The last decade has seen an explosive growth in the use of color centers for metrology applications, the paradigm example arguably being the nitrogen-vacancy (NV) center in diamond. While ambient operation has been key to their success, bringing NVs to cryogenic conditions creates opportunities for control schemes not possible at room temperature. Indeed, orbital averaging of the NV first excited manifold — fast at 300 K — effectively vanishes below ~20 K leading to a set of narrow, spin selective optical transitions, already exploited, e.g., in demonstrations of spin-photon and photon-mediated, inter-spin entanglement.
In this presentation, we first leverage recent example applications to review the principles governing NV precision sensing with focus on the regime of cryogenic temperatures. We then describe recent studies in our group where we use narrow-band laser excitation to attain multi-fold improvement in NV spin detection sensitivity relative to standard methods, largely due to a boost in readout contrast and integrated photon count. We also show how to exploit nuclear spin-lattice relaxation under resonant optical excitation to polarize the 14N host, which we then prove beneficial for DC and AC magnetometry. With the help of practical applications to materials platforms of interest, we finally illustrate the opportunities these results open in the investigation of condensed matter systems, particularly those exhibiting superconducting, (anti‑)ferromagnetic, or topological phases selectively present at low temperatures.