Loss-tolerant optical characterization based on post-selected interferometry

Optical characterization of materials using quantum techniques harvests high sensitivity under low photon flux but fails in high-loss scenarios. We demonstrate a post-selected optical sensing scheme that can work in high-loss scenarios. The protocol combines single-photon detection with exclusive OR gate-based coincidence counting in a Mach–Zehnder interferometer to concentrate and achieve Fisher information improvement for a limited number of measurements. The interferometer-native post-selection framework is robust against sample absorption loss, light-detector coupling loss, and zero-mean technical noise, while Fisher information is enhanced over the traditional method. This protocol can potentially be used for various optical characterizations, including optical reflectivity, polarization rotation, and optical phase.