Ultracold Quantum Gravimeters: An Introduction for Geophysicists

This paper aims at providing an accessible introduction to ultracold quantum gravimeters tailored for geophysicists. We do not focus here on geophysical applications, as these are already well known to geophysicists, but rather provide a pedagogical exposition of the quantum-mechanical concepts needed to understand the operation of quantum gravimeters. We present a review of gravimeters based on two- and three-level atomic systems, focusing on the fundamental mechanisms of atomic interferometry. The functioning of Mach-Zehnder interferometers is discussed through the action of $\pi/2$ and $\pi$ pulses, showing how the resulting phase shift encodes gravitational acceleration. The effect of noise is briefly discussed.