Abstract
A nitrogen-vacancy (NV−) centre in a nanodiamond, levitated in high vacuum, has recently been proposed as a probe for demonstrating mesoscopic centre-of-mass superpositions and for testing quantum gravity. Here, we study the behaviour of optically levitated nanodiamonds containing NV− centres 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− centre’s spin coherence time. These values of Ti make it clear that the diamond is not melting, contradicting a recent suggestion. Additionally, using the measured damping rate of a levitated nanoparticle at a given pressure, we propose a new way of determining its size.
Highlights
Even though diamond is thermodynamically metastable in ambient conditions, it has extremely high thermal conductivity, Young’s modulus, electrical resistivity, chemical stability, and optical transparency[1,2,3,4]
Based on the idea that an oxygen-less environment may be a cure to this problem, we have studied the behaviour of levitated nanodiamonds in a nitrogen environment
We have demonstrated that nanodiamonds burn in air while they graphitize in a nitrogen ambient by absorbing trapping laser (1064 nm) light as the cooling due to gas molecules becomes less effective with decreasing pressure
Summary
It can be observed that at pressures > 10 mB the scattering intensity the size of a nanodiamond remains unchanged; even though temperature is quite high (see Fig. 3) This is due to the fact that for burning to occur, a nanodiamond requires oxygen which is absent in a nitrogen rich environment. Given the uncertainty in the shape of nanodiamonds as visible, the nanodiamonds that we have used to find Tis in air and nitrogen ambients are of similar size This is in good agreement with the technique (initial scattering intensities) that we have utilized to trap similar size nanodiamonds in different runs of an experiment. We believe that the method developed here for the determination of size of an individual particle can be used in any levitated experiment
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