  We investigated the Raman pulse duration effect in a gravity gradiometer with
two atom interferometers. Since the two atom clouds in the gradiometer
experience different gravitational fields, it is hard to compensate the Doppler
shifts of the two clouds simultaneously by chirping the frequency of a common
Raman laser, which leads to an appreciable phase shift. When applied to an
experiment measuring the Newtonian gravitational constant G, the effect
contributes to a systematic offset as large as -49ppm in Nature 510, 518
(2014). Thus an underestimated value of G measured by atom interferometers can
be partly explained due to this effect.
