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Physical Review A

Eliminating cold-collision frequency shifts

Kurt Gibble, BOUDEWIJN J. VERHAAR

Published Oct 1, 1995• 57 citations
Publisher

Abstract

A technique to cancel the frequency shift due to cold collisions of laser-cooled atoms is proposed. Results for future clocks based on $^{135}\mathrm{Cs}$ and $^{137}\mathrm{Cs}$ are presented. We find a $^{137}\mathrm{Cs}$ fountain clock can be operated with no cold-collision shift by adjusting the population ratios in the fountain, and it may also be possible for $^{135}\mathrm{Cs}$. This technique can also be applied to other phase-sensitive measurements using cold atoms, including atom interferometers.

DOI
10.1103/physreva.52.3370

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APS•Apr 1, 1997•0 citations
A technique to cancel the frequency shift due to cold collisions of laser-cooled atoms is proposed. Results for future clocks based on 135Cs^{135}\mathrm{Cs}135Cs and 137Cs^{137}\mathrm{Cs}137Cs are presented. We find a 137Cs^{137}\mathrm{Cs}137Cs fountain clock can be operated with no cold-collision shift by adjusting the population ratios in the fountain, and it may also be possible for 135Cs^{135}\mathrm{Cs}135Cs. This technique can also be applied to other phase-sensitive measurements using cold atoms, including atom interferometers.
We measure a cold collision frequency shift in an 87Rb{}^{87}\mathrm{Rb}87Rb fountain clock that is fractionally 30 times smaller than that for Cs. The shift is $\ensuremath{-}0.38(8)\mathrm{mHz}$ for a density of $1.0(6)\ifmmode\times\else\texttimes\fi{}{10}^{9}{\mathrm{cm}}^{\ensuremath{-}3}$. We study the cavity pulling of the atomic transition and use it to cancel the cold collision shift. We also measure the partial frequency shifts of each clock state finding $2({\ensuremath{\lambda}}_{10}\ensuremath{-}{\ensuremath{\lambda}}_{20})/({\ensuremath{\lambda}}_{10}+{\ensuremath{\lambda}}_{20})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.1(6)$.
A few years ago atomic fountains using cold ^133Cs atoms led to a breakthrough in the field of atomic frequency standards(A. Clairon, C. Salomon, S. Guellati, and W. D. Phillips, Europhys. Lett. 16), 165 (1991); K. Gibble and S. Chu, Phys. Rev. Lett. 70, 1771 (1993).. It was soon found that the frequency shifts induced by collisions between atoms during their fountain orbit stand in the way to drawing the full benefits from this development. A possible way out is to switch to another atomic species(K. Gibble and B.J. Verhaar, Phys. Rev. A 52), 3370 (1995).. Recent experiments have made it possible to determine cold collision parameters for pairs of rubidium atoms with unprecedented accuracy(J.M. Vogels, C.C. Tsai, R.S. Freeland, S.J.J.M.F. Kokkelmans, B.J. Verhaar, and D.J. Heinzen (submitted).). Making use of these parameters we predict the collisional frequency shifts for a ^87Rb and a ^85Rb laser-cooled clock. Our results show the prospects for new atomic clocks based on ultracold rubidium to be promising.