A free-falling nanodiamond containing a nitrogen vacancy centre in a spin superposition should experience a superposition of forces in an inhomogeneous magnetic field. We propose a practical design that brings the internal temperature of the diamond to under 10 K. This extends the expected spin coherence time from 2 ms to 500 ms, so the spatial superposition distance could be increased from 0.05 nm to over 1 μm, for a 1 μm diameter diamond and a magnetic inhomogeneity of only 104 T/m. The low temperature allows single-shot spin readout, reducing the number of nanodiamonds that need to be dropped by a factor of 10,000. We also propose solutions to a generic obstacle that would prevent such macroscopic superpositions.
@article{arxiv.1810.07045,
title = {Matter and spin superposition in vacuum experiment (MASSIVE)},
author = {Sougato Bose and Gavin W. Morley},
journal= {arXiv preprint arXiv:1810.07045},
year = {2018}
}