, ionization spectrum, angular distribution and high-order harmonic generation are all investigated. Our studies reveal the universal behavior of the total ionization rate, excess-photon ionization spectrum and angular distribution of the ionization rate in the stabilization regime, and achieve a deep insight into the dynamics of high-order harmonic generation in the stabilization regime. Received 6 June 2001 and Received in final form 31 August 2001     

双模光场与运动三能级原子作用系统的反聚束效应

采用求解Schrdinger方程和数值计算方法,研究了双模纠缠相干光场与运动V型三能级原子相互作用过程中的聚束和反聚束效应.结果表明:平均光子数变动不大,系统就会由聚束效应跃变为反聚束效应,关联程度最强;平均光子数取一定数值时,原子运动速度增大引起时间演化曲线显著上移,振荡周期变小,对系统的聚束和反聚束效应也有较强影响.当平均光子数较大时,原子初态和双模纠缠相干光场的纠缠度无任何影响;仅当平均光子数较小时,原子初态和双模纠缠相干光场的纠缠度变化引起曲线振荡幅度变化,位置发生小幅度移动,产生弱关联.     

Preparation and control of entangled states in the two-mode coherent fields interacting with a moving atom via two-photon process

We investigate the preparation and the control of entangled states in a system with the two-mode coherent fields interacting with a moving two-level atom via the two-photon transition. We discuss entanglement properties between the two-mode coherent fields and a moving two-level atom by using the quantum reduced entropy, and those between the two-mode coherent fields by using the quantum relative entropy. In addition, we examine the influences of the atomic motion and field-mode structure parameter $p$ on the quantum entanglement of the system. Our results show that the period and the duration of the prepared maximal atom-field entangled states and the frequency of maximal two-mode field entangled states can be controlled, and that a sustained entangled state of the two-mode field, which is independent of atomic motion and the evolution time, can be obtained, by choosing appropriately the parameters of atomic motion, field-mode structure, initial state and interaction time of the system.     

Ionization of Rydberg atoms in THz-laser fields at the transition from low to high scaled frequencies

We have studied the ionization of Rydberg-excited xenon atoms in THz-laser fields and by quantum dynamical calculations. The experimental threshold laser field strength for 10% ionization probability follows an n^*-1.68 (1.04 THz) dependence (n^* effective principal quantum number) with additional weak resonance structures and shows that ionization does not occur by a Landau-Zener mechanism. At scaled frequencies of to 5.6 the simulated threshold fields for ionization in oscillatory fields show a dependence on the principal quantum number n of n^-4.1 to n^-1.35. Received: 17 February 1998 / Revised: 20 April 1998 / Accepted: 21 April 1998     

Quantum signatures in the dynamics of two dipole-dipole interacting soft dimers

The quantum covariances of physically transparent pairs of observables relative to two dimers hosted in a solid matrix are exactly investigated in the temporal domain. Both dimers possess fermionic and bosonic degrees of freedom and are dipolarly coupled. We find out and describe clear signatures traceable back to the presence and persistence of quantum coherence in the time evolution of the system. Manifestations of a competition between intramolecular and intermolecular energy migration mechanisms are brought to light. The experimental relevance of our results is briefly commented.     

Quantum entanglement between the two-mode fields and atomic entropy squeezing in the system of a moving atom interacting with two-mode entangled coherent field

This paper investigates the entropy squeezing of a moving two-level atom interacting with the two-mode entangled coherent field via two-photon transition by using an entropic uncertainty relation and the degree of entanglement between the two-mode fields by using quantum relative entropy. The results obtained from numerical calculation indicate that the squeezed period, the duration of entropy squeezing and the maximal squeezing can be controlled by appropriately choosing the intensity of the light field, the atomic motion and the field-mode structure. The atomic motion leads to the periodic recovery of the initial maximal degree of entanglement between the two-mode fields. Moreover, there exists a corresponding relation between the time evolution properties of the atomic entropy squeezing and those of the entanglement between the two-mode fields.     

Non-adiabatic quantum molecular dynamics: General formalism and case study H<Subscript>2</Subscript><Superscript>+</Superscript> in strong laser fields

In Rydberg atoms subject to static and harmonic collinear electric fields, intrashell transition can be induced by the first order perturbation from a small perpendicular electric or magnetic field, or by effects of the second order in the major fields. Both mechanisms lead to resonances that are suppressed under certain conditions, and high-frequency interference oscillations in case of non-adiabatic field switching. Recent measurements of microwave ionization signals show very rich and fascinating structures similar to the ones predicted for intrashell mixing. We show that the observed ionization structures may be explained by diabatic electric-field ionization and the consistent use of perturbation theory for intrashell mixing. In particular, the dominant oscillation frequency is successfully interpreted in terms of interference between first and second order transition amplitudes. New predictions are provided. The present approach gives a comprehensive picture of intrashell transitions, which may be tested in future experiments designed to observe such transitions directly. Received 2 May 2002 / Received in final form 23 September 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: Valentin.Ostrovsky@pobox.spbu.ru RID="b" ID="b"e-mail: horsdal@ifa.au.dk     

Conductance properties in spin field-effect transistors

Conductance properties in spin field-effect transistors (SFET) are studied by taking into account the Rashba spin-orbit coupling strength, the presence of external magnetic field, the angle between the direction of magnetization and the conductance band mismatch between the ferromagnetic contacts and the channel. It is shown that the conductance of the SFET has high peaks while the value of external magnetic field varies. These peaks become more and more pronounced with the potential barriers strength increasing. The conductance peaks also appear by increasing the strength of the spin-orbit coupling. It is found that the conductance exhibits quantum oscillating behavior when varying the angle between the direction of magnetization in the two contacts. The influence of conductance band mismatch between the contacts and channel is also discussed.