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 type quantum-based instrument: compact, transportable, differential quantum gravimeter capable measuring simultaneously absolute values both gravitational acceleration, $g$, its vertical gradient, $\Gamma_{zz}$. While sensitivity to g is competitive with best gravimeters, on $\Gamma_{zz}$ reaches limit set by projection noise-leading an unprecedented long-term stability 0.1 E ($1E=1\times 10^{-9}s^{-2}$). This unique, dual-purpose instrument, paves way applications in geophysics, civil engineering, gravity-aided navigation, where accurate mapping field plays important role.