Mesoscopic Magnetic Resonance Spectroscopy with a Remote Spin Sensor

Quantum sensing based on nitrogen-vacancy (N-V) centers in diamond has been developed as a powerful tool for microscopic magnetic resonance. However, the reported sensor-to-sample distance is limited within tens of nanometers resulting from the cubic decrease of the signal of spin fluctuation with the increasing distance. Here we extend the sensing distance to tens of micrometers by detecting spin polarization rather than spin fluctuation. We detect the mesoscopic magnetic resonance spectra of polarized electrons of a pentacene-doped crystal, measure its two typical decay times, and observe the optically enhanced spin polarization. This work paves the way for the N-V-based mesoscopic magnetic resonance spectroscopy and imaging at ambient conditions.