Optimisation and Scaling of Diamond Quantum Computers

Abstract

The nitrogen-vacancy (NV) centre in diamond stands out among solid-state platform for quantum technologies due to its remarkable spin properties at room temperature. It allows high-fidelity initialisation, control, readout, and long coherence times for storing quantum information. These attributes are further enhanced at cryogenic temperatures and can be interfaced with photonic channels. Its vast applications span quantum sensing, networking, as well as a scalable quantum information processing platform. Large-scale room temperature diamond quantum computers offer unique advantages, including prospects for miniaturisation, robustness, deployability, and seamless integration with classical devices in the rapidly evolving quantum landscape. However, their realisation is hindered by challenges associated with (i) high-fidelity control, (ii) individual initialisation and readout of NV centres using photoelectrical methods, (iii) development of scalable designs and (iv) fabrication techniques for densely packed and precisely aligned arrays of NV centres.

This thesis addresses critical knowledge gaps associated with the first three challenges. Firstly, there are gaps in the comprehension and approach towards the optimal control of diamond quantum processors. The first aim is to address these gaps by developing an accurate Hamiltonian and comprehensive quantum control models for multi-qubit diamond quantum processors, and assessing their effectiveness through simulated quantum process tomography. Secondly, photoelectrical readout of the NV electron spin is the only scalable readout method at room temperature. However, scalable implementation of this method necessitates deep understanding regarding photoelectrical dynamics of the NV centre. The second aim is to address these gaps by rigorously deriving the photoionisation pathways of NV0, simulating the bound hole states, multi-scale modelling of critical macroscopic properties, elucidating charge carrier dynamics and modelling the photoelectrical dynamics of an isolated NV centre. Thirdly, the key parameters to inform a scalable design of diamond quantum processors are not well understood. The third aim is to assess the scalability of the magnetic dipolar coupling architecture for large-scale diamond quantum computers. This entails a systematic study of the architecture focusing on magnetic field gradients and charge state control. Combining theory, electrostatic modelling, and first-principles calculations, this thesis culminates in (a) error models for diamond quantum processor to inform design choices, (b) the first complete photoelectrical model of an isolated NV centre, and (c) key ranges for separation of NV centres, packing density, and magnetic field gradient. These advancements inform fabrication requirements and processor designs, which allow for the understanding of opportunities and constraints of diamond quantum computing, thereby assessing its potential and utility as a technology. Show more