Engineering a quantum future: exploiting properties of nanodiamond materials
thesisposted on 28.03.2022, 21:50 authored by Matthew van Breugel
Nanodiamond is a unique material that combines the extreme properties of diamond with the alluring properties of nanomaterials. Moreover, diamond can host colour centres - optically active defects that act like artificial atoms - some of which are renowned for their spinoptical properties. This makes nanodiamond material a prime candidate for implementing a range of future solid state quantum technologies. The practical implementation of diamond nanotechnologies in general relies on our capability to understand both diamond as a material and the properties of its colour centres. One particular defect, the nitrogen-vacancy (NV) colour centre, can be credited for launching diamond as a platform for quantum information processing, ultra-high resolution sensing, and biomedical applications. This thesis explores a set of different aspects of nanodiamond material containing NV centres, from spin to optical to vibrations degrees of freedom, with a particular eye to potential applications. Firstly, a macroscopic dielectric loaded resonator microwave cavity was investigated as a new technology for driving the NV spin. The cavity is suspended ∼ 1 cm above the surface of a sample, delivering a highly uniform driving field and negating sample heating effects. Implementing a Hahn spin-echo pulse sequence to measure the spin dephasing rates was ultimately unsuccessful due to the microwave cavity being unable to produce properly formed pulse shapes at short time scales. Secondly, optical properties of densely-packed NV centres in nanodiamonds are investigated and the observation of room-temperature superradiance from single diamond nanocrystals is presented. These results represent the scientific apogee of this thesis. It is shown that nanodiamonds packed with a sufficiently high density of NV centres can exhibit cooperative effects, which are interrogated through the observation of superradiance. NV lifetimes as short as 1.1 ns are observed, which is a significant (10×) speed-up in the photon emission rate compared to isolated NV centres. This is consistent with a model of cooperative effects, which is further confirmed by observing super-Poissonian photon statistics as predicted by our model. The superradiance investigation uncovers the need to accurately measure the temperature of individual nanodiamond crystals. Raman spectroscopy methods for thermometry are developed, enabled by a novel ultra-high resolution échelle spectrograph. The analysis reveals that NDs on glass in air can be heated up to ∼ 900 K with ∼ 160 mW of focussed off-resonant laser illumination. This remarkable optical heating is concluded to occur for nanodiamonds in poor thermal contact with the substrate. Discrepancies are found when fitting the established 4-phonon decay model with the experimental data, however, individual nanodiamond data could be matched to a reference measurement in bulk diamond by altering the optical density of states. This is attributed to Mie resonances on the nanoparticles. Finally, substantial efforts in development, modernisation, and automation of lab systems are reported. This work demonstrates how these efforts have already enabled semiautonomous measurements to be conducted and have catalysed a change in our method of lab operation -- abstract.