A team of researchers has proposed an experiment capable of testing whether gravity can generate quantum entanglement between a levitated micrometre-scale particle and an array of ultra-precise nuclear clocks. The idea is to measure whether the gravitational interaction between the two systems leaves an observable quantum signature in the laboratory, something that has so far only been proposed with neutral masses lacking internal degrees of freedom.

The proposal differs from conventional matter-wave interferometry tests because it probes a genuinely relativistic effect: the contribution of the clocks' internal energy to active gravitational mass. In a Newtonian scheme, two fixed masses could not produce this signal; it is precisely the internal energy of the nuclear clocks that comes into play, making the entanglement an unambiguous signature of the quantised nature of active gravitational mass.

The design harnesses the collective interaction between the microscopical particle, held in levitation, and an array of ultra-precise nuclear clocks. By accumulating the signal across many clocks at once, the scheme boosts sensitivity into a regime where gravitationally mediated entanglement could be detected with existing or near-term technology.

Observing this entanglement would constitute direct evidence that active gravitational mass behaves quantum mechanically, a hypothesis that has not been tested experimentally to date. The result would open a new avenue for studying the frontier between gravity and quantum mechanics without needing to reach Planck energies or extreme astrophysical phenomena.