||In a quantum network, interconnected nodes use shared entangled
states as a resource for communication. The nitrogen-vacancy (NV) centre in diamond is a promising candidate for the realization of a such a node. It provides a solid state qubit that can be initialized and read out optically and manipulated via microwave pulses. However, for any practical implementation, control mechanisms that maintain the resonance of the excitation and emission frequencies need to be in place. Additionally, to guarantee phase stability as required for long distance entanglement, it is necessary to realize a frequency stabilized excitation laser.
We demonstrate an autonomous routine for the optimization of excitation and emission frequencies, that recovers resonance conditions automatically when sudden jumps in the emission frequencies occur. Furthermore, an optical setup for the stabilization of excitation frequencies in a Pound-Drever-Hall scheme is presented. An upper bound on the excitation linewidth of 1.7 kHz is measured, yielding a phase deviation lower than 5 over a distance of 1 km. These developments will be essential in the development of a stand-alone quantum node involving the NV centre, on the road to a global quantum internet.