High-efficiency resonant amplification of weak magnetic fields for   single spin magnetometry
  We demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen-vacancy (NV) magnetometer and a target spin, the magnetometer sensitivity is increased dramatically. Specifically, using materials and techniques already experimentally available, we find that by taking advantage of the ferromagnetic resonance the minimum magnetic moment that can be measured is smaller by four orders of magnitude in comparison to current state-of-the-art magnetometers. As such, our proposed setup is sensitive enough to detect a single nuclear spin at a distance of $30$~nm from the surface within less than one second of data acquisition at room temperature. Our proposal opens the door for nanoscale NMR on biological material under ambient conditions. 
Luka Trifunovic, Fabio L. Pedrocchi, Silas Hoffman, Patrick   Maletinsky, Amir Yacoby, Daniel Loss
cond-mat.mes-hall cond-mat.other