  Experimental proposals for testing quantum gravity-induced entanglement of
masses (QGEM) typically involve two interacting masses which are each in a
spatial superposition state. Here, we propose a QGEM experiment with two
particles which are each in a superposition of rotational states, this amounts
to a superposition of mass through mass-energy equivalence. Our proposal relies
on the fact that rotational energy gravitates. This approach would test a
feature unique to gravity since it amounts to sourcing a spacetime in
superposition due to a superposition of 'charge'. We propose and analyse a
concrete experimental protocol and discuss challenges.
