Laser engineering of defects in diamond for quantum technologies

Abstract

Colour centre defects in diamond are promising candidates for many quantum technologies because they act as isolated two level systems in the solid-state that can be controlled and read-out through photonics [1][2][3]. Realisation of these technologies requires the placement of many highly coherent centres in a regular array with high positional accuracy and high fabrication yield [4]. Previous fabrication techniques have lacked the ability to produce high yields with high positional accuracy without causing irreparable damage to the lattice which reduced the quality of the spin and optical properties [5]. Ultra-fast laser writing has been shown to produce highly coherent nitrogen vacancy (NV) colour centres within the diamond lattice with positional accuracies of order hundreds of nanometers and a stochastic yield. In this case, the yield and positional accuracy is held back by the need to thermally anneal the diamond within a furnace to convert laser generated defects into colour centres; a fabrication step in which there is little to no control over individual site [6]. In this thesis, the ultra-fast pulsed laser writing technique is broached in detail from both a theoretical and experimental standpoint. The theory behind the highly non-linear light-matter interactions is studied and a hypothesis is developed for the energy transfer between photo-excited carriers and the lattice via the non-radiative recombination of self-trapped multi-excitonic states [7]. In addition, this thesis presents an expansion on the laser writing of colour centres through broaching the generation of different colour centres that have some preferential properties over the NV [8], and the development of a new engineering technique involving a local laser anneal [9]. The yield of generated centres is increased from stochastic to deterministic by replacing the global thermal anneal with the local laser anneal in combination with a fluorescence feedback mechanism. In addition, the use of the laser to locally anneal generated centres leads to a factor of five improvement in the positional accuracy due to the highly non-linear interaction of the laser with the material. These results culminate in a key step forward in the development of a large scale quantum device and improved understanding of the highly dynamical processes that occur upon femtosecond laser interaction with a wide bandgap material.