Nonlinear resonances in the near-field interaction between atoms

It has been shown that nonlinear near-field optical resonances occur in diatomic nanostructures consisting of identical or different two-level atoms in the presence of a radiation field when the dipole-dipole interaction is taken into account. The frequencies of these resonances depend strongly on the intensity of the external optical radiation, on the initial conditions, on the polarization of the external field with respect to the axis of the nanostructure, and on the interatomic distance. The interatomic interaction is taken into account beyond perturbation theory. For this reason, the effective polarizabilities of the atoms of the nanostructure are expressed in terms of the polynomials of both the interatomic distance and the electric field strength of the external optical wave. A “falling tower” effect that is caused by the nonlinear behavior of the local dipole moments of atoms in the nanostructure is predicted.     

Kerr介质中双光子T-C模型光场的量子特性

研究了存在Kerr介质时，耦合双原子与单模压缩真空场双光子跃迁相互作用系统光场的量子特性，讨论了Kerr介质和原子间偶极-偶极相互作用对光场量子特性的影响. 结果表明：当Kerr效应和偶极-偶极相互作用可以忽略时，光场U2分量的涨落能被周期性地压缩，随着Kerr效应和偶极-偶极相互作用的增强，光场的压缩逐渐变浅，压缩次数减少；Kerr效应和偶极-偶极相互作用的影响使光场的二阶相干度时间演化曲线呈现周期性的崩塌-回复现象，但不论耦合强度如何，光子总是呈现聚束效应. 关键词： Kerr介质 压缩真空场 耦合双原子 光场的量子特性     

Tavis-Cummings模型中原子间偶极相互作用对场熵演化特性的影响

研究了单模辐射场与耦合双原子相互作用系统场熵的演化特性,讨论了原子间偶极相互作用对场熵演化特性的影响.研究结果表明,当原子间偶极偶极相互作用不太强时,场熵的时间演化行为与单光子JC模型相似;当原子间偶极偶极相互作用足够强时,场熵的时间演化行为与双光子JC模型相似 关键词： 单模辐射场 耦合双原子 场熵演化     

One-dimensional Rydberg gas in a magnetoelectric trap

We study the quantum properties of Rydberg atoms in a magnetic Ioffe-Pritchard trap which is superimposed by a homogeneous electric field. Trapped Rydberg atoms can be created in long-lived electronic states exhibiting a permanent electric dipole moment of several hundred Debye. The resulting dipole-dipole interaction in conjunction with the radial confinement is demonstrated to give rise to an effectively one-dimensional ultracold Rydberg gas with a macroscopic interparticle distance. We derive analytical expressions for the electric dipole moment and the required linear density of Rydberg atoms.     

内禀退相干下Tavis-Cummings模型中原子的纠缠演化与贝尔不等式破坏

通过求解系统的Milburn方程，研究了两个二能级原子和单模场相互作用系统中原子间纠缠和贝尔不等式破坏随时间的演化特性，讨论了偶极相互作用、场与原子的失谐量对纠缠度以及贝尔不等式破坏的影响.结果表明：原子间偶极-偶极相互作用对纠缠度和贝尔不等式破坏有显著影响，失谐量增大会使两原子的纠缠度和贝尔不等式破坏变大，并且两原子所能达到稳定的纠缠受偶极相互作用系数与失谐量两者之差的影响.同时还发现两原子的纠缠与贝尔不等式破坏并不是单调的函数关系，很小的纠缠也可以产生贝尔不等式破坏. 关键词： Milburn理论 偶极-偶极相互作用 失谐量 贝尔不等式破坏     

Distribution function for random interaction fields in disordered magnets: Spin and macrospin glass

Systems with an arbitrary dependence of exchange integral on the distance between atoms which are randomly scattered in an amorphous substance are investigated by averaging over random fields of interaction in the framework of the Ising model. This method is also used for describing long-term magnetization relaxation in a system of single-domain particles scattered in a nonmagnetic matrix. Random field distribution functions are obtained for the dipole-dipole and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interactions. Long-term relaxation in macrospin glasses is investigated.     

Quantum correlations in a system of two two-level atoms

The dynamics of appearance of a steady entangled state in an ensemble of two collectively decaying two-level atoms is studied on the basis of the Peres-Horodecki criterion with regard to the dipole-dipole interaction between the atoms and their frequency detuning. It is ascertained that, in the absence of dipole-dipole interaction, the steady-state entanglement is in many respects due to the coincidence of the frequencies of transitions in the atoms, whereas a difference in the frequencies, related to different positions of the atoms in a crystal or their thermal motion, destroys the steady-state entanglement. Upon a dipole-dipole interaction, a steady-state entanglement also exists and, in this case, depends strongly on the relationship between the magnitude of the dipole-dipole interaction, the constant of coupling with a thermostat, and the phase of the resonance wave; the entanglement appears only when the thermostat coupling constant is dominant.     

非旋波近似下两纠缠原子的纠缠特性

采用了相干态正交化法研究了耦合强度以及偶极相互作用对Tavis-Cummings模型中两原子的纠缠的影响.与旋波近似比较发现,在弱耦合强度下,非旋波近似下两原子间的纠缠与旋波近似下的结果符合得很好,在强耦合区,原子之间的纠缠出现了突然死亡现象.研究同时发现耦合强度越大,原子间处于可分离态的时间越长,表明了原子间处于退纠缠的时间的长短是依赖于原子-光场的耦合强度的.而考虑了偶极相互作用时,随着偶极-偶极相互作用的加强,原子间的纠缠也将被加强.     

压缩真空场与耦合双原子Raman相互作用系统场熵的演化特性

利用全量子理论,研究了压缩真空场与耦合双原子Raman相互作用系统的场熵演化特性,讨论了系统耦合常数和光场初始压缩因子对场熵演化特性的影响.结果表明,场熵的时间演化规律与原子布居差的时间演化规律非常相似.当原子间的偶极-偶极相互作用较弱时,场熵演化呈现周期性的崩塌与回复现象;当原子间的偶极-偶极相互作用较强时,场熵演化呈现不规则振荡,崩塌与回复周期现象消失.     

Cooperative and interference effects in the resonance fluorescence of two identical three-level atoms at high photon densities: II. Numerical results

Numerical calculations are presented for the excitation spectrum of two identical three-level atoms interacting with a strong resonant laser field. The atoms interact through their dipole-dipole interaction and radiate to each other as well. The spectrum of the symmetric and antisymmetric modes due to the radiative decay from the higher to the lower excited state of the interacting atoms is considered without and with taking into account the effects of the strong pumping process. In the absence of strong pumping, the dipole-dipole interaction in the spectrum of the symmetric modes gives rise to an asymmetric doublet whose ratio of intensities is 2:1, while the spectrum of the antisymmetric modes consists of two peaks one of which represents a stable mode indicating the trapping of a photon between the atoms and a radiative one which has a lifetime one-half that of the isolated atom. In the presence of strong pumping, asymmetries due to the dipole-dipole interaction arise enhancing certain peaks while diminishing the intensity of others and a new pair of sidebands is induced as well. The computed spectra are presented graphically for different values of the Rabi frequencies and the dipole-dipole interaction, respectively.     

Submicrometer position control of single trapped neutral atoms

We optically detect the positions of single neutral cesium atoms stored in a standing wave dipole trap with a subwavelength resolution of 143 nm rms. The distance between two simultaneously trapped atoms is measured with an even higher precision of 36 nm rms. We resolve the discreteness of the interatomic distances due to the 532 nm spatial period of the standing wave potential and infer the exact number of trapping potential wells separating the atoms. Finally, combining an initial position detection with a controlled transport, we place single atoms at a predetermined position along the trap axis to within 300 nm rms.     

A nanofiber-based optical conveyor belt for cold atoms

We demonstrate optical transport of cold cesium atoms over millimeter-scale distances along an optical nanofiber. The atoms are trapped in a one-dimensional optical lattice formed by a two-color evanescent field surrounding the nanofiber, far red- and blue-detuned with respect to the atomic transition. The blue-detuned field is a propagating nanofiber-guided mode while the red-detuned field is a standing-wave mode which leads to the periodic axial confinement of the atoms. Here, this standing wave is used for transporting the atoms along the nanofiber by mutually detuning the two counter-propagating fields which form the standing wave. The performance and limitations of the nanofiber-based transport are evaluated and possible applications are discussed.     

The recoil effect in a strong electromagnetic field

The recoil effect in a strong resonance field of a standing electromagnetic wave has been studied. In order to find the response to the external field (the induced dipole momentum) it is necessary to take into account the variations in the motion of the atoms in this field: the response and the energy spectrum of the atoms are determined from the system of wave equations for the multi-level atoms. The problem of a weak signal absorption in the presence of a strong standing wave which is in resonance with the adjacent transition, is solved. In this case the contour of the absorption line is shown to diverge into two wide bands, their width being proportional to the strong field amplitude. The contribution of continuous and discrete states of the atoms in a standing wave field has been found.     

两二能级原子在共同环境下的量子关联动力学

通过精确求解带有偶极-偶极相互作用的两个二能级原子与一个共同热库相互作用模型, 得到了两原子间量子纠缠和量子失谐(quantum discord)的解析表达式. 综合考虑了环境的非马尔可夫效应、原子间的偶极-偶极相互作用以及原子的本征频率同腔模中心频率之间的失谐量对两原子间量子纠缠和quantum discord的影响. 研究显示: 在非马尔可夫机制下, 且原子的本征频率与腔模中心频率是共振时, 当两原子初态处于纠缠态时, 原子间偶极-偶极相互作用可以显著抑制包括量子纠缠和quantum discord等量子关联的衰减, 更特别的是, 如果原子的本征频率同腔模中心频率有一定的失谐时, 利用原子间偶极-偶极相互作用可大大地延长两原子退纠缠的时间; 当两原子初态处于可分离态时, 从短时间来看, 原子间偶极-偶极相互作用可以提高量子纠缠和quantum discord振荡的振幅,而在长时间极限下, 原子间偶极-偶极相互作用不会改变量子纠缠和quantum discord达到的稳定值. 最后, 讨论了原子间偶极-偶极相互作用对量子纠缠和quantum discord动力学不同的影响. 关键词： 量子纠缠 量子失谐 共同环境 偶极-偶极相互作用     

压缩真空场与耦合双原子Raman相互作用过程中光场的相位演化特性

采用Pegg-Barnett相位理论，研究了压缩真空场与耦合双原子Raman相互作用过程中光场的相位演化特性.具体计算了场的相位概率分布函数及相位涨落，给出了在极坐标中概率分布变化曲线.讨论了原子与场相互作用、两原子间偶极-偶极相互作用以及原子初始状态对光场相位性质的影响. 关键词： 相位特性 压缩真空场 耦合双原子 Raman相互作用     

Continous coherent radiation in methane at λ=3.39 μm in spacially separated fields

Continuous coherent radiation in a gas observed in a spacially separated standing wave fields is reported for the first time. The radiation was observed in the center of lineF ₂ ⁽²⁾ in methane at the interaction of atoms with two standing waves separated by the distance of 3.5 cm.     

Optical holography of nanostructure diatomic objects for different polarizations of the external wave and dimensional resonances

For the combined system of equations of field and atomic variables for two different atoms in the ground state, a stationary solution is obtained, which takes into account their dipole-dipole interaction in the field of external emission. Atoms are treated as linear dipole oscillators with different natural frequencies and linear polarizabilities. Formulas for effective polarizabilities of atoms in a nanostructure object, whose dispersion properties substantially differ from the dispersion properties of isolated atoms in the region of their natural resonances, are obtained. It is found that a nanostructure object consisting of two different atoms has four dimensional resonances, whose frequencies strongly depend on the interatomic separation and the object orientation with respect to the direction of propagation of an external wave. Using interference from the coherent field of dipoles of a small object with a reference coherent wave in a certain plane of observation points in the wave region far from a small object, an optical hologram of a small object is obtained. It is shown by numerical experiments that a small object forms interference fringes with good contrast, which makes possible the use of optical quasi-resonant emission for the development of a nondestructive method of study of small objects.     

Elastic interaction of two atoms adsorbed on a solid surface

The long-range interaction of two adsorbed atoms mediated by the elastic distortion of the substrate is calculated classically for an elastically isotropic substrate. For identical atoms, the interaction is repulsive; for different atoms, it can be repulsive or attractive. It varies as ρ^?3 with the distance ρ between the two adsorbed atoms. This is the same spatial dependence as for the dipole - dipole interaction between two adsorbed atoms. For two xenon atoms adsorbed on gold, the elastic interaction is somewhat smaller than the dipole-dipole interaction. The interaction energy is inversely proportional to the shear modulus of the substrate, so that it may become quite large near a distortive phase transition.     

Acceleration of Mass Transfer under Dynamic Loading

Under dynamic loading, the interaction of unloading waves with each other and with the faces causes the deformation of the sample due to the formation of standing waves, at the nodes of which the localized- deformation bands arise (if the high-speed tension does not exceed the spall strength, so the material in the zone of interference of unloading waves preserves its continuity). A consequence of deformation localization is the mass transfer of atoms and the doping phase particles to nascent localized-deformation bands. The duration of stress oscillations in standing waves in the ultrasonic frequency range exceeds the duration of the initial impulse by at least two orders of magnitude, which ensures an increase in the distance traveled by atoms and dispersed particles during deformation in standing waves.