Witnessing Non-Stationary and Non-Markovian Environments with a Quantum Sensor

Quantum sensors are sensitive to nanoscale fluctuations in the magnetic field. At these length scales, non-stationary effects, such as spin diffusion, as well as non-Markovian dynamics, play critical roles. We demonstrate how a quantum sensor can be used to characterize the statistical behavior of a noise environment, distinguishing between stationary and non-stationary behavior, as well as between Markovian and non-Markovian dynamics. Using nitrogen-vacancy (NV) centers as a platform, we develop a physical noise model that captures the essential dynamical features of realistic environments, and provides analytical predictions for Ramsey decay under each regime. These predictions are confirmed experimentally by measuring Ramsey decay curves for NV centers subject to injected noise with engineered correlation functions. The use of a quantum sensor to characterize the statistical properties of a noise source can provide insight into its physical origin and aid in the development of strategies to control or mitigate the resulting decoherence.