Diamond as a material has the potential to hold a million qubits on a single centimetre square. This is possible if you can network the electronic spin of a defect called a nitrogen vacancy centre - or NV centre - with the nuclear spins within the material itself. The Hub's work in this area focuses on engineering these devices for quantum applications.
One arm of our research is our laser writing work, where we use a high powered laser to write nitrogen vacancy centres with a high degree of precision or accuracy, giving us the ability to write excellent qubits, exactly where we want them. Our researchers also fabricate microcavity devices around the NV centre, to provide enhanced light-matter interaction towards creating a scalable content network.
Scalable quantum computer chips in diamond
Diamond nitrogen-vacancy (NV) centres provide coherent spin-photon interfaces, and an interface between nuclear spins that offer coherence times in excess of 1 minute. In QCS we are working towards a ~1 million qubit quantum computer consisting arrays nodes on a chip, connected via an optical network.
Laser writing of NV centre qubits
Our team pioneered the use of femtosecond laser processing to generate vacancies in diamond which can then be annealed to form NV centres. Thermal annealing has resulted in qubits with superlative optical and spin properties but with a relatively low yield. Laser-induced annealing allows local control and deterministic writing (yield >95%). We are working on combining the benefits of the two techniques to achieve increased yield of high quality qubits.
Processing of diamond membranes
High quality, uniform diamond membranes are needed to realise the node chip devices. The fabrication of these membranes whilst maintaining the NV properties presents challenges which we are working to overcome with a collaborative programme of process development.
Modelling laser-induced defect formation
To optimize the laser writing process we need to understand how the laser pulse delivers energy to the diamond lattice and its dependence on the various laser pulse parameters (wavelength, duration, energy). We are developing a finite- difference-time-domain (FDTD) model which is beginning to yield useful results and compares well with experiments.
Modelling defect interactions and dynamics
During NV formation we observe intermittent fluorescence from the colour centre which suggests complex dynamics attributable to interactions between point defects. We are modelling these interactions using Density Functional Theory (DFT), with initial focus on the hybridization of orbitals between an NV centre and carbon interstitial.