Clifford Will is the Editor-in-Chief of Classical and Quantum Gravity

The Weak Equivalence Principle (WEP) is one of the three pillars that support all metric theories of gravity, and testing it to high precision has occupied experimentalists for over 100 years. Although many successful tests have been performed, there is still room for new experiments (see this recent CQG focus issue on tests of WEP).

This paper describes in detail a concept called STE-QUEST for testing WEP in space. What makes this different from other space experiments, such as MICROSCOPE, due for launch in 2016, and STEP, still only a design concept, is that those experiments use macroscopic bodies, while STE-QUEST will use fundamentally quantum-mechanical systems: Bose-Einstein condensates of rubidium isotopes. Using atom interferometry, the STE-QUEST team proposes to measure any differential acceleration in the Earth’s field between two clouds of atoms, one of ⁸⁵Rb, the other of ⁸⁷Rb, to a few parts in 10¹⁵.

The experiment is being designed as a candidate for a medium-class mission within the Cosmic Vision program of the European Space Agency. Although it was not selected in the 2014 round of considerations, it may be put forward for future mission possibilities.

Read the full article in Classical and Quantum Gravity:
STE-QUEST — test of the universality of free fall using cold atom interferometry
D N Aguilera et al
Class. Quantum Grav. 31 115010

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