How does quantum sensing with NV-centers in diamond work?

The NV-center is currently the workhorse for quantum sensing applications. It is an atom-like system whose electronic spins can be optically initialized, read out, and coherently manipulated with microwave pulses. In a typical measurement, a defined quantum state is prepared first (typically by optically initializing the NV-center in the |0> state and applying a p/2 pulse to prepare a coherent superposition). Second, the superposition interacts with the environment, i.e., the quantum state will evolve under the Hamiltonian measurement. Third, the final quantum state will be read out by fluorescence, from which information about the interaction (e.g., with a magnetic field) can be deduced. Since the NV-center can be brought close to the diamond surface and addressed individually, nanoscale sensing can be performed.