Light and color: photonic resources for quantum metrology

A finite precision is always associated with the estimation of a parameter, whether it is time, length, or a rotation angle. What does fundamentally limit this precision, given a fixed amount of resources—such as total energy—that are used in parameter estimation? The answer depends on whether classical or quantum strategies are employed. In this paper, we explore the fundamental precision limits of metrological protocols, with a focus on how quantum optics and photonic devices can achieve a quadratic improvement in precision compared to classical setups while using the same amount of resources. We analyze both theoretical aspects and experimental demonstrations, highlighting the respective roles of field statistics and spectral properties in enhancing precision.