Assessing Feasibility of Secure Quantum Communications Involving Underwater Assets

In this paper, we apply a mathematical model of the quantum bit error rate to assess the viability of quantum key distribution (QKD) protocols for secure and covert underwater communications. We consider scenarios that may include passive sensor arrays, coordinated underwater vehicles, and surface and aerial assets. This analysis suggests that single-photon QKD can potentially be used effectively at depths between 60 and 110 m in clear waters, with the precise depth depending in part on ambient illumination levels. We discuss how diurnal variations in background illumination can be exploited in some applications to achieve improved communications rate and/or reliability when using QKD or other secure optical protocol.