Improved tests of Local Position Invariance using 87Rb and 133Cs fountains

TL;DR

This paper reports 14-year measurements using atomic fountains to test local position invariance, setting new limits on the variation of fundamental constants and gravitational redshift effects with high precision.

Contribution

It provides the first limits on Rb/Cs ratio variation with gravitational potential and improves constraints on temporal variation of hyperfine frequency ratios.

Findings

No significant variation of the Rb/Cs ratio over 14 years.

First limit on fractional variation with gravitational potential.

Enhanced constraints on fundamental constant variations.

Abstract

We report tests of local position invariance based on measurements of the ratio of the ground state hyperfine frequencies of 133Cs and 87Rb in laser-cooled atomic fountain clocks. Measurements extending over 14 years set a stringent limit to a possible variation with time of this ratio: d ln(nu_Rb/nu_Cs)/dt=(-1.39 +/- 0.91)x 10-16 yr-1. This improves by a factor of 7.7 over our previous report (H. Marion et al., Phys. Rev. Lett. 90, 150801 (2003)). Our measurements also set the first limit to a fractional variation of the Rb/Cs ratio with gravitational potential at the level of c^2 d ln(nu_Rb/nu_Cs)/dU=(0.11 +/- 1.04)x 10^-6, providing a new stringent differential redshift test. The above limits equivalently apply to the fractional variation of the quantity alpha^{-0.49}x(g_Rb/g_Cs), which involves the fine structure constant alpha and the ratio of the nuclear g-factors of the two alkalis. The link with variations of the light quark mass is also presented together with a global analysis combining with other available highly accurate clock comparisons.