运动三能级原子与驻波激光场斜交相互作用的理论分析

分析了一个运动的三能级原子与一个驻波激光场地斜交相互作用时的动量传递行为。结果表明，当原子和光场由于多普勒效应满足一定条件时，将产生受激拉曼跃迁。如果作用光相对于原子而言为一个“π／２脉冲”光时，那么经过作用后，原子将处于一个相干迭加态，其中一个态与加始相同。     

Landau-Zener transition of a two-level system driven by spin chains near their critical points

The Landau-Zener (LZ) transition of a two-level system coupling to spin chains near their critical points is studied in this paper. Two kinds of spin chains, the Ising spin chain and XY spin chain, are considered. We calculate and analyze the effects of system-chain coupling on the LZ transition. A relation between the LZ transition and the critical points of the spin chain is established. These results suggest that LZ transitions may serve as the witnesses of criticality of the spin chain. This may provide a new way to study quantum phase transitions as well as LZ transitions.     

Quantum carpets woven by cold atoms in a laser field

Propagation of wave packets of cold two-level atoms in a standing-wave laser field can be interpreted in the dressed-state basis as motion in two optical potentials. The three distinct regimes of the wavepacket motion are specified by the ratio of the squared atom–laser detuning to the normalized Doppler shift. We calculate the momentum and position probability densities, which form patterns with minima and maxima of probability both in the momentum and the position spaces known as quantum carpets. At small and large detunings, the atomic motion is substantially adiabatic, and the quantum carpets have a simple form. At intermediate detunings, the wave packet moves nonadiabatically, splitting at each node of the standing wave, which causes a proliferation or branching of atomic trajectories with a single atom. Nonadiabatic transitions produce beautiful quantum carpets with a rich structure.     

Localization and kinetics of an atom in the spectral filtration of its resonance fluorescence

It is shown that spectral filtration of a significant fraction of radiation of a resonantly fluorescing atom changes its kinetics. The effect of a spectral observation event on the behavior of an atom is demonstrated by two examples: localization of an atom at its flight through a region occupied by a standing light wave and translatory dynamics of an atom at its motion along a standing light wave. In the first case, localization probabilities are calculated in the absence of spontaneous emission events and for one photoemission event. The arising distribution over the atomic momentum, which is sensitive to spectral filtration, is also calculated for one photoemission event. In the second example, it is shown that spectral filtration of spontaneous emission leads to the occurrence of an anomalous additive to the force acting on an atom in the standing-wave field.     

光晶格动量依赖偶极势中原子运动

研究了原子在光晶格偶极势依赖原子动量情况下的运动, 特别考虑了偶极势对原子动量的依赖特性. 对动量和位置的方差研究表明, 原子的动量方差呈现压缩性质, 位置方差呈现放大性质.据此我们预言光晶格动量依赖偶极势中的单粒子态可能接近动量压缩线态. 研究结果还表明, 红失谐情况下原子的动量演化可分为三个过程: 第一个过程是慢减速过程, 初始动量较大的原子, 动量以近似阻尼振荡的形式衰减; 第二个过程是快减速过程, 当动量被减速到接近到光子动量时, 动量迅速减小到hk(Ω/γ)², 其中hk为光子动量, Ω为拉比频率, γ为原子波函数衰减函数; 第三个过程是原子被囚禁过程, 当原子动能被降低到小于势井深度时, 原子被囚禁在晶格波腹附近. 关键词： 动量演化 光晶格 压缩态     

Mesure de l'impulsion echangee au cours de l'interaction onde evanescente-atome

In vacuo, during an interaction between a moving atom and a surface wave of frequency v, the exchanged momentum is greater than hv/c. First we show, using a semi-classical treatment, that this momentum is ?k_x in agreement with De Broglie's relation p = ?k, but unlike the usual notion of wave momentum attached to the Poynting vector. We present experimental methods to measure this momentum and we give results for two atom speeds.     

Berry's Phases of the Alkali Atom in a SlowlyChanging Strong Magnetic Field and Non-Adiabatic Transition

In this paper the high-order adiabatic approximation (HOAA) method is formulated in a new form ko that the calculation is greatly simplified. using this improved HOAA method, we study the Berry phase effects of the Alkali atom in a slowly-changing strong magnetic field and also the non-adiabatic transitions between the instantaneous angular momentum states. The possible observability is also pointed out.     

Proliferation of atomic wave packets at the nodes of a standing light wave

A quantum analysis is presented of the motion and internal state of a two-level atom in a strong standing-wave light field. Coherent evolution of the atomic wave-packet, atomic dipole moment, and population inversion strongly depends on the ratio between the detuning from atom-field resonance and a characteristic atomic frequency. In the basis of dressed states, atomic motion is represented as wave-packet motion in two effective optical potentials. At exact resonance, coherent population trapping is observed when an atom with zero momentum is centered at a standing-wave node. When the detuning is comparable to the characteristic atomic frequency, the atom crossing a node may or may not undergo a transition between the potentials with probabilities that are similar in order of magnitude. In this detuning range, atomic wave packets proliferate at the nodes of the standing wave. This phenomenon is interpreted as a quantum manifestation of chaotic transport of classical atoms observed in earlier studies. For a certain detuning range, there exists an interval of initial momentum values such that the atom simultaneously oscillates in an optical potential well and moves as a ballistic particle. This behavior of a wave packet is a quantum analog of a classical random walk of an atom, when it enters and leaves optical potential wells in a seemingly irregular manner and freely moves both ways in a periodic standing light wave. In a far-detuned field, the transition probability between the potentials is low, and adiabatic wave-packet evolution corresponding to regular classical motion of an atom is observed.     

Diffraction of the wave packet of a three-level Λ atom in the field of a multifrequency standing light wave

The diffraction of the wave packet of a three-level atom in a multifrequency optical radiation field is studied. A new type of coherent beam splitter for atoms that employs the scattering of a wave packet in the field of four standing light waves with different spatial shifts is proposed on this basis. It is shown that this interaction scheme makes it possible to obtain large splittings (>100ℏk) of the wave packet of a three-level Λ atom in momentum space into only two coherent components. In addition, the atoms in these coherent components are in long-lived atomic states, which substantially simplifies the experimental implementation of such a splitter. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 386–391 (25 September 1997)     

Probing the thermal atoms of a Bose gas through Raman transition

We explore the many body physics of a Bose condensed atom gas at finite temperature through the Raman transition between two hyperfine levels. Unlike the Bragg scattering where the phonon-like nature of the collective excitations has been observed, a different branch of thermal atom excitation is found theoretically in the Raman scattering. This excitation is predicted in the generalized random phase approximation (GRPA) and has a gapped and parabolic dispersion relation. The gap energy results from the exchange interaction and is released during the Raman transition. The scattering rate is determined versus the transition frequency ω and the transferred momentum q and shows the corresponding resonance around this gap. Nevertheless, the Raman scattering process is attenuated by the superfluid part of the gas. The macroscopic wave function of the condensate deforms its shape in order to screen locally the external potential displayed by the Raman light beams. This screening is total for a condensed atom transition in order to prevent the condensate from incoherent scattering. The experimental observation of this result would explain some of the reasons why asuperfluid condensate moves coherentlywithout any friction with its surrounding.     

Coherent trapping of a three-level atom in a circularly polarized light

Using semiclassical theory, we study coherent trapping of a three-level atom, where the atom possesses a momentum of its center-of-mass motion and is irradiated only by a classical circularly polarized electromagnetic wave. We find that if the atom is initially in a coherent trapping state of it, under the zero- or first-order approximation, the atom is absolutely or nearly in the state hereafter.     

Specific features of the resonance interaction of a coherent wave with an ensemble of impurity atoms of a photonic crystal

Two-quantum relaxation transitions in an impurity atom that are activated by its resonance interaction with a monochromatic wave lead to hole burning in the distribution of atoms populating the lower energy level over detunings from the resonance. In this case, the levels of an impurity atom lying within the gap or the pseudogap in the density of photon states of a photonic crystal act as a trap. The impurity atoms change to these levels in the process of interaction of a monochromatic wave with the atomic transition that is not influenced by specific spectral features of a photonic crystal.     

Influence of a Kerr-Like Medium and the Detuning Parameter on the Statistical Aspects of the Intensity-Dependent-Coupling Hamiltonian

We study the interaction between a one-mode electromagnetic field and a two-level atom in the presence of a Kerr-like medium when the atom is prepared initially in the momentum eigenstate. The wave function is calculated by using the Schrodinger equation for a coherent electromagnetic field and an atom in the excited state. The effects of the Kerr-like medium and the detuning parameters on the statistical aspects of the intensity-dependent-coupling Hamiltonian such as, atomic momentum increment, momentum diffusion, the radiation force, and the field entropy are calculated. We investigate the effect of the detuning, Kerr-like medium and photon number operator on the field entropy.     

硼原(离)子内壳激发高自旋态能级和辐射跃迁

采用Rayleigh-Ritz变分方法计算了B原子(离子)内壳层激发高自旋态(~(4,5,6)L,L=S,P)里德伯系列的能量和精细结构劈裂,利用截断变分方法改进非相对论能量,并利用一阶微扰理论计算了相对论能量修正和质量极化效应修正,利用屏蔽的类氢公式计算了量子电动力学效应和高阶相对论效应,从而得到了高精度的组态能量.利用精确计算的波函数,计算了这些高自旋态的电偶极辐射跃迁波长、振子强度和辐射跃迁概率.通过长度规范和速度规范计算的振子强度的一致性证明了本文计算的波函数是精确的.相比其他理论计算结果,本文计算的高自旋态的能级及跃迁波长数据与实验数据符合得更好.对于一些高位的内壳层激发高自旋态,相关的能级和跃迁数据为首次报道,本文的计算结果对相关实验光谱谱线标定具有重要意义.     

Scattering of atoms in the field of counterpropagating light waves. Effect of initial conditions

The scattering of an atom in the field of counterpropagating light waves is studied under conditions such that the state of the atom is a superposition of the ground and excited states. For the case in which this superposition is created by the field of a traveling wave, the momentum distribution function of the atom after scattering by a standing wave is found analytically in the approximation of a short interaction time, when the atom’s motion can be neglected. Longer interactions of the atom with the field are studied numerically. We also consider the case of counterpropagating light waves consisting of Gaussian or supergaussian pulses. Zh. éksp. Teor. Fiz. 113, 563–572 (February 1998)     

Inversion of an Atomic Wave Packet in a Circularly Polarized Electromagnetic Wave

We study behavior of an atomic wave packet in a circularly polarized electromagnetic wave,and particularly calculate the atomic inversion of the wave packet.A general method of calculation is presented.The results are interesting.For example,if the wave packet is very narrow or /and the interaction is very strong,no matter the atom is initially in its ground state or excited state,the atomic inversion approaches zero as time approaches infinity.If the atom is initially in its ground state and excited state with the probability 1/2 respectively,and if the momentum density is an even function,then the atomic inversion equals zero at any time.     

Dirac Particle in an Aharonov-Bohm Potential: The Structure of the First Order S-matrix

The structure of the interaction Hamiltonian in the first order S-matrix element of a Dirac particle in an Aharonov-Bohm (AB) field is analyzed and shown to have interesting interesting algebraic properties. It is demonstrated that as a consequence of these properties, this interaction Hamiltonian splits both the incident and outgoing waves in the the first order components (eigenstates of the third component of the spin). The matrix element can then be viewed as the sum of two transitions taking place in these two channels of the spin. At the level of partial waves, each partial wave of the conserved total angular momentum is split into two partial waves of the orbital angular momentum in a manner consistent with the conservation of the total angular momentum quantum number.     

An approximate projection technique for the calculation of electromagnetic properties of deformed nuclei

A three-dimensional angular momentum projection is carried out for cranking model wave functions. The projected matrix elements of electromagnetic operators are evaluated using a method originally developed by Kamlah for the case of projected energy, which is valid for large deformations and weakly triaxial nuclei. The calculated spectroscopic quadrupole moments deviate substantially from the predictions of a rigid rotor model with axial symmetry. For E2 transitions the deviations are small. Projected values of the magnetic moments are almost identical with those of a semiclassical calculation. Cranking model wave functions are decomposed into its components having good angular momentum.     

Splitting of atomic beams by light for creation of high-resolution spatial structures in optical nanolithography

Diffraction of atomic wave packets from a standing laser wave with a Gaussian profile is studied theoretically and numerically in pursuing the aim of creating high-resolution spatial structures in optical nanolithography. To this end, we propose to use nonadiabatic transitions between two optical potentials which take place when square of the value of detuning off the resonance is approximately equal to the Doppler shift. In this case, atomic wave packets experience splitting at nodes of the standing wave, which allows creating atomic structures on a substrate with a period substantially smaller than the standard nanofabrication limit equal to half the wavelength of light. We propose a scheme of the experiment for the observation of nonadiabatic transitions and splitting of the wave of matter caused by them. A number of computer simulations with parameters corresponding to real atoms have been performed, which exhibit this effect in both momentum and coordinate spaces.