Free-falling atoms yield a theory-aligned phase shift in a new measurement

Comparing a falling path with a stationary path

The team reportedly used microwave and magnetic pulses to split rubidium atoms into a quantum superposition, a state in which one object can follow more than one possible path. One path was sent upward and allowed to fall back under gravity, while the other was magnetically supported. Bringing the paths back together allowed their wave phases to be compared. The reported increase in phase with longer free fall was consistent with theory and with the equivalence principle, which holds that free fall is locally indistinguishable from the absence of gravity.

Although atom interferometers have existed for decades, the reported account says none had been able to compare the quantum phase of one atom along a freely falling route with that of its stationary counterpart in the required way.

A 2.5% difference from the prediction

A newly described Quantum Galileo Interferometer (QGI) reportedly put rubidium atoms into two simultaneous trajectories—one falling freely and one held in place—and measured a phase difference that increased with fall time. The result was reported to sit 2.5 percent from the theoretical prediction.

Quantum mechanics and relativity are both highly successful theories but remain difficult to reconcile. The reported experiment adds a way to test quantum behavior during free fall, while its result did not reveal the incompatibility between the theories that researchers ultimately seek to probe.