A Test of CPT and Lorentz Symmetry Using a K-3He Co-magnetometer

A K-3He co-magnetometer has been developed for a test of Lorentz and CPT symmetry. Polarized K vapor forms a spin-exchange relaxation-free (SERF) magnetometer that has record sensitivity of about 1 fT/ √ Hz. The polarized 3He effectively suppresses sensitivity to the magnetic fields and gradients. Together, the K-3He comagnetometer retains sensitivity to anomalous, CPTand Lorentz-violating fields that couple to electron and nuclear spins differently than a normal magnetic field. Data over the course of 15 months provide upper limits on the coupling energy of a CPT-violating field to neutron spin, b̃n < 1.4 × 10−31 GeV, to proton spin, b̃p < 4.4× 10−30 GeV, and to electron spin, b̃e < 1.0× 10−28 GeV. These limits are consistent with the existing limits of b̃n < 1.1× 10−31 GeV (Bear et al., 2002) and b̃e < 3.0× 10−29 GeV (Heckel et al., 2000). The proton sensitivity is better than the published limit of b̃p < 1.8× 10−27 GeV (Phillips et al., 2001). The long-term sensitivity of the co-magnetometer was significantly limited by sources of systematic noise. The co-magnetometer provides a robust platform for precision measurements primarily due to its inherent insensitivity to magnetic field drift and field gradients. Detailed analytic and numerical modeling of the coupled spin ensemble dynamics provides good agreement with steady state and transient response measurements.