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