164 research outputs found

    Effect of topology on the transport properties of two interacting dots

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    The transport properties of a system of two interacting dots, one of them directly connected to the leads constituting a side-coupled configuration (SCD), are studied in the weak and strong tunnel-coupling limits. The conductance behavior of the SCD structure has new and richer physics than the better studied system of two dots aligned with the leads (ACD). In the weak coupling regime and in the case of one electron per dot, the ACD configuration gives rise to two mostly independent Kondo states. In the SCD topology, the inserted dot is in a Kondo state while the side-connected one presents Coulomb blockade properties. Moreover, the dot spins change their behavior, from an antiferromagnetic coupling to a ferromagnetic correlation, as a consequence of the interaction with the conduction electrons. The system is governed by the Kondo effect related to the dot that is embedded into the leads. The role of the side-connected dot is to introduce, when at resonance, a new path for the electrons to go through giving rise to the interferences responsible for the suppression of the conductance. These results depend on the values of the intra-dot Coulomb interactions. In the case where the many-body interaction is restricted to the side-connected dot, its Kondo correlation is responsible for the scattering of the conduction electrons giving rise to the conductance suppression

    Accurate spectroscopy of Sr atoms

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    We report the frequency measurement with an accuracy in the 100 kHz range of several optical transitions of atomic Sr : 1S03P1^1S_0- ^3P_1 at 689 nm, 3P13S1^3P_1- ^3S_1 at 688 nm and 3P03S1^3P_0- ^3S_1 at 679 nm. Measurements are performed with a frequency chain based on a femtosecond laser referenced to primary frequency standards. They allowed the indirect determination with a 70 kHz uncertainty of the frequency of the doubly forbidden 5s^2^1S_0- 5s5p^3P_0 transition of 87^{87}Sr at 698 nm and in a second step its direct observation. Frequency measurements are performed for 88^{88}Sr and 87^{87}Sr, allowing the determination of 3P0^3P_0, 3P1^3P_1 and 3S1^3S_1 isotope shifts, as well as the 3S1^3S_1 hyperfine constants.Comment: 12 pages, 16 figure

    D-mesons in dense nuclear matter

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    The D-meson properties in dense nuclear matter are studied. The D-meson spectral density is obtained within the framework of a coupled-channel self-consistent calculation assuming, as bare meson-baryon interaction, a separable potential. The Λc(2593)\Lambda_c(2593) resonance is generated dynamically in our coupled-channel model. The medium modifications of the D-meson properties due to Pauli blocking and the dressing of D-mesons, nucleons and pions are also studied. We conclude that the self-consistent coupled-channel process reduces the in-medium effects on the D-meson compared to previous literature which do not considered the coupled-channel structureComment: 4 pages, 4 figures, to appear in the proceedings of Hard Probes 2004, Ericeira, Portugal, November 4-10, 2004 (European Physical Journal C

    Accumulation of chromium metastable atoms into an Optical Trap

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    We report the fast accumulation of a large number of metastable 52Cr atoms in a mixed trap, formed by the superposition of a strongly confining optical trap and a quadrupolar magnetic trap. The steady state is reached after about 400 ms, providing a cloud of more than one million metastable atoms at a temperature of about 100 microK, with a peak density of 10^{18} atoms.m^{-3}. We have optimized the loading procedure, and measured the light shift of the 5D4 state by analyzing how the trapped atoms respond to a parametric excitation. We compare this result to a theoretical evaluation based on the available spectroscopic data for chromium atoms.Comment: 7 pages, 5 Figure

    T-odd Correlations in the Decay of Scalar Fermions

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    We define a CP sensitive asymmetry in the sfermion decays \ti f \to f \ti\chi^0_j \ell \bar \ell, f \ti\chi^0_j q \bar q, based on triple product correlations between the momenta of the outgoing fermions. We study this asymmetry in the MSSM with complex parameters. We show that the asymmetry is sensitive to the phases of the parameters μ\mu and M1M_1. The leading contribution stems from the decay chain \ti f\to f \ti\chi^0_j\to f \ti\chi^0_1 Z\to f \ti\chi^0_1 \ell \bar \ell (f \ti\chi^0_1 q \bar q), for which we obtain analytic formulae for the amplitude squared. The asymmetry can go up to 3% for \ti f\to f \ti\chi^0_1 \ell \bar \ell, and up to 20% for \ti f\to f \ti\chi^0_1 q \bar q. We also estimate the rates necessary to measure the asymmetry.Comment: 18 pages, 5 figures, 2 tables; comments and references added; two tables added; version to appear in Eur. Phys.

    Coherence length of an elongated condensate: a study by matter-wave interferometry

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    We measure the spatial correlation function of Bose-Einstein condensates in the cross-over region between phase-coherent and strongly phase-fluctuating condensates. We observe the continuous path from a gaussian-like shape to an exponential-like shape characteristic of one-dimensional phase-fluctuations. The width of the spatial correlation function as a function of the temperature shows that the condensate coherence length undergoes no sharp transition between these two regimes.Comment: 8 pages, 6 figure, submitted to EPJ

    Zemach and magnetic radius of the proton from the hyperfine splitting in hydrogen

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    The current status of the determination of corrections to the hyperfine splitting of the ground state in hydrogen is considered. Improved calculations are provided taking into account the most recent value for the proton charge radius. Comparing experimental data with predictions for the hyperfine splitting, the Zemach radius of the proton is deduced to be 1.045(16)1.045(16) fm. Employing exponential parametrizations for the electromagnetic form factors we determine the magnetic radius of the proton to be 0.778(29)0.778(29) fm. Both values are compared with the corresponding ones derived from the data obtained in electron-proton scattering experiments and the data extracted from a rescaled difference between the hyperfine splittings in hydrogen and muonium

    Geometrical Models for Substitutions

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    International audienceWe consider a substitution associated with the Arnoux-Yoccoz interval exchange transformation (IET) related to the tribonacci substitution. We construct the so-called stepped lines associated with the fixed points of the substitution in the abelianization (symbolic) space. We analyze various projections of the stepped line, recovering the Rauzy fractal, a Peano curve related to work in [Arnoux 88], another Peano curve related to the work of [McMullen 09] and [Lowenstein et al. 07], and also the interval exchange transformation itself

    86-km optical link with a resolution of 2.10-18 for RF frequency transfer

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    RF frequency transfer over an urban 86 km fibre has been demonstrated with a resolution of 2.10-18 at one day measuring time using an optical compensator. This result is obtained with a reference carrier frequency of 1 GHz, and a rapid scrambling of the polarisation state of the input light in order to reduce the sensitivity to the polarisation mode dispersion in the fibre. The limitation due to the fibre chromatic dispersion associated with the laser frequency fluctuations is highlighted and analyzed. A preliminary test of an extended compensated link over 186 km using optical amplifiers gives a resolution below 10-17 at 1 day
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