RESUMO

We describe a ^{3}He-^{129}Xe comagnetometer using ^{87}Rb atoms for noble-gas spin polarization and detection. We use a train of ^{87}Rb π pulses and σ^{+}/σ^{-} optical pumping to realize a finite-field Rb magnetometer with suppression of spin-exchange relaxation. We suppress frequency shifts from polarized Rb by measuring the ^{3}He and ^{129}Xe spin precession frequencies in the dark, while applying π pulses along two directions to depolarize Rb atoms. The plane of the π pulses is rotated to suppress the Bloch-Siegert shifts for the nuclear spins. We measure the ratio of ^{3}He to ^{129}Xe spin precession frequencies with sufficient absolute accuracy to resolve Earth's rotation without changing the orientation of the comagnetometer. A frequency resolution of 7 nHz is achieved after integration for 8 h without evidence of significant drift.