Casimir-Polder interaction of atoms with magnetodielectric bodies

A general theory of the Casimir-Polder interaction of single atoms with dispersing and absorbing magnetodielectric bodies is presented, which is based on QED in linear, causal media. Both ground-state and excited atoms are considered. Whereas the Casimir-Polder force acting on a ground-state atom can conveniently be derived from a perturbative calculation of the atom-field coupling energy, an atom in an excited state is subject to transient force components that can only be fully understood by a dynamical treatment based on the body-assisted vacuum Lorentz force. The results show that the Casimir-Polder force can be influenced by the body-induced broadening and shifting of atomic transitions — an effect that is not accounted for within lowest-order perturbation theory. The theory is used to study the Casimir-Polder force of a ground-state atom placed within a magnetodielectric multilayer system, with special emphasis on thick and thin plates as well as a planar cavity consisting of two thick plates. It is shown how the competing attractive and repulsive force components related to the electric and magnetic properties of the medium, respectively, can — for sufficiently strong magnetic properties — lead to the formation of potential walls and wells.     

Long-range Rydberg-Rydberg interactions and molecular resonances

We present a detailed theoretical treatment to describe the lineshape of molecular resonances in a cold dense gas of rubidium Rydberg atoms. Molecular potentials in Hund's case (c) are calculated by diagonalization of an interaction matrix. We show how the strong ℓ-mixing due to long-range Rydberg-Rydberg interactions can lead to resonances in excitation spectra. Such resonances were first reported in [S.M. Farooqi et al., Phys. Rev. Lett. 91, 183002 (2003)], where single UV photon excitations from the 5s ground state occurred at energies corresponding to normally forbidden transitions or very far detuned from the atomic energies. Here, we focus our attention on resonances at energies corresponding to excited atom pairs (n - 1)p_3/2+(n + 1)p_3/2. Very good agreement between the theoretical and experimental lineshapes is found.     

Quantum theory of van der Waals interactions between excited atoms and birefringent dielectric surfaces

A theory of van der Waals (vdW) interaction between an atom (in ground or excited state) and a birefringent dielectric surface with an arbitrary orientation of the principal optic axis (C-axis) is presented. Our theoretical approach is based on quantum-mechanical linear response theory, using generalized susceptibilities for both atom and electromagnetic field. Resonant atom-surface coupling is predicted for excited-state atoms interacting with a dispersive dielectric surface, when an atom de-excitation channel gets into resonance with a surface polariton mode. In the non-retarded regime, this resonant coupling can lead to enhanced attractive or repulsive vdW surface forces, as well as to a dissipative coupling increasing the excited-state relaxation. We show that the strongly non-scalar character of the interaction with the birefringent surface produces a C-axis-dependent symmetry-breaking of the atomic wavefunction. Changes of the C-axis orientation may also lead to a frequency shift of the surface polariton mode, allowing for tuning on or off the resonant coupling, resulting in a special type of engineering of surface forces. This is analysed here in the case of cesium 6D _3/2 level interacting with a sapphire interface, where it is shown that an adequate choice of the sapphire C-axis orientation allows one to transform vdW surface attraction into repulsion, and to interpret recent experimental observations based on selective reflection methods [H. Failache etal., Phys. Rev. Lett. 83, 5467 (1999)]. Received 24 January 2001     

Ionisation of phosphorus, arsenic, antimony, and bismuth by electron impact

Total ionization cross sections of neutral phosphorus, arsenic, antimony, and bismuth atoms by electron impact are reported and compared to the only available experimental results by Freund et al. [Phys. Rev. A 41, 3575 (1990)]. These calculations take into account the possibilities that some target atoms used in the experiments were in metastable states close to the ground state, the excitation-autoionization of nsnp⁴ excited states may be substantial, and the ions produced in experiments may be in excited, low-lying metastable states. The cross sections for direct ionization calculations are based on the BEB model by Kim and Rudd [Phys. Rev. A 50, 3954 (1994)]. Plane-wave Born cross sections scaled by the method developed by Kim [Phys. Rev. A 64, 3954 032713 (2001)] are used to determine the contributions from excitation-autoionization. The combination of the BEB model and the scaled Born cross sections is in agreement with the experimental data by Freund et al. These theoretical data are useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies.     

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.     

Calculation of stopping power for partially stripped ions using an oscillator model

Collision of swift ions with atoms was considered in this paper. The projectile and target atoms were modeled as assemblies of quantum oscillators and it was assumed that both, target and projectile could be excited or ionized, without charge exchange. The model presented here is an extension of the one given by Sigmund and Haagerup [Phys. Rev. A 34, 892 (1986)]. The number of electrons bound to the projectile, as a function of the projectile velocity, was used from Cabrera-Trujillo et al. [Phys. Rev. A 55, 2864 (1997)]. Contributions to energy loss from excitation of the projectile and targets were separately considered. It has been found that projectile excitation contributes up to 20% to the total energy loss in the lower energy region. Comparisons with other authors, including SRIM 2003, are also given and good agreement was found.     

Demonstration of the approximation of eliminating atomic excited populations in an atomben cavity system

Using the master equation approach to a V-type three-level atom inside a high-finesse single-mode cavity in the strong coupling condition, we demonstrate the approximation of eliminating populations of atomic excited states, which is widely used in the field of the atom-cavity systems [Hechenblaikner G, Gangl M, Horak P and Ritsch H 1998 Phys. Rev. A 58 3030]; Liu L W, Tan T and Xu Y 2008 J. Mod. Opt. 56 968; Cho J, Angelakis D G and Bose S 2008 Phys. Rev. A 78 062338. This is reflected in the deviation of the population δ, of which the value is 10^-3～10^-2. We further find the deviation of the dipole force and demonstrate that the deviation of atomic population will not notably affect the dipole force of the atom in the strong coupling condition. A relevant experimental case is also presented.     

Twin-correlations in atoms

We discuss the possibility of preparing an atomic sample of atoms with minimum fluctuations in the difference between populations of two levels. A first scheme involves absorption of twin beams of light, and it presents a variant of a recent proposal for atomic spin squeezing within an excited state manifold [Kuzmich et al., Phys. Rev. Lett. 79, 4782 (1997)]. A second scheme involves atoms with two stable states, and we suggest that by use of quantum non-demolition detection and feed-back optical pumping, we may ensure a perfect agreement between the number of atoms in these two states. Received: 14 May 1998 / Revised: 10 August 1998 / Accepted: 8 October 1998     

Dynamic Properties for BEC in an Optical Cavity with Atom-Photon Nonlinear Interaction

In this paper we investigate the dynamics of physical properties of the system introduced in Dimer et al. (Phys. Rev. A 75, 013804, 2007) and Zhao et al. (Phys. Rev. A 90, 023622, 2014) consisting of an ensemble of four-level atoms in Bose-Einstein condensate (BEC) state and a single-mode quantized field in which nonlinear interaction is taken into account. In fact, we start with a four-level atom and then explain how this model can be reduced to an effective two-level one via the adiabatic elimination. Also, our presentation is free of any classical approximation and so it is fully quantized. In this regard, we introduce the dynamical Hamiltonian of the system in terms of angular momentum operators and use the Dicke model to achieve the state of atomic sub-system. After obtaining the analytical solution of the state vector associated with the quantized BEC-field system, various physical properties such as atomic population inversion, quantum statistics of the field, squeezing in atomic and field subsystems as well as the degree of entanglement between the “BEC atoms” and the “photons” are numerically evaluated. It is shown that, the nonlinear interaction and other involved parameters in the presented model can dramatically affect the dynamics of the system. The collapse-revival phenomenon in the population inversion, Mandel parameter and atomic squeezing is a superb feature of the system which can be controlled by tuning the chosen parameters. Meanwhile, we propose an efficient way for the generation of sub-Poissonian and squeezed fields as well as squeezed atoms via nonlinear interaction of quantized filed with atomic BEC. In addition, it is found that, after the onset of interaction the system is always entangled. Altogether, under particular conditions, the approximated sudden death and then revival of entanglement can be observed.

     

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.     

Optics of moving media

Light experiences a moving medium as an effective gravitational field. In the limit of low medium velocities the medium flow plays the role of a magnetic vector potential. We review the background of our theory [U. Leonhardt and P. Piwnicki, Phys. Rev. A 60, 4301 (1999); Phys. Rev. Lett. 84, 822 (2000)], including our proposal of making optical black holes. Received: 4 July 2000 / Revised version: 17 October 2000 / Published online: 6 December 2000     

Two-atom van der Waals interaction between polarizable/magnetizable atoms near magnetoelectric bodies

The van der Waals potential of two atoms in the presence of an arbitrary arrangement of dispersing and absorbing magnetoelectric bodies is studied. Starting from a polarizable atom placed within a given geometry, its interaction with a second polarizable/magnetizable atom is deduced from its Casimir-Polder interaction with a weakly polarizable/magnetizable test body. The general expressions for the van der Waals potential obtained thusly are illustrated by considering first the case of two atoms in free space, with special emphasis on the interaction between (i) two polarizable atoms and (ii) a polarizable and a magnetizable atom. Furthermore, the influence of magnetoelectric bodies on the van der Waals interaction is studied in detail for the example of two atoms placed near a perfectly reflecting plate or a magnetoelectric half space, respectively. The text was submitted by the authors in English.     

Microscopic theory of modified spontaneous emission in a dielectric

The modification of the radiative decay rate of a source atom embedded in a uniform, isotropic dielectric is calculated to first order in the density of the dielectric atoms using a microscopic approach. In contrast to the recent results of Crenshaw and Bowden [Phys. Rev. Lett. 85, 1851 (2000)]], the decay rate is found to be consistent with macroscopic theories based on quantization of the field in the dielectric.     

Reduction of magnetic noise in atom chips by material optimization

We discuss the influence of the material type in metal wires to the electromagnetic fluctuations in magnetic microtraps close to the surface of an atom chip. We show that significant reduction of the magnetic noise can be achieved by replacing the pure noble metal wires with their dilute alloys. The alloy composition provides an additional degree of freedom which enables a controlled reduction of both magnetic noise and resistivity if the atom chip is cooled. In addition, we provide a careful re-analysis of the magnetically induced trap loss observed by Yu-Ju Lin et al. [Phys. Rev. Lett. 92, 050404 (2004)] and find good agreement with an improved theory.     

Stopping of swift hydrogen diclusters: oscillator model

Enhanced stopping of swift hydrogen diclusters has been analysed theoretically. The target has been modeled as a gas of harmonic-oscillator atoms of variable density. This model predicts a proximity effect, i.e., enhanced stopping at high beam energy, and an oscillatory behavior at low energy. Both features get less pronounced with increasing target density due to increased screening of the ion-target interaction by polarization of the medium. Static screening by electrons accompanying the cluster likewise reduces the proximity effect. The Barkas-Andersen correction has been estimated in the Z₁³Z_1^3 limit. Our findings are in contrast with measurements on SiO₂ [S.M. Shubeita et al., Phys. Rev. B 77, 115327 (2008)] which showed a pronounced step in the energy dependence of the proximity effect.     

The boundary element approach to Van der Waals interactions

We develop a boundary element method to calculate Van der Waals interactions for systems composed of domains of spatially constant dielectric response of a general boundary shape. We achieve this by rewriting the interaction energy expression presented in Phys. Rev. B, 62 (2000) 6997 exclusively in terms of surface integrals of surface operators. We validate this approach in the Lifshitz case and give numerical results for the interaction of two spheres as well as the van der Waals self-interaction of a uniaxial ellipsoid. Our method is simple to implement and is particularly suitable for a full, non-perturbative numerical evaluation of non-retarded van der Waals interactions between objects of a completely general shape.     

Interference of Bose-Einstein condensates and entangled single-atom state in a spin-dependent optical lattice

We present a theoretical model to investigate the interference of an array of Bose-Einstein condensates loaded in a one-dimensional spin-dependent optical lattice, which is based on an assumption that for the atoms in the entangled single-atom state between the internal and the external degrees of freedom each atom interferes only with itself. Our theoretical results agree well with the interference patterns observed in a recent experiment by Mandel et al. [Phys. Rev. Lett. 91, 010407 (2003)]. In addition, an experimental suggestion of nonuniform phase distribution is proposed to test further our theoretical model and prediction. The present work shows that the entanglement of a single atom is sufficient for the interference of the condensates confined in a spin-dependent optical lattice and this interference is irrelevant with the phases of individual condensates, i.e., this interference arises only between each condensate and itself and there is no interference effect between two arbitrary different condensates.     

Chemical reaction and diffusion: A comparison of molecular dynamics simulations with continuum solutions

Molecular dynamics simulations using the Lennard-Jones energy potential are compared with continuum solutions of reaction and diffusion in a dilute gas. The reaction model is a passive one in which high-energy bath atoms create a species, at dilute concentrations, which may have a very fast consumption reaction. This construction is designed based on typical fast reaction pathways involved in the fuel breakup in a hydrocarbon flame. Using reaction rates and diffusivities obtained from the molecular simulations allows the continuum solution to describe the reactive atom density spatial distribution with good accuracy. Based on this agreement, it is possible to estimate which reaction rates will produce negligible diffusive spreading, and hence, which species might be assumed to be in chemical equilibrium in continuum reacting flow calculations.     

Spontaneous emission in dielectric nanoparticles

An analytical expression is obtained for the radiative-decay rate of an excited optical center in an ellipsoidal dielectric nanoparticle (with sizes much less than the wavelength) surrounded by a dielectric medium. It is found that the ratio of the decay rate A _nano of an excited optical center in the nanoparticle to the decay rate A _bulk of an excited optical center in the bulk sample is independent of the local-field correction and, therefore, of the adopted local-field model. Moreover, the expression implies that the ratio A _nano/A _bulk for oblate and prolate ellipsoids depends strongly on the orientation of the dipole moment of the transition with respect to the ellipsoid axes. In the case of spherical nanoparticles, a formula relating the decay rate A _nano and the dielectric parameters of the nanocomposite and the volumetric content c of these particles in the nanocomposite is derived. This formula reduces to a known expression for spherical nanoparticles in the limit c ≪ 1, while the ratio A _nano/A _bulk approaches unity as c tends to unity. The analysis shows that the approach used in a number of papers {H. P. Christensen, D. R. Gabbe, and H. P. Jenssen, Phys. Rev. B 25, 1467 (1982); R. S. Meltzer, S. P. Feofilov, B. Tissue, and H. B. Yuan, Phys. Rev. B 60, R14012 (1999); R. I. Zakharchenya, A. A. Kaplyanskii, A. B. Kulinkin, et al., Fiz. Tverd. Tela 45, 2104 (2003) [Phys. Solid State 45, 2209 (2003)]; G. Manoj Kumar, D. Narayana Rao, and G. S. Agarwal, Phys. Rev. Lett. 91, 203903 (2003); Chang-Kui Duan, Michael F. Reid, and Zhongqing Wang, Phys. Lett. A 343, 474 (2005); K. Dolgaleva, R. W. Boyd, and P. W. Milonni, J. Opt. Soc. Am. B 24, 516 (2007)}, for which the formula for A _nano is derived merely by substituting the bulk refractive index by the effective refractive index of the nanocomposite must be revised, because the resulting ratio A _nano/A _bulk turns out to depend on the local-field model. The formulas for the emission and absorption cross sections σ_nano for nanoparticles are derived. It is shown that the ratios σ_nano/σ_bulk and A _nano/A _bulk are not equal in general, which can be used to improve the lasing parameters. The experimentally determined and theoretically evaluated decay times of metastable states of dopant rare-earth ions in crystalline YAG and Y₂O₃ nanoparticles are compared with the corresponding values for bulk crystals of the same structure. Original Russian Text ? K.K. Pukhov, T.T. Basiev, Yu.V. Orlovskii, 2008, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2008, Vol. 88, No. 1, pp. 14–20.