  Optically active point defects in crystals have gained widespread attention
as photonic systems that can find use in quantum information technologies.
However challenges remain in the placing of individual defects at desired
locations, an essential element of device fabrication. Here we report the
controlled generation of single nitrogen-vacancy (NV) centres in diamond using
laser writing. The use of aberration correction in the writing optics allows
precise positioning of vacancies within the diamond crystal, and subsequent
annealing produces single NV centres with up to 45% success probability, within
about 200 nm of the desired position. Selected NV centres fabricated by this
method display stable, coherent optical transitions at cryogenic temperatures,
a pre-requisite for the creation of distributed quantum networks of solid-state
qubits. The results illustrate the potential of laser writing as a new tool for
defect engineering in quantum technologies.
