A nitrogen-vacancy (NV−) center in a nanodiamond, levitated in high vacuum, has recently been proposed as a probe for demonstrating mesoscopic center-of-mass superpositions \cite{Scala2013, Zhang2013} and for testing quantum gravity \cite{Albrecht2014}. Here, we study the behavior of optically levitated nanodiamonds containing NV− centers at sub-atmospheric pressures and show that while they burn in air, this can be prevented by replacing the air with nitrogen. However, in nitrogen the nanodiamonds graphitize below ≈10 mB. Exploiting the Brownian motion of a levitated nanodiamond, we extract its internal temperature (Ti) and find that it would be detrimental to the NV− center's spin coherence time \cite{Toyli2012}. These values of Ti make it clear that the diamond is not melting, contradicting a recent suggestion \cite{Neukirch2015}. Additionally, using the measured damping rate of a levitated nanoparticle at a given pressure, we propose a new way of determining its size.
@article{arxiv.1510.07555,
title = {Burning and graphitization of optically levitated nanodiamonds in vacuum},
author = {A. T. M. A. Rahman and A. Frangeskou and M. S. Kim and S. Bose and G. W. Morley and P. F. Barker},
journal= {arXiv preprint arXiv:1510.07555},
year = {2017}
}