Optimal control on diamond-based information processing




Quantum information processing and its applications using nitrogen-vacancy (N-V) centres in diamond have become very attractive research due to the centre's remarkable properties that  can be engineered at room temperature. Spins associated with the centre can be initialised and measured by optical means, controlled by microwave (or radio-frequency) field, and have long coherence times (few milliseconds for electron). Several milestones towards a  diamond-based quantum  computer  have  been  demonstrated, e.g. observation of Rabi oscillations of the electron and nuclear spins and quantum register based on coupled  electron spins.  Some technologies e.g highly precise magnetometry and imaging have also been realised using N-V centres.               




Moreover, there is a need for fast and robust spin manipulations whose the aims are to increase a number of quantum  operations and to combat detrimental effects of decoherence and imperfections. Those can be achieved via techniques of optimal control. A set of conventional fields controlling the spins, e.g. resonant fields with constant amplitudes, can be substituted by a set of numerically-shaped fields from a particular optimisation algorithm. These engineered fields should  provide faster quantum operations with or higher fidelity and robust against noise. One of our group's research interests is to investigate thoroughly optimal control methods applied in N-V spin-based quantum information processing. We currently focus on numerical optimisations to perform single qubit rotations of the N-V electron spin in the strong driving regime. This regime where the amplitudes of the control fields are comparable with the spin  transition has not been extensively studied yet, but offers opportunities for fast qubit operations. We collaborate with Prof. Jelezko's quantum optics group (Ulm) to experimentally realise such optimised pulses in diamond.                 




G. D. Fuchs, et. al., Gigahertz dynamics of strongly driven single quantum spin, Science, 326, 1520 (2009).

G. Waldherr, et. al., High-dynamic-range magnetometry with a single nuclear spin in diamond, Nature Nanotechnology, 7, 105 (2011).