  While nitrogen-vacancy (NV-) centers have been extensively investigated in
the context of spin-based quantum technologies, the spin-state readout is
conventionally performed optically, which may limit miniaturization and
scalability. Here, we report photoelectric readout of ground-state
cross-relaxation features, which serves as a method for measuring electron spin
resonance spectra of nanoscale electronic environments and also for
microwave-free sensing. As a proof of concept, by systematically tuning NV
centers into resonance with the target electronic system, we extracted the
spectra for the P1 electronic spin bath in diamond. Such detection may enable
probing optically inactive defects and the dynamics of local spin environment.
We also demonstrate a magnetometer based on photoelectric detection of the
ground-state level anticrossings (GSLAC), which exhibits a favorable detection
efficiency as well as magnetic sensitivity. This approach may offer potential
solutions for determining spin densities and characterizing local environment.
