Observation of quantum free fall and the consistency with the equivalence principle

TL;DR

This paper demonstrates a quantum test of the equivalence principle using a novel cold-atom interferometer, confirming that quantum objects in free fall behave consistently with classical gravity predictions.

Contribution

It introduces a new cold-atom interferometer setup that measures quantum phases in free fall, providing experimental evidence supporting the quantum version of the equivalence principle.

Findings

Quantum phase of free-falling atoms matches predictions

Supports applicability of equivalence principle in quantum regime

Enables further exploration of quantum gravity interface

Abstract

The unification of quantum theory and the general theory of relativity - describing gravity, is one of the most important challenges in science. Einstein's general theory of relativity is based on the principle of equivalence, and has been confirmed to great accuracy for large bodies. However, in the quantum domain the equivalence principle has been predicted to take a unique form involving a gauge phase, equal to the quantum phase of a free-falling object. To measure this phase, we realize a novel cold-atom interferometer in which one wave-packet stays static in the laboratory frame while the other is in free fall. The observed relative-phase of the wave-packets confirms the predicted phase of a free-falling object, and shows that in our low energy regime, the equivalence principle may be applied to the quantum domain. Our observation constitutes a fundamental test of the interface between quantum theory and gravity. The new interferometer also opens the door for further probing of the latter interface, as well as to searches for new physics.