Breakdown of wave diffusion in 2D due to loops

The validity of the diffusion approximation for the intensity of multiply scattered waves is tested with numerical simulations in a strongly scattering 2D medium of finite extent. We show that the diffusion equation underestimates the intensity and attribute this to both the neglect of recurrent scattering paths and interference within diffusion theory. We present a theory to quantify this discrepancy based on counting all possible scattering paths between point scatterers. Interference phenomena, due to loop paths, are incorporated in a way similar to coherent backscattering.     

Multiple scattering of light by atoms in the weak localization regime

Coherent backscattering is a multiple scattering interference effect which enhances the diffuse reflection off a disordered sample in the backward direction. Classically, the enhanced intensity is twice the average background under well chosen experimental conditions. We show how the quantum internal structure of atomic scatterers leads to a significantly smaller enhancement. Theoretical results for double scattering in the weak localization regime are presented which confirm recent experimental observations.     

Theoretical Investigation of Coherent Enhancement for Resonant Two-Photon Transitions

We theoretically investigate the coherent enhancement of resonant two-photon transitions （TPT） in a three-level atomic system. The TPT can be coherently enhanced by modulating spectral amplitude due to eliminating the destructive interference, though partial laser energy losses. Maximal enhancement of TPT can be achieved by modulating spectral phase due to establishing completely constructive interference. Our research provides a theoretical basis for experimental investigation and appears to have potential application on coherent control in the complicated quantum system.     

Coherent control of spontaneous emission: Effect of counter-rotating terms

We study the coherent control of spontaneous emission in a driven three-level atomic system. In particular we consider the quantum interference effects including energy shifts due to the counter-rotating terms. We show that the quantum interference resulting from the energy shifts has great influence on the evolution of the atomic population and the spontaneous emission spectrum. This makes it feasible to observe the effect of the counter-rotating terms in the long time limit.     

Coherent control of optical precursors in a warm atomic system with Doppler effects

We theoretically study coherent control of optical precursors via active Raman gain (ARG) in an N-type warm atomic system. When a step pulse passes through an ARG window, main fields are advanced due to fast-light effect and constructively interference with optical precursors, then an enhanced transient pulse appears. As the control field decreases, the interference effect is strengthened, and the transient pulse builds up and becomes narrow. Moreover, its peak intensity is inverse to the system temperature and also determined by the input-pulse form. The scheme may be useful in designing optical devices in optical communication.     

Ultrafast coherent excitation of a trapped ion qubit for fast gates and photon frequency qubits

We demonstrate ultrafast coherent excitation of an atomic qubit stored in the hyperfine levels of a single trapped cadmium ion. Such ultrafast excitation is crucial for entangling networks of remotely located trapped ions through the interference of photon frequency qubits, and is also a key component for realizing ultrafast quantum gates between Coulomb-coupled ions.     

Coherent atom-trimer conversion in a repulsive Bose-Einstein condensate

We show that the use of a generalized atom-molecule dark state permits the enhanced coherent creation of triatomic molecules in a repulsive atomic Bose-Einstein condensate, with further enhancement being possible in the case of heteronuclear trimers via the constructive interference between two chemical reaction channels.     

Continuous-wave four-wave mixing with linear growth based on electromagnetically dual induced transparency

Using Schrodinger-Maxwell formalism, we propose and analyze a continuous-wave four-wave mixing (FWM) scheme for the generation of coherent light in a six-level atomic system based on electromagnetically dual induced transparency. We derive the corresponding explicit analytical expressions for the generated mixing field. We find that the scheme greatly enhances FWM production efficiency and is also capable of inhibiting and delaying the onset of the detrimental three-photon destructive interference by choosing the proper decay rate in the second electromagnetically induced transparency (EIT) process.In addition, such an optical process also provides possibilities for producing short-wave-length coherent radiation at low pump intensities.     

原子束多光束干涉实验的一种方法

提出了一种实现原子物质波干涉的新设想.采用一个菲涅耳波带片来压缩原子束线宽,以此照明一块刻有四缝的铜箔,观察原子束的干涉和全息现象,用来测量原子束的时间相干长度 关键词： 原子束 干涉 全息     

Wave propagation in a disordered array of monopole scatterers

We study scalar wave propagation in a disordered static array of spherical scatterers. Due to a hard core repulsion the scatterers do not overlap. The wave is scattered by a δ-function potential at the center of each of the spheres. To this monopole model we apply the previously developed cluster expansion for the self-energy. We find the root of the dispersion equation for the coherent wave for a range of volume fraction⁵. It turns out that the monopole model develops an instability when the scattering is too strong.     

Inhibition of Two-Photon Absorption in a Four-Level Atomic System with Closed-Loop Configuration

We theoretically investigate the features of two-photon absorption in a coherently driven four-level atomic system with closed-loop configuration. It is found that two-photon absorption can be completely suppressed just by properly adjusting the relative phase of four coherent low-intensity driving fields and the atomic system becomes trans- parent against two-photon absorption. From a physical point of view, we explicitly explain these results in terms of quantum interference induced by two different two-photon excitation channels.     

Interference effects in backscattering of light by a layer of a discrete random medium

Multiple backscattering of light by a layer of a discrete random medium is considered. A brief derivation of equations for describing the coherent and incoherent components of scattered light is presented. These equations are solved numerically in the approximation of doubled scattering of light by a semi-infinite medium of spherical scatterers having a size comparable with the wavelength in order to study the effect of the properties of particles on the angular dependence of interference effects. Calculations show that the half-width of the interference peak decreases upon an increase in lateral scattering by particles and that the degree of polarization has a complex angular dependence on the properties of the particles. For an optically thin layer of the medium, the relations defining the interference peak half-width and the scattering angle upon extreme linear polarization as functions of the effective refractive index are given.     

Linear Growth of Continuous-Wave Four-Wave Mixing with Dual Induced Transparency

Using Schrödinger-Maxwell formalism, we propose and analyze an optical four-wave mixing (FWM) scheme for the generation of coherent light in a coherent six-level atomic medium based on dual electromagnetically induced transparency (EIT). We show that the significantly enhanced conversion efficiency enabled by ultraslow propagation of pump waves has no direct relationship with the single-photon detuning, which is different from the FWM with a single EIT. The most important feature is that our scheme is also capable of inhibiting and delaying the onset of the detrimental three-photon destructive interference that looks like a recent scheme [Phys. Rev. Lett. 91 (2003) 243902] and may be used for generating short-wave-length coherent radiation.     

A proposal for testing complementarity with cavity QED techniques

We propose a method to test Bohr complemetarity with cavity QED techniques. It involves an atomic beam passing through two Ramsey zones and a nonresonant cavity initially filled with a strong coherent field. In the absence of the cavity field the probability of finding the atom in a definite state exhibits interference. Due to the dispersive atom-field interaction the paths by which the atom reach the definite state are remarked and thus the interference is destroyed. The associated quantum eraser is also presented.     

Detection of elements with coherent reflectivity inside a multiscatterers incoherent media

In this paper we use the Spatial Compound method to detect a long element with coherent reflectivity within a vast incoherent media. We consider the case in which the echographics temporal signals of the coherent element, and of the scatterers of the media in which it is hidden are of the same order of amplitude. We calculate analytically the spatial coherent function of the acoustic pressure signals considering space-temporal averages. We find experimentally that when there is a coherent long scatter this function is broader (in the spatial direction along the scatter) than when there is only incoherent media. By selecting short temporal windows of analysis we show the possibility of detecting the depth where the coherent element is located.     

Approximate calculation of coherent backscattering for semi-infinite discrete random media

We describe an approximate method for the calculation of all characteristics of coherent backscattering for a homogeneous, semi-infinite particulate medium. The method allows one to transform a system of integral equations describing coherent backscattering exactly into a system of linear algebraic equations affording an efficient numerical solution. Comparisons of approximate theoretical results with experimental data as well as with benchmark numerical results for a medium composed of nonabsorbing Rayleigh scatterers have shown that the method can be expected to give a good accuracy.     

Experimental study on off-axis scattering of flat top partially coherent laser beams when propagating under water in the presence of moving scatterers

Off-axis underwater scattering of spatially partially coherent Multi-Gaussian Schell-Model (MGSM) beams are compared with fully coherent Gaussian beams in both a stationary setting and in the presence of mechanically agitated scatterers in underwater environments. The analysis is carried out by comparing the mean intensities of scattered light, the normalized variance, and the scintillation index in various scenarios. Results indicate that fully coherent beams have increased off-axis scattered light variations in the presence of moving scatterers as compared with a spatially partially coherent MGSM beam. Additionally, in a stationary environment the coherent beam has less overall variations as expected due to the nature of constructing partially coherent MGSM beams. Metrics of normalized variance, scintillation index, and overall average intensity are discussed in the context of potential beam localization, reduced scattering, and off-axis detection.     

Optical echo holography

The basic physics and applications of an unconventional area in holography that is based on the interference of light-induced atomic coherent superposition states in a resonant medium are discussed.     

V形三能级原子的辐射压力和激光冷却

研究了压缩真空中V形三能级原子在单色行波场中的辐射压力和激光冷却. 从系统的哈密顿量出发,利用玻恩-马尔科夫近似,推导出了原子的光学布洛赫方程. 利用绝热近似,给出了平均辐射压力的表达式. 通过量子回归定理和爱因斯坦关系,给出了系统所达到的平衡温度的表达式. 讨论了量子相干强度、平均光子数和拉比频率对原子的自发辐射压力和冷却的最终温度的影响. 结果表明:低于多普勒极限的温度可以获得. 关键词： 压缩真空 自发辐射 量子干涉     

Hot Scatterers and Tracers for the Transfer of Heat in Collisional Dynamics

We introduce stochastic models for the transport of heat in systems described by local collisional dynamics. The dynamics consists of tracer particles moving through an array of hot scatterers describing the effect of heat baths at fixed temperatures. Those models have the structure of Markov renewal processes. We study their ergodic properties in details and provide a useful formula for the cumulant generating function of the time integrated energy current. We observe that out of thermal equilibrium, the generating function is not analytic. When the set of temperatures of the scatterers is fixed by the condition that in average no energy is exchanged between the scatterers and the system, different behaviours may arise. When the tracer particles are allowed to travel freely through the whole array of scatterers, the temperature profile is linear. If the particles are locked in between scatterers, the temperature profile becomes nonlinear. In both cases, the thermal conductivity is interpreted as a frequency of collision between tracers and scatterers.