Test of Einstein Equivalence Principle for 0-spin and half-integer-spin atoms: Search for spin-gravity coupling effects

Abstract

We report on a conceptually new test of the equivalence principle performed by measuring the acceleration in Earth's gravity field of two isotopes of strontium atoms, namely, the bosonic ${}^{88}$Sr isotope which has no spin vs the fermionic ${}^{87}$Sr isotope which has a half-integer spin. The effect of gravity upon the two atomic species has been probed by means of a precision differential measurement of the Bloch frequency for the two atomic matter waves in a vertical optical lattice. We obtain the values $\hat{I}\cdot =(0.2\pm 1.6)\times 10^{-7}$ for the Eötvös parameter and $k=(0.5\pm 1.1)\times 10^{-7}$ for the coupling between nuclear spin and gravity. This is the first reported experimental test of the equivalence principle for bosonic and fermionic particles and opens a new way to the search for the predicted spin-gravity coupling effects.

5 pages, 4 figures. New spin-gravtity coupling analysis on the data added to the manuscript