Physicists confirm Einstein’s equivalence principle in quantum experiments

An international team of physicists has successfully conducted the first direct measurement of the quantum phase accumulated when atoms fall freely under gravity. Published in Science Advances, the study demonstrates that Einstein’s equivalence principle remains consistent with the behavior of matter in the quantum realm.

Using a device known as a Quantum Galileo Interferometer, researchers cooled rubidium atoms to near absolute zero and placed them into a quantum superposition. This allowed the atoms' waves to travel two distinct paths simultaneously: one path was held magnetically against gravity, while the other followed a ballistic free-fall trajectory. When the paths were reunited, the resulting interference pattern matched the phase shift predicted by Einstein’s principle.

While the experiment does not unify quantum mechanics with general relativity or prove that gravity is a quantum phenomenon, it provides experimental support for the compatibility of the two frameworks. The research was led by Ben-Gurion University of the Negev, with collaborators from the University of Oxford and Ulm. Future research may involve heavier objects, such as nanodiamonds, to explore regimes where current theories might break down.