Free-space optical communication channels offer secure links with low probability of interception and detection. Despite their point-to-point topology, additional security features may be required in privacy-critical applications. Encryption can be achieved at the physical layer by using quantized values of photons, which makes exploitation of such quantum communication links extremely difficult. One example of such technology is keyed communication in quantum noise, a novel quantum modulation protocol that offers ultra-secure communication with competitive performance characteristics. Its utilization relies on specific coherent measurements to decrypt the signal. The process of measurements is complicated by the inherent and irreducible quantum noise of coherent states. This problem is different from traditional laser communication with coherent detection; therefore continuous efforts are being made to improve the measurement techniques. Quantum-based encryption systems that use the phase of the signal as the information carrier impose aggressive requirements on the accuracy of the measurements when an unauthorized party attempts intercepting the data stream. Therefore, analysis of the secrecy of the data becomes extremely important. In this paper, we present the results of a study that had a goal of assessment of potential vulnerability of the running key. Basic results of the laboratory measurements are combined with simulation studies and statistical analysis that can be used for both conceptual improvement of the encryption approach and for quantitative comparison of secrecy of different quantum communication protocols.
Free-space optical communication channels offer secure links with low probability of interception and detection. Despite their point-to-point topology, additional security features may be required in privacy-critical applications. Encryption can be achieved at the physical layer by using quantized values of photons, which makes exploitation of such quantum communication links extremely difficult. One example of such technology is keyed communication in quantum noise, a novel quantum modulation protocol that offers ultra-secure communication with competitive performance characteristics. Its utilization relies on specific coherent measurements to decrypt the signal. The process of measurements is complicated by the inherent and irreducible quantum noise of coherent states. This problem is different from traditional laser communication with coherent detection; therefore continuous efforts are being made to improve the measurement techniques. Quantum-based encryption systems that use the phase of the signal as the information carrier impose aggressive requirements on the accuracy of the measurements when an unauthorized party attempts intercepting the data stream. Therefore, analysis of the secrecy of the data becomes extremely important. In this paper, we present the results of a study that had a goal of assessment of potential vulnerability of the running key. Basic results of the laboratory measurements are combined with simulation studies and statistical analysis that can be used for both conceptual improvement of the encryption approach and for quantitative comparison of secrecy of different quantum communication protocols.
Optical fibre networks are advancing rapidly to meet growing traffic demands. Security issues, including attack management, have become increasingly important for optical communication networks owing to the vulnerabilities associated with tapping light from optical fibre link. Physical layer security often requires restricting access to the channel and periodic inspection of the link performance. In this thesis, we report how quantum communication techniques can be utilized to detect a physical layer attack. We present an efficient method for monitoring the physical layer security of a high data rate classical optical communication network using a modulated continuous variable quantum signal. We describe the theoretical and experimental underpinnings of this monitoring system, and the monitoring accuracy for different monitored parameters. We analyze its performance in both unamplified and amplified optical links. The technique represents a novel approach in applying quantum signal processing to practical optical communication networks and compares well with classical monitoring methods. We also discuss the challenges in its practical application, its difference with existing quantum key distribution, and its usage in future secure optical transport network planning.
Optical fibre networks are advancing rapidly to meet growing traffic demands. Security issues, including attack management, have become increasingly important for optical communication networks because of the vulnerabilities associated with tapping light from optical fibre links. Physical layer security often requires restricting access to channels and periodic inspections of link performance. In this paper, we report how quantum communication techniques can be utilized to detect a physical layer attack. We present an efficient method for monitoring the physical layer security of a high-data-rate classical optical communication network using a modulated continuous-variable quantum signal. We describe the theoretical and experimental underpinnings of this monitoring system and the monitoring accuracy for different monitored parameters. We analyse its performance for both unamplified and amplified optical links. The technique represents a novel approach for applying quantum signal processing to practical optical communication networks and compares well with classical monitoring methods. We conclude by discussing the challenges facing its practical application, its differences with respect to existing quantum key distribution methods, and its usage in future secure optical transport network planning.
We develop a general mathematical formalism and computational method suitable for analyzing the performance of quantum communication systems utilizing coherent radiation states (Schrodinger states). The key motivation is to demonstrate how the analysis and design of quantum communication systems may benefit from the integration of the physical structure (here, the optical quantum coherent state) with the quantum signal processing aspects (here, quantum estimation and prediction theory). As an application, we show how the quantum-electromagnetic signature of optical radiation emitted by quantum antennas, the Schrodinger's coherent state structure, may be exploited to jointly design the transmitter and receiver of a K-ary digital communication link. We present a concrete example comprised of a quantum quadrature-amplitude modulation (QAM) system (with ), including a complete description of the required general design principles developed from quantum mechanics and the quantum antenna's radiated coherent state structure. The simulation results illustrate improvement in spectral efficiency due to the use of over smaller values of K. We also compare the quantum antenna-based link performance with classical QAM utilizing classical antenna-based communication systems and report superiority of the quantum link over the classical version. To provide for security protection, our system is equipped with a quantum encryption protocol for quantum key distribution, and a demonstration of the complete quantum QAM system with encryption is presented. The main message of the article is the fruitfulness of incorporating a multidisciplinary approach to our thinking about electromagnetic wireless systems through the joint deployment of electromagnetic, quantum, and communication theories in the design and development process of current and future advanced technologies.
Free-space optical communication channels offer unsurpassed advantages over traditional radio frequency systems. They can be implemented in a point-to-point topology and, if necessary, augmented with additional security features for privacy-critical applications. The adoption of quantum mechanical principles in optical communication networks became a foundation for quantum communication protocols that offer added security without the mathematical complexity of traditional cryptography. Encryption can be achieved at the physical layer by using quantized values of photons, which makes exploitation of such communication links extremely difficult. Additional challenges are encountered when the focus is shifted from point-to-point links to multi-access communication systems arranged in a hub-and-spokes topology. To facilitate connectivity, the “hub” can use a single aperture to establish connection to a target platform within its fieldof- view. Polarization entanglement is proposed for data encoding, and additional degrees of freedom can be achieved for each quantum state by using hyper-entanglement. For example, if carrier waves arriving at the same time from multiple transmitters (spokes) are assigned specific frequencies in the 200 GHz ITU grid, their messages can be processed simultaneously by a receiver (hub) that uses a hyperspectral quantum optical circuit. In this paper, we present analysis of the components in the optical trains and propagation of hyper-entangled states in the quantum circuits. The results obtained in this project can be used as the first step before physical implementation of the quantum communication systems.
The last two decades have witnessed an exciting advanced research field that stems from non-classical atomic theory, the quantum mechanics. This research promises an interesting applicability in computation, known as quantum computation, and also in secure data communications, known as quantum cryptography. Quantum cryptography capitalizes on the inherent random polarization state of single photons, which are associated with binary logic values. Because the polarization state of a photon is not reproducible by an eavesdropper between the source and the destination, polarized photons are used with an intelligent algorithm to disseminate the cryptographic key with high security from the source to the destination, a process known as quantum key distribution. However, although the polarization state of a photon remains intact in free-space propagation, it does not remain so in dielectric medium and thus quantum cryptography is not problem-free. In this paper we review quantum cryptography and we identify the various steps in the quantum key identification process. We then analyze and discuss issues related to quantum key distribution that rise in pragmatic fiber-optic transmission and in communication network topologies. In addition, we identify a major weakness of the method that is prone to attacking and which incapacitates quantum cryptography in fiber communications.
Secure free-space data links can be established using conventional laser communication technology or, if necessary, they can be further enhanced with quantum encryption. Security features of these systems are based on the protocols that make use of the inherent properties of laser light. In this case, encryption does not rely on complex mathematical algorithms that add overhead to the communication stream, but instead it is based on physical-layer processes in the laser sources and other modulating components. One promising approach is based on polarization entanglement between correlated photon pairs to achieve data encryption in quantum communication systems. The foundation of security lies in the response of photons to polarization measurements. Additional degrees of freedom can be added to each “singleparticle” state by using hyper-entanglement. The situation can be visualized when several carrier waves are assigned specific frequencies in the 100 GHz International Telecommunication Union (ITU) grid. The two technologies that can be eventually integrated to achieve this task include hyperspectral quantum circuits and the entangled pair source and detection systems. This results in frequency/polarization hyper-entanglement, which can be processed with additional wavelength-division multiplexing (WDM) components to achieve efficient separation of the signals. It is important to understand that most of the previous work is theoretical and assumes ideal properties of all optical parts. In reality, many non-ideal features of the quantum circuits and their components can change the way the quantum states are processed, and this constitutes the main focus of our paper.