“…For instance, it is possible to measure the acceleration of gravity with an accuracy of 1 part per billion (ppb) [13], the rotation of the Earth with an accuracy better than 1 millidegree per hour [14,15], or to detect minute changes in gravity caused by mass displacements [16] or ocean tides [17]. These devices are so precise that they are used today as references for fundamental constants (mass, gravity), and are powerful candidates to test the theory of General Relativity on surface-based [18,19,20], subterranean [21] or in Space-based laboratories [22,23]. Projects are currently underway to verify the universality of free fall (UFF) [19,24,20,23,25,26,27], to detect gravitational waves in a frequency range yet unreachable with current laser-based detectors [28,29,30], and to test dark energy [31,32].…”