Interferometer-Type Structures for Guided Atoms

We experimentally demonstrate interferometer-type guiding structures for neutral atoms based on dipole potentials created by micro-fabricated optical systems. As a central element we use an array of atom waveguides being formed by focusing a red-detuned laser beam with an array of cylindrical microlenses. Combining two of these arrays, we realize X-shaped beam splitters and more complex systems like the geometries for Mach-Zehnder and Michelson-type interferometers for atoms.Comment: 4 pages, 6 figure

AC Stark shift of the Cs microwave atomic clock transitions

We analyze the AC Stark shift of the Cs microwave atomic clock transition theoretically and experimentally. Theoretical and experimental data are in a good agreement with each other. Results indicate the absence of a magic wavelength at which there would be no differential shift of the clock states having zero projections of the total angular momentum

Controlling the cold collision shift in high precision atomic interferometry

We present here a new method based on a transfer of population by adiabatic passage that allows to prepare cold atomic samples with a well defined ratio of atomic density and atom number. This method is used to perform a measurement of the cold collision frequency shift in a laser cooled cesium clock at the percent level, which makes the evaluation of the cesium fountains accuracy at the $10^{-16}$ level realistic. With an improved set-up, the adiabatic passage would allow measurements of atom number-dependent phase shifts at the $10^{-3}$ level in high precision experiments.Comment: 4 pages, 3 figures, 2 table

Efficiency improvement of LDO ouput based linear regulator with supercapacitor energy recovery - a versatile new technique with an example of a 5v to 1.5 v version

Supercapacitors are used in various industrial applications and the supercapacitors technology is gradually progressing into a mature state. Common applications of supercapacitors are in electric vehicles, hybrid electric vehicles, uninterruptible power supply (UPS) and in portable devices such as cellular phones and laptops. The capacitance values range from fractional Farads to few thousand Farads and their continuos DC voltage ratings are from 2V to 6V. At University of Waikato, a team works on using supercapacitors for improving the efficiency of linear voltage regulators. In particular, this patented technique aims at combining off the shelfs LDO ICs and a supercapacitor array for improving end to end efficiency of linear regulator. My work is aimed at developing the theoretical background and designing prototype circuitry for a voltage regulator for the case of unregulated input supply is more than 3 times of the minimum input voltage requirement of the LDO which is applicable for a 5V to 1.5V regulator. Experimental results are indicated with future suggestions for improvement

1S-2S Spectrum of a Hydrogen Bose-Einstein Condensate

We calculate the two-photon 1S-2S spectrum of an atomic hydrogen Bose-Einstein condensate in the regime where the cold collision frequency shift dominates the lineshape. WKB and static phase approximations are made to find the intensities for transitions from the condensate to motional eigenstates for 2S atoms. The excited state wave functions are found using a mean field potential which includes the effects of collisions with condensate atoms. Results agree well with experimental data. This formalism can be used to find condensate spectra for a wide range of excitation schemes.Comment: 13 pages, 4 figure

Collective dynamics of internal states in a Bose gas

Theory for the Rabi and internal Josephson effects in an interacting Bose gas in the cold collision regime is presented. By using microscopic transport equation for the density matrix the problem is mapped onto a problem of precession of two coupled classical spins. In the absence of an external excitation field our results agree with the theory for the density induced frequency shifts in atomic clocks. In the presence of the external field, the internal Josephson effect takes place in a condensed Bose gas as well as in a non-condensed gas. The crossover from Rabi oscillations to the Josephson oscillations as a function of interaction strength is studied in detail.Comment: 18 pages, 2 figure

Cold atom Clocks and Applications

This paper describes advances in microwave frequency standards using laser-cooled atoms at BNM-SYRTE. First, recent improvements of the $^{133}$Cs and $^{87}$Rb atomic fountains are described. Thanks to the routine use of a cryogenic sapphire oscillator as an ultra-stable local frequency reference, a fountain frequency instability of $1.6\times 10^{-14}\tau^{-1/2}$ where $\tau$ is the measurement time in seconds is measured. The second advance is a powerful method to control the frequency shift due to cold collisions. These two advances lead to a frequency stability of $2\times 10^{-16}$ at $50,000s for the first time for primary standards. In addition, these clocks realize the SI second with an accuracy of$7\times 10^{-16}$, one order of magnitude below that of uncooled devices. In a second part, we describe tests of possible variations of fundamental constants using$^{87}$Rb and$^{133}$Cs fountains. Finally we give an update on the cold atom space clock PHARAO developed in collaboration with CNES. This clock is one of the main instruments of the ACES/ESA mission which is scheduled to fly on board the International Space Station in 2008, enabling a new generation of relativity tests.Comment: 30 pages, 11 figure

An experimental study of the spin-exchange frequency shift in a laser-cooled cesium fountain frequency standard

The spin-exchange frequency shift due to cold collisions between ground-state atoms appears to be the systematic effect which could limit the accuracy of a laser-cooled cesium fountain operating as a frequency standard. We have investigated this shift for atoms distributed among all the Zeeman substates of either the F=4 or F=3 hyperfine level of the $6S_{1/2}$ ground state of cesium and for the case where most of the atoms are prepared in F=3, MF=0 sublevel. The measured relative frequency shifts are respectively $-1.0\cdot10^{-21}$, $-0.6\cdot10^{-21}$ and $-2.0\cdot10^{-21}\ (\rm at/cm^3)^{-1}$. These results agree with the measurements performed by Gibble and Chu at higher atom densities with atoms prepared in F=3, MF=0 sublevel. However, the precision of our frequency measurements is much better and is only limited at $2\cdot10^{-15}$ by the H-maser used as a reference oscillator. Finally, we show that the relative frequency shift due to cold collisions can be reduced to 10-15, while preserving a short-term frequency stability of about $10^{-13}\tau^{-1/2}$

ELABORATION D’UNE TECHNIQUE DE REGENERATION DE L’ACTINIDIA CHINENSIS PAR EMBRYOGENESE SOMATIQUE

Dans des études réalisées sur des espèces ligneuses, les embryons sont régénérés à partir des tissus de folioles ou des segments des pousses avec passage ou non par cal en présence du 2,4D sur un milieu de MURASHIG et SKOOG (Walali, 1993). Dans notre étude, l’objectif visé est l’étude de l’influence du matériel végétal de l’Actinidia sur la réponse à l’embryogénèse somatique où très peu de travaux ont été réalisés. On a observé l’induction puis la maturation des embryons somatiques produits. Les graines utilisées, en nombre de trois cent proviennent de la Station Expérimentale Boufarik (Algérie) et de la Station de Jourdain (Toulouse, France). Ces graines sont mises à germer dans des boites de Pétri après désinfection. Après 25 jours, on a récolté des folioles, qui sont ensuite sectionnées en segments et placées sur un milieu d’induction d’embryogénèse somatique M2 composée MS+25 µ M (2,D) à raison de 4 explants par boite de Pétri. Un traitement de développement et de maturation des embryons somatiques formés et ensuite appliqué sur tous les explants. Un premier repiquage à lieu sur le milieu M3 (MS+750 mg Glutamine) suivi d’un deuxième repiquage M4 (MS+5,37 µ M NAA+ 2,5 µ M AG3). La calogénèse s’est manifestée pour chaque type d’explant et pour chaque durée d’exposition au 2,4 D après un transfert dans un milieu enrichi en Glutamine mais dépourvu de 2,4 D. L’effet stimulant du 2,4 D pour la calogénèse est inhibiteur d’embryogénèse somatique et il a été observé aussi par Tetu et al. (1987) chez la betterave