Photon-resolved Floquet theory approach to spectroscopic quantum sensing

Spectroscopic methods play a vital role in quantum sensing, which uses the quantized nature of atoms or molecules to reach astonishing precision for sensing of, e.g., electric or magnetic fields. In the theoretical treatment, one typically invokes semiclassical methods to describe the light-matter interaction between quantum emitters, e.g., atoms or molecules, and a strong coherent laser field. However, these semiclassical approaches struggle to predict the stochastic measurement fluctuations beyond the mean value, necessary to estimate the sensitivity of spectroscopic quantum sensing protocols. Here, we develop a theoretical framework based on the recently developed photon-resolved Floquet theory (PRFT), which is capable of predicting the measurement statistics describing higher-order cumulants of coherent quantum states of light. The PRFT constructs flow equations for the cumulants of the photonic measurement statistics utilizing only the semiclassical dynamics of the matter system. We apply the PRFT to spectroscopic quantum sensing using dissipative two-level and four-level systems (describing electric-field sensing with Rydberg atoms), and demonstrate how to calculate the Fisher information of the measurement statistics with respect to various system parameters. In doing so, we demonstrate that the PRFT is a flexible tool allowing for improving the sensitivity of spectroscopic quantum sensing devices by several orders of magnitude.