Gravity Entangles Light and a Rotating Object express
Spacetime can be imagined as a tightly stretched fabric. A massive body dents it, guiding light. Rotation twists the fabric into a spiral. Such a gravitational funnel can entangle a passing photon with the very source of rotation — say, a tiny mirror. Quantum entanglement springs up: an invisible thread binding their fates. Even the weakest of forces, gravity, reliably weaves the particle of light together with a tangible object. The strength of this bond directly depends on the direction of rotation — clockwise or counterclockwise.
By measuring entropy, a measure of entanglement, for both cases, scientists can test the conjectures of Einstein and Wheeler about the quantum nature of curved spacetime. Such experiments will show whether gravity is truly woven from elusive quanta, gravitons, that give rise to gravitational waves.
Original abstract
as written by the authors arXiv:2606.09991
One of the key tests of the quantum nature of gravity is to test whether the virtual mediator of gravity between matter and photon gives rise to the quantum light-bending phenomenon. The off-shell degrees of freedom, involving the spin-2 and spin-0 components of graviton, reproduce the classical deviation of light rays, as well as have been predicted to generate entanglement between matter and photon. This paper explores the generation of entanglement due to the quantum gravitational interaction in an optomechanical setup with a quantum rotor and photon. The virtual exchange of a graviton provides entanglement between the photon degrees of freedom and the spatial position of the quantum rotor, with the rotational state affecting its magnitude. We analyze the case of a high spinning rotor, in an approximately classical state of angular momentum, and quantify its effect on the gravitationally induced entanglement between the photon and the position of the quantum rotor. We show that the difference in the linear entanglement entropies, of prograde-and-retrograde motion of the photon with respect to the quantum rotor, provide tangible observable consequences.
A single graviton is so weak that to detect it, you'd have to build a detector the size of Jupiter.