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Thomann, Pierre

Nom
Thomann, Pierre
Affiliation principale
Fonction
Professeur honoraire
Email
pierre.thomann@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/481

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  • Publication
    Accès libre
    Évaluation métrologique de l'étalon primaire de fréquence à atomes froids de césium FOCS-2
    (2012)
    Devenoges, Laurent 
    ;
    Mileti, Gaetano 
    ;
    Thomann, Pierre 
    Ce travail de recherche s'inscrit dans la continuité des études, menées depuis 20 ans à l'Observatoire Cantonal de Neuchâtel, pour réaliser un étalon primaire de fréquence fonctionnant avec un jet continu d'atomes froids et lents. Ces développements théoriques et expérimentaux ont conduit à la construction de deux horloges à fontaine continue FOCS-1 et FOCS-2. Ce document expose les dernières améliorations et les premières mesures d'évaluation du second étalon primaire de fréquence effectuées ces trois dernières années au Laboratoire Temps-Fréquence de l'Université de Neuchâtel.
    Dans la première partie, nous présentons le développement et l'implémentation d'une nouvelle méthode de préparation d'état utilisée pour améliorer la stabilité de fréquence à court terme de l'étalon. Nous avons montré qu'en utilisant un schéma de pompage optique à deux lasers, il est possible de combiner simultanément préparation d'état et refroidissement Sisyphe. Grâce à cette technique, nous avons réussi à préparer 60% des atomes dans le niveau
  • Publication
    Accès libre
    Improvement of the frequency stability below the dick limit with a continuous atomic fountain clock
    (2012)
    Devenoges, Laurent 
    ;
    Stefanov, A.
    ;
    Joyet, Alain 
    ;
    Thomann, Pierre 
    ;
    Di Domenico, Gianni 
    The frequency instability of a shot-noise limited atomic fountain clock is inversely proportional to its signal-to- noise ratio. Therefore, increasing the atomic flux is a direct way to improve the stability. Nevertheless, in pulsed operation, the local oscillator noise limits the performance via the Dick effect. We experimentally demonstrate here that a continuous atomic fountain allows one to overcome this limitation. In this work, we take advantage of two-laser optical pumping on a cold cesium beam to increase the useful fountain flux and, thus, to reduce the frequency instability below the Dick limit. A stabil- ity of 6 • 10-14 τ-1/2 has been measured with the continuous cesium fountain FOCS-2.
  • Publication
    Accès libre
    Fourier analysis of Ramsey fringes observed in a continuous atomic fountain for in situ magnetometry
    (2011)
    Di Domenico, Gianni 
    ;
    Devenoges, Laurent 
    ;
    Stefanov, A.
    ;
    Joyet, A.
    ;
    Thomann, Pierre 
    Ramsey fringes observed in an atomic fountain are formed by the superposition of the individual atomic signals. Due to the atomic beam residual temperature, the atoms have slightly different trajectories and thus are exposed to a different average magnetic field, and a velocity-dependent Ramsey interaction time. As a consequence, both the velocity distribution and magnetic field profile are imprinted in the Ramsey fringes observed on Zeeman sensitive microwave transitions. In this work, we perform a Fourier analysis of the measured Ramsey signals to retrieve both the time-averaged magnetic field associated with different trajectories and the velocity distribution of the atomic beam. We use this information to reconstruct Ramsey fringes and establish an analytical expression for the value of the microwave frequency for which individual Ramsey fringes add most constructively and are thus visible in the microwave spectrum.
  • Publication
    Accès libre
    Combined quantum state preparation and laser cooling of a continuous beam of cold atoms
    (2010)
    Di Domenico, Gianni 
    ;
    Devenoges, Laurent 
    ;
    Dumas, Claire
    ;
    Thomann, Pierre 
    We use two-laser optical pumping on a continuous atomic fountain in order to prepare cold cesium atoms in the same quantum ground state. A first laser excites the F=4 ground state to pump the atoms toward F=3 while a second π -polarized laser excites the F=3 -> F'=3 transition of the D2 line to produce Zeeman pumping toward m=0. To avoid trap states, we implement the first laser in a 2D optical lattice geometry, thereby creating polarization gradients. This configuration has the advantage of simultaneously producing Sisyphus cooling when the optical lattice laser is tuned between the F=4 -> F'=4 and F=4 -> F'=5 transitions of the D2 line, which is important to remove the heat produced by optical pumping. Detuning the frequency of the second π-polarized laser reveals the action of a new mechanism improving both laser cooling and state preparation efficiency. A physical interpretation of this mechanism is discussed.
  • Publication
    Accès libre
    First uncertainty evaluation of the FoCS-2 primary frequency standard
    Jallageas, Antoine 
    ;
    Devenoges, Laurent 
    ;
    Petersen Mangin, Michael 
    ;
    Morel, J
    ;
    Bernier, L. G
    ;
    Schenker, Dominique
    ;
    Thomann, Pierre 
    ;
    Südmeyer, Thomas 
    We report the uncertainty evaluation of the Swiss continuous primary frequency standard FoCS-2 (Fontaine Continue Suisse). Unlike other primary frequency standards which are working with clouds of cold atoms, this fountain uses a continuous beam of cold caesium atoms bringing a series of metrological advantages and specific techniques for the evaluation of the uncertainty budget. Recent improvements of FoCS-2 have made possible the evaluation of the frequency shifts and of their uncertainties in the order of 1 × 10−15. When operating in an optimal regime a relative frequency instability of 8 × 10−14 (τ/s) −1/2 is obtained. The relative standard uncertainty reported in this article, 1.99 × 10−15, is strongly dominated by the statistics of the frequency measurements.
  • Publication
    Accès libre
    Measurement of the magnetic field profile in the atomic fountain clock FoCS-2 using Zeeman spectroscopy
    Devenoges, Laurent 
    ;
    Di Domenico, Gianni 
    ;
    Stefanov, André
    ;
    Jallageas, Antoine 
    ;
    Morel, Jacques
    ;
    Südmeyer, Thomas 
    ;
    Thomann, Pierre 
    We report the evaluation of the second-order Zeeman shift in the continuous atomic fountain clock FoCS-2. Because of its continuous operation and geometrical constraints, the methods used in pulsed fountains are not applicable. We use here time-resolved Zeeman spectroscopy to probe the magnetic field profile in the clock. Pulses of ac magnetic excitation allow us to spatially resolve the Zeeman frequency and to evaluate the Zeeman shift with a relative uncertainty smaller than 5 × 10−16.
  • Publication
    Accès libre
    Status and prospect of the Swiss continuous Cs fountain FoCS-2
    Jallageas, Antoine 
    ;
    Devenoges, Laurent 
    ;
    Petersen, Michael
    ;
    Morel, Jacques
    ;
    Bernier, Laurent-Guy
    ;
    Thomann, Pierre 
    ;
    Südmeyer, Thomas 
    The continuous cesium fountain clock FoCS-2 at METAS presents many unique characteristics and challenges in comparison with standard pulsed fountain clocks. For several years FoCS-2 was limited by an unexplained frequency sensitivity on the velocity of the atoms, in the range of 140 · 10-15. Recent experiments allowed us to identify the origin of this problem as undesirable microwave surface currents circulating on the shield of the coaxial cables that feed the microwave cavity. A strong reduction of this effect was obtained by adding microwave absorbing coatings on the coaxial cables and absorbers inside of the vacuum chamber. This breakthrough opens the door to a true metrological validation of the fountain. A series of simulation tools have already been developed and proved their efficiency in the evaluation of some of the uncertainties of the continuous fountain. With these recent improvements, we are confident in the future demonstration of an uncertainty budget at the 10-15 level and below.