Quantum sensors have recently achieved to detect the magnetic moment of few
or single nuclear spins and measure their magnetic resonance (NMR) signal.
However, the spectral resolution, a key feature of NMR, has been limited by
relaxation of the sensor to a few kHz at room temperature. The spectral
resolution of NMR signals from single nuclear spins can be improved by, e.g.,
using quantum memories, however at the expense of sensitivity. Classical
signals on the other hand can be measured with exceptional spectral resolution