Precisely mapping the magnetic field gradient in vacuum with an atom interferometer

The magnetic field gradient has been measured with an atom interferometer using the magnetic sublevels of ⁸⁷Rb atoms. The Doppler-insensitive measurement effectively eliminates the contribution from gravity and background vibration noise, and the differential measurement also can reject some systematic errors. A resolution of $300$ pT/mm has been demonstrated with a $90$-s integration time and a spatial resolution of $1.4$ mm. The gradiometer was then used to measure the magnetic field gradient in an ultrahigh-vacuum environment. The technique will also be very useful to subtract the systematic error arising from the magnetic field inhomogeneity in precision atom-interferometry experiments, such as gravity measurement.