  Diamond has emerged as a highly promising platform for quantum network
applications. Color centers in diamond fulfill the fundamental requirements for
quantum nodes: they constitute optically accessible quantum systems with
long-lived spin qubits. Furthermore, they provide access to a quantum register
of electronic and nuclear spin qubits and they mediate entanglement between
spins and photons. All these operations require coherent control of the color
center's spin state. This review provides a comprehensive overview of the
state-of-the-art, challenges, and prospects of such schemes, including, high
fidelity initialization, coherent manipulation, and readout of spin states.
Established microwave and optical control techniques are reviewed, and
moreover, emerging methods such as cavity-mediated spin-photon interactions and
mechanical control based on spin-phonon interactions are summarized. For
different types of color centers, namely, nitrogen-vacancy and group-IV color
centers, distinct challenges persist that are subject of ongoing research.
Beyond fundamental coherent spin qubit control techniques, advanced
demonstrations in quantum network applications are outlined, for example, the
integration of individual color centers for accessing (nuclear) multi-qubit
registers. Finally, we describe the role of diamond spin qubits in the
realization of future quantum information applications.
