Simultaneous accurate determination of both gravity and its vertical gradient

We present a method for accurate measurements of both the gravity acceleration and its vertical gradient using a dual-atom interferometer, in principle, free from any uncertainty related to the absolute or relative positions of the two atomic samples. The method relies on the use of a dual-lock technique, which simultaneously stirs the chirp rate applied to the frequency difference between the interferometer lasers to compensate the gravity acceleration and the frequency jump applied to the lasers at the mid pulse of the interferometer to compensate for the gravity gradient. This allows one, in the end, to determine the two inertial quantities of interest in terms of frequencies.