Burning and graphitization of optically levitated nanodiamonds in vacuum

TL;DR

This study investigates the behavior of optically levitated nanodiamonds with NV centers in vacuum, revealing their tendency to burn or graphitize depending on the environment, and proposes new methods for temperature measurement and size estimation.

Contribution

It provides new insights into nanodiamond stability in vacuum, clarifies the internal temperature effects on NV centers, and introduces a novel approach to determine nanoparticle size from damping rates.

Findings

Nanodiamonds burn in air but can be stabilized in nitrogen.

Graphitization occurs below approximately 10 mB in nitrogen.

Internal temperature estimates suggest no melting, contradicting previous claims.

Abstract

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 $\approx 10$ mB. Exploiting the Brownian motion of a levitated nanodiamond, we extract its internal temperature ($T_i$) and find that it would be detrimental to the NV$^-$ center's spin coherence time \cite{Toyli2012}. These values of $T_i$ 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.