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 quantumenhanced 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.
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 quantumenhanced 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.
Quantum cryptography promises secure communication protocols that surpass the limitations of classical cryptography. By leveraging the principles of quantum mechanics, particularly the phenomenon of quantum entanglement and the uncertainty principle, quantum cryptography protocols offer provable security guarantees against eavesdropping attacks. In this paper, we provide an overview of quantum cryptography, discussing its theoretical foundations, key protocols such as quantum key distribution (QKD), and experimental implementations. We highlight the advantages of quantum cryptography over classical cryptographic techniques and explore its potential applications in secure communication networks, financial transactions, and data privacy. Furthermore, we discuss ongoing research efforts and challenges in the practical deployment of quantum cryptography systems, including the development of robust quantum hardware and the integration of quantum cryptographic protocols into existing communication infrastructures. Overall, quantum cryptography holds great promise for enabling secure communication channels that are resilient to quantum attacks, paving the way for a new era of ultra-secure information exchange.
Quantum information and quantum optics offer powerful innovative tools for secure communication and cryptography, with Quantum Key Distribution (QKD) becoming a standard technology in the cryptographic world. By exploiting fundamental principles such as quantum superposition, entanglement, and the no-cloning theorem, QKD enables two users to establish a shared secret key with information-theoretic security. Quantum communication is a fundamental element for the realization of the quantum internet, a network of distant nodes connected by quantum channel. The realization of such networks requires methods to distribute states and correlations with high fidelity and low losses. This thesis explores the use of innovative photonic technologies for the realization of experiment aiming at improving quantum communication and quantum channels. Single photons based on QD are generated on-demand and show high purity, near-optimal indistinguishability and low multi-photons emission. By exploiting the features of these photons, a method to realize entangled states is implemented. Using the polarization degree of freedom, these entangled states are ideal candidates for free-space QKD protocols based on the Bell’s inequality. To address the problem of the reference frame alignment using the polarization, hybrid states are studied and implemented. The specific combination of polarization and orbital angular momentum (OAM) can produce photons that are not modified by rotation of the reference frame. We implemented an experiment to realize a QKD that is independent on the relative rotation of the two user. The final goal of my thesis was devoted to the in-field demonstration of quantum teleportation as a fundamental building block of distributed quantum networks, enabling the reliable transmission of quantum information between remote nodes. Exploiting the free-space infrastructure in the "Sapienza" University of Rome, a link of around ∼ 300 m, we implemented the quantum teleportation between two different QDs showing the possibility of using this technology into real-case scenario. The results obtained show not only that QDs are ideal sources for quantum communication, but also the possibility of using new states to improve current technologies, advancing the development of efficient and reliable quantum networks.
Due to the recent rapid growth of computing technologies, today's encrypted information based on classical computational complexities will soon no longer remain secure. Quantum cryptography, or quantum key distribution (QKD), relying on the physical laws of quantum mechanics, stands out as a more powerful cryptographic solution that enables the secret key to be shared securely over publicly unsecured communication channels in the presence of eavesdroppers. QKD can be possibly implemented over both optical fiber and free-space optical (FSO) links. Compared to optical fiber, FSO has the immediate advantage of flexibility and cost-effectiveness in terms of infrastructure deployment. More interestingly, recent advancements in satellite communications using FSO links promise the future of a global QKD network for highly secure applications. This paper reviews the development of QKD over FSO for both terrestrial and satellite channels, which highlights the most up-to-date QKD protocols. Owing to how the information is encoded, different QKD protocols are classified into technology-focused categories, where their properties are reviewed and compared. The feasibility of current QKD protocols is then investigated with respect to its specific application scenarios for terrestrial and satellite FSO links, equipped with results from both theoretical and experimental studies. Based on the latest free-space QKD achievements, novel perspectives for future developments and challenges to enhance the secrecy performance and reduce implementation cost are then summarized and comprehensively discussed. The potential combination of QKD and physical layer cryptography for the newly emerging wireless mobile communications networks involved with unmanned aerial vehicles (UAV) is also introduced.
Quantum cryptography is an emerging field that ensures secure communication by leveraging principles of quantum mechanics. Unlike classical cryptography methods that rely on mathematical complexity, quantum cryptographic protocols, Quantum Key Distribution (QKD) protocols derive their security from the fundamental laws of physics. Among these, the BB84 protocol is widely recognized for enabling secure key exchange between communicating parties, with any eavesdropping attempts being inherently detectable. The invention of quantum computing poses a significant threat to classical encryption algorithms, and thereby necessitating both post-quantum cryptography and quantum-based approaches. This paper presents a comprehensive overview of quantum cryptography, emphasizing its theoretical principles foundations of quantum cryptography, emphasizing its advantages over traditional encryption methods, implementation challenges, and real-world application. It also outlines the limitations of quantum technology, e.g., hardware limitations and interference by noise, which restrict large-scale application. A detailed comparison between classical, quantum, and hybrid cryptographic approaches is presented to highlight the key advancement, including improved eavesdropping detection, enhanced key generation rates, and security through quantum entanglement. As quantum networks evolve rapidly, quantum cryptography is poised to become a cornerstone of nextgeneration ultra-secure communication systems.
The rapid advancement of quantum computing poses a significant threat to classical cryptographic systems that rely on the computational hardness of mathematical problems such as integer factorization and discrete logarithm problems. In this context, quantum cryptography has emerged as a promising paradigm for secure communication based on the fundamental principles of quantum mechanics rather than on computational assumptions. This paper presents a comprehensive review of quantum cryptography, with a particular focus on Quantum Key Distribution (QKD), the most mature application. The study discusses the theoretical foundations of quantum security, including superposition, entanglement, and the No-cloning theorem, which collectively enable eavesdropping detection and guarantee information-theoretic security. Furthermore, the review examines major QKD protocols, such as BB84 and E91, as well as their advanced variants designed to address practical vulnerabilities and enhance performance. Recent progress in real-world implementations, including fiber-optic networks, free-space communication, and satellite-based systems such as the Micius satellite, is also analyzed. In addition, the paper highlights critical challenges related to scalability, hardware limitations, and security loopholes arising from imperfect devices. Finally, emerging research directions, including hybrid cryptographic frameworks that integrate quantum and post-quantum approaches, are discussed to provide insights into the future of secure communication. This review aims to provide a structured, up-to-date understanding of quantum cryptography, bridging the gap between theoretical developments and practical implementations, and emphasizing its crucial role in shaping next-generation cybersecurity systems.
Quantum communication is a rapidly evolving field that leverages quantum physics to enable secure and efficient information exchange. A cornerstone of quantum cryptography is Quantum Key Distribution (QKD), a secure key exchange mechanism that ensures the confidentiality of transmitted data by employing the no-cloning theorem and the uncertainty principle of quantum mechanics. This study explores key aspects of quantum networks and communication, including quantum states, QKD, and quantum cryptographic protocols, with a focus on photon polarization states and entangled qubits as fundamental building blocks of quantum information. Additionally, two well-established quantum cryptographic protocols, BB84 and E91, are analyzed for their principles and advantages in secure communication. However, challenges such as quantum state loss in communication channels hinder the long-distance transmission of quantum information. To address these issues, error detection, measurement, and correction techniques are investigated, with quantum error correction methods playing a crucial role in mitigating noise and imperfections, ensuring accurate quantum information transmission, and enhancing the overall efficiency of quantum communication systems. Beyond conventional networks, quantum communication holds vast potential for cybersecurity applications, paving the way for next-generation secure communication frameworks.