The objective of this four-year FWO project (2019-2023) is to use ab-initio modeling to theoretically predict and design a novel type of solid-state spin defects made of group IV (Si, Ge, Sn, Pb) – vacancy complexes (XV complexes) in diamond. Presenting very high Zero Field Splitting, these defects could enable high fidelity spin readout and thus be an interesting alternative to nitrogen-vacancy centres for applications to quantum information science at ambient temperature. Based on these theoretical predictions, we aim at engineering the XV complexes in ultrapure diamond and experimentally study their electronic structure and quantum properties. As a first step towards quantum processors or quantum registers with enhanced performance and scaling, our goal is then to implement small arrays of XV spin qubits, to achieve the coherent driving of these qubits and to demonstrate their photo-electric readout (so far only established on NV centres in diamond).