Probing Lorentz invariance and other fundamental symmetries in 3He/129Xe clock-comparison experiments

We discuss the design and performance of a very sensitive low-field magnetometer based on the detection of free spin precession of gaseous, nuclear polarized 3He or 129Xe samples with a SQUID as magnetic flux detector. Characteristic spin precession times T*2 of up to 60 h were measured in low magnetic fields (about 1μT) and in the regime of motional narrowing. With the detection of the free precession of co-located 3He/129Xe nuclear spins (clock comparison), the device can be used as ultra-sensitive probe for non-magnetic spin interactions, since the magnetic dipole interaction (Zeeman-term) drops out in the weighted frequency difference, i.e., Δω = ωHe− γHe/γXe·ωXe. We report on searches for a) Lorentz violating signatures by monitoring the Larmor frequencies of co-located He/129Xe spin samples as the laboratory reference frame rotates with respect to distant stars (sidereal modulation) and b) spin-dependent short-range interactions induced by light, pseudoscalar bosons such as the axion invented to solve the strong CP problem.