Second-harmonic light scattering near two-photon resonance

The light scattered by a quantum system, two levels of which are distant by an energy equal to that of two photons of the incident beam, is shown to contain three lines: a central line at 2ω, and two satellites at 2ω±δ, with δ and intensity-dependent level splitting term. The transition probabilities for the three lines are calculated in terms of the time evolution operator.     

量子微腔中原子俘获的绝热微扰分析

详尽地研究了驻波腔场中两能级原子运动的能量转移和动力学演化的非绝热修正。从而定量地阐述了实现原子俘获的绝热近似条件。     

A New First-Order Phase Transition for an Extended Jaynes–Cummings–Dicke Model with a High-Finesse Optical Cavity in the BEC System<Superscript>†</Superscript>

We present a two-level atomic Bose–Einstein condensate (BEC) with dispersion, which is coupled to a high-finesse optical cavity. We call this model the extended Jaynes–Cummings–Dicke (JC-Dicke) model and introduce an effective Hamiltonian for this system. From the direct product of Heisenberg–Weyl (HW) coherent states for the field and U(2) coherent states for the matter, we obtain the potential energy surface of the system. Within the framework of the mean-field approach, we evaluate the variational energy as the expectation value of the Hamiltonian for the considered state. We investigate numerically the quantum phase transition and the Berry phase for this system. We find the influence of the atom–atom interactions on the quantum phase transition point and obtain a new phase transition occurring when the microwave amplitude changes. Furthermore, we observe that the coherent atoms not only shift the phase transition point but also affect the macroscopic excitations in the superradiant phase.     

Population Dynamics of Ground State Sublevels: Influence on Polarization Properties of High Harmonics

Within the framework of the non-perturbative light–atom interaction theory, we consider the population dynamics of the ground-state sublevels corresponding to the different values of the orbital quantum number (l) projections and its influence on the high optical harmonics. We study the problem of high optical harmonics generation in two geometries: (1) two linearly polarized fields at frequencies ω and 2ω for different angles of azimuthal projection difference and arbitrary orientation with respect to the angular momentum of the atom direction; (2) two elliptically polarized fields at frequencies ω and 2ω rotating in opposite directions with variable mutual ellipticity. We show that the unequal population dynamics of the levels with different projections of the atom angular momentum (magnetic quantum number) has a significant impact on the value of the ellipticity of the generated radiation.     

Side bands of the vibrational spectrum of interstitial elements in a metal lattice

The dynamics of oxygen atoms in Ta-O solid solution has been studied by the slow-neutron inelastic scattering method. Indications have been obtained for the existence of vibration-rotation excitations of an interstitial atom in a metal lattice. In addition to the peaks corresponding to the fundamental oscillations of a harmonic oscillator (?ω_1,2 ≈ 42 meV and ?ω₃ ≈ 82 meV), side bands with an energy of ? ≈ ?ω₃ ± 6 meV are observed in the atomic oxygen spectrum. Analysis of the spectral structure leads to the assumption that the observed satellites are attributed to vibration-rotation excitations of an impurity oxygen atom in the field of metal atoms surrounding it. The oxygen atom is probably displaced in the basal plane from the center of the octahedral interstice of the crystal lattice and can freely move along a slightly corrugated energy channel around the geometric center of the octahedron. The energy position of the side bands are in good agreement with the excitation energies estimated in the model of the superposition of two circular motions of the oxygen atom in the basal plane of the tantalum lattice near the center of the octahedral interstice.     

柱形量子点中弱耦合磁极化子的性质

应用线性组合算符方法和幺正变换方法,研究在抛物势作用下的柱形量子点中磁极化子的性质。对ZnS量子点的数值计算表明,量子点中磁极化子的基态能量随特征频率、回旋共振频率的增大而增加,这是由于特征频率增加时振动能量、回旋共振频率增加时外磁场中的附加能量增加所致。当特征频率(或回旋共振频率)增加到某一值时,磁极化子能量由负变为正。基态能量随柱高的减小而增加,且柱高越小,增加越快;当柱高减小到某一值时,磁极化子能量也由负变为正。总之,柱形量子点中的磁极化子,其基态能量与量子点的尺度、外磁场、特征频率等有关。     

Kerr效应和虚光场效应对三能级原子-场系统原子占居态几率的影响

研究类克尔介质中非旋波近似下三能级原子与场相互作用系统的原子占居态几率的时间演化;讨论了光场频率ω及类克尔介质常量x对原子占居态几率的影响。结果表明:虚光场的作用使原子占居态几率的时间演化曲线中出现量子噪音,而Kerr介质效应会抑制量子噪音的产生;原子吸收率随x的增大而降低;系统的粒子数反转随x的增大明显减弱,但随ω的增大有所增强。     

强度依存耦合J-C模型中光场强度对原子共振荧光的影响

本文应用量子电动力学理论,研究了强度依存耦合的二能级原子与单模光场相互作用系统中,光场强度对原子共振荧光的影响.证明了系统的共振荧光仍有三峰带结构,光场强度的增加,将使三峰带结构更加明显,但当光场强度很大,使得本征谱分裂值等于一个激光光子能量时,三峰带结构变为双峰带结构,而且边峰带由单光子跃迁变为双光子跃迁.     

光腔中两组分玻色-爱因斯坦凝聚体的受激辐射特性和量子相变

研究了单模光腔中两组分玻色-爱因斯坦凝聚的基态性质和相关的量子相变.通过利用自旋相干态变换将等效赝自旋哈密顿算符对角化并求得基态能量泛函.基态能量泛函对其经典场变量进行变分并取极小值,得到光子数解和相边界曲线.通过稳定性讨论发现系统除了出现正常相和超辐射相之外,还得到了多稳的宏观量子态;受激辐射来自于原子数反转的集体态,单组分的Dicke系统中并没有此现象;受激辐射只能从一组分的原子中产生,而另外的仍保持在普通超辐射状态.通过调整相关的原子-场耦合强度和频率失谐,超辐射和受激辐射态的顺序可以在原子的两个组分之间互换.     

Spectroscopic properties of the molecular ions BeX+ (X=Na,K, Rb): forming cold molecular ions from an ion–atom mixture by stimulated Raman adiabatic process

In this theoretical work, we calculate potential energy curves, spectroscopic parameters and transition dipole moments of molecular ions BeX⁺ (X=Na, K, Rb) composed of alkaline ion Be and alkali atom X with a quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarisation potentials and full configuration interaction. We study in detail collisions of the alkaline ion and alkali atom in quantum regime. Besides, we study the possibility of the formation of molecular ions from the ion–atom colliding systems by stimulated Raman adiabatic process and discuss the parameters regime under which the population transfer is feasible. Our results are important for ion–atom cold collisions and experimental realisation of cold molecular ion formation.     

Superfluidity of Paired Bosons from Correlated Tunneling

We study superfluidity of paired Bosonic atoms in optical lattices. The atoms have strong repulsive on-site energy. Single atom tunneling is severely suppressed while the atom-pair may co-tunnel by the second order quantum transition, which induces paired superfluidity as repulsive nearest-neighbor interactions are included. The mean-field phase diagram and low energy excitations are explored for a square lattice system.     

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.     

Optical stark effect and dressed exciton states in a Mn-doped CdTe quantum dot

We report on the observation of spin-dependent optically dressed states and the optical Stark effect on an individual Mn spin in a semiconductor quantum dot. The vacuum-to-exciton or the exciton-to-biexciton transitions in a Mn-doped quantum dot are optically dressed by a strong laser field, and the resulting spectral signature is measured in photoluminescence. We demonstrate that the energy of any spin state of a Mn atom can be independently tuned by using the optical Stark effect induced by a control laser. High resolution spectroscopy reveals a power-, polarization-, and detuning-dependent Autler-Townes splitting of each optical transition of the Mn-doped quantum dot. This experiment demonstrates an optical resonant control of the exciton-Mn system.     

Radiative Energy Shifts of an Atom Coupled to the Derivative of a Scalar Field near a Reflecting Boundary

We study the radiative energy level shifts of a two-level atom in dipole coupling to the derivative of a massless scalar quantum field in a spacetime with a perfectly reflecting boundary, and calculate the contributions of vacuum fluctuations and radiation reaction to the level shift. It is found that the energy level shift of the excited state is an oscillating function of the atom＇s distance from the boundary and it can either be positive or negative, while that of the ground state is always positive. The most remarkable feature is that the energy level shift of the ground state behaves like 1/z^4 when the atom＇s distance from the boundary, z, is very large as compared to the transition wavelength of the atom, while it behaves like 1/z^3 when z is very small     

Chimera states in an ensemble of linearly locally coupled bistable oscillators

Effects of quantum deviation of a two-level atom at coherent scattering on an inhomogeneous optical potential created by crossed electromagnetic fields are considered. The region of interaction is formed by a lowfrequency quantized standing wave from a micromaser and a coherent traveling optical wave generated by an optical fiber located inside a cavity. The atom interacts with both fields under the conditions of two-photon two-wave resonance. It is shown that two effects of quantum deviation of translational motion of the atom can be observed. Interaction with the standing wave is caused under these conditions by a harmonic potential the character of scattering of the atom on which depends significantly on the initial conditions of preparation of the atom and quantized mode. The other effect—deviation of the atom by the classical traveling wave—is also completely quantum mechanical under these conditions and is produced by the noncommutative contribution of the kinetic energy operator of the atom and the interaction energy.     

Dissipation of the energy of excited atoms located near an absorptive medium surface

The nonradiative process of transfer of the excited atom energy to an absorptive medium is considered. The probability of the nonradiative EL-transition is calculated for an excited atom placed near a macroscopic medium surface with the complex dielectric function ? (ω₀). In the limit of very small distances the discussed process yields a main contribution to the level weight and determines the lifetime of the excited state.     

与氢原子有关的原子光谱跃迁问题

本文以氢原子为例,阐述了玻尔的氢原子理论及引入相对论效应及量子理论后氢原子光谱的精细结构和超精细结构。同时,进一步在理论上深入探讨谱线精细结构、跃迁概率、谱线轮廓、谱线强度对原子光谱跃迁的影响,更深入地理解了原子光谱跃迁问题。     

Optical spin orientation of a single manganese atom in a quantum dot

The magnetic state of a single magnetic atom (Mn) embedded in an individual semiconductor quantum dot is optically probed using micro-spectroscopy. A high degree of spin polarization can be achieved for an individual Mn atom localized in a quantum dot using quasi-resonant or fully-resonant optical excitation at zero magnetic field. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magnetic field dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. The Mn spin distribution prepared by optical pumping is fully conserved for a few microseconds. This opens the way to full optical control of the spin state of an individual magnetic atom in a solid state environment.     

Quantum phase transition and entanglement in Li atom system

By use of the exact diagonalization method, the quantum phase transition and entanglement in a 6-Li atom system are studied. It is found that entanglement appears before the quantum phase transition and disappears after it in this exactly solvable quantum system. The present results show that the von Neumann entropy, as a measure of entanglement, may reveal the quantum phase transition in this model.     

Polarization fields in the positronium atom undergoing emission or absorption of optical photons

This paper solves the problem of the interaction of an electron and positron via the field of soft and hard photons with emission or absorption of a real photon. The interaction is interpreted as a third-order QED effect in the coordinate representation. The role of intermediate states with positive and negative frequencies is studied. A general expression is derived for the matrix elements of the operator of the effective electron-positron interaction energy for different types of quantum transitions. The expression makes it possible to calculate the probabilities of the corresponding transitions in the nonrelativistic approximation. Electric dipole transitions in the positronium atom accompanied by emission (absorption) of an optical photon are investigated. Two-particle wave functions of the positronium atom are used to introduce the concept of polarization fields inside the positronium atom. It is found that the polarization fields depend on the coordinates and time and on the choice of the pair of states between which a quantum transition with emission or absorption of a photon takes place. Zh. éksp. Teor. Fiz. 113, 471–488 (February 1998)