Whenever photons are the bearers of information in any application involving communication, acquisition or processing of information, the fundamental performance limits are governed by the laws of quantum mechanics. In addition to processing speedup, exploiting the quantum nature of the photon affords physics-based guarantees of security in various cryptographic and communications-privacy primitives, where security derives from the laws of physics unlike having to rely on the perceived hardness of computational problems, as is the norm in conventional cryptographic techniques. I will start with some examples of performance gaps between conventional systems and the respective quantum limits in the context of optical communications, sensing, and computation, and will discuss how one might conceive of building systems---often exploiting non-classical sources, processes and detection schemes---that outperform conventional ones. I will then delve in more detail into some recent work on physics-based communications security---both when the content of the communication must be kept secret (undecodable) from an all-powerful adversary, as well as in with a stronger notion of security where the transmission attempt must be kept covert (undetectable) while conveying information reliably. I will end my talk with a discussion of challenges and open problems in building a quantum information network, which will need to draw upon an interdisciplinary set of expertise, viz., in quantum optics, information theory, resource allocation and network communications theory.
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