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.
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.
The subject of this work is cross-disciplinary and involves interaction between electromagnetic theory, quantum physics, digital communications, and security studies. It has been written with emphasis on addressing the widest possible audience so we included extensive literature for references and the main ideas were explained from first principles whenever possible. The main message of the paper 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.
The subject of this work is cross-disciplinary and involves interaction between electromagnetic theory, quantum physics, digital communications, and security studies. It has been written with emphasis on addressing the widest possible audience so we included extensive literature for references and the main ideas were explained from first principles whenever possible. The main message of the paper 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.
Born about a century ago, Quantum Mechanics has revolutionized the description and the interpretation of Physics at sub-microscopic level. In the last decades, due to the influence of mathematical and engineering research fields, Quantum Mechanics has given birth to related research areas like Quantum Computation, Quantum Information and Quantum Communication. With the discovery of the laser, and later the development of fiber optics and satellite networks, Quantum Communication and Quantum Optics seems to have a natural field of application in Communication Systems. Despite this, the interest in this technology and studies for communication purpose has been overshadowed by the great results in communication networks achieved in the last decades with classical paradigms. However, due to the increasing demand of communication data rate, system designers are now looking at Quantum Mechanics for new and more performanting solutions in communication purposes. Early theoretical studies on Quantum Discrimination Theory and Quantum Information predict better performance for Communication Systems that take advantage of the quantum laws. In addition, Quantum Mechanics provides the deepest description of the physical phenomena, and there are scenarios where a quantum model fits best, as in in deep space communications, where the received signal is really weak, or in a satellite networks, where we are interested in strongly reducing the power of transmitted signals, possibly without sacrificing performance significantly. However, if on one side Quantum Communication Theory promises great gains in the performance of communication systems, on the other hand it fails to describe how to implement physical devices that reach these ultimate limits. So far, only a few architectures achieving these performances are known, and only for simple modulation formats. We are interested in the scenario of optical communications, where the message transmitted is encoded in a sequence of coherent states. Transmitter devices for coherent modulation are well known and consist in laser pulse generators. Instead, receiver implementations working at the quantum limit performance limit are yet to be found. In this Thesis I deal with different topics in the quantum transmission scenario. First, I review existing classical (suboptimal) and quantum (suboptimal and optimal) receiver schemes for the binary coherent modulation. I present a new formulation of the optimal scheme known as Dolinar Receiver with the multiple copies problem, focusing on the information gained during the measurement. Second, I analyze the binary communication in a noisy environment, studying the error probability and the capacity of the binary channel induced. Given the description of the quantum channel, I optimize both the transmitted quantum states and the measurement operators employed in the communication. Third, I consider the Pulse Position Modulation, that is particularly suitable for space and satellite communication due to its simplicity of implementation and high capacity. I review some known suboptimal receivers, and I propose a receiver scheme which approaches the limit performance predicted with quantum theory outperforming the existing schemes. To sum up the results of this Thesis, in order to approach the limit performance predicted by Quantum Mechanics, an optimization is always necessary to exceed the classical effects and trigger the quantum phenomena. In particular, the information gained during the measurement plays an important role, for example in the definition of adaptive receivers. In this Thesis both these aspects have been deeply investigated.
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.
Quantum communication offers long-term security especially, but not only, relevant to government and industrial users. It is worth noting that, for the first time in the history of cryptographic encoding, we are currently in the situation that secure communication can be based on the fundamental laws of physics (information theoretical security) rather than on algorithmic security relying on the complexity of algorithms, which is periodically endangered as standard computer technology advances. On a fundamental level, the security of quantum key distribution (QKD) relies on the non-orthogonality of the quantum states used. So even coherent states are well suited for this task, the quantum states that largely describe the light generated by laser systems. Depending on whether one uses detectors resolving single or multiple photon states or detectors measuring the field quadratures, one speaks of, respectively, a discrete- or a continuous-variable description. Continuous-variable QKD with coherent states uses a technology that is very similar to the one employed in classical coherent communication systems, the backbone of today's Internet connections. Here, we review recent developments in this field in two connected regimes: (i) improving QKD equipment by implementing front-end telecom devices and (ii) research into satellite QKD for bridging long distances by building upon existing optical satellite links.This article is part of the themed issue 'Quantum technology for the 21st century'.
This paper proposes a novel communication protocol leveraging the principles of quantum coherence decay for enhanced security. The core idea is to utilize the inherent fragility of quantum coherence – the tendency of a quantum system to lose its superposition and entanglement – to both protect and encrypt quantum information during transmission. The protocol utilizes a specific measurement strategy designed to exploit the decay of coherence, introducing a level of uncertainty that significantly increases the difficulty for eavesdroppers to intercept and reconstruct the transmitted information. Mathematical formalism is presented to describe the key aspects of the protocol, including the encoding scheme based on coherent state manipulation and the measurement process designed to detect and mitigate decoherence. The proposed approach represents a significant advancement in quantum communication security by directly addressing the fundamental vulnerability of quantum states to environmental noise. The protocol's effectiveness is demonstrated through theoretical analysis, highlighting the potential for creating secure quantum communication channels.