An experiment comparing falling and stationary rubidium atomic waves found a quantum phase difference consistent with Einstein’s equivalence principle.
 

A rubidium atom can behave as a wave that researchers can split between two paths. This allows the same atom to effectively follow both paths at once, without being broken into pieces. Physicists have now used that property to hold one part of the wave still while letting the other fall under gravity, then bring them back together to check a prediction rooted in Einstein’s theory of gravity.