In situ characterization of a photon-subtraction device via heralding counts and homodyne detection
The study proposes an in situ method to simultaneously estimate a photon-subtraction device's beam splitter transmissivity ($ au$) and detector efficiency ($\eta$) using only measurement data generated during operation. By combining click statistics from the heralding detector and homodyne measurements on the transmitted light, the authors show that joint estimation yields a superior lower bound on parameter uncertainty compared to sequential estimation.