Quantum Technologies for Secure Communications in Space

Quantum technologies have been proved useful for space applications, such as for the well-known application of quantum key distribution (QKD). However, QKD shows a number of serious practical limitations and therefore we are interested in different ways of using quantum resources and readily available quantum technology for secure communication in space. Towards this aim, we first of all provide an overview of quantum resources and state-of-the art quantum technologies, specifically sources and detectors. Then, we identify two realistic and related applications for the short-term. The first one is quantum-enhanced communication as quantified by Shannon rates using single-photon detection technology and lasers. In this case, we show illustrative potential gains for Optical On/Off Keying (O3K) communications. The second one is quantum physical layer cryptography, which builds upon quantum-enhanced communications. In this case, we show how to realize secure communication in space with quantum resources, cryptographic primitives and without the use of any key, which we call Quantum Keyless Privacy (QKP). It is a variant of the quantum wiretap channel principle hybridized with primitives and technology of QKD. In this case, we discuss the security of QKD and of our method and show that both methods provide information theoretical security.