Quantum key distribution (QKD) and quantum random number generation (QRNG) will play a key role in the future of data communication security. QKD can be used by trusted parties to share a secret key, leading to long-term secure communications. QRNG allows the production of fully unpredictable and certifiable random numbers, which can be used in numerous applications, including cryptography and large stochastic simulations. Both QKD and QRNG can be implemented using commercially available photonic components, which are mostly bulky and assembled into a discrete module. Although this approach can benefit from the superior performance and maturity of each individual component, it does not guarantee the large-scale deployment and commercial viability of the technology. A preferable alternative relies on integrating some or all functionalities in a single photonic integrated circuit (PIC) fabricated at the wafer scale, in this way reducing size, weight, complexity, cost, and power consumption. Integrated photonics can thus dramatically improve the performance and reliability of QKD systems and QRNG devices. Here, we review recent literature on designs, related materials, and fabrication processes, which is representative of state-of-the-art PIC-based QKD and QRNG. We conclude the paper by pointing out the challenges that need to be addressed in the future for reaching a wide-scale deployment of these integrated technologies.
Quantum key distribution (QKD) and quantum random number generation (QRNG) will play a key role in the future of data communication security. QKD can be used by trusted parties to share a secret key, leading to long-term secure communications. QRNG allows the production of fully unpredictable and certifiable random numbers, which can be used in numerous applications, including cryptography and large stochastic simulations. Both QKD and QRNG can be implemented using commercially available photonic components, which are mostly bulky and assembled into a discrete module. Although this approach can benefit from the superior performance and maturity of each individual component, it does not guarantee the large-scale deployment and commercial viability of the technology. A preferable alternative relies on integrating some or all functionalities in a single photonic integrated circuit (PIC) fabricated at the wafer scale, in this way reducing size, weight, complexity, cost, and power consumption. Integrated photonics can thus dramatically improve the performance and reliability of QKD systems and QRNG devices. Here, we review recent literature on designs, related materials, and fabrication processes, which is representative of state-of-the-art PIC-based QKD and QRNG. We conclude the paper by pointing out the challenges that need to be addressed in the future for reaching a wide-scale deployment of these integrated technologies.
Quantum key distribution (QKD) relies on the fundamental principles of quantum mechanics and can theoretically achieve unconditionally secure communication that is provable by information theory. Quantum random number generators, on the other hand, utilize the inherent randomness of quantum phenomena and are capable of generating a truly random entropy source that is unpredictable, unbiased and unrepeatable. These two technologies are crucial for building highly trustworthy and secure communication systems resistant to quantum attacks. However, their large-scale deployment still faces challenges such as system performance optimization, cost control and scale production. Relying on wafer-level fabrication platforms and micro-nanometer processing, integrated photonics technology integrates the core devices of traditional QKD systems (e.g., light source, modulator, and detector) in a single chip at high density. It significantly improves the miniaturization, operational stability and cost-effectiveness of the system, and enhances the intrinsic security, and becomes a key enabling platform to drive QKD and QRNG from laboratory to engineering applications. In this paper, we systematically review the recent breakthroughs of photonic integrated QKD based on different material platforms (SOI/InP/TFLN/Si3N4) in terms of core metrics, such as transmission distance and key rate, as well as the significant breakthroughs of integrated QRNG in terms of random number generation rate and system integration. Finally, the future development direction of this field is discussed and outlooked from the four dimensions of practical security of QKD systems, on-chip implementation of cutting-edge QKD protocols, practical fully-integrated QKD systems, and synergistic optimization of high performance and high integration of integrated QRNG.
Quantum key distribution (QKD) offers the highest possible levels of communication secrecy. Using the laws of quantum mechanics, QKD protocols allow two distant parties to establish symmetric encryption keys that can be proven information theoretically secure. In order to make this technology accessible to a wide range of sectors, it is essential to address the questions of cost, volume production and compatibility with standard Telecom/Datacom infrastructures. While over the last few years, a number of works were devoted to the demonstration of photonic integrated circuits for quantum communications, a practical solution to interface these chips in a complete system remained an elusive goal. We review our efforts in integrating the core optical functions of quantum key distribution onto quantum photonic chips and in demonstrating the first standalone photonic integrated QKD system. Our approach tackles various system integration challenges related to packaging, optoelectronic design and power consumption. The quantum hardware is assembled in pluggable interconnects that guarantee efficient thermal management and forward compatibility of a same host electronics with successive generations of chips. Autonomous operation and long-term stability are demonstrated in realistic operation conditions. Our work offers new pathways for practical implementations of QKD and its viable deployment at large scales.
The limited range of quantum key distribution (QKD) in fiber based systems led to several projects aiming for the development of a satellite based QKD infrastructure, like the conduction of quantum limited measurements from a geostationary satellite [1] or the MICIUS mission, which impressively demonstrated QKD on a global scale [2]. However, due to the high costs of satellite launches the profitability of commercial systems would benefit dramatically from further reduction in size, weight and power. Photonic integration [3] addresses these points by allowing the integration of all optical components of a QKD system on a photonic integrated circuit (PIC). In this work, we are going to demonstrate building blocks for quantum communication from space based on photonic integration technology by building a payload for the CubeSat mission QUBE [4] consisting of an integrated sender for weak coherent states as well as an integrated Quantum Random Number Generator (QRNG).
Abstract Quantum key distribution (QKD) represents a cornerstone of secure communication in the quantum era. While discrete-variable QKD (DV-QKD) protocols were historically the first to demonstrate secure key exchange, continuous-variable QKD (CV-QKD) has emerged as a more practical alternative due to its seamless compatibility with current telecommunications infrastructure. CV-QKD relies on coherent and squeezed states of light, offering significant advantages for integration into modern optical networks. This review comprehensively explores the theoretical underpinnings, technological advancements, and practical challenges of CV-QKD. Special attention is given to the role of photonic integrated circuits (PICs) in enabling scalable and efficient implementation of CV-QKD systems. Furthermore, recent advances in machine learning have been leveraged to optimize CV-QKD performance, with data-driven techniques enhancing noise estimation, parameter optimization, and system security. Additionally, tensor networks provide efficient computational tools for analyzing complex quantum correlations, improving the efficiency and robustness of quantum key distribution protocols. These developments, combined with ongoing improvements in quantum photonic integration, pave the way for the practical deployment of large-scale, high-speed quantum-secure networks.
Quantum technologies are rapidly transforming the landscape of secure communication and computation by exploiting the fundamental principles of quantum mechanics. Among these, Quantum Key Distribution (QKD) offers an unprecedented level of security in communications, provided by physical principles rather than computational assumptions. However, the realization of scalable and practical quantum networks remains challenging. Key technological hurdles include the need for high-sensitivity and high-speed single-photon detectors, stable and integrated optical platforms, and robust and fast true random number generators. Overcoming these challenges is essential to bridge the gap between laboratory demonstrations and the real-world deployment of quantum networks. This thesis addresses some of these critical issues through work in single-photon detection technologies, integrated QKD system implementation, and high-speed Quantum Random Number Generators (QRNGs). Single-Photon Avalanche Diodes are fundamental detectors for quantum technologies, enabling high-sensitivity measurements at the single-photon level. This thesis investigates the operating principles, limitations, and advancements of Single-Photon Avalanche Diodes, with a focus on high-speed dual-anode designs. Their photon detection efficiency, dark count rate, afterpulsing probability, and timing jitter are analyzed, while optimized control electronics and capacitance management strategies are developed. The characterization of Single-Photon Avalanche Diodes demonstrates their suitability for quantum communication, particularly in quantum key distribution and asynchronous heralded photon sources, with pathways for further improvements in speed and integration. Building on these detector technologies, a proof-of-principle integrated quantum key distribution system based on the BB84 protocol is presented. The system incorporates time-bin encoding, decoy-state methods, and photonic integrated circuits for both transmitter and receiver. Key challenges, such as chromatic dispersion and interferometer stability, are addressed through novel circuit and system-level designs. System-level testing and field deployment validate the feasibility of compact, high-performance integrated quantum key distribution implementations. Finally, the thesis explores quantum random number generation through semi-device-independent protocols. An experimental homodyne-based SDI-QRNG is realized, supported by custom transimpedance amplifier design and photonic integrated circuit integration. The setup achieves high bandwidth, strong quantum-to-classical noise separation, and stable operation, enabling practical random number generation rooted in fundamental quantum processes. Overall, this work advances the development of integrated quantum technologies by improving room-temperature single-photon detection, demonstrating scalable QKD prototypes, and implementing a high-speed QRNG. Together, these contributions pave the way toward secure, integrated quantum communication systems and practical quantum information applications ready to deploy in real world networks.