Applications of Atomic and Molecular Theory to Calculations in Space Science and Engineering

A systematic elaboration is given on atomic and molecular theory problems encountered in dealing with space science and engineering. Three sections are presented in the paper on calculations for gas thermodynamic and transfer properties, characteristics of the optical radiation from the reentry' bodies, and the interaction between surfaces of man-made satellites and incident particles. Researches on them are much related to the fundamental problems regarding the atomic and molecular theory.

Dressed Four-Wave Mixing Spectroscopy Modified by Polarization Interference and Atom-Wall Collision in Micrometric Thin Cells

Dressed four-wave mixing （DFWM） spectroscopy is investigated theoretically in some micrometric thin cells. It is found that DFWM spectra can be modified by polarization interference of atoms and transient effects induced by atom-wall collision. This modification can lead to width-narrowing of DFWM lines and facilitates to implement experiment of high resolution DFWM spectroscopy in a confined atomic system.

Progress of the 87Rb Fountain Clock

A fountain atomic clock based on cold 87Rb atoms has been in operation in our laboratory for several months. We therefore report the design of the rubidium fountain clock including its physical package, optical system and daily operation. Ramsey fringes have been attained with the signal to noise ratio of about 100.

Theoretical Investigation of Femtosecond-Resolved Photoelectron Spectra of the Li2 Molecule

The time-dependent quantum wave packet method is used to investigate the dynamics for the Li2 molecule, and the time-resolved photoelectron spectra （TRPES） of the Li2 molecule are calculated. At the short delay time, the particular phenomenon of TRPES with four peaks is qualitatively interpreted in a dressed state picture by analyzing wave packet motion on light-induced potential （LIP）. The significant difference in the electronic structure of E1∑g^＋ between the inner and outer turning points has an impact on the TRPES. The control for the first excited state A1∑u^＋ of the initial wave packet is discussed.

Preparation of Arbitrary Four-Qubit W State with Atomic Ensembles via Rydberg Blockade

The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme （PRA 79, 022304） has been suggested for generating Greenberger-Horne-Zeilinger state and cluster state with atomic ensembles based on the Rydberg blockade. Using similar resources as the earlier scheme, here we propose an experimentally feasible scheme of preparing arbitrary four-qubit W class of maximally and non- maximally entangled states with atomic ensembles in a single step. Moreover, we carefully analyze the realistic noises and predict that four-qubit W states can be produced with high fidelity （F - 0.994） via our scheme.

Destructive and Constructive Interference of High-Order Harmonic Generation in Mixture of He and Ne Gases

Using the single-atom induced dipole moment under strong field approximation as a source, we suggest a model to simulate the macroscopic high-order harmonic generation （HHG） from the mixed gases （He and Ne） interacting with intense infrared laser by solving the three-dimensional Maxwell＇s equation of the harmonic field. Regular destructive interference （DI） and constructive interference （CI） are observed in the macroscopic HHG spectra when the gas jet is put at a good phase-matching position. A semiclassical model of short and long electron trajectories is applied to interpret the DI and CI of HHG qualitatively.

Analysis of Nanometer Structure for Chromium Atoms in Gauss Standing Laser Wave

The equation of motion of two-level chromium atoms in Gauss standing laser wave is discussed and the distribution of chromium atoms is given under different transverse velocity conditions. The results show that the focusing position of atoms will be affected by the transverse velocity of atoms. Based on the four-order Runge- Kutta method, the locus of chromium atoms in Gauss standing laser wave is simulated. The three-dimensional characteristics of nanometer structures are stimulated under perfect and emanative conditions.

Scheme for Generating a χ-Type Four-Atom Entangled State in Cavity QED

We propose a scheme for generating a χ-type four-atom entangled state in cavity QED. In the present scheme, the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a strong classical field. The scheme is insensitive to the cavity decay and the thermal field, which is of importance from the experimental point of view.

Using Gamma-Radiation for Drug Releasing from MWNT Vehicle

A drug delivery system via multi-walled carbon nanotube （MWNT） vehicle was synthesized in aqueous solution. MWNTs were first noncovalently functionalized with chitosan oligomers （CS） with a molecule weight of 4000-6000, making MWNTs water-soluble, and then a cancer ancillary drug tea polyphenols （TP） was conjugated mainly via the hydrogen bond between CS and TP molecules, making MWNTs efficient vehicle for drug delivering. The release of drug molecules can be realized by pH variation and γ-radiation, leading to new methods for controlling drug release from carbon nanotubes carrier. Due to the high penetrability of γ-rays, γ-radiation shows up new opportunities in controlled drug release, possibly facilitating the future cancer treatment in vivo.

Implementing a Multi-Qubit Quantum Phase Gate Encoded by Photonic Qubit

A protocol is proposed to implement a three-qubit phase gate for photonic qubits in a three-mode cavity. The idea can be extended to directly implement a N-qubit phase gate. We also show that the interaction time remains unchanged with the increasing number of qubits. In addition, the influence of cavity decay and atomic spontaneous emission on the gate fidelity and photon loss probability is also discussed by numerical calculation.

Simulation of Chromium Atom Deposition Pattern in a Gaussain Laser Standing Wave with Different Laser Power

One-dimensional deposition of a neutral chromium atomic beam focused by a near-resonant Gaussian standing- laser field is discussed by using a fourth-order Runge-Kutta type algorithm. The deposition pattern of neutral chromium atoms in a laser standing wave with different laser power is discussed and the simulation result shows that the full width at half maximum （FWHM） of a nanometer stripe is 115nm and the contrast is 2.5：1 with laser power 3.93mW; the FWHM is 0.8nm and the contrast is 27：1 with laser power 16mW, the optimal laser power; but with laser power increasing to 50mW, the nanometer structure forms multi-crests and the quality worsens quickly with increasing laser power.

Coulomb Explosion and Energy Loss of Energetic C20 Clusters in Dense Plasmas

The molecular dynamics （MD） method is used to simulate the interactions of energetic C20 clusters with the dense plasma targets within the framework of the linear Vlasov-Poisson theory. The influences of various clusters （H2, N2, C20 and C60 respectively） on stopping power are discussed. The simulation results show that the vicinage effects in the Coulomb explosion dynamics and the stopping power are strongly affected by the variations in the cluster speed and the plasma parameters. Coulomb explosions are found to proceed faster for higher speeds, lower plasma densities and higher electron temperatures. In addition, the cluster stopping power is strongly enhanced in the early stages of Coulomb explosions due to the vicinage effect, but this enhancement eventually diminishes, after the cluster constituent ions are sufficiently separated. For the large and heavy clusters, the stopping power ratio reaches much higher values in the early stage of Coulomb explosion owing to the constructive interferences in the vicinage effect.

Rotational and Vibrational State Distributions of CsH and Relative Reactivity in Reactions of Cs（6^2D,7^2D） with H2

By using a pump-probe technique, the nascent rotational and vibrational state distributions of CsH are obtained in the Cs（6^2 D,7^2 D） plus H2 reaction. The nascent CsH molecules are found to populate the lowest two vibrational （v″ = 0 and 1） levels of the ground electronic state. By comparing the spectral intensities of the CsH action spectra with those of pertinent Cs atomic fluorescence excitation spectra, the relative reactivity with 1-12 is in an order of6^2D3/2 〉 6^2D5/2 〉 7^2D3/2 〉 7^2D5/2. The rotational temperatures are found to be slightly below the cell temperature. The relative fractions （〈fV〉, 〈fR〉, 〈fT〉） of average energy disposal are derived as （0.2,0.12,0.68）, （0.2,0.12,0.68）, （0.07,0.04,0.89） and （0.07,0.04,0.89） for the 6^2D3/2, 6^2D5/2, 7^2D3/2 and 7^2D5/2, respectively. The major available energy is released as translation. These results support that the reaction mechanism of Cs（6^2 D,7^2 D） plus 112 is primarily a eollinear abstraction and not an insertion.

Quantum Phase Transition of the Bosonic Atoms near the Feshbach Resonance in an Optical Lattice

The quantum phase transition from the Mott insulator to the superfluid phases of the bosonic atoms trapped in an optical lattice, in which the on-site interaction carl be tuned by a Feshbach resonance, is investigated by a variational approach within mean-field theory. We derive an extended Bos^Hubbard model to describe this ultracold atomic system. By theoretical calculation and analysis, the phase diagram is shown clearly, and we find an exciting and novel phenomenon that is the appearance of the Mort insulator-sea （MI-sea）. Meanwhile, the experimental feasibility of observing the MI-sea is discussed by analyzing the published data related to the Fashbaeh resonance at present. Finally, the potential application of the MI-sea for quantum information processing and quantum computation is also discussed in detail

Ground State of Fermions in a 1D Trap with δ Function Interaction

The ground state of fermions in a 1D trap with δ function interaction is studied mathematically with group theory ideas.

Electron Correlation in Nonsequential Double Ionization of Helium by Two-Color Pulses

We investigate the momentum and energy correlations between the two electrons from nonsequential double ionization （NSDI） of helium by strong two-color pulses with the classical three-dimensional ensemble model. The correlated momentum distribution in the direction parallel to the laser field exhibits an arc-like structure and the sum-energy spectrum shows a sharp peak for the NSDI of helium in the two-color fields. Back analysis reveals that the narrow time interval during which recollisions occur, the low returning energy and the short time delay between recollision and double ionization lead to the novel momentum and energy correlations.

The n-Qubit W State of Ground-State Atoms Using Cavity QED and Single Photon Detection

We present a simple scheme for the probabilistic generation of the $n$-qubit W state of three-level systems in cavity quantum electrodynamics. Once the W state is prepared, it will be insensitive to the spontaneous emission of atoms due to the fact that only the two degenerate ground states of the three-level atoms are involved. With time evolution of the system, the success probability and the experimental feasibility are also discussed.

Coherent Population Trapping-Ramsey Interference in Cold Atoms

We demonstrate an experimental observation of coherent population trapping-Ramsey interference in cold 87Rb atoms by employing the time-domain separated oscillatory fields＇ method. The interference fringe with line width of 80 Hz is obtained. We propose a novel method to measure the cold atom number. The measurement is insensitive to the pump beam intensity, the single photon detuning and even the initial state population. We use this method to normalize the interference signal and to improve the signal-to-noise ratio significantly.

Collapse and Revival of an Atomic Beam Interacting with a Coherent State Light Field

We report on the phenomena of the periodic spontaneous collapse and revival in the dynamics of an atomic beam interacting with a single-mode and coherent-state light field. Conventional collapse and revival by Eberly et al. [Phys. Rev. Lett. 44（1980）1323 ] are presented in the case of the evolution with time of the population inversion. Here, we study the evolution with coupling strength of population inversion. We define the collapse and revival coupling strengths as characteristic parameters to describe the above collapse and revival. Furthermore, we present the analytic formulas for the population inversion, the collapse and revival coupling strengths.

Spatial Splitting and Intensity Suppression of Four-Wave Mixing in V-Type Three-Level Atomic System

We illustrate our experimental observation of coexisting the controllable spatial splitting and intensity suppression of four-wave mixing （FWM） beam in a V-type three-level atomic system. The peak number and separation distance of the FWM beam are controlled by the intensities and frequencies of the laser beams, as well as atomic density.