MULTI-PHOTON TOLERANT QUANTUM KEY DISTRIBUTION PROTOCOLS FOR SECURED GLOBAL COMMUNICATION

This dissertation investigates the potential of multi-photon tolerant protocols for satellite-aided global quantum key distribution (QKD). Recent investigations like braided single-stage protocol and the implementation of the three-stage protocol in fiber have indicated that multi-photon tolerant protocols have wide-ranging capabilities for increasing the distance and speed of quantum-secure communication. This dissertation proposes satellite-based network multicasting and its operation that can profitably use multi-photon tolerant protocols for quantum-secure global communication. With a growingly interconnected world and an increasing need for security in communication, communication satellites at Lower Earth Orbits (LEO), Medium Earth Orbit (MEO) and Geostationary Earth Orbit (GEO) have a potential role in serving as a means to distribute secure keys for encryption among distant endpoints. This dissertation systematically evaluates such a role. The dissertation proposes a layered framework using satellites and fiber optic links that can form a composite system for carrying the information payload and distributing quantum-secure keys for encrypting information in transit. Quantum communications links are currently point-to-point. Considering the concept of global QKD network, there is need for multicast quantum links. Multi casting can be achieved in quantum networks by (a) using multiple wavelengths, or (b) using use specific set of bases. In efforts to develop a composite quantum secure global communication system; this dissertation also introduces the concept of multi-photon tolerant quantum threshold cryptography. The motivation for development of threshold cryptography is that a secret can be encrypted with multiple users and requires multiple users to decrypt. The quantum threshold cryptography is proposed by using idea of multiple bases. This can be considered as step forward towards multiparty quantum communication. This dissertation also proposed layered architecture for key distribution. Concisely, this dissertation proposes the techniques like multicasting in quantum scenario, quantum threshold cryptography to achieve the goal of secured global communication

A Survey on Quantum Channel Capacities

Quantum information processing exploits the quantum nature of information. It offers fundamentally new solutions in the field of computer science and extends the possibilities to a level that cannot be imagined in classical communication systems. For quantum communication channels, many new capacity definitions were developed in comparison to classical counterparts. A quantum channel can be used to realize classical information transmission or to deliver quantum information, such as quantum entanglement. Here we review the properties of the quantum communication channel, the various capacity measures and the fundamental differences between the classical and quantum channels.Comment: 58 pages, Journal-ref: IEEE Communications Surveys and Tutorials (2018) (updated & improved version of arXiv:1208.1270

Telecommunications Networks

This book guides readers through the basics of rapidly emerging networks to more advanced concepts and future expectations of Telecommunications Networks. It identifies and examines the most pressing research issues in Telecommunications and it contains chapters written by leading researchers, academics and industry professionals. Telecommunications Networks - Current Status and Future Trends covers surveys of recent publications that investigate key areas of interest such as: IMS, eTOM, 3G/4G, optimization problems, modeling, simulation, quality of service, etc. This book, that is suitable for both PhD and master students, is organized into six sections: New Generation Networks, Quality of Services, Sensor Networks, Telecommunications, Traffic Engineering and Routing

Optics for AI and AI for Optics

Artificial intelligence is deeply involved in our daily lives via reinforcing the digital transformation of modern economies and infrastructure. It relies on powerful computing clusters, which face bottlenecks of power consumption for both data transmission and intensive computing. Meanwhile, optics (especially optical communications, which underpin today’s telecommunications) is penetrating short-reach connections down to the chip level, thus meeting with AI technology and creating numerous opportunities. This book is about the marriage of optics and AI and how each part can benefit from the other. Optics facilitates on-chip neural networks based on fast optical computing and energy-efficient interconnects and communications. On the other hand, AI enables efficient tools to address the challenges of today’s optical communication networks, which behave in an increasingly complex manner. The book collects contributions from pioneering researchers from both academy and industry to discuss the challenges and solutions in each of the respective fields

Towards a General Framework for Practical Quantum Network Protocols

The quantum internet is one of the frontiers of quantum information science. It will revolutionize the way we communicate and do other tasks, and it will allow for tasks that are not possible using the current, classical internet. The backbone of a quantum internet is entanglement distributed globally in order to allow for such novel applications to be performed over long distances. Experimental progress is currently being made to realize quantum networks on a small scale, but much theoretical work is still needed in order to understand how best to distribute entanglement and to guide the realization of large-scale quantum networks, and eventually the quantum internet, especially with the limitations of near-term quantum technologies. This work provides an initial step towards this goal. The main contribution of this thesis is a mathematical framework for entanglement distribution protocols in a quantum network, which allows for discovering optimal protocols using reinforcement learning. We start with a general development of quantum decision processes, which is the theoretical backdrop of reinforcement learning. Then, we define the general task of entanglement distribution in a quantum network, and we present ground- and satellite-based quantum network architectures that incorporate practical aspects of entanglement distribution. We combine the theory of decision processes and the practical quantum network architectures into an overall entanglement distribution protocol. We also define practical figures of merit to evaluate entanglement distribution protocols, which help to guide experimental implementations

Quantum communications between Earth and Space

In this society people are always connected, and everyday they manage a lot of personal data also risking to be eavesdropped. Quantum science is one the most promising field of the next years, from quantum computing to quantum communications and above all quantum cryptography. Quantum cryptography is the first commercial application of quantum physics and moreover it results one of the most reliable solution for security problem. Using Quantum Physic law's it is possible to establish secure communications between two users, guaranteeing unconditionally security in the transmission of data. Unfortunately due to the intrinsic losses inside optical fibers, it is not possible to establish a quantum link over $300$ km until quantum repeater will be achievable. The natural extension of terrestrial quantum links are space communications, where however the problems due to environment, temperature and pressure are totally new for quantum devices. The study investigated the possibility of sending quantum signals through atmosphere, in particular trying to realize quantum communications between Earth and Space. In this perspective we used Laser Ranging corner-cubes mounted into satellites to recreate a space quantum link. It was possible to prove that even with high losses, variable attenuation, and high backgorund a quantum key distribution system works, and an unconditionally secure key, needful for encryption, can be generated. With this experiments we demonstrate that not only free-space quantum key distribution is a ready technology, but also that quantum satellite communications is nowadays possible and realizable. Moreover these results open the way to look towards a global space quantum network, where optical station (OGS) could talk with satellite and vice-versa. This work was supported by the Strategic Project QUANTUMFUTURE of University of Padova, by ESAGNSS program and realized in Luxor laboratories in Padova. The principal tests were made at Telespazio (Matera) using the Matera Laser Ranging Observatory and into Thales Alenia Space (Torino)

Analysing and reducing the limitations of continuous-variable quantum cryptography and quantum networks

Due to a recent influx of attention, the field of quantum information is rapidly progressing towards the point at which quantum technologies move from the laboratory to widespread community use. However, several difficulties must be overcome before this milestone can be achieved. Two such difficulties are addressed in this thesis. The first is the ever-growing security threat posed by quantum computers to existing cryptographic protocols and the second is the missing knowledge regarding the performance differences between quantum and classical communications over various existing network topologies. Continuous-variable (CV) quantum key distribution (QKD) poses a practical solution to the security risks implied by the advancement of quantum information theory, with the promise of provably secure communications. Unfortunately, the maximum range of many CV-QKD protocols is limited. Here, this limitation is addressed by the application of post-selection, firstly, to a scenario in which two parties communicate using terahertz frequency radiation in the atmosphere, and secondly, to measurement-device-independent QKD, in which two parties communicate through the medium of an untrusted relay. In both cases, the introduction of post-selection enables security over distances substantially exceeding those of equivalent existing protocols. The second difficulty is addressed by a comparison of the quantum and classical networking regimes of the butterfly network and a group of networks constructed with butterfly blocks. By computing the achievable classical rates and upper bounds for quantum communication, the performance difference between the two regimes is quantified, and a range of conditions is established under which classical networking outperforms its quantum counterpart. This allows for guidance to be provided on which network structures should be avoided when constructing a quantum internet