Wise, David Frederick; (2021) Could NV centres in diamond be used to measure donor spins in silicon? Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis primarily studies two spin species bound to defects in solid state semiconduc- tors: the electron spin bound to donors in silicon, and the nitrogen vacancy (NV) centre in diamond. Both of these spins have properties that have made them candidates for qubits in a quantum processor. Donor electron spins have exceptionally long coherence times, in excess of seconds under ideal circumstances. In addition, the industrial ex- pertise for fabrication of silicon devices are unrivalled. Efficient measurement of single donor spins has, however, proved challenging. The NV centre in diamond also shows excellent quantum properties with measurable quantum coherence even at room tem- perature. Furthermore, its spin state can be efficiently measured via optically detected magnetic resonance with relative ease and it makes for a highly sensitive, nanoscale mag- netic field sensor. Fabrication technologies in diamond however, lag behind the silicon industry. If these two qubit types could be combined in a hybrid device, it may well allow for the best of both worlds. This work performs an initial study into the potential for such a device, focussing on the question of whether a single NV centre could measure a single donor electron spin. I will examine the potential impact of laser illumination on the quantum properties of donor electron spins, the behaviour of near surface NV centres at the cryogenic temper- atures needed for donor electron spins to gain their most attractive qualities, and study single NV centre atomic force microscope probes designed for single spin detection. As well as the experimental results presented, I also show the results of a machine learning technique designed to efficiently extract the qubit noise spectrum. The qubit noise spectrum is useful both from the point of view of extending qubit coherence via bespoke pulse sequences and also for providing insight into the qubit surroundings. This technique performs well when compared with alternative techniques, offering accuracy that is similar to state of the art approaches but with significantly fewer experimental resources.

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