Guiding neutral atoms with two current-carrying wires and a vertical bias field on the atom chip

We demonstrate the guiding of neutral atoms with two parallel microfabricated current-carrying wires on the atom chip and a vertical magnetic bias field. The atoms are guided along a magnetic field minimum parallel to the current-carrying wires and confined in the other two directions. We describe in detail how the precooled atoms are efficiently loaded into the two-wire guide. We present a detailed experimental study of the motional properties of the atoms in the guide and the relationship between the location of the guide and the vertical bias field. This two-wire guide with vertical bias field can be used to realize large area atom interferometer.

Laser cooling of rubidium atoms from background vapor in diffuse light

In this paper we describe an experiment on laser cooling of Rb-87 atoms directly from a vapor background in diffuse light. Diffuse light is produced in a ceramic integrating sphere by multiple scattering of two laser beams injected through multimode fibers. A probe beam, whose propagation direction is either horizontal or vertical, is used to detect cold atoms. We measured the absorption spectra of the cold atoms by scanning the frequency of the probe beam, and observed both the absorption signal and the time of flight signal after we switched off the cooling light, from which we estimated the temperature and the number of cold atoms. This method is clearly attractive for building a compact cold atom clock.

Nonlinear spectroscopy of cold atoms in diffuse laser light

The nonlinear spectroscopy of cold atoms in the diffuse laser cooling system is studied in this paper. We present the theoretical models of the recoil-induced resonances (RIR) and the electromagnetically-induced absorption (EIA) of cold atoms in diffuse laser light, and show their signals in an experiment of cooling Rb-87 atomic vapor in an integrating sphere. The theoretical results are in good agreement with the experimental ones when the light intensity distribution in the integrating sphere is considered. The differences between nonlinear spectra of cold atoms in the diffuse laser light and in the optical molasses are also discussed. (c) 2009 Optical Society of America

1. Ultrasonic studies of binary liquid structure in the critical region. Theory and experiment for the 2,6-lutidine/water system. 2. Hartree-Fock calculations of electric polarizabilities of some simple atoms and molecules, and their practicality. 3. Calculation of vibrational transition probabilities in collinear atom-diatom and diatom-diatom collisions with Lennard-Jones interaction

Part 1. Many interesting visual and mechanical phenomena occur in the critical region of fluids, both for the gas-liquid and liquid-liquid transitions. The precise thermodynamic and transport behavior here has some broad consequences for the molecular theory of liquids. Previous studies in this laboratory on a liquid-liquid critical mixture via ultrasonics supported a basically classical analysis of fluid behavior by M. Fixman (e. g., the free energy is assumed analytic in intensive variables in the thermodynamics)--at least when the fluid is not too close to critical. A breakdown in classical concepts is evidenced close to critical, in some well-defined ways. We have studied herein a liquid-liquid critical system of complementary nature (possessing a lower critical mixing or consolute temperature) to all previous mixtures, to look for new qualitative critical behavior. We did not find such new behavior in the ultrasonic absorption ascribable to the critical fluctuations, but we did find extra absorption due to chemical processes (yet these are related to the mixing behavior generating the lower consolute point). We rederived, corrected, and extended Fixman's analysis to interpret our experimental results in these more complex circumstances. The entire account of theory and experiment is prefaced by an extensive introduction recounting the general status of liquid state theory. The introduction provides a context for our present work, and also points out problems deserving attention. Interest in these problems was stimulated by this work but also by work in Part 3.

Part 2. Among variational theories of electronic structure, the Hartree-Fock theory has proved particularly valuable for a practical understanding of such properties as chemical binding, electric multipole moments, and X-ray scattering intensity. It also provides the most tractable method of calculating first-order properties under external or internal one-electron perturbations, either developed explicitly in orders of perturbation theory or in the fully self-consistent method. The accuracy and consistency of first-order properties are poorer than those of zero-order properties, but this is most often due to the use of explicit approximations in solving the perturbed equations, or to inadequacy of the variational basis in size or composition. We have calculated the electric polarizabilities of H₂, He, Li, Be, LiH, and N₂ by Hartree-Fock theory, using exact perturbation theory or the fully self-consistent method, as dictated by convenience. By careful studies on total basis set composition, we obtained good approximations to limiting Hartree-Fock values of polarizabilities with bases of reasonable size. The values for all species, and for each direction in the molecular cases, are within 8% of experiment, or of best theoretical values in the absence of the former. Our results support the use of unadorned Hartree-Pock theory for static polarizabilities needed in interpreting electron-molecule scattering data, collision-induced light scattering experiments, and other phenomena involving experimentally inaccessible polarizabilities.

Part 3. Numerical integration of the close-coupled scattering equations has been carried out to obtain vibrational transition probabilities for some models of the electronically adiabatic H₂-H₂ collision. All the models use a Lennard-Jones interaction potential between nearest atoms in the collision partners. We have analyzed the results for some insight into the vibrational excitation process in its dependence on the energy of collision, the nature of the vibrational binding potential, and other factors. We conclude also that replacement of earlier, simpler models of the interaction potential by the Lennard-Jones form adds very little realism for all the complication it introduces. A brief introduction precedes the presentation of our work and places it in the context of attempts to understand the collisional activation process in chemical reactions as well as some other chemical dynamics.

Spectroscopic analysis of atoms and molecules

151 p.

The formation and electronic structures of 3d transition-metal atoms doped in silicon nanowires

Using first-principles methods, we systematically study the mechanism of defect formation and electronic structures for 3d transition-metal impurities (V, Cr, Mn, Fe, and Co) doped in silicon nanowires. We find that the formation energies of 3d transition-metal impurities with electrons or holes at the defect levels always increase as the diameters of silicon nanowires decrease, which suggests that self-purification, i.e., the difficulty of doping in silicon nanowires, should be an intrinsic effect. The calculated results show that the defect formation energies of Mn and Fe impurities are lower than those of V, Cr, and Co impurities in silicon nanowires. It indicates that Mn and Fe can easily occupy substitutional site in the interior of silicon nanowires. Moreover, they have larger localized moments, which means that they are good candidates for Si-based dilute magnetic semiconductor nanowires. The doping of Mn and Fe atom in silicon nanowires introduces a pair of energy levels with t(2) symmetry. One of which is dominated by 3d electrons of Mn or Fe, and the other by neighboring dangling bonds of Si vacancies. In addition, a set of nonbonding states localized on the transition-metal atom with e symmetry is also introduced. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3000445]

Method for generating maximally entangled states of multiple three-level atoms in cavity QED

We propose a scheme to generate maximally entangled states (MESs) of multiple three-level atoms in microwave cavity QED based on the resonant atom-cavity interaction. In the scheme, multiple three-level atoms initially in their ground states are sequently sent through two suitably prepared cavities. After a process of appropriate atom-cavity interaction, a subsequent measurement on the second cavity field projects the atoms onto the MESs. The practical feasibility of this method is also discussed.

Generation of a supersinglet of three three-level atoms in cavity QED

We propose a scheme to generate a supersinglet of three three-level atoms in microwave cavity quantum electrodynamics based on the resonant atom-cavity interaction. In the scheme, three three-level atoms in suitable initial states are sequentially sent through three cavities originally prepared in their vacuum states. After an appropriate atom-cavity interaction process, in the subsequent measurement on the third cavity field the atoms are projected onto the desired supersinglet. The practical feasibility of this method is discussed.

Interlayer segregation of Cu atoms in Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve multilayers and its influence on magnetic properties

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm), and Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (H-ex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta. (C) 2002 American Institute of Physics.

Interlayer segregation of Cu atoms in metal multilayers

The experimental results show that the exchange coupling field H.. of NiFe/FeMn for TalNiFe/FeMn/Ta multilayers is higher than that for the spin valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. The composition and chemical states at the surface of Ta(12nm)/NiFe(7nm), Th(12nm)/NiFe(7nm)/Cu(4nm) and Ta(12nm)/NiFe(7nm)/Cu(3 nm)/NiFe(5 mn) were studied by using x-ray photoelectron spectroscopy. The results show that no element from the underlayers Boats out or segregates to the surface for Th(12 nm)/NiFe(7nm), Ta(12 nm)/NiFe(7nm)/Cu(4 mn). However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7nm)/Cu(3nm)/NiFe(5nm) multilayers, i.e. to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which will cause the exchange coupling field H.. of Ta/NiFe/FeMn/Ta multilayers to be higher than that of Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers.

Observation of "ghost" islands and surfactant effect of surface gallium atoms during GaN growth by molecular beam epitaxy

We observe "ghost" islands formed on terraces during homoepitaxial nucleation of GaN. We attribute the ghost islands to intermediate nucleation states, which can be driven into "normal" islands by scanning tunneling microscopy. The formation of ghost islands is related to excess Ga atoms on the surface. The excess Ga also affect island number density: by increasing Ga coverage, the island density first decreases, reaching a minimum at about 1 monolayer (ML) Ga and then increases rapidly for coverages above 1 ML. This nonmonotonic behavior points to a surfactant effect of the Ga atoms.