We present a
gravity–gradiometer based on atom interferometry, developed for a precise
determination of the Newtonian
gravitational constant G.
The interferometer is
realized applying a sequence of
− π − π/2 vertical Raman pulses on free falling cold
atoms in an atomic fountain. The resulting phase contains information
related to the local vertical acceleration. Two cold atomic clouds are
launched upwards with a juggling scheme in order to have two displaced
sensors in rapid sequence. The Raman pulses simultaneously act on both
samples. Heavy source masses are placed around the gradiometer region and
accurately moved in two different positions along the vertical direction.
The double differential measurement drastically reduces common mode spurious
signals. The apparatus has been already tested using preliminary lead masses
providing first results.