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European Frequency and Time Forum

First observation of Feshbach resonances at very low magnetic field in a

H. Marion, S. Bize, L. Cacciapuoti, D. Chambon, Franck Pereira dos Santos, Giorgio Santarelli, Peter Wolf, Andr  Clairon, Andre Nicholas Luiten, Michael Edmund Tobar, S. J. J. M. F. Kokkelmans, Ch Salomon

Published Jan 1, 2004• 8 citations
Publisher

Abstract

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.

DOI
10.1049/cp:20040815

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First observation of feshbach resonances at very low magnetic field in a 133Cs fountain

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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 10E-3 of its value. A calibration of Zeeman sub-states 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.

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We present a new method based on a transfer of population by adiabatic passage that allows one 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 fountain accuracy at the 10(-16) level realistic. With improvements, the adiabatic passage would allow measurements of density-dependent phase shifts at the 10(-3) level in high precision experiments.

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S. Ghezali, Philippe Laurent, S.N. Lea +1 more

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 6 S 1/2 ground state of cesium and for the case where most of the atoms are prepared in F = 3, M F = 0 sublevel. The measured relative frequency shifts are respectively − 1.0·10 −21 , − 0.6·10 −21 and − 2.0·10 −21 (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, M F = 0 sublevel. However, the precision of our frequency measurements is much better and is only limited at 2·10 −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 τ −1/2 .

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Advances in 133Cs Fountains: Control of the Cold Collision Shift and Observation of Feshbach Resonances

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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.

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We analyze all of the cold-collision data for Cs, consisting of atomic fountain frequency shifts and elastic scattering rates, to determine phase parameters that completely characterize cold collisions between two ground-state cesium atoms. We show that the fast decays of spin-polarized gas samples in two recent attempts to reach Bose-Einstein condensation in cesium are due to potential and Feshbach resonances which enhance the depolarizing atom-atom collisions. We discuss the prospects for realizing Bose-Einstein condensation in ${}^{133}\mathrm{Cs}$ and in ${}^{135}\mathrm{Cs}$.

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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

Conference on Precision Electromagnetic Measurements•Jun 1, 2004•6 citations
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.
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 10E-3 of its value. A calibration of Zeeman sub-states 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.
We present a new method based on a transfer of population by adiabatic passage that allows one 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 fountain accuracy at the 10(-16) level realistic. With improvements, the adiabatic passage would allow measurements of density-dependent phase shifts at the 10(-3) level in high precision experiments.
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 6 S 1/2 ground state of cesium and for the case where most of the atoms are prepared in F = 3, M F = 0 sublevel. The measured relative frequency shifts are respectively − 1.0·10 −21 , − 0.6·10 −21 and − 2.0·10 −21 (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, M F = 0 sublevel. However, the precision of our frequency measurements is much better and is only limited at 2·10 −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 τ −1/2 .
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.
We analyze all of the cold-collision data for Cs, consisting of atomic fountain frequency shifts and elastic scattering rates, to determine phase parameters that completely characterize cold collisions between two ground-state cesium atoms. We show that the fast decays of spin-polarized gas samples in two recent attempts to reach Bose-Einstein condensation in cesium are due to potential and Feshbach resonances which enhance the depolarizing atom-atom collisions. We discuss the prospects for realizing Bose-Einstein condensation in 133Cs{}^{133}\mathrm{Cs}133Cs and in 135Cs{}^{135}\mathrm{Cs}135Cs.
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