Tidal Effects in Gravitation Measurements by Light-Pulse Atom Interferometry

The acceleration measured by a light-pulse Atom Interferometer (AI) in a non uniform gravitational field systematically deviates from the true acceleration by a term to first order in the gravity gradient. A recent proposal to (ideally) cancel out the gravity gradient by means of an appropriate frequency shift of one laser pulse overcomes the shortcomings of previous proposals based on physical reversal of the instrument axis, and has already been shown to be effective. However, it does not eliminate the deviation. This tidal acceleration error affects the absolute measurement of the local gravitational acceleration at a level that is relevant for the current uncertainty, but it is negligible in drop tests of the Universality of Free Fall with a dual AI as long as they can rely on the same laser frequency to interrogate the different atoms species. In gravity gradiometers based on atom interferometry and used for the measurement of the universal constant of gravity and the detection of gravitational waves the relevance of the deviation needs to be assessed relative to the target of the experiment.