Secure quantum communication technologies and systems: From labs to markets

We provide a broad overview of current quantum communication by analyzing the recent discoveries on the topic and by identifying the potential bottlenecks requiring further investigation. The analysis follows an industrial perspective, first identifying the state or the art in terms of protocols, systems, and devices for quantum communication. Next, we classify the applicative fields where short- and medium-term impact is expected by emphasizing the potential and challenges of different approaches. The direction and the methodology with which the scientific community is proceeding are discussed. Finally, with reference to the European guidelines within the Quantum Flagship initiative, we suggest a roadmap to match the effort community-wise, with the objective of maximizing the impact that quantum communication may have on our society

Data security in photonic information systems using quantum based approaches

The last two decades has seen a revolution in how information is stored and transmitted across the world. In this digital age, it is vital for banking systems, governments and businesses that this information can be transmitted to authorised receivers quickly and efficiently. Current classical cryptosystems rely on the computational difficulty of calculating certain mathematical functions but with the advent of quantum computers, implementing efficient quantum algorithms, these systems could be rendered insecure overnight. Quantum mechanics thankfully also provides the solution, in which information is transmitted on single-photons called qubits and any attempt by an adversary to gain information on these qubits is limited by the laws of quantum mechanics. This thesis looks at three distinct different quantum information experiments. Two of the systems describe the implementation of distributing quantum keys, in which the presence of an eavesdropper introduces unavoidable errors by the laws of quantum mechanics. The first scheme used a quantum dot in a micropillar cavity as a singlephoton source. A polarisation encoding scheme was used for implementing the BB84, quantum cryptographic protocol, which operated at a wavelength of 905 nm and a clock frequency of 40 MHz. A second system implemented phase encoding using asymmetric unbalanced Mach-Zehnder interferometers, with a weak coherent source, operating at a wavelength of 850 nm and pulsed at a clock rate of 1 GHz. The system used depolarised light propagating in the fibre quantum channel. This helps to eliminate the random evolution of the state of polarisation of photons, as a result of stress induced changes in the intrinsic birefringence of the fibre. The system operated completely autonomously, using custom software to compensate for path length fluctuations in the arms of the interferometer and used a variety of different single-photon detector technologies. The final quantum information scheme looked at quantum digital signatures, which allows a sender, Alice, to distribute quantum signatures to two parties, Bob and Charlie, such that they are able to authenticate that the message originated from Alice and that the message was not altered in transmission

Urban geography of digital networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2003.Includes bibliographical references.This dissertation examines the development of digital network infrastructure in the world's great cities at the turn of the 20th century. Drawing upon the concept of cities as information systems and techniques of communications geography, it analyzes how the physical components of digital networks were deployed in major urban areas during the 1990s. It finds that historical processes and pre-existing differences between places shaped the evolution of this infrastructure at multiple spatial scales; global, metropolitan, and neighborhood. As a result, rather than bringing about the "death of distance", digital network infrastructure actually reinforced many of the pre-existing differences between connected and disconnected places. With the telecom bust of 2000-2002, these differences were likely to persist for a decade or more. Yet just as the development of wired digital network infrastructure slowed, wireless technologies emerged as a more flexible, intuitive, and efficient form of connecting users to networks in everyday urban settings. As a result, an untethered model for digital networks emerged which combining the capacity and security of wired networks over long distances with the flexibility and mobility of wireless networks over short distances. This new hybrid infrastructure provided the technology needed to begin widespread experimentation with the creation of digitally mediated spaces, such as New York City's Bryant Park Wireless Network.by Anthony M. Townsend.Ph.D