克尔介质中"耦合双原子-场"模型的光场压缩效应

利用全量子理论，研究克尔介质中耦合二能级双原子与场相互作用的压缩效应，着重讨论了克尔介质对光场压缩效应的影响，并揭示了初始场强及原子间耦合系数的变化与光场压缩效应的关系。     

Kerr介质中耦合V型三能级原子与相干态光场作用场的量子性质

研究了Kerr介质中相干态光场与耦合V型三能级原子相互作用过程中场的量子性质.利用量子光学中光场与原子相互作用的耦合Tavis-Cummings模型,对系统的动力学过程进行了求解.讨论了系统初始状态、失谐量、原子间偶极相互作用强度及Kerr系数对光场量子性质随时间演化的影响.数值计算结果表明:初态中场的平均光子数比较小时,光场能够展现出明显的量子效应|初始时刻原子激发态概率幅从小变大时,光场的反聚束效应变得越明显,而光场的压缩深度会先增大后减小|失谐量的变化对场的量子性质的影响不大,只是改变光场二阶相关函数和压缩参量振荡的周期|原子间耦合强度的增大使光场的反聚束效应减弱和光场的压缩深度变浅|Kerr系数的增大会增强光场的反聚束效应,而使光场的压缩深度变浅.     

Optical resonant processes in thin excited films

It is shown that coherent processes of elastic scattering of resonant radiation form a “buffer” electromagnetic field near the boundary of excited media. This part of radiation is not governed by the standard refractive index, but precisely this part of radiation forms the beams reflected and refracted by the excited medium. The presence of the “buffer” field causes the suppression of stimulated emission near the boundary and leads to the appearance of a frequency angular broadening of the beam transmitted through a thin film of excited atoms at an oblique angle.     

On the Sub-Doppler Spectroscopy of Optically Excited Atoms in a Thin Gas Cell

This work continues a theoretical investigation of the capabilities of the well-known method based on using a monochromatic probe light beam in combination with optical pumping of atoms (molecules) of a rarefied-gas medium by a broadband radiation in a thin cell the diameter of which is much larger than its internal thickness. In contrast to calculations carried out in the previous publications on this method of spectroscopy, here, we consider the case of arbitrary values of pump intensity and thickness of a cylindrical gas cell. Thus, all the possible mechanisms and specificities of velocity selection of atoms in optically excited levels caused by transit-time relaxation of such atoms in gas cells of this kind are analyzed. Within the framework of this approach, sub-Doppler absorption resonances of the probe light beam corresponding to quantum transitions from the upper level excited by optical pumping are investigated. The obtained results can be used in high-resolution spectroscopy of atoms (molecules), as well as for laser-frequency stabilization to established narrow spectral resonances.     

Possible laser modification of field ion microscopy

A modification of field ion microscope, based on radical reduction of intensity of electric field essential for field-ionization of imaging gas atoms, is suggested. For this purpose the imaging gas atoms are excited by a laser radiation to quantum states nearby the ionization limit. As excited atoms approach the point the field ionization must occur in rather weak fields (～10⁷ V/cm) which eliminate electric field induced effects of molecular evaporation and decomposition.     

Nonclassical Radiation from Two Atoms and Quantum Search Algorithms

We discuss the non-classical aspects of the radiation emitted from a system of two atoms. We first consider the radiation emitted from independently radiating quantum systems. If the atoms are excited by coherent light then the radiation exhibits the usual interference fringes in the far field as the point of observation is varied. By contrast,if the system is incoherently excited no interferences can be seen in the far held intensity pattern, 1. e. tne first order correlation function. However, if the second order correlation function is considered interferences appear even if the system is incoherently excited, i.e. even if the emitted photons are uneorrelated .This can be understood in terms of interferences between multiple pathways for quantum transitions as well as the detection induced entanglement. We show the non-classical nature of these intensity-intensity correlations. Such quantum interferences can be used for range of applications, i.e. for information processing or in applications to quantum search algorithms.We also consider the ease when the atoms are dose to each other so that the dipole-dipole interaction between them is significant. In this ease it is demonstrated that as a function of the detector position we can probe the decay either in the symmetric space or in the antisymmetrie space.     

Liquid-glass transition as the freezing of characteristic acoustic frequencies

Half-quantum interpretation is proposed for the liquid-glass transition as the freezing of characteristic acoustic frequencies (degrees of freedom) that are related to the molecular mobility of delocalized excited kinetic units, namely, linear quantum oscillators. There exists a correlation between the energy quantum of an elementary excitation (atom delocalization energy) and the glass transition temperature, which is proportional to the characteristic Einstein temperature. By analogy with the Einstein theory of the heat capacity of solids, the temperature range of the concentration of excited atoms in an amorphous medium is divided into the following two regions: a high-temperature region with a linear temperature dependence of this concentration and a low-temperature region, where the concentration of excited atoms decreases exponentially to the limiting minimum value (about 3%). At this value, the viscosity increases to a critical value (about 10¹² Pa s), which corresponds to the glass transition temperature, i.e., the temperature of freezing the mobility of excited kinetic units. The temperature dependence of the free activation energy of viscous flow in the glass transition range is specified by the temperature dependence of the relative number of excited atoms.     

The Mott Problem in One Dimension

In the α decay of a nucleus, the tracks left in the medium by the α particle are linear, even though its initial wave function is spherically symmetric. Understanding this quantum phenomenon has been called “the Mott problem”, ever since Mott’s fundamental paper on the subject (Mott in Proc. R. Soc. London Ser. A 126:79 1929). Here we study a one dimensional version of the Mott problem. The particle emitted in the decay is represented as a superposition of waves, one traveling to the left, the other to the right. The atoms with which the particle interacts are modeled as two level systems. The wave equation obeyed by the particle is taken to be the massless Dirac equation. For a certain space-time structure for the particle-atom interaction, it is possible to derive an explicit space-time solution for the entire system, for an arbitrary number of atoms. In the one dimensional solution, the coherent superposition of right and left-moving wave packets leaves behind tracks of excited atoms. The Mott problem on the nature of the tracks left behind is addressed using the reduced density matrix, defined by taking the trace over all particle degrees of freedom. It is found that the reduced density matrix is the incoherent sum of two terms, one involving excited atoms only on the right; the other involving excited atoms only on the left, implying that tracks will show excited atoms on one side or the other. In one dimension, tracks which involve excited atoms exclusively on one side or the other are the analog of straight tracks in three dimensions.     

非旋波近似下类克尔介质中“单模光场-受激三能级原子”系统的光子统计演化分析

本文研究了非旋波近似下类克尔介质对“单模光场-受激三能级原子”系统的光子统计演化特性的影响.数值计算的结果表明:类克尔介质的作用直接影响着受激辐射场的平均光子数< n(t) >的Rabi振荡的幅度和频率;而虚光场的影响则表现为受激辐射场的量子噪音,它与激发场强的变化及场与介质的耦合程度密切相关.另外,本文还对< n(t)>进行了频谱分析,结果发现该非线性系统存在着一系列高次谐波;并且,各高次谐波成分和振幅的变化情况完全依赖于激发场强及与介质的耦合程度.     

有限深抛物势量子盘中极化子的激发态性质

量子点作为一种重要的低维纳米结构, 近年来在单光子光源和新型量子点单光子探测器的研究引起了人们的广泛关注, 对各种势阱中量子点性质的研究已取得了重要成果. 但是大多理论研究都局限于无限深势阱, 而有限深势阱更具有实际意义. 利用平面波展开、幺正变换和变分相结合的方法研究了有限深势阱中极化子激发态能量及激发能随势阱形状和量子盘大小的变化规律. 数值计算结果表明: 极化子的激发态能量、激发能随势垒高度或宽度的增大而增大, 原因是势垒愈高、愈宽, 电子穿透势垒的可能性愈小, 电子在阱内运动的可能性愈大, 进而导致极化子的激发态能量和激发能均随势垒高度和宽度的增大而增大; 极化子的激发态能量和激发能随量子盘半径的增大而减小, 表明量子盘具有显著的量子尺寸效应; 极化子的激发态能量随有效受限长度的增加而减小, 原因是有效受限长度愈大, 有效受限强度愈小, 电子受到的束缚愈弱、振动愈慢、势能愈小, 进而导致基态能量、激发态能量减小; 同时由于激发态能量较基态能量减小慢, 使得激发能随之增加. 研究结果对量子点的应用具有一定的理论指导意义.     

利用相位可控光场实现量子态波函数时域演化的量子控制

研究了相位可控光场与二能级原子相互作用问题.解析地描述了激发态布居概率在时域的量子衍射现象;细致地分析了波函数演化规律的物理内涵.利用波函数的Cornu蜷线和波函数的实部和虚部随时间的演化形式,展示了原子极化过程的物理细节.阐明了相位可控光场对波函数的时域演化过程、原子极化过程以及光场传输过程的操控机理.     

稀薄里德伯原子气体中的两体纠缠

量子纠缠是量子信息处理和量子计算中不可或缺的物理资源,制备稳定可操控的量子纠缠是研究的热点之一.里德伯原子具有不同于普通中性原子的特点,长寿命和原子之间强烈的偶极相互作用,使得它成为量子信息处理和量子计算的最优候选者.本文在稀薄里德伯原子气体中,构建了空间四面体排布的里德伯原子模型(空间等距的四个原子模型),通过数值求解主方程来研究两体纠缠和里德伯激发的稳态和瞬态动力学性质,发现偶极阻塞机制下的量子纠缠最大,其他满足反偶极阻塞条件的高阶激发引起的纠缠较小,进而从理论上分析了这两种机制下量子纠缠的物理实质.     

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.     

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     

Changes in quantum states of atoms in a markovian thermostat

We solve the nonlinear Schrödinger equation, taking into account self-interaction through the surrounding medium. We have found that such atoms have a countable set of stable equilibrium states, coinciding with the wave eigenfunctions of an individual atom. We show that transitions of an atom from equilibrium quantum states corresponding to less excited levels to more excited levels occur in jumps, while transitions from equilibrium states corresponding to upper levels to lower levels may occur either as radiationless transitions or be accompanied by spontaneous emission at the eigenfrequency of the quantum transition. We have found the conditions for which a change in the topological structure of the atomic wavefunction is possible.     

Interaction of a three-level atom with an elliptically polarized wave

The interaction of elliptically polarized radiation with a resonant medium consisting of atoms with an excited state split into a doublet was studied theoretically. Interference terms associated with the coherent interaction of the field with the excited sublevels of the doublet were found to appear in the refractive index. The dispersion dependence of the refractive index was studied. It was shown that the decay constants for the multipole moments of the current of a dipole-forbidden atomic transition can be determined by the choice of the wave polarization.     

Selected aspects of the quantum dynamics and electronic structure of atoms in magnetic microtraps

We analyze the quantum properties of atoms in a magnetic quadrupole field. The quantum dynamics of ground state atoms in this field configuration is studied firstly. We formulate the Hamiltonian and perform a symmetry analysis. Due to the particular shape of the quadrupole field in general there exist no stable states. We provide resonance energies, lifetimes and calculate the density of states and investigate under what conditions quasi-bound states occur that possess long lifetimes. An effective scalar Schrödinger equation describing such states is derived. As a next step we explore the influence of a high gradient quadrupole field on the electronic structure of excited atoms. An effective one-body approach together with the fixed nucleus approximation is employed in order to derive the electronic Hamiltonian. We present the energy spectrum and discuss peculiar features such as non-trivial spin densities and magnetic field induced electric dipole moments.     

Reflection and refraction of light by a system of interfering atomic states

The boundary problem of nonlinear optics was investigated for a trial wave reflected (refracted) by an excited region of a nonlinear medium considered as a system of multilevel atoms in the spectrum of which there are two closely-spaced energy levels excited by a powerful quasi-resonant radiation. It is shown that under interference conditions of the atomic states in the field of the trial and resonance waves there exist three types of waves: an inverse wave and two polarization waves. By way of extension of the Ewald-Oseen procedure to this case a formula for the complex refractive index of a nonlinear medium for the three types of waves as well as a generalized extinction theorem have been obtained. It is shown that the trial wave can be amplified without inversion of the interfering atomic states and that the refractive index can be markedly changed at certain concentrations of atoms in the medium. General formulas for the amplitudes of the reflected and refracted waves have been obtained. Ul’yanovsk State University, 42, Tolstoi Str., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 568–575, July–August, 1998.     

在V型系统中原子相干对吸收—色散关系的影响

在V型能级系统原子介质中,若利用外场产生相干,则弱光场在该介质中的吸收-色散关系将展现出新的特性.特别是当弱场具有某一特定频率时,介质对光的吸收为零但光折射率大于1.