Speaker
Description
The ratio of two atomic transition frequencies is by definition independent of the unit of frequency and therefore its value depends only on fundamental constants such as the fine-structure constant $\alpha$ or fundamental properties of particles like for instance the electron mass. Repeated measurements of frequency ratios performed in the laboratory, with suitable atomic structure calculations, are therefore a direct test of the present-day stability of fundamental constants with respect to space-time and, via the motion of the Earth, gravitational potential. Such tests are independent from any cosmological models and complementary to astrophysical tests.
At LNE-SYRTE we operate an ensemble of atomic clocks both in the microwave (hyperfine transition in the ground state of $^{133}$Cs and $^{87}$Rb) and in the optical part of the spectrum (1S$_{0}$ - 3P$_{0}$ in $^{87}$Sr and $^{199}$Hg) providing for several atomic frequency comparisons [1]. In this talk we will report more specifically on highly accurate Rb/Cs hyperfine frequency comparisons performed with atomic fountains over more than 15 yr. They provide stringent limits on possible time variations of a particular linear combination of constants, or its coupling to gravity, involving $\alpha$ and the quark mass scaled to the chromodynamics mass scale [2]. The results also constitute a stringent differential redshift test for the Rb/Cs couple. Besides, they provide improved constraints on the coupling of a putative massive scalar dark matter field to standard matter [3]. We will also present repeated accurate measurements of the Sr/Cs and Hg/Cs frequency ratios which complement similar measurements performed in other laboratories, and for the first time, measurements of Sr/Rb and Hg/Rb frequency ratios which are sensitive to other linear combinations of constants [4][5].
[1] M. Abgrall et al., C.R. Physique 16, 461-470 (2015)
[2] J. Guéna et al., Phys. Rev. Lett. 109, 080801 (2012)
[3] A. Hees et al., submitted, available at arXiv:1604.08514 (2016)
[4] Le Targat et al., submitted, available at arXiv:1605.03878 (2016)
[5] R. Tyumenev et al., submitted, available at arXiv:1603.02026 (2016)
