We have observed Larmor spin precession in the ground state of laser-cooled ${}^{85}\mathrm{Rb}$ atoms through paramagnetic Faraday rotation. We have been able to obtain a precision of $18\mathrm{pT}$ in the determination of the applied magnetic field, which proves the usefulness of laser-cooled atoms as an atomic magnetometer.

• Received 3 August 1998

DOI:https://doi.org/10.1103/PhysRevA.59.4836