Universal squash model for optical communications using linear optics and threshold detectors

Abstract

Quantum communications often rely on single photons as information carriers in order to exploit their quantum mechanical properties. However, practical detectors are often threshold detectors that are incapable of resolving the number of photons received. This apparently subtle issue has surprisingly immense implication to many quantum communications protocols. In fact, it has been shown that this issue leads to many problems including fake violation of Bell's inequality, insecurity of quantum key distribution, and false entanglement verification. The source of these problems is the discrepancy between the theoretical consideration where single-photon signals are assumed and the actual experiments where multi-photon signals may be detected. We report a universal solution to bridge this gap between theory and experiments.