  A promising approach for multi-qubit quantum registers is to use optically
addressable spins to control multiple dark electron-spin defects in the
environment. While recent experiments have observed signatures of coherent
interactions with such dark spins, it is an open challenge to realize the
individual control required for quantum information processing. Here we
demonstrate the initialisation, control and entanglement of individual dark
spins associated to multiple P1 centers, which are part of a spin bath
surrounding a nitrogen-vacancy center in diamond. We realize projective
measurements to prepare the multiple degrees of freedom of P1 centers - their
Jahn-Teller axis, nuclear spin and charge state - and exploit these to
selectively access multiple P1s in the bath. We develop control and single-shot
readout of the nuclear and electron spin, and use this to demonstrate an
entangled state of two P1 centers. These results provide a proof-of-principle
towards using dark electron-nuclear spin defects as qubits for quantum sensing,
computation and networks.
