Nuclear spin identification and control of novel hydrogen defect in diamond for quantum-enhanced sensing

Achieving selective control over large numbers of environmental dark spins around a single NV center in diamond is key to advancing entanglement-enhanced sensing with solid-state qubits. Past studies on dark spin qubits in diamond have focused on using P1 nitrogen substitutional defects, which exist in high concentrations relative to the NV center. This reduces coherence times of the qubits and leads to spectral crowding, ultimately limiting the number of addressable spins. In this work, we report the discovery of a novel electron-nuclear defect originating from a proton impurity featuring unique hyperfine components, and discuss how a hydrogen-based electron-nuclear spin register surrounding the NV can increase scalability. We introduce an electron-nuclear double resonance (ENDOR) protocol to characterize this defect and to achieve polarization and readout of the nuclear spin qubit, providing a robust quantum memory for the electronic spin. We outline how entangling the hydrogen and nitrogen nuclear spins can be used for long-time storage of entanglement and enable distributed memory-based quantum sensing protocols.