We report the demonstration of a sensitive absolute gravity gradiometer based on light-pulse atom interference techniques. The gradiometer consists of two absolute accelerometers operated in a differential mode. We report a differential acceleration sensitivity of 4 × 10 −9 g/Hz 1/2 and an inferred differential acceleration accuracy of less than 10 −9 g. This corresponds to a gravity gradient sensitivity of 4 E/Hz 1/2 (1 E = 10 −9 s −2 ) and an accuracy of better than 1 E for a 10 m separation between accelerometers. We demonstrate that the instrument can be used to detect nearby masses in a vibrationally noisy environment and characterize instrument sensitivity to spurious acceleration and rotation noise.

We measured the Newtonian constant of gravity, G , using a gravity gradiometer based on atom interferometry. The gradiometer measures the differential acceleration of two samples of laser-cooled Cs atoms. The change in gravitational field along one dimension is measured when a well-characterized Pb mass is displaced. Here, we report a value of G = 6.693 × 10 –11 cubic meters per kilogram second squared, with a standard error of the mean of ±0.027 × 10 –11 and a systematic error of ±0.021 × 10 –11 cubic meters per kilogram second squared. The possibility that unknown systematic errors still exist in traditional measurements makes it important to measure G with independent methods.

We report the demonstration of an atom interferometer-based gravity gradiometer. The gradiometer uses stimulated two-photon Raman transitions to measure the relative accelerations of two ensembles of laser cooled atoms. We have used this instrument to measure the gradient of the Earth's gravitational field. [S0031-9007(98)06679-4]