Analog Control of the Diamond Quantum Processor

Abstract

Diamond quantum processors, based on the nitrogen-vacancy (NV) centre, offer long coherence times and high-fidelity optical control at room temperature, making them a promising platform for quantum technologies. Until now, they have been operated almost exclusively using the gate-based digital quantum computing (DQC) paradigm. This thesis introduces a novel derivation of the fully controllable Ising model from the diamond control Hamiltonian, laying the groundwork for this architecture to support computational paradigms beyond the gate model. With this result, analog control becomes feasible on diamond hardware for the first time, enabling a novel approach to quantum annealing. Diamond quantum annealing is evaluated through simulations of a room-temperature device based on a single NV-centre cluster, incorporating realistic effects such as decoherence and crosstalk. To improve robustness, open-loop optimisation protocols are introduced for annealing schedule design, showing improved performance. A new hardware-specific quality factor is also proposed, which benchmarks adiabaticity based on the system's minimum transition frequency spacing and decoherence time. This metric suggests that diamond may support purely quantum annealing, without relying on thermalisation. For contrast, the metric is applied to both the proposed diamond quantum annealer and superconducting flux qubit devices, using parameter estimates from D-Wave's Advantage platform. Finally, this work demonstrates that diamond is also capable of stepped digital-analog quantum computation (sDAQC), marking a second potential shift in how quantum algorithms can be realised on this platform. Building on this result, a hardware-specific technique- interleaved circuit compression (ICC)- is also introduced to exploit the newly derived control Hamiltonian. By combining Ising coupling gates with arbitrary-axis rotations, ICC enables substantial compression of gate-based quantum circuits on diamond hardware. This is illustrated using the quantum Fourier transform (QFT), where circuit depth is reduced from O(n^2) under standard digital compilation to O(n) with ICC. Show more