Spin-clocks: Test of fundamental symmetries in nature
Prof. Dr. W. Heil (Institut für Physik, Mainz)

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 100 h were measured in low magnetic fields (about 1µT) and in the regime of motional narrowing. The achieved signal-to-noise ratio of more than 5000:1 leads to an expected sensitivity level (Cramer-Rao Lower Bound) of δB≈1∫T after an integration time of 220s and of δB≈10^-4∫T (100 Zeptotesla) after one day.
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=ω_He -γ_He/γ_Xe⋅ω_Xe. 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. Finally, a new proposal is presented to measure the electric dipole moment (EDM) of Xenon.