Overview
- An international team using an atom chip and atom-interferometry directly measured the tiny quantum phase difference between two ultracold rubidium wavepackets when one was held and the other allowed to fall under gravity.
- The measured phase matched the value obtained by applying Einstein’s equivalence principle to a quantum wave, confirming that a freely falling quantum object experiences gravity in the way the principle predicts.
- Researchers created the superposition with microwave pulses, used tunable on-chip magnetic fields to hold one wavepacket stationary, and recombined the packets to read out the phase by interference.
- The study, published in Science Advances, explicitly warns the result does not prove gravity is a quantum force nor provide a unifying theory of gravity and quantum mechanics.
- By establishing an experimental method to read out free-fall quantum phase, the work gives physicists a practical foothold for scaled-up tests with larger masses and longer timescales that could begin to test collapse proposals and quantum-gravity ideas.