paper

Cold atom Clocks and Applications

arXiv:physics/0502117 · doi:10.1088/0953-4075/38/9/002

Abstract

This paper describes advances in microwave frequency standards using laser-cooled atoms at BNM-SYRTE. First, recent improvements of the $^{133}$ Cs and $^{87}$ Rb atomic fountains are described. Thanks to the routine use of a cryogenic sapphire oscillator as an ultra-stable local frequency reference, a fountain frequency instability of $1.6 \times 1 0^{- 14} I ¨ ^{- 1/2}$ where $I ¨ $ 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 $2 \times 1 0^{- 16}$ at $50, 000 s f or t h e f i r s tt im e f or p r ima r y s t an d a r d s . I na dd i t i o n, t h esec l oc k sr e a l i z e t h e S I seco n d w i t hana cc u r a cy o f$ 7\times 10^{-16} $, o n eor d er o f ma g ni t u d e b e l o w t ha t o f u n coo l e dd e v i ces . I na seco n d p a r t, w e d escr ib e t es t so f p oss ib l e v a r ia t i o n so f f u n d am e n t a l co n s t an t s u s in g$ ^{87} $R ban d$ ^{133}$Cs 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.

30 pages, 11 figures