Due to the fragile nature of quantum states, precision measurements using quantum objects are often confined to systems that are well protected from their environment. This can limit the practical use of such quantum sensors and exclude critical systems of interest such as live biological specimens or fragile molecules. A sensor with sufficient sensitivity, nanoscopic resolution and robustness in ambient conditions would make a powerful quantum metrology tool.
In the past decade or so the nitrogen-vacancy (NV) centre in diamond has proven itself to be a remarkably powerful tool for nanoscale quantum sensing and quantum information processing at ambient temperature and pressure. Despite these achievements, there are still several fundamental features of the NV centre which are not completely understood and hence overlooked. This research addresses these areas in two parts, firstly the mechanical properties and secondly the thermal properties of the NV centre.
The effect of crystal stress or strain on the spin resonances on the NV centre ground state is theoretically described and then experimentally characterised. This effect is demonstrated by force sensing in a microscopic diamond cantilever using a single NV centre. New concepts of force sensing and metrology based on the NV spin-mechanical interaction are explored, providing fundamentally unique mechanical sensing with additional hybrid (magnetic, electric, thermal) sensing capabilities. Apart from metrology, this characterisation will help investigate coupled spin-mechanical effects such as non-classical vibrations, phonon-cooling/lasing, spin-squeezing and quantum control using mechanical interactions. These parameters and models will also prove useful in ab-initio studies for defect discovery and defect engineering of similar solid-state defects.
The thermal properties of the NV centre’s optical and spin resonances are theoretically described and then experimentally characterised allowing for the full extent of the NV centre’s useful thermometry range to be described. Changes in the crystal lattice due to changes in temperature are used to probe the nanoscopic description of the NV wavefunctions and their interactions with crystal vibrations. Magnetic circular dichroism spectroscopy measurements help unpick the nature of the fundamental spin-dynamics of the NV centre and the neutral-charge nitrogen vacancy, the last remaining great mysteries of the NV centre. Understanding these spin-dynamics and charge states will allow for the limiting properties of the NV centre to be investigated and potentially improved, making the NV centre an even better quantum tool.