Sensitive absolute-gravity gradiometry using atom interferometry

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 $4\times {10}^{-9}g/{\mathrm{Hz}}^{1/2}$ and an inferred differential acceleration accuracy of less than ${10}^{-9}g.\mathrm{}$ This corresponds to a gravity-gradient sensitivity of $4E/{\mathrm{Hz}}^{1/2}$ ${(1E=10\mathrm{}}^{-9}{\mathrm{s}}^{\mathrm{-}2})$ and an accuracy of better than $1E$ 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.