Figure 1 : Schematic of the experiment.

From: Quantum test of the equivalence principle for atoms in coherent superposition of internal energy states

Figure 1

Two laser-cooled clouds of 87Rb atoms are launched vertically and prepared in the internal state by velocity-selective Raman pulses. Before the interferometric sequence, a microwave pulse transfers the lower atomic cloud in any superposition of the and states. The Bragg interferometer simultaneously interrogates both atomic clouds, measuring the acceleration of the lower cloud with respect to the upper cloud, which is used as a common reference. The external source masses are positioned to maximize the gravity gradient and optimize the extraction of the differential acceleration from the measurements.