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Conference on Precision Electromagnetic Measurements

BNM-SYRTE fountains: Recent results

H. Marion, Franck Pereira dos Santos, D. Chambon, François Narbonneau, Michel Abgrall, Ivan Maksimovic, L. Cacciapuotti, C. Vian, Jan Grünert, P. Rosenbusch, S. Bize, Giorgio Santarelli, Philippe Laurent, Andr  Clairon, Michael Edmund Tobar, Andre Nicholas Luiten, Ch Salomon

Published Jun 1, 2004• 6 citations
Publisher

Abstract

This paper describes several recent improvements of the BNM-SYRTE 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 of133Cs 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 10-14tau-frac12is obtained routinely

DOI
10.1109/cpem.2004.305328

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For a long time, 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 (AP) allowing to prepare cold atomic samples with a well defined ratio of atomic density as well as atom number we have a better measurement of this effect. By improving the method we found out some unexpected properties of cold collisions, confirming that 133Cs is a rich atom to study cold collisions. Those results lead to fine comparisons with cold collision theory and may constraint some parameters of cesium.

European Frequency and Time Forum•Jan 1, 2004•8 citations
This paper describes several recent improvements of the BNM-SYRTE 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 of133Cs 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 10-14tau-frac12is obtained routinely
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.
The well-known MOT technique is used to trap and cool 133 Cs atoms to reproduce the SI second in an atomic fountain. About 10 8 cesium atoms are caught in a magnetooptical trap from a vapor cell at room temperature. The fountain has a (1,1,1)-geometry for the laser cooling and launching operation. The three upper beams have the same polarization, opposite to the three lower ones. The interrogation and preparation cavities have also been constructed, as well as characterized, concerning the temperature tunability in vacuum. The microwave synthesizer has been constructed in collaboration with BNM-SYRTE, time-and-frequency group. The synthesizer has been compared to a very stable oscillator at BNM-SYRTE resulting in a short-term stability of 9.7 × 10 -14 τ -1/2 .
For a long time, 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 (AP) allowing to prepare cold atomic samples with a well defined ratio of atomic density as well as atom number we have a better measurement of this effect. By improving the method we found out some unexpected properties of cold collisions, confirming that 133Cs is a rich atom to study cold collisions. Those results lead to fine comparisons with cold collision theory and may constraint some parameters of cesium.