Herriott-cavity-assisted closed-loop Xe isotope comagnetometer

We present in this paper a Herriott-cavity-assisted closed-loop Xe isotope gas comagnetometer. In system, $^{129}$Xe and $^{131}$Xe atoms are pumped probed by polarized Rb atoms, continuously driven oscillating magnetic fields, whose frequencies kept on resonance phase-locked loops (PLLs). Different from other schemes, we use Herriott cavity to improve the magnetometer sensitivity instead of parametric modulation method, passive method is aimed system stability while maintaining sensitivity. This has demonstrated an angle random walk (ARW) 0.06 $^\circ$/h$^{1/2}$, bias instability 0.2 $^\circ$/h (0.15 $\mu$Hz) with bandwidth 1.5 Hz. By adding comagnetometer, can extend dual simultaneously working comagnetometers sharing same cell. extended wide applications precision measurements, where independently measure coupling anomalous fields proton spin neutron spin.