Atom interferometer-based gravity gradiometer measurements.

摘要

A cold source, Cesium atomic fountain instrument was constructed to measure gravitational gradients based on atomic interference techniques. Our instrument is one of the first gradiometers that is absolute. The defining ruler in our apparatus is the wavelength of the cesium ground-state hyperfine splitting, which has an accuracy of ≤1 part per thousand determined by the oscillators used in our clocks. The gradiometer is based on the light pulse atom interferometer technique employing a π/2 − π − π/2 pulse sequence on two identical ensembles of cesium atoms. We have achieved a differential acceleration sensitivity of 4 × 10−9g/$Hz$ with an accuracy of ≤ 1 × 10−9g in a vertical gravity gradiometer configuration. A detection system was implemented to suppress sensitivity to laser amplitude and frequency noise. Immunity to vibration-induced acceleration noise was implemented with a data analysis technique not requiring the use of an active vibration isolation system. The gravity gradiometer was characterized against systematic environmental effects including reference platform tilt and vibration.; The accuracy of the gradiometer was characterized through a measurement of the Newtonian gravitational constant, G. The change in the gravitational field along one dimension was measured when a well-characterized lead, Pb, mass is displaced. A value of G = (6.693 ± 0.027 ± 0.021) × 10−11 m3/( kg · s2) is reported with the two errors representing statistics and systematics, respectively. The experiment introduces a new class of precision measurement experiments to determine G through the quantum mechanical description of atom-photon interactions, vastly different from existing methods with their unresolved systematics. Straightforward enhancements to our technique could lead to an absolute uncertainty in G that reaches or exceeds that of the best current measurements.; As a proof of principle we performed a demonstration of an atom interferometer based horizontal gravity gradiometer measuring the T_z,x component of the gravitational gradient tensor was performed. The horizontal configuration is maximally sensitive to angular accelerations of the platform. A proof of principle angular acceleration sensitivity of 2 × 10−6$rads/Hz$ is observed for a T = 15ms interferometer time. A T_z,x has the potential to aid in inertial navigation, especially on the long term time scale where the atomic gyroscope suffers from drift.