  Coherently coupled pairs or multimers of nitrogen-vacancy defect electron
spins in diamond have many promising applications especially in quantum
information processing (QIP) but also in nanoscale sensing applications.
Scalable registers of spin qubits are essential to the progress of QIP. Ion
implantation is the only known technique able to produce defect pairs close
enough to allow spin coupling via dipolar interaction. Although several
competing methods have been proposed to increase the resulting resolution of
ion implantation, the reliable creation of working registers is still to be
demonstrated. The current limitation are residual radiation-induced defects,
resulting in degraded qubit performance as trade-off for positioning accuracy.
Here we present an optimized estimation of nanomask implantation parameters
that are most likely to produce interacting qubits under standard conditions.
We apply our findings to a well-established technique, namely masks written in
electron-beam lithography, to create coupled defect pairs with a reasonable
probability. Furthermore, we investigate the scaling behavior and necessary
improvements to efficiently engineer interacting spin architectures.
