Limit on Lorentz-Invariance- and CPT-Violating Neutron Spin Interactions Using a 3He-129Xe Comagnetometer

We performed a search for a Lorentz-invariance- and CPT-violating coupling of the 3He and [Formula: see text]Xe nuclear spins to posited background fields. Our experimental approach is to measure the free precession of nuclear spin polarized 3He and [Formula: see text]Xe atoms using SQUIDs as detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the co-located spin samples. As a result we obtain an upper limit on the equatorial component of the background field [Formula: see text] GeV (68% C.L.). This experiment is currently the most precise test of spin anisotropy due to the excellent long spin-coherence time.