  The search for long-lived quantum memories, which can be efficiently
interfaced with flying qubits is longstanding. One possible solution is to use
the electron spin of a color center in diamond to mediate interaction between a
long-lived nuclear spin and a photon. Realizing this in a nanodiamond
furthermore facilitates the integration into photonic devices and enables the
realization of hybrid quantum systems with access to quantum memories. Here, we
investigated the spin environment of negatively-charged Silicon-Vacancy centers
in a nanodiamond and demonstrate strong coupling of its electron spin, while
the electron spin's decoherence rate remained below 1 MHz. We furthermore
demonstrate multi-spin coupling with the potential to establish registers of
quantum memories in nanodiamonds.
