Compact differential gravimeter at the quantum projection-noise limit

Atom interferometry offers new perspectives for geophysics and inertial sensing. We present the industrial prototype of a quantum-based instrument: a compact, transportable, differential quantum gravimeter capable of measuring simultaneously the absolute values of both gravitational acceleration g and its vertical gradient Γzz. While the sensitivity to g is competitive with the best industrial gravimeters, the sensitivity on Γzz reaches the limit set by quantum projection noise---leading to a long-term stability of 0.10.28em0exE (10.28em0exE=1×10^-90.28em0exs^-2). This dual-purpose instrument constitutes the industrial integration of cold atom sensors for practical applications. It paves the way for different applications in geophysics, civil engineering, and gravity-aided navigation, where accurate mapping of the gravitational field plays an important role.