Reporter-Spin-Assisted T1 Relaxometry

The detection of fluctuating electromagnetic fields through single-spin relaxometry affords important insight into the dynamics of solid-state systems and chemical processes, but its sensitivity is often limited by the proximity of the sensor spin to the target. This study proposes the use of an auxiliary reporter spin to improve sensitivity by as much as a factor of 100, and experimentally verifies the method with a single shallow nitrogen-vacancy center in diamond. This work motivates the development of engineered spin systems as relaxation sensors without the need for optical initialization or readout.