Nuclear quantum sensing and nitrogen-vacancy centers in diamond

Below is from Nature

https://www.nature.com/articles/s41534-023-00724-6

Spin-based quantum sensors can be employed to measure a wide range of relevant physical quantities, including magnetic or electric fields, temperature, or rotary motion. This abundance of potential observables, combined with their high sensitivity at the nano-scale makes quantum sensors highly interesting for many fields of application, such as life sciences, geological sciences, navigation, and material sciences.

Nitrogen-Vacancy (NV) centers in diamond are a particularly promising platform for such spin-based quantum sensing applications, because they host a single electron spin with long coherence times even at room temperature. Upon optical excitation with green light, the NV center emits spin-dependent red photoluminescence (PL), which enables all-optical electron spin readout. At the same time, such optical excitation pumps the NV electron spin into a specific spin eigenstate, enabling all-optical spin initialization. Time-varying (AC) driving fields, mostly in the microwave (MW) or radio-frequency (RF) domain can then be used to coherently control the spin, and create superposition states for sensing. This combination of optical initialization, readout, and coherent spin manipulation by AC driving fields form the basis of almost all established spin-based approaches to sensing.