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

TL;DR

This study tests the universality of free fall using atoms in different spin states with a Mach-Zehnder atom interferometer, finding no violation within experimental uncertainty and setting limits on spacetime torsion gradients.

Contribution

First precise test of free fall universality with atoms in opposite spin orientations, employing a double differential measurement to mitigate magnetic inhomogeneity effects.

Findings

No violation of UFF detected within 1.2×10^{-7} precision.

Set an upper limit of 1.1×10^{-21} GeV/m on spacetime torsion gradient.

Validated measurement method through magnetic field modulation experiment.

Abstract

We report a test of the universality of free fall (UFF) 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 magnetic sublevels, and the resultant E$\rm{\ddot{o}}$tv$\rm{\ddot{o}}$s ratio is ${\eta _S} =(0.2\pm1.2)\times 10^{-7}$. This also gives an upper limit of $1.1\times 10^{-21}$ GeV/m for possible gradient field of the spacetime torsion. The interferometer using atoms in $m_F=\pm 1$ is highly sensitive to the magnetic field inhomogeneity, and a double differential measurement method is developed to alleviate the inhomogeneity influence. Moreover, a proof experiment by modulating the magnetic field is performed, which validates the alleviation of the inhomogeneity influence in our test.