Quantum Communication is a groundbreaking technology that promises to revolutionize our current telecommunication systems. However, being a relatively new field, many challenges are yet to be confronted. This Doctoral thesis is dedicated to the advancement of Quantum Communications for fundamental studies and applications. Here, satellite-based, free-space and optical-fiber links are exploited to test and develop different Quantum Communication protocols. Different technologies, in particular free-space optics, fiber-based components and silicon photonic integrated circuits, are adopted to manipulate the quantum states of light. Different types of studies are performed ranging from fundamental tests of physics, to technological advancements, up till the development of fully-functioning Quantum Key Distribution systems. The work described in this thesis, I hope, represents a substantial contribution in the effort to transition Quantum Communications from the laboratories to a wide-spread deployment in future telecommunication infrastructures.
Quantum information technologies are poised to fundamentally transform global communication. Unlike classical systems, quantum communication leverages phenomena like quantum entanglement to offer unprecedented capabilities. This not only revolutionizes security and computational methods, but also drives advancements in specialized applications such as advanced sensing and precise time synchronization. These developments hold significant implications for critical sectors including medicine and health, materials science, and energy. At the core of this transformation is the concept of a quantum Internet, built upon the unique properties of quantum entanglement. The strategic use of entanglement as a communication resource is expected to profoundly impact the future evolution of the Internet and the development of 6G networks. This paper explores the path from current quantum entanglement research to a global quantum network. It highlights the advantages of satellite-based quantum communications for routing quantum information and discusses the simulation tools essential for designing and optimizing these advanced communication systems.
Massless particle photon has been serving as the information carrier in a large number of classical communication systems in the form of electromagnetic waves. With the advancements in quantum optics, due to the progress in the design and development of high-quality optical cavities and improvements in the connement of atoms, ions, and molecules using sophisticated optical traps and optical lattices, individual photons can now be generated, manipulated, and guided. These capabilities of controlling individual photons herald the emergence of quantum communication systems used in quantum optics [1-4]. Quantum communication is the art of communicating quantum states between spatially separated locations. A photon is generally used as the carrier for transferring quantum information (encoded into quantum states) from the transmit node to the receive node of the quantum communication system.
Satellite-based quantum communications represent a critical advancement in the pursuit of secure, global-scale quantum networks. Leveraging the principles of quantum mechanics, these systems offer unparalleled security through Quantum Key Distribution (QKD) and other quantum communication protocols. This review provides a comprehensive overview of the current state of satellite-based quantum communications, focusing on the evolution from terrestrial to space-based systems. We explore the distinct advantages and challenges of discrete-variable (DV) and continuous-variable (CV) quantum communication technologies in the context of satellite deployments. The paper also discusses key milestones such as the successful implementation of quantum communication via the Micius satellite and outlines the primary challenges, including atmospheric turbulence and the development of quantum repeaters, that must be addressed to achieve a global quantum internet. This review aims to consolidate recent advancements in the field, providing insights and perspectives on the future directions and potential innovations that will drive the continued evolution of satellite-based quantum communications.