An international team of physicists has demonstrated one of the key effects of Albert Einstein's general theory of relativity on a quantum object for the first time, according to the publication Qubit. The result could mark an important step toward understanding how quantum mechanics and gravity interact.
The research was carried out by a team from Ben-Gurion University in Israel, Ulm University and the University of Oxford, working together with Nobel Prize-winning physicist Roger Penrose.
How the experiment worked
The scientists used a specially designed device they called a quantum Galilean interferometer, built around rubidium atoms cooled to a temperature close to absolute zero. At such temperatures, the atoms display distinctly quantum behaviour, including the ability to exist in a superposition of states.
The researchers split the quantum wave of an atom into two parts that moved simultaneously along different paths. A magnetic field held one half of the wave suspended in place, while the other half was allowed to fall freely under gravity. The two halves were then recombined.
Their interaction produced an interference pattern, which allowed the physicists to measure an extremely small phase difference caused by the effect of gravity.
What the result confirmed
The outcome matched predictions based on Einstein's equivalence principle, which holds that an observer in free fall locally stops experiencing the effects of gravity. A classic illustration is a person in a falling lift, who briefly feels weightless.
Gravity has previously been measured many times using quantum particles. What set this experiment apart, the researchers said, was that it tested the equivalence principle on a quantum object that behaves as a wave and can exist on multiple paths at once.
The researchers stressed that the result does not amount to a final unification of quantum mechanics and general relativity. Even so, they said the experiment stands as one of the most precise confirmations yet that Einstein's theories continue to hold up in the quantum world.
Roger Penrose and the mass limit question
Roger Penrose, who took part in the study, is a British mathematical physicist and 2020 Nobel laureate known for his work on general relativity and black holes.
What comes next
The scientists are already preparing the next stage of the research. They plan to test the same method on considerably heavier objects, including nanodiamonds.
Beyond gravity research, the team said such experiments could also help test Penrose's hypothesis that there is a certain mass threshold above which quantum laws may cease to apply and a system begins to behave classically.
