Cold atom clocks and applications

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 × 10 −14 τ −1/2 where τ 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 × 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. In a second part, we describe tests of possible variations of fundamental constants using 87 Rb and 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.

Transitionless quantum drivings for the harmonic oscillator

“…In particular laser beams detuned with respect to the atomic transition form effective potentials for the ground state depending on Rabi frequency Ω and detuning ∆ as Ω 2 /4∆ by adiabatic elimination of the excited state, thus forming attractive or repulsive potentials. This effective interaction can be made time dependent by varying the laser intensity, the frequency, or both [1], since the optical frequencies are many orders of magnitude larger than Rabi frequencies or detunings, and the changes will be slowly varying in the scale of optical periods. The intensity of a dipole trap can be changed by three or four orders of magnitude in 100 ns using acousto-optics or electrooptics modulators.…”

Testing the time-invariance of fundamental constants using microwave spectroscopy on cold diatomic radicals

“…6 The current best microwave standard-the caesium fountain clock-has a fractional frequency uncertainty of 10 À16 , which corresponds to an absolute frequency uncertainty of 1 mHz. 10 Whereas in atoms a near degeneracy between levels of different symmetry is very rare, in molecules this happens rather frequently. DeMille et al 11 proposed a test based on a near degeneracy between the a 3 S u + (v ¼ 37) and the X 1 S g + (v ¼ 138) in Cs 2 .…”

Optical Atomic Coherence at the 1-Second Time Scale

“…Given the superior S/N from the large number of quantum absorbers, we expect this system to be competitive among the best performing clocks in terms of stability. Accuracy is already approaching the level of the best atomic fountain clocks (30,31), and absolute frequency measurement is limited by the Cs-clock-calibrated maser signal available to us via a fiber link (32). An all-optical clock comparison is necessary to reveal its greater potential.…”