Test of the universality of free fall with atoms in different spin Orientations

TL;DR

This study tests the universality of free fall by comparing gravity acceleration of rubidium atoms with opposite spin orientations using atom interferometry, finding no significant difference within experimental uncertainty.

Contribution

It introduces a method to compare free fall of atoms with different spin orientations, highlighting the impact of magnetic field inhomogeneity on measurement precision.

Findings

No observable violation of UFF within experimental error

Magnetic field inhomogeneity limits measurement precision

Provides a foundation for future high-precision spin-dependent UFF tests

Abstract

We report a test of the universality of free fall (UFF) related to spin-gravity coupling effects by comparing the gravity acceleration of the $^{87}$Rb atoms in $m_F=+1$ versus that in $m_F=-1$, where the corresponding spin orientations are opposite. A Mach-Zehnder-type atom interferometer is exploited to sequentially measure the free fall acceleration of the atoms in these two sublevels, and the resultant E$\rm{\ddot{o}}$tv$\rm{\ddot{o}}$s ratio determined by this work is ${\eta_S} =(-0.2\pm1.5)\times 10^{-5}$. The interferometer using atoms in $m_F=+1$ or $m_F=-1$ is highly sensitive to magnetic field inhomogeneity, which limits the current experimental precision of our UFF test. The work here provides a stepping stone for future higher precision UFF test related to different spin orientations on atomic basis.