Physicists have directly observed for the first time how gravity alters the quantum phase of a freely falling atom – confirming that Einstein’s equivalence principle also holds for quantum objects.
The Quantum Galileo Interferometer
For the experiment, the researchers split ultracold rubidium atoms into a quantum superposition: one part of the wave packet was held stationary while the other fell freely under gravity. They then recombined the two paths and measured the tiny difference in quantum phase that the falling atom had accumulated relative to the resting one. The technique, dubbed the „Quantum Galileo Interferometer“, carries Galileo’s famous falling-body experiment into the world of individual atoms.
The measured phase shift matched the value obtained by applying Einstein’s equivalence principle – the equality of gravitational and inertial mass – to a quantum object. The effect had long been predicted but never directly demonstrated.
What the result means – and what it does not
The work involved Ben-Gurion University of the Negev, the University of Ulm and the University of Oxford; the team included Professor Ron Folman, Professor Vlatko Vedral and Nobel laureate Sir Roger Penrose. The study appeared on 2 September 2026 in the journal „Science Advances“.
- The experiment does not unite quantum mechanics and gravity.
- It does not prove that gravity itself is quantum.
- It does not test Penrose’s proposal of a collapse for massive objects.
The results remain at laboratory scale for now. Future tests aim to include heavier objects such as nanodiamonds, probing further the boundary between the quantum and classical worlds.
Sources: EurekAlert · University of Oxford · ScienceDaily
