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arXiv:physics/0407064

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

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 Jul 13, 2004• 4 citations
arXivHTMLPDF

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 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.

DOI
10.48550/arxiv.physics/0407064

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

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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.

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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.
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.
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 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 .
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.
We have observed Feshbach resonances for 133Cs{}^{133}\mathrm{Cs}133Cs 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 static-field 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 coupled-channels calculations, which are in excellent agreement with our measurements. We show that these are sss-wave 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.