A $^{3}$He-$^{129}$Xe co-magnetometer with $^{87}$Rb magnetometry

We report progress on a $^{3}$He-$^{129}$Xe co-magnetometer detected with a $^{87}$Rb magnetometer. The noble-gas co-magnetometer is insensitive to any long-term bias field drifts, but the presence of hot Rb can cause instability in the ratio of $^{3}$He-$^{129}$Xe precession frequencies. We use a sequence of Rb $\pi$ pulses to suppress the instability due to Rb-noble gas interactions by a factor of $10^4$ along all three spatial axes. For detection, our $^{87}$Rb magnetometer operates using single-axis $^{87}$Rb $\pi$ pulses with $\sigma_+/\sigma_-$ pumping---this technique decouples the $^{87}$Rb magnetometer from bias fields, and allows for SERF operation. We are presently investigating systematic effects due to combinations of several imperfections, such as longitudinal noble gas polarization, imperfect $^{87}$Rb $\pi$ pulses, and $^{87}$Rb pump light shifts. Thus far, our $^{87}$Rb magnetometer has a sensitivity of 40 fT/$\sqrt{\text{Hz}}$, and our $^{3}$He-$^{129}$Xe co-magnetometer has achieved a single-shot precession frequency ratio error of 20 nHz and a long-term bias drift of 8 nHz at 7 h. We are developing the co-magnetometer for use as an NMR gyro, and to search for possible spin-gravity interactions.