  Many phenomena and fundamental predictions, ranging from Hawking radiation to
the early evolution of the Universe rely on the interplay between quantum
mechanics and gravity or more generally, quantum mechanics in curved
spacetimes. However, our understanding is hindered by the lack of experiments
that actually allow us to probe quantum mechanics in curved spacetime in a
repeatable and accessible way. Here we propose an experimental scheme for a
photon that is prepared in a path superposition state across two rotating
Sagnac interferometers that have different diameters and thus represent a
superposition of two different spacetimes. We predict the generation of genuine
entanglement even at low rotation frequencies and show how these effects could
be observed even due to the Earth's rotation. These predictions provide an
accessible platform in which to study the role of the underlying spacetime in
the generation of entanglement.
