Atoms near magnetodielectric bodies: van der Waals energy and the Casimir-Polder force

Based on macroscopic QED in linear, causal media, a consistent theory for the Casimir-Polder force acting on an atom positioned near dispersing and absorbing magnetodielectric bodies is presented. The perturbative result for the van der Waals energy is shown to exhibit interesting new features in the presence of magnetodielectric bodies. To go beyond perturbation theory, we start with the center-of-mass equation of motion and derive a dynamical expression for the Casimir-Polder force acting on an atom prepared in an arbitrary electronic state. For a nondriven atom in the weak coupling regime, the force as a function of time is shown to be a superposition of force components that are related to the electronic density matrix elements at a chosen time. These force components depend on the position-dependent polarizability of the atom, which correctly accounts for the body-induced level shifts and broadenings.     

Casimir-Polder interaction of excited media

The potential of long-range interaction between two dissimilar atoms, one of which is excited, drops as 1/R ₂ with the distance for the Casimir-Polder limit of large distances in comparison with the wave-length of atom transitions (E.A. Power and T. Thirunamachandran, Phys. Rev. A 51, 3660 (1995)). It is shown that such a dependence, obtained with the help of perturbation technique, results in a divergence for the interaction potential between an excited atom and a medium of dilute gas. We develop a nonperturbative method based upon quantum Green’s functions (Yu. Sherkunov, Phys. Rev. A 72, 052703 (2005)) to calculate the interaction potential for an excited atom and a ground-state atom embedded in a dielectric medium, taking into account the absorption of photons in the dielectric medium. The exponential suppression of the interaction between the atoms is demonstrated. The force acting on an excited atom near the interface of dilute gas medium is calculated. The result is no more divergent. The force between gas media in Casimir-Polder regime is calculated as well. The text was submitted by the author in English.     

Thermal Casimir versus Casimir-Polder forces: equilibrium and nonequilibrium forces

We critically discuss whether and under what conditions Lifshitz theory may be used to describe thermal Casimir-Polder forces on atoms or molecules. An exact treatment of the atom-field coupling reveals that for a ground-state atom (molecule), terms associated with virtual-photon absorption lead to a deviation from the traditional Lifshitz result; they are identified as a signature of nonequilibrium dynamics. Even the equilibrium force on a thermalized atom (molecule) may be overestimated when using the ground-state polarizability instead of its thermal counterpart.     

Casimir-Polder力对左手材料板附近的原子的动力学作用

本文研究了初始处于激发态的两能级原子在左手材料附近运动时Casimir-Polder力对原子动力学的影响. 左手材料有两个的作用: 一是在距离界面波长区域内提供了较强的Casimir-Polder共振力, 二是在这一范围原子的自发辐射受到抑制, 延长了作用时间. 这两种效应使得依靠原子自发辐射这一过程中的Casimir-Polder力能对原子的运动学产生影响, 并将一定初速度的原子排斥远离界面. 由于原子偶极矩的取向会影响Casimir-Polder力的性质, 因此对于某些初始条件(初速度和初始位置), 不同偶极矩取向的原子有不同的运动学结果, 会被吸引到界面或反射出去, 从而对具有不同偶极矩方向的原子进行筛选. 当然由于Casimir-Polder力很小, 能够反射的初速度也很小, 但是已经可以反抗极低温的热涨落, 我们的理论预估值约为15 μupK. 如果和其他约束手段同时作用, 便能对原子的动力学产生更为有利的控制.     

Vacuum correlators of the electromagnetic field and the Casimir-Polder forces in the field of a cosmic string

Vacuum correlators of the electric and magnetic fields are calculated in the geometry of a cosmic string. Formulas for the vacuum expectation values for the squares of field components are derived. The forces acting on an atom due to the vacuum fluctuations (Casimir-Polder forces) are investigated. For atoms with isotropic tensor of polarizability these forces are attractive with respect to the string. In the anisotropic case, depending on the eigenvalues of the polarizability tensor, the Casimir-Polder forces can be either attractive or repulsive.     

Casimir force on amplifying bodies

Based on a unified approach to macroscopic QED that allows for the inclusion of amplification in a limited space and frequency range, we study the Casimir force as a Lorentz force on an arbitrary partially amplifying system of linearly locally responding (isotropic) magnetoelectric bodies. We demonstrate that the force on a weakly polarisable/magnetisable amplifying object in the presence of a purely absorbing environment can be expressed as a sum over the Casimir-Polder forces on the excited atoms inside the body. As an example, the resonant force between a plate consisting of a dilute gas of excited atoms and a perfect mirror is calculated.     

The dynamical Casimir-Polder force in relativistic atomic motion near the surface of a thick plate

The dynamical Casimir-Polder force between a neutral atom (in the ground state) and a thick plate in relativistic motion of the atom in the direction parallel to the surface has been calculated. The material properties have been considered in the framework of the oscillator model of the atom and the Drude dielectric function for a plate. The limiting cases of the nonrelativistic velocity and perfectly conducting material of the plate have been discussed. A complex dependence of the force on the velocity (energy), the distance, and the material properties of the surface has been found.     

Bosonic enhancement of spontaneous emission near an interface

We show how the spontaneous emission rate of an excited two-level atom placed in a trapped Bose-Einstein condensate of ground-state atoms is enhanced by bosonic stimulation. This stimulation depends on the overlap of the excited matter-wave packet with the macroscopically occupied condensate wave function, and provides a probe of the spatial coherence of the Bose gas. The effect can be used to amplify the distance-dependent decay rate of an excited atom near an interface.     

Electronic Casimir-Polder Force in a One-dimensional Tight-Binding Nanowire at Finite Temperature

We study the effect of two non-interacting impurity atoms near by a one-dimensional nanowire, which is modeled as a tight-binding hopping model. The virtual single-electron hopping between two impurities will induce an additional energy depending on the distance of two impurities, which gives a electronic Casimir-Polder effect. We find that the Casimir-Polder force between the two impurities decreases with the impurity-impurity distance exponentially. And the effects of nanowire and finite temperature on the Casimir-Polder force are also discussed in detail, respectively.     

Measurement of the temperature dependence of the Casimir-Polder force

We report on the first measurement of a temperature dependence of the Casimir-Polder force. This measurement was obtained by positioning a nearly pure 87Rb Bose-Einstein condensate a few microns from a dielectric substrate and exciting its dipole oscillation. Changes in the collective oscillation frequency of the magnetically trapped atoms result from spatial variations in the surface-atom force. In our experiment, the dielectric substrate is heated up to 605 K, while the surrounding environment is kept near room temperature (310 K). The effect of the Casimir-Polder force is measured to be nearly 3 times larger for a 605 K substrate than for a room-temperature substrate, showing a clear temperature dependence in agreement with theory.     

Use of lasers to study magnetic resonance and magnetic relaxation

Optical methods of recording ESR, which were developed in the early 1950s to record magnetic resonance of excited atoms, are extensively used at present in investigations of ESR of the ground and excited states of atoms and paramagnetic centers in condensed media [1]. Attention is called in the present communication to additional capabilities of optical ESR and of paramagnetic relaxation methods, which are realizable through the use of laser sources.S. I. Vavilov State Optical Institute, Leningrad. Translated from Primenenie Lazerov v Atomnoi, Molekulyarnoi i Yadernoi Fiziki — Trudy II Vsesoyuznoi Shkoly, pp. 3–11, 1981.     

Laser cooling of quasi-free atoms in a nondissipative optical lattice

A quasi-classical theory of laser cooling is applied to the analysis of cooling of unbound atoms with the angular momenta 1/2 in the ground and excited states in a one-dimensional nondissipative optical lattice. In the low-saturation limit with respect to the pumping field, the mechanisms of cooling can be interpreted within the framework of an effective two-level system of ground-state sublevels. In the limit of weak Raman transitions, the mechanism of cooling of unbound atoms is similar to the Doppler mechanism known in the theory of a two-level atom; in the limit of strong transitions, the mechanism of cooling is analogous to the well-known Sisyphys mechanism. In the slow-atom approximation, analytical expressions are obtained for the friction (drag) coefficient and the induced and spontaneous diffusion, and the kinetic temperature is estimated.     

Calculation of the interaction potential for excited alkali element atoms with the mercury atom. Rb*-Hg interaction

Using a new form for the polarization interaction potential obtained by calculating the most important polarization diagrams of perturbation theory in the Thomas — Fermi approximation, the pseudopotential method is employed to calculate interatomic potentials in a system alkali element in ground and excited states — mercury atom. Calculations of quasimolecular terms based on this technique are presented for the system A-Hg, where A = Na, Rb, some for the first time. A comparison is made to available experimental and theoretical data.Odessa Hydrometeorological Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 31–38, June, 1994.     

Calculation of the potential of interaction of excited atoms of alkali elements with a mercury atom: A-Hg interaction (A=K,Fr)

The interatomic potentials in the system (alkali atom in the ground and excited states)—((mercury atom) are calculated on the basis of the effective pseudopotential method using a new form of the polarized interaction potential obtained from calculations of the most important polarization patterns of perturbation theory in the Thomas-Fermi approximation. This method is used to calculate the intermolecular terms of the system A-Hg (A=K, Fr), some of which have been obtained previously.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 84–88, January, 1996.     

Possible excitation of a fast sodium beam by laser irradiation

We present results of model calculations concerning the fraction of excited atoms obtained by laser irradiation of a fast sodium atom beam (100–400 eV kinetic energy). We calculated relative absorption probabilities as a function of the intersection angle between the two beams, the atom-beam energy, the atom-beam energy spread and the atom-beam divergence. The fraction of excited atoms that can be obtained at 300 eV is at least a factor of 5 smaller than in the case of a thermal beam, due to the divergence and energy spread of the fast atom beam giving rise to a large Doppler broadening.     

Spin correlations in a pair of atoms induced by spontaneous emission of photons

An analysis is presented of the state that arises after photons have been spontaneously emitted by a pair of spatially separated excited two-level atoms with spin-1/2 ground and excited states. Selection of possible decay scenarios conditioned on the helicities of the photons (even on the helicity of the one emitted first) makes it possible to reveal ground-state spin-projection correlations between atoms. The correlations are due to quantum interference between alternative scenarios (the atom that has emitted a particular photon cannot be identified). The correlations obtained by the chosen selection method are classical.     

Probing the structural,electronic and magnetic properties of small Au4M (M = Sc–Zn) clusters

Density-functional method PW91 has been selected to investigate the structural, electronic and magnetic properties of Au₄M (M =Sc–Zn) clusters. Geometry optimisations show that the M atoms in the ground-state Au₄M clusters favour the most highly coordinated position. The ground-state Au₄M clusters possess a solid structure for M = Sc and Ti and a planar structure for M = V–Zn. The characteristic frequency of the doped clusters is much greater than that of pure gold cluster. The relative stability and chemical activity are analysed by means of the averaged binding energy and highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap for the lowest energy Au₄M clusters. It is found that the dopant atoms can enhance the thermal stability of the host cluster except for Zn atom. The Au₄Ti, Au₄Mn and Au₄Zn clusters have relatively higher chemical stability. The vertical detachment energy, electron affinity and photoelectron spectrum are calculated and simulated theoretically for all the ground-state structures. The magnetism calculations reveal that the total magnetic moment of Au₄M cluster is mainly localised on the M atom and vary from 0 to 5 μ_B by substituting an Au atom in Au₅ cluster with different transition-metal atoms.     

弱磁场下三阱光学超晶格中自旋为1的超冷原子特性研究

双阱光学超晶格中的超冷原子是近期冷原子物理领域的研究热点. 本文推广提出了实现三阱光学超晶格的方案, 并采用精确对角化的方法分别研究了弱磁场下对称三阱 光学超晶格中铁磁性和反铁磁性的自旋为1的原子系统的基态, 发现二者的相图很不相同: 反铁磁性原子对应的相图中没有沿磁场方向总自旋磁量子数为±2的基态, 而铁磁性原子对应的相图中可能有. 在负的二次塞曼能量区域, 铁磁性原子的相图中只有完全极化态. 分析了可控参数影响基态的物理本质. 由于这些量子自旋态可以通过调节外磁场和光势垒的高度非常简便而精确地控制, 适合用来研究自旋纠缠. 关键词： 三阱光学超晶格 自旋为1的原子 弱磁场     

Spontaneous emission of light from a crystal

In the paper a quantum field model crystal — an infinite system of two-level atoms interacting with continuum modes of electromagnetic field — is proposed. Within the framework of this model the spontaneous transition of the crystal from a singly excited state to the ground state accompanied by emission of one photon is studied.     

Theoretical study of the migration of the hydrogen atom adsorbed on aluminum nanowire

We study the behavior of a hydrogen atom adsorbed on aluminum nanowire based on density functional theory. In this study, we focus on the electronic structure, potential energy surface (PES), and quantum mechanical effects on hydrogen and deuterium atoms. The activation energy of the diffusion of a hydrogen atom to the axis direction is derived as 0.19 eV from PES calculations. The probability density, which is calculated by including quantum effects, is localized on an aluminum top site in both cases of hydrogen and deuterium atoms of the ground state. In addition, some excited states are distributed between aluminum atoms on the surface of the nanowire. The energy difference between the ground state and these excited states are below 0.1 eV, which is much smaller than the activation energy of PES calculations. Thus using these excited states, hydrogen and deuterium atoms may move to the axial direction easily. We also discuss the electronic structure of the nanowire surface using quantum energy density defined by one of the authors.