565,824 research outputs found

    Distinguishing coherent atomic processes using wave mixing

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    We are able to clearly distinguish the processes responsible for enhanced low-intensity atomic Kerr nonlinearity, namely coherent population trapping and coherent population oscillations in experiments performed on the Rb D1 line, where one or the other process dominates under appropriate conditions. The potential of this new approach based on wave mixing for probing coherent atomic media is discussed. It allows the new spectral components to be detected with sub-kHz resolution, which is well below the laser linewidth limit. Spatial selectivity and enhanced sensitivity make this method useful for testing dilute cold atomic samples.Comment: 9 pages, 5 figure

    Atomic relaxation processes near conducting and superconducting surfaces

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    The aim of this thesis is to investigate the interaction of neutral atoms with conducting and superconducting surfaces. Experimental advances in the magnetic confinement of ultracold atoms have shown that they can act as a powerful tool in a wide range of phenomena such as electric and magnetic field imaging and matter wave interferometry. Coherent manipulation of atoms and ever smaller magnetic traps are essential elements in the implementation of integrated quantum devices for fundamental research, quantum information processing and precision measurements. This thesis considers main influences on atoms placed within three different environments which are useful in achieving miniaturization and efficient control in atomic magnetic traps: carbon nanotubes, dielectric surfaces and superconducting thin films. The possibility of holding atoms near the outside of a carbon nanotubes will be addressed. In order to give a qualitative analysis of the atom-nanotube interaction, thermally induced spin-flips and the Casimir-Polder potential have been considered. The comparison between these two effects is presented in this thesis. It indicates that the Casimir-Polder force is the dominant loss mechanism and an estimation of the minimum trapping distance is given based on its effect. Secondly, a first-principles derivation of spatial atomic-sublevel decoherence near dielectric and metallic surfaces will be presented. The rate obtained for the decay of spatial coherence has dual implications, on one hand, it can be considered as a measure of the coherence length of the fluctuations of the electromagnetic field arising from a given substrate. On the other hand, it turns out to be relevant for quantum information encoding in double well potentials. Finally, the known spin-flip transition rate will be linked to the flux noise spectrum in superconducting thin films showing the feasibility of using cold atomic clouds in the investigation of vortex dynamics.Imperial Users onl

    Ultracold scattering processes in three-atomic helium systems

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    We review results on scattering observables for 4^4He--4^4He2_2 and 3^3He--4^4He2_2 collisions. We also study the effect of varying the coupling constant of the atom-atom interaction on the scattering length

    Teleportation of an atomic ensemble quantum state

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    We propose a protocol to achieve high fidelity quantum state teleportation of a macroscopic atomic ensemble using a pair of quantum-correlated atomic ensembles. We show how to prepare this pair of ensembles using quasiperfect quantum state transfer processes between light and atoms. Our protocol relies on optical joint measurements of the atomic ensemble states and magnetic feedback reconstruction

    Prediction of forbidden ultraviolet and visible emissions in comet 67P/Churyumov-Gerasimenko

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    Remote observation of spectroscopic emissions is a potential tool for the identification and quantification of various species in comets. CO Cameron band (to trace \cod) and atomic oxygen emissions (to trace H2_2O and/or CO2_2, CO) have been used to probe neutral composition in the cometary coma. Using a coupled-chemistry emission model, various excitation processes controlling CO Cameron band and different atomic oxygen and atomic carbon have been modelled in comet 67P-Churyumov-Gerasimenko at 1.29~AU (perihelion) and at 3~AU heliocentric distances, which is being explored by ESA's Rosetta mission. The intensities of CO Cameron band, atomic oxygen and atomic carbon emission lines as a function of projected distance are calculated for different CO and CO2_2 volume mixing ratios relative to water. Contributions of different excitation processes controlling these emissions are quantified. We assess how CO2_2 and/or CO volume mixing ratios with respect to H2_2O can be derived based on the observed intensities of CO Cameron band, atomic oxygen, and atomic carbon emission lines.The results presented in this work serve as base line calculations to understand the behaviour of low out-gassing cometary coma and compare them with the higher gas production rate cases (e.g. comet Halley). Quantitative analysis of different excitation processes governing the spectroscopic emissions is essential to study the chemistry of inner coma and to derive neutral gas composition.Comment: 46 pages, 12 figures, Accepted in The Astrophysical Journa
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