Witnessing non-stationary and non-Markovian environments with a quantum sensor

Abstract

Quantum sensors offer exceptional sensitivity to nanoscale magnetic field fluctuations, where nonstationary effects—such as spin diffusion—and non-Markovian dynamics arising from coupling to few environmental degrees of freedom play critical roles. Because fully reconstructing the microscopic structure of realistic spin baths is often infeasible, a practical challenge is to identify the dynamical features that are actually encoded in the sensor’s decoherence signal. Here we demonstrate how quantum sensors can operationally characterize the statistical nature of environmental noise, distinguishing between stationary and nonstationary behaviors, as well as Markovian and non-Markovian dynamics. Using nitrogen-vacancy centers in diamond as a platform, we develop a physical noise model that captures the essential dynamical features of realistic environments relevant to sensor observables—independently of the microscopic bath details— and provides analytical predictions for Ramsey decay across different regimes. These predictions are experimentally validated through controlled noise injection with tunable correlation properties. Our results showcase the capability of quantum sensors to isolate and identify key dynamical properties of complex environments, without requiring full microscopic bath reconstruction. This work clarifies the operational signatures of nonstationarity and non-Markovian behavior at the nanoscale and lays the foundation for strategies that mitigate decoherence while exploiting environmental dynamics for enhanced quantum sensing.