Publications (29)36.28 Total impact
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ABSTRACT: We have observed Feshbach resonances for 133 Cs atoms in two different hyperfine states at static magnetic fields of a few milligauss. These resonances are unusual for two main reasons. First, they are the lowest staticfield resonances investigated up to now, and we explain their multipeak structure in these ultralow fields. Second, they are robust with respect to temperature effects. We have measured them using an atomic fountain clock and reproduced them using coupledchannels calculations, which are in excellent agreement with our measurements. We show that these are swave resonances due to a very weakly bound state of the triplet molecular Hamiltonian. We also describe a model explaining their asymmetric shape in the regime where the kinetic energy dominates over the coupling strength.  [Show abstract] [Hide abstract]
ABSTRACT: We have observed Feshbach resonances for 133Cs atoms in two different hyperfine states at ultralow static magnetic fields by using an atomic fountain clock. The extreme sensitivity of our setup allows for high signaltonoiseratio observations at densities of only 2*10^7 cm^{3}. We have reproduced these resonances using coupledchannels calculations which are in excellent agreement with our measurements. We justify that these are swave resonances involving weaklybound states of the triplet molecular Hamiltonian, identify the resonant closed channels, and explain the observed multipeak structure. We also describe a model which precisely accounts for the collisional processes in the fountain and which explains the asymmetric shape of the observed Feshbach resonances in the regime where the kinetic energy dominates over the coupling strength.  [Show abstract] [Hide abstract]
ABSTRACT: Nous décrivons le travail réalisé au LNESYRTE (Observatoire de Paris) ces dernières années, en vue de l'amélioration et de l'utilisation d'étalons de fréquence microonde fondés sur l'utilisation d'atomes refroidis par laser. Nous exposons les améliorations récentes des fontaines atomiques à 133Cs et 87Rb. La précision atteinte sur la réalisation de la seconde avec de tels systèmes (une exactitude relative de 7.1016) permet de mener des expériences de physique fondamentale poussées et ouvre un champ d'applications dans les domaines de la navigation et des télécommunications.  [Show abstract] [Hide abstract]
ABSTRACT: In this article, we describe a new frequency synthesis system that includes a low phase noise cryogenic sapphire oscillator (CSO) and an Hmaser to provide metrological lownoise signals to time and frequency experiments. Implementing this system as a local oscillator for a Cs cold atom fountain, a record frequency stability of 1.6×10<sup>14</sup>τ<sup>1/2</sup> is obtained.  [Show abstract] [Hide abstract]
ABSTRACT: We present a comparison between SYRTE's Cs fountain FO1 and CsRb fountain FO2 using a cryogenic sapphire oscillator (CSO) to generate an ultrastable interrogation signal. A description of the experimental setup is given and the clock accuracies are discussed. For the first time, a frequency resolution in the low 10<sup>16</sup> is achieved in the comparison between two primary standards. The paper also summarizes recent contributions of these fountains to research activities such as test of the stability of fundamental constants, timekeeping and test of subsystems of the PHARAO space clock.  [Show abstract] [Hide abstract]
ABSTRACT: In 2003, we remeasured the frequency of the 1 S ( F = 1, m F = ± 1) 2 S ( F ' = 1, m F ' = ± 1) two photon transition in atomic hydrogen with a selfreferenced optical frequency comb relative to the 133 Cs groundstate hyperfine splitting. By comparison with an earlier measurement made in 1999, we can set an upper limit on its time variation of 29(57) Hz within 44 months. Combining this result with recently published abso lute frequency measurements of optical transitions in single trapped Hg + and Yb + ions, we deduce ( ∂ / ∂ t )ln α = (0.3 ± 2.0) × 10 15 yr 1 and ( ∂ / ∂ t )ln( µ Cs / µ B ) = (2.4 ± 6.8) × 10 15 yr 1 as limits on the fractional time variation of the fine structure constant α and the ratio of the 133 Cs nuclear magnetic moment µ Cs and the Bohr magneton µ B , respectively. Using frequency comparisons of microwave 87 Rb and 133 Cs fountain clocks, we deduce addi tional stringent limits on the fractional time variation of µ Rb / µ Cs and µ Rb / µ B , where µ Rb is the magnetic moment of the 87 Rb nucleus. All limits are compatible with zero drift and, for the first time, do not require any model assumptions about the relative drifts of fundamental constants.  [Show abstract] [Hide abstract]
ABSTRACT: This paper describes the work performed at BNM‐SYRTE (Observatoire de Paris) over the past few years toward the improvement and the use of microwave frequency standards using laser‐cooled atoms. First, recent improvements of the 133Cs and 87Rb atomic fountains are described. An important advance is the achievement of a fractional frequency instability of 1.6 × 10−14τ−1/2 where τ is the measurement time in seconds, thanks to the routine use of a cryogenic sapphire oscillator as an ultra‐stable local frequency reference. 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 × 10−16 at 50 000 s for the first time for primary standards. In addition, these clocks realize the SI second with an accuracy of 7 × 10−16, one order of magnitude below that of uncooled devices. © 2005 American Institute of Physics 
Article: BNMSYRTE fountains: recent results
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ABSTRACT: Recent improvements of Bureau National de Me´trologie Syste`mes de Re´fe´rence Temps Espace (BNMSYRTE) fountains FO1 and FO2 are described. Fractional frequency instabilities of 2.9×10<sup>14</sup>τ<sup>1</sup>2/ for FO1 and 1.6×10<sup>14</sup>τ<sup>1</sup>2/ for FO2 have been demonstrated. A preliminary estimate of the systematic frequency shifts gives an uncertainty of ±7.2×10<sup>16</sup> for FO1 and ±6.5×10<sup>16</sup> for FO2. Furthermore, we present a direct comparison between the two fountains. When a realtime measurement of the collisional shift is included, we observe a stability of the comparison of 5.0×10<sup>14</sup>τ<sup>1</sup>2/ and a frequency difference of δ=4×10<sup>16</sup>, well within the combined uncertainties. 
Article: Cold atom clocks and applications
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ABSTRACT: This paper describes advances in microwave frequency standards using lasercooled atoms at BNMSYRTE. First, recent improvements of the 133Cs and 87Rb atomic fountains are described. Thanks to the routine use of a cryogenic sapphire oscillator as an ultrastable local frequency reference, a fountain frequency instability of 1.6 × 10−14 τ−1/2 where τ 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 × 10−16 at 50 000 s for the first time for primary standards. In addition, these clocks realize the SI second with an accuracy of 7 × 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 87Rb and 133Cs 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. 
Article: BNMSYRTE fountains: recent results.
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ABSTRACT: This paper describes several recent improvements of the BNMSYRTE fountain ensemble. A new method for controlling the cold collision shift with improved accuracy has been proposed and demonstrated. A thorough investigation of some cold collision properties of 133Cs is presented, including the observation of molecular Feshbach resonances. Finally, a new microwave synthesis scheme based on a fully operational cryogenic oscillator is presented. With this, a fractional frequency instability below 2 times 1014taufrac12 is obtained routinely  [Show abstract] [Hide abstract]
ABSTRACT: At SYRTE, we have performed a direct local comparison between two atomic fountains, FO1 and FO2 using as the interrogation oscillator a cryogenic sapphire resonator oscillator weakly phaselocked to a hydrogen maser. The best short term stabilities measured against this interrogation oscillator are 2.9 and 1.6 × 1014 at 1 s, respectively. When accounting for the real time measurement of the cold collision shift as well as correction for all the other systematic shifts, we measure combined stability of 5.0 × 1014, going down to 2.2 × 1016 at 50000 s. The measured systematic frequency difference is (4 ± 2.2) × 1016. It is fully consistent with the clock accuracies of 7.5 × 1016 for FO1 and 6.5 × 1016 for FO2. 
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ABSTRACT: We report a test of the stability of fundamental constants based on laboratory experiments. This test relies on highprecision comparisons of atomic frequencies. The ground state hyperfine frequencies of 87Rb and 133Cs are compared over five years using atomic fountains. These measurements lead to the following constraint {d / {dt}} ln ( {(g{C} {s} /g{Rb} )alpha 0.44 } ; ) = (0.2 ± 7.0) × 10{  16} {yr}{  1} (1sigma uncertainty) where g is the nuclear gfactor and alpha the fine structure constant.  [Show abstract] [Hide abstract]
ABSTRACT: Cet article présente les derniers résultats des horloges en fontaine du BNMSYRTE avec leurs stabilités et exactitudes respectives (FOM : 1,7.10$^{13}\tau ^{1/2}$, 0,8.10$^{15}$ ; DF$_{Cs}$ : 3,5.10$^{14}\tau ^{1/2}$, 0,8.10$^{15 }$; DF$_{Rb}$ : 1,4.10$^{14}\tau ^{1/2}$, 0,7.10$^{15}$). Pour la détermination du déplacement collisionel une nouvelle méthode de mesure différentielle des densités a été mis en place. La méthode de passage adiabatique permet la préparation des atomes avec 50% ou 100% de la densité maximale. Les comparaisons entre les fontaines ont abouti à un test de la variation éventuelle de la constante de structure fine $\alpha$. En supposant que seule $\alpha$ varie la variation relative est ($0,4 \pm 16$).10$^{16}$ an$^{1}$. 
Article: Advances in atomic fountains
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ABSTRACT: This article describes the work performed at BNMSYRTE (Observatoire de Paris) in the past few years, toward the improvement and the use of microwave frequency standards using lasercooled atoms. First, recent improvements of the 133Cs and 87Rb atomic fountains are described. An important advance is the achievement of a fractional frequency instability of 1.6×10−14τ−1/2 where τ is the measurement time in seconds, thanks to the routine use of a cryogenic sapphire oscillator as an ultrastable local frequency reference. The second advance is a powerful method to control the frequency shift due to cold collisions. These two advances lead to a fractional frequency in stability of 2×10−16 at 50 000 s between two independent primary standards. In addition, these clocks realize the SI second with an accuracy of 7×10−16, one order of magnitude below that of uncooled devices. Tests of fundamental physical laws constitute an important field of application for highly accurate atomic clocks. In a second part, we describe tests of possible variations of fundamental constants using 87Rb and 133Cs fountains. The third part is 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 will fly on board the International Space Station in 20072008, enabling a new generation of relativity tests. To cite this article: S. Bize et al., C. R. Physique 5 (2004).  [Show abstract] [Hide abstract]
ABSTRACT: We describe two experimental tests of the Equivalence Principle that are based on frequency measurements between precision oscillators and/or highly accurate atomic frequency standards. Based on comparisons between the hyperfine frequencies of 87Rb and 133Cs in atomic fountains, the first experiment constrains the variability of fundamental constants. The second experiment is based on a comparison between a cryogenic sapphire oscillator and a hydrogen maser. It tests Local Lorentz Invariance. In both cases, we report recent results which improve significantly over previous experiments.  [Show abstract] [Hide abstract]
ABSTRACT: In 2003 we have measured the absolute frequency of the (1S, F=1, mF= 1)[(a)\dot]/a = ¶/¶t(lna)=(0.9±2.9)1015\dot{\alpha}/\alpha=\partial/{\partial t}(\ln \alpha)=(0.9\pm 2.9)\times 10^{15}yr–1 and for the ratio of 87Rb and 133Cs nuclear magnetic moments ¶/¶t(ln[mRb/mCs])=(0.5±1.7)1015\partial/{\partial t}(\ln[\mu_{\rm {Rb}}/\mu_{\rm {Cs}}])=(0.5\pm 1.7)\times 10^{15}yr–1. This is the first precise restriction for the fractional time variation of made without assumptions about the relative drifts of the constants of electromagnetic, strong and weak interactions.  [Show abstract] [Hide abstract]
ABSTRACT: One of the main limitations of cesium atomic fountains has been the cold collision frequency shift. By using a method based on a transfer of population by adiabatic passage allowing to prepare cold atomic samples with a well defined ratio of atomic density as well as atom number the collisional shift is controlled at the 10E3 of its value. A calibration of Zeeman substates contribution to the clock shift as a function of the field has been performed. Feshbach resonances have been observed for the first time at very low magnetic field and with a very good resolution. A Monte Carlo simulation has been performed and could fit properly some of experimental data. This constrains some parameters of the theory of collisions.  [Show abstract] [Hide abstract]
ABSTRACT: We have remeasured the absolute 1S2S transition frequency nu(H) in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of (29+/57) Hz for the drift of nu(H) with respect to the ground state hyperfine splitting nu(Cs) in 133Cs. Combining this result with the recently published optical transition frequency in 199Hg+ against nu(Cs) and a microwave 87Rb and 133Cs clock comparison, we deduce separate limits on alpha/alpha=(0.9+/2.9) x 10(15) yr(1) and the fractional time variation of the ratio of Rb and Cs nuclear magnetic moments mu(Rb)/mu(Cs) equal to (0.5+/1.7) x 10(15) yr(1). The latter provides information on the temporal behavior of the constant of strong interaction. 
Conference Paper: High performance flywheel source for atomic fountains and advanced metrology applications
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ABSTRACT: Atomic fountain frequency standard have the potential to reach a frequency stability of about 10<sup>−14τ−1/2</sup>, if the interrogation oscillator frequency noise which degrades the stability via the “Dick effect” ([2, 7]) is made negligible. In this aim a Sapphire Cryogenic Oscillator (SCO) is used as very low noise frequency source σ y (τ) ≤ 1 – 2 × 10<sup>−15</sup> 1 s ≪ τ ≪ 1000 s. In this paper, we describe a low phase/frequency noise flywheel sourcea for atomic fountains and other demanding metrological applications (cold atom inertial sensors, optical frequency standards, optical synthesizer based on femtosecond laser).
Publication Stats
1k  Citations  
36.28  Total Impact Points  
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Institutions

2012

Pierre and Marie Curie University  Paris 6
Lutetia Parisorum, ÎledeFrance, France


2005

Laboratoire National de Métrologie et d'Essais
Lutetia Parisorum, ÎledeFrance, France


20032005

Observatoire de Paris
 Systèmes de Référence TempsEspace (SYRTE)
Lutetia Parisorum, ÎledeFrance, France
