Quantum communication entails transmission of quantum information over a classical or quantum channel, in free space or in optical fiber. This talk will focus on development of resources for efficiently implementing quantum optical communications over the standard telecom infrastructure.
Humanity’s social, economic, and technological progress could not have been made without communications infrastructure. The need to attain the sophistication of long-distance communication has grown steadily since the dawn of civilization. The modern global communications system is the single greatest infrastructural project in human history. The global telecommunications grid which uses satellites, deep-sea fiber-optic systems, Wi-Fi, Bluetooth, microwave and other radio, and optical-frequency communications networks are tremendous in coverage, unparalleled in connection, and ubiquitous in application. As we approach the middle of the 21st century, this system’s next major update will incorporate quantum communications technology. Quantum communication, in tandem with quantum computing and quantum sensing, constitutes one of the three pillars of second-generation quantum technology and promises an array of novel applications. Considering the reliable transmission of quantum information often requires the transport of individual particles of light photons through a world inundated by trillions upon trillions of photons, quantum communication systems are an engineering marvel. To provide a technological alternative for existing public-key encryption protocols, which are now susceptible to the threat posed by future quantum computing systems, nascent commercial quantum communication networks aim to realize the potential for cryptographic security provided by the laws of quantum mechanics. However, a number of obstacles must be overcome before quantum communications can be widely adopted. This study focuses on the current state of quantum communication, the promise of its prospects in the near and far future, the obstacles it faces, and the breakthroughs and applications developed by the United Arab Emirates.
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.
Keeping in mind the ubiquitous standard optical fiber for long‐distance transmission and the widespread availability of efficient active and passive fiber devices, we have been developing telecom‐band resources for practical quantum communication and cryptography in wave‐division‐multiplexed (WDM) optical networks. In this talk I present our recent results on two fronts: i) telecom‐band in‐fiber entanglement generation, storage, and long‐distance distribution and ii) quantum‐noise protected high‐speed data encryption through an optically‐amplified WDM line. Along the first front, with our in‐fiber entanglement source all four Bell states can be readily produced and we have demonstrated violation of Bell’s inequalities by up to 10 standard deviations of measurement uncertainty. With such a source we have demonstrated storage of entanglement for up to 1/8 of a millisecond. Furthermore, when each photon of the entangled pair is propagated in separate 25km‐long standard fibers, high visibility quantum interference is still observed, demonstrating that this system is capable of long‐distance (> 50 km) entanglement distribution. Along the second front, we have implemented a new quantum cryptographic scheme, based on Yuen’s KCQ protocol, in which the inherent quantum noise of coherent states of light is used to perform the cryptographic service of data encryption. In this scheme a legitimate receiver, with use of a short, shared, secret‐key, executes a simple binary decision rule on every transmitted bit. An eavesdropper, on the other hand, who does not possess the secret‐key, is subjected to an irreducible quantum uncertainty in each measurement, even with the use of ideal detectors. We have implemented this scheme to demonstrate quantum‐noise‐protected data encryption at 650 Mbps through a 200 km, in‐line amplified, WDM line. The line simultaneously carried two 10 Gbps standard data channels, 100 GHz on either side of the encrypted channel, which shows that this scheme is compatible with the widely deployed WDM fiber‐optic infrastructure.
Free-space quantum key distribution opens up new possibilities for the development of quantum communication systems, facilitating the deployment of quantum networks in physically hard-to-reach areas and across wide landscapes without the use of optical fibers. This approach overcomes restrictions associated with cable laying and provides a more flexible infrastructure for quantum information transmission. Together with the use of continuous-variable protocols, it becomes possible to organize secure information transfer using optimal scalable communication systems despite deleterious environmental influences. This paper reviews key achievements and technical aspects of implementing continuous-variable quantum key distribution in atmospheric channels, considering the main atmospheric effects such as turbulence, scattering, and beam wandering. We present the current state of continuous-variable quantum key distribution systems in free space and their practical implementations, including successful experimental projects and prototypes. Prospects for further development, including integration with existing telecommunications networks and potential application areas, are discussed.