Lorentz-Symmetry Test at Planck-Scale Suppression With a Spin-Polarized 133Cs Cold Atom Clock

We present the results of a local Lorentz invariance (LLI) test performed with the
¹³³
Cs cold atom clock FO2, hosted at SYRTE. Such a test, relating the frequency shift between
¹³³
Cs hyperfine Zeeman substates with the Lorentz violating coefficients of the standard model extension (SME), has already been realized by Wolf
et al
. and led to state-of-the-art constraints on several SME proton coefficients. In this second analysis, we used an improved model, based on a second-order Lorentz transformation and a self-consistent relativistic mean field nuclear model, which enables us to extend the scope of the analysis from purely proton to both proton and neutron coefficients. We have also become sensitive to the isotropic coefficient
$\tilde {c}_{\text {TT}}$
, another SME coefficient that was not constrained by Wolf
et al.
The resulting limits on SME coefficients improve by up to 13 orders of magnitude the present maximal sensitivities for laboratory tests and reach the generally expected suppression scales at which signatures of Lorentz violation could appear.