Towards a test of quantum gravity with a levitated nanodiamond containing a spin

There is significant interest in potential experimental tests of macroscopic quantum effects, both to test potential modifications to quantum theory and to probe the quantum nature of gravity. A proposed platform with which to generate the required macroscopic quantum spatial superposition is a nanodiamond containing a negatively charged nitrogen vacancy (${\text{NV}}^{-}$) centre. In this review, methods to fabricate nanodiamonds containing ${\text{NV}}^{-}$ suitable for these quantum applications are discussed. The proposed probes of the macroscopic limits of quantum theory are presented along with the spin physics of the ${\text{NV}}^{-}$ centre relevant to those tests.