Thermal and superthermal noise signals as resources for underwater quantum communication

Quantum technologies have opened new perspectives for enhancing communication speed and security, particularly in challenging underwater environments, where conventional protocols rely on acoustic wave propagation. In this study, we introduce an innovative communication protocol built upon the utilization of mesoscopic twin-beam (TWB) states, entangled in the number of photons, and photon-number-resolving detectors. Our approach involves transmitting information by mixing the part of TWB that propagates through water with two signals having identical mean values but different statistical distributions. Specifically, we explore the advantages and limitations associated with employing pseudothermal states and two distinct types of superthermal states in our communication protocol. Through both theoretical analysis and experimental investigation, we assess the feasibility of accurately discriminating which state has been superimposed onto the TWB by evaluating the noise reduction factor. Our findings demonstrate promis- ing outcomes, suggesting the practical implementation of this protocol in real-world underwater communication scenarios.