Search

In this article, we introduce a generalization of one-way superdense coding to two-way communication protocols for transmitting classical bits by using entangled quantum pairs. The proposed protocol jointly addresses the provision of entangled pairs and superdense coding, introducing an integrated approach for managing entanglement within the communication protocol. To assess the performance of the proposed protocol, we consider its data rate and resource usage, and we analyze this both in an ideal setting with no decoherence and in a more realistic setting where decoherence must be taken into account. In the ideal case, the proposal offers a 50% increase in both data rate and resource usage efficiency compared to conventional protocols. Even when decoherence is taken into consideration, the quantum protocol performs better as long as the decoherence time is not extremely short. Finally, we present the results of implementing the protocol in a computer simulation based on the NetSquid framework. We compare the simulation results with the theoretical values.

In this article, we propose and experimentally demonstrate a novel synchronization method for quantum key distribution (QKD) systems. The method consists of maximizing the visibility of frequency-domain interference of optical sidebands about an optical carrier at the receiver node. The sidebands are generated by phase modulation of the optical carrier by an radio-frequency (RF) signal whose phase can be dynamically varied. The phase-variable RF signal is generated by the field-programmable gate array (FPGA) at the transmitter and the receiver using GTX transceivers. In order to facilitate this, we use square waveforms for RF signal instead of the conventional sinusoidal signals. We derive mathematical expressions for sideband power as a function of the phase difference between RF signals at transmitter and receiver. The phase is adjusted using dynamic phase shifter module, implemented by the FPGA. We propose a complete workflow that allows transmitter and receiver synchronization to within 12.6 ps directly over the quantum channel of QKD systems. Once synchronized, the same system can be switched over to quantum transmission by user-defined time delay. The workflow was implemented on a Xilinx Kintex-7 KC705 FPGA board. We studied the robustness of our technique by evaluating the stability of the interferometer over an operation of 10 min with standard deviation of interference to be less than 9% of the mean detection amplitude.

Abstract The authors present a novel approach to Quantum Key Distribution (QKD) research, emphasising cost‐effectiveness and practicality using a single photon polarisation‐encoded system employing mainly commercial off‐the‐shelf components. This study diverges from previous high‐cost, high‐end setups by exploring the viability of QKD in more accessible and realistic settings. Our approach focuses on practical measurements of the signal‐to‐noise ratio by analysing polarisation‐encoded photonic qubits over various transmission scenarios. The authors introduce a simplified evaluation method that incorporates experimental measurements, such as noise sources and losses, into a semi‐empirical theoretical framework. This framework simulates the standard DS‐BB84 protocol to estimate Secure Key Rates (SKRs), offering an alternative approach on the evaluation of the practical implementation of QKD. Specifically, the authors examine the feasibility of QKD over a 2.2 km intra‐campus fibre link in coexistence scenarios, identifying optimal Wavelength‐Division Multiplexing allocations to minimise Raman noise, achieving an expected SKR of up to 300 bps. Additionally, the authors’ study extends to 40 m indoor and 100 m outdoor Free‐Space Optical (FSO) links using low‐cost components, where the authors recorded Quantum Bit Error Rate (QBER) values below 3.2%, allowing for possible SKRs up to 600 bps even in daylight operation. The converged fibre/FSO scenario demonstrated robust performance, with QBER values below 3.7% and an expected SKR of over 200 bps. Our research bridges the gap between high‐end and economical QKD solutions, providing valuable insights into the feasibility of QKD in everyday scenarios, especially within metropolitan fibre based and FSO links. By leveraging cost‐effective components and a simplified single photon exchange setup, the authors work paves the way for the effortless characterisation of deployed infrastructure, highlighting its potential in diverse settings and its accessibility for widespread implementation.

Abstract Teleporting energy to remote locations is new challenge for quantum information science and technology. Developing a method for transferring local energy in laboratory systems to remote locations will enable non‐trivial energy flows in quantum networks. From the perspective of quantum information engineering, we propose a method for distributing local energy to a large number of remote nodes using hyperbolic geometry. Hyperbolic networks are suitable for energy allocation in large quantum networks since the number of nodes grows exponentially. To realise long‐range quantum energy teleportation (QET), we propose a hybrid method of quantum state telepotation and QET. By transmitting local quantum information through quantum teleportation and performing conditional operations on that information, QET can theoretically be realized independent of geographical distance. The method we present will provide new insights into new applications of future large‐scale quantum networks and potential applications of quantum physics to information engineering.

Abstract In free‐space implementations of Quantum key distribution (QKD), the wide adoption of near‐Infrared wavelengths has led to the common use of silicon single‐photon avalanche diodes (Si‐SPAD) for receiver systems. While the impacts of some SPAD properties on QKD have been explored extensively, the relationship of spot‐size and spatial position on the full instrumental response and thus quantum bit error rate (QBER) has been studied little. Changes in spot size and spatial position can result from atmospheric turbulence and pointing and tracking errors. Here, An empirical analysis of that relationship is presented utilising a large active area, 500 μm, free‐space coupled Si‐SPAD designed for free‐space QKD. A baseline full‐width at half‐maximum timing jitter of 182 ps and a QBER contribution of 0.1 % for a 1 GHz clock frequency QKD system and 100 ps time‐gating window are reported. The impacts of spot‐size and spatial position can increase the QBER to over 0.3%. The link between the spot‐size and timing jitter will allow the understanding of tolerancing for the alignment of Si‐SPADs within free‐space QKD receiver systems—an important factor in designing properly engineered practical systems and the equipment needed to compensate for atmospheric turbulence and pointing and tracking.

Abstract Quantum key distribution (QKD) is one of the major applications of quantum information technology. It can provide ultra‐secure key distribution with security guaranteed by the laws of quantum physics. Quantum key distribution is necessary to protect data transmission from quantum computing attacks in future communication networks. The laws of quantum mechanics dictate that as opposed to microwave frequencies, quantum coherence is preserved at room temperatures for terahertz (THz) frequencies. This makes the THz band a promising solution for room‐temperature QKD implementation in future wireless communication networks. The authors present the principles of continuous variable QKD (CV‐QKD) systems and review the latest developments in the design and analysis of CV‐QKD systems operating at microwave and THz frequencies. The authors also discuss how multiple‐input multiple‐output transmission can be incorporated into the quantum communications framework to improve the secret key rates and increase the coverage distances of the THz CV‐QKD system. Furthermore, major hardware challenges that must be surmounted to practically realise THz CV‐QKD systems are highlighted.

Abstract The authors present a novel token exchange scheme with an example of an electronic cash (eCash) transaction scheme that ensures quantum security, addressing the vulnerabilities of existing models in the face of quantum computing threats. The authors’ comprehensive analysis of various quantum blind signature mechanisms revealed significant shortcomings in their applicability to eCash transactions and their resilience against quantum adversaries. In response, the authors drew inspiration from D. Chaum's original classical eCash scheme and innovated a quantum‐secure transaction framework. The authors detail the developed protocol and rigorously evaluate its security aspects. The protocol's adherence to critical security requirements such as blindness, non‐forgeability, non‐deniability, and prevention of double spending is analysed. Moreover, the scheme against Intercept and Resend, Denial of Service, Man‐in‐the‐Middle, and Entangle‐and‐Measure attacks is rigorously tested. The authors’ findings indicate a robust eCash transaction model capable of withstanding the challenges posed by quantum computing advancements.

Abstract The integration of lattice‐based cryptography principles with Quantum Key Distribution (QKD) protocols is explored to enhance security in the context of Internet of Things (IoT) ecosystems. With the advent of quantum computing, traditional cryptographic methods are increasingly susceptible to attacks, necessitating the development of quantum‐resistant approaches. By leveraging the inherent resilience of lattice‐based cryptography, a synergistic fusion with QKD is proposed to establish secure and robust communication channels among IoT devices. Through comprehensive Qiskit simulations and theoretical analysis, the feasibility, security guarantees, and performance implications of this novel hybrid approach are thoroughly investigated. The findings not only demonstrate the efficacy of lattice‐based QKD in mitigating quantum threats, but also highlight its potential to fortify IoT communications against emerging security challenges. Moreover, the authors provide valuable insights into the practical implementation considerations and scalability aspects of this fusion approach. This research contributes to advancing the understanding of quantum‐resistant cryptography for IoT applications and paves the way for further exploration and development in this critical domain.

Abstract Quantum Key Distribution (QKD) is increasingly pivotal in securing communication channels against the looming threats posed by quantum computing. However, existing QKD protocols encounter challenges related to efficiency and transmission capabilities. In response, this research investigates the integration of metamaterials into QKD systems, aiming to fortify security and enhance practicality. In the current landscape of quantum communication, where the vulnerability of classical encryption methods is magnified by rapid advancements in quantum computing, finding innovative solutions is imperative. This study is motivated by the need to strengthen the security and viability of QKD protocols to meet the demands of evolving cryptographic threats. By integrating metamaterials, the authors optimise quantum state control, improve signal‐to‐noise ratio (SNR), and enable longer transmission distances. Through mathematical modelling and simulations, the authors demonstrate how metamaterials reduce errors and enhance the robustness of QKD systems. Our findings show significant improvements in transmission efficiency and security, making Metamaterial‐Based Quantum Key Distribution (MQKD) a promising approach for future quantum communication networks. The study not only advances the understanding of the theoretical foundations, but also presents simulated results illustrating the practical effectiveness of MQKD. The exploration of these innovative techniques contributes to the ongoing efforts to secure quantum communication channels.

Abstract The reconciliation method for continuous variable quantum key distribution systems is usually chosen based on its reconciliation efficiency. Nonetheless, one must also consider the requirements of each reconciliation method in terms of the amount of information transmitted on the classical channel. Such may limit the achievable key rates. For instance, multidimensional reconciliation of dimension 8 demands a classical channel bandwidth 43 times greater than that of the quantum channel baud rate. Decreasing the dimension to 4 halves the required bandwidth, allowing for higher quantum channel baud rates and higher key rates for shorter transmission distances, despite the lesser reconciliation performance.

Abstract Integration of Quantum Key Distribution (QKD) in existing telecommunication infrastructure is crucial for the widespread adoption of this quantum technology that offers the distillation of unconditionally secure keys between users. The authors report a field trial between the Points of Presence placed in Treviso and in Venezia—Mestre, Italy, exploiting the QuKy commercial polarisation‐based QKD platforms developed by ThinkQuantum S.r.l. and two different standards of single‐mode optical fibres, that is, G.652 and G.655 as a quantum channel. In this field trial, several configurations were tested, including the co‐existence of classical and quantum signals over the same fibre, providing a direct comparison between the performances of the G.652 and G.655 fibre standards for QKD applications.

Abstract Quantum machine learning (QML) can be employed in solving complicated machine learning tasks although the performance in examining the regression processes is only barely understood. Knowledge gaps are intended to be closed by studying modelling performance of QML in regression tasks, with emphasis being dedicated to scaling up and ability to resist noise. The regression part offers the following functions that include straight line and complex operations. Furthermore, the authors employ quantum neural networks generated using Qiskit to perform experiments. The results demonstrate that QML has a remarkable level of accuracy in basic regressions, reaching a maximum of 97%. Nevertheless, there are difficulties in representing intricate functions, such as 5 × cos(x), which results in a noticeable decline in performance. The work deals with the influence of noise and IERs from imperfect hardware on the efficiency of QML algorithms providing insight into the core obstacles. The result of a detailed examination of the results that have tested the powers and limits of QML in the development of regression applications is represented. The future direction of research and development will be defined by the results obtained in it.

Abstract Entanglement‐assisted quantum key distribution (QKD) has attracted significant attention for its ability to provide highly secure wireless systems. This work explores the employment of quantum teleportation and the quantum Fourier transform (QFT) in entanglement‐assisted QKD to enhance security. By integrating the concepts of entanglement, teleportation, and QFT, the key distribution strategy is significantly improved, leading to more secure communication. The system has been thoroughly tested for quantum bit error rate, secure key rate, and reconciliation efficiency. The results show that this technique outperforms the standard BB84 protocol. Based on their simulations, this protocol appears to be a promising technique for providing quantum‐level security to next‐generation wireless communication systems.

Abstract Designing optimal measurement operators for quantum state discrimination (QSD) is an important problem in quantum communications and cryptography applications. Prior works have demonstrated that optimal quantum measurement operators can be obtained by solving a convex semidefinite program (SDP). However, solving the SDP can represent a high computational burden for many real‐time quantum communication systems. To address this issue, a majorisation‐minimisation (MM)‐based algorithm, called Quantum Majorisation‐Minimisation (QMM) is proposed for solving the QSD problem. In QMM, the authors reparametrise the original objective, then tightly upper‐bound it at any given iterate, and obtain the next iterate as a closed‐form solution to the upper‐bound minimisation problem. Our numerical simulations demonstrate that the proposed QMM algorithm significantly outperforms the state‐of‐the‐art SDP algorithm in terms of speed, while maintaining comparable performance for solving QSD problems in quantum communication applications.

Abstract As a special voting method, one‐vote veto voting also has a wide range of applications. A veto means that when the voting council puts forward a proposal, it cannot pass unless all the voters agree to it. If there is a no vote, the proposal will be rejected, but no one will know how anyone else votes. In most existing quantum anonymous one‐vote veto voting protocols, an absolutely honest third party is generally required to assist the voting. However, it is difficult to find a fully trusted third party in reality. In addition, the existing quantum anonymous one‐vote veto protocol does not consider the attack from the insider voters. Therefore, based on the characteristics of entanglement swapping between the Cat state and Bell state, the authors propose a new quantum anonymous one‐vote veto protocol, which can not only calculate the voting result quickly and effectively but also demonstrate higher security.

Access to information can destroy nations and change the course of history altogether. Communication is very important, and in today's internet age, nothing moves without real-time information support. For securing communication, a commonly know technique is to use cryptography and public channels. Engineers have been working to create a better and more secure cryptographic system. Quantum key distribution stands at the top of this security system. Although QKD, based on principles of physics, provides a near-perfect security solution. It has a few drawbacks of its own, like low key generation rates and vulnerability to cyberattacks. Owning to these limitations, authors propose an adaptive quantum key distribution system based on software-defined networks. The authors propose to introduce redundancy in the key generation, thereby increasing the key generation rate and improving the resilience to cyberattacks. A performance comparison of novel quantum key distribution was done with BB84 and B92 quantum key distribution protocols.

Abstract Artificial intelligence (AI) and classical machine learning (ML) techniques have revolutionised numerous fields, including quantum communication. Quantum communication technologies rely heavily on quantum resources, which can be challenging to produce, control, and maintain effectively to ensure optimum performance. ML has recently been applied to quantum communication and networks to mitigate noise‐induced errors and analyse quantum protocols. The authors systematically review state‐of‐the‐art ML applications to advance theoretical and experimental central quantum communication protocols, specifically quantum key distribution, quantum teleportation, quantum secret sharing, and quantum networks. Specifically, the authors survey the progress on how ML and, more broadly, AI techniques have been applied to optimise various components of a quantum communication system. This has resulted in ultra‐secure quantum communication protocols with optimised key generation rates as well as efficient and robust quantum networks. Integrating AI and ML techniques opens intriguing prospects for securing and facilitating efficient and reliable large‐scale communication between multiple parties. Most significantly, large‐scale communication networks have the potential to gradually develop the maturity of a future quantum internet.

Abstract Quantum key distribution (QKD) provides a method of ensuring security using the laws of physics, avoiding the risks inherent in cryptosystems protected by computational complexity. Here, the authors investigate the feasibility of satellite‐based quantum key exchange using low‐cost compact nano‐satellites. The first prototype of system level quantum key distribution aimed at the Cube satellite scenario is demonstrated. It consists of a transmitter payload, a ground receiver and simulated free space channel to verify the timing and synchronisation (T&S) scheme designed for QKD and the required high loss tolerance of both QKD and T&S channels. The transmitter is designed to be deployed on various up‐coming nano‐satellite missions in the UK and internationally. The effects of channel loss, background noise, gate width and mean photon number on the secure key rate (SKR) and quantum bit error rate (QBER) are discussed. The authors also analyse the source of QBER and establish the relationship between effective signal noise ratio (ESNR) and noise level, signal strength, gating window and other parameters as a reference for SKR optimisation. The experiment shows that it can tolerate the 40 dB loss expected in space to ground QKD and with small adjustment decoy states can be achieved. The discussion offers valuable insight not only for the design and optimisation of miniature low‐cost satellite‐based QKD systems but also any other short or long range free space QKD on the ground or in the air.

Abstract Quantum key distribution (QKD) offers information‐theoretic security by leveraging the principles of quantum mechanics. This means the security is independent of all future advances in algorithm or computational power. However, due to the non‐availability of single‐photon sources, most traditional QKD protocols are vulnerable to various attacks, such as photon number‐splitting (PNS) attacks. Also, the imperfections in the measuring devices open a loophole for side channels that an eavesdropper may exploit to launch attacks such as large‐pulse attacks. As a result, this compromises the security of transmitted information. To address these challenges, the authors present a QKD protocol that is secure against both large‐pulse attacks and PNS attacks at zero‐error, in which the eavesdropper does not introduce any error, but still, the legitimate users of the system cannot distil a secure key. A notable feature of the proposed protocol is that it promotes greater robustness against both attacks than the Bennett‐Brassard 1984 (BB84) protocol or the Scarani‐Acin‐Ribordy‐Gisin 2004 (SARG04) protocol.

Abstract Quantum technology harnesses the principles of quantum mechanics to accomplish tasks in a different way as compared to the classical technologies. This includes quantum computing, which uses qubits for parallel information processing, greatly enhancing computation speed and entanglement and empowering problem‐solving abilities. Quantum communication provides secure data transmission through quantum cryptography, while quantum sensing offers improved measurement precision, benefiting areas such as cryptography, material science, and pharmaceuticals. Additionally, the implementation and commercialisation of quantum technology involve transitioning theoretical quantum concepts into practical applications and marketable products. To achieve widespread adoption of quantum industry, significant research efforts are crucial among academia, industry, and government.

In the rapidly evolving field of quantum communication, the regulatory framework plays a crucial role in ensuring security, standardization, and international cooperation. This article examines various approaches employed by countries to regulate quantum communication. The purpose of this research is to comprehensively analyze and compare different international approaches to the regulation of quantum communication to identify key features characteristic of the current stage of development and regulation of quantum communication, as well as to develop recommendations for optimizing and improving regulatory governance in this area. The methodological basis of the study consisted of general scientific and special methods. A detailed study of various legal documents, strategies, and standards related to quantum communication was conducted using the following general scientific methods: analysis, synthesis, induction, and system analysis. Among the special legal methods used was the comparative legal method, which made it possible to identify general trends, differences, and unique approaches in the regulation of quantum communication, as well as the formal-legal method for studying legal categories and legislative techniques used in various acts in the studied area. The study systematically examines legislative measures, government policies, and industry standards to determine the relationship between technological innovation and regulatory governance in the field of quantum communication. The research revealed that the regulation of quantum communication is primarily carried out at the level of strategic documents, such as national roadmaps, which contain recommendations and guidelines for regulating quantum communication. It was found that technical standards play a vital role in the development of quantum communication, with this development occurring at both national and international levels. Special groups and centers have been established for the effective implementation, development, and regulation of quantum communication, which allows for the identification of social, legal, political, and ethical issues. The main conclusions include the need to monitor administrative barriers, identify priority sectors for the implementation of quantum communication, and recognize quantum communication as a dual-use technology. It is recommended that an international certification and tracking system be created for quantum communication devices for export and import control purposes.

Quantum technology has the potential to transform computing, communication, and security, and it holds significant implications for national security. This paper examines the development of quantum technology in India and its national security implications for Pakistan. India's significant investment in quantum technology, primarily through the National Quantum Mission (NQM), is expected to establish India as an influential state in the field. This paper aims to fill a critical gap in the existing body of knowledge by answering important questions: how India is planning to develop quantum technology? How this could be a potential national security issues for Pakistan? These concerns include the weakening of conventional security measures and the necessity to strengthen cyber and defense capabilities. This study employs a qualitative methodology, utilizing primary and secondary data. The results emphasize the need for Pakistan to allocate resources towards quantum research, produce quantum-resistant technology, and bolster its intelligence and surveillance infrastructure to maintain strategic stability.

The leading countries across the world have entered the race to develop quantum technologies that will enable them to ensure their continued economic prosperity. Among these technologies, a special place is occupied by quantum communication, which is designed to ensure information security in an era where a quantum computer is capable of compromising a number of cryptography algorithms. In this article, this new digital technology includes quantum key distribution and encryption methods that are cryptographically resistant to a quantum computer. The study does not consider the regulation of the quantum communication sub-technology, the so-called “quantum internet,” due to the technical limitations of the existing equipment. The authors note that their predictions about the cryptographic strength of encryption algorithms are based solely on modern knowledge about the capabilities of quantum computing and do not take into account its hidden potential, for example, in terms of cryptanalysis information systems based on a machine learning model generated by a quantum computer. Currently, the only data protection system that is not subject to quantum threats is the technology of quantum key distribution. In today’s information and digital age, information security systems are an important element of critical infrastructure. Given the importance of these technologies, different states use different methods to regulate this field. This article puts forward and substantiates the hypothesis that the implementation of a combination of regulatory legal acts could have a greater positive impact on the development of quantum communication and ensure an acceptable level of information security in the post-quantum era. The analysis showed that a significant number of states and interstate associations are conducting research in this area, relying only on investment growth. This strategy has prevented any country from achieving the competencies of the People’s Republic of China. The authors also analyzed the methods of legal support used by China, Russia, and other countries in the field of quantum communication, which made it possible to identify a model of legal regulation of quantum communication that stimulates this technology’s development.

Abstract Joint Remote State Preparation provides a useful way to securely transfer the known quantum states to the distant nodes. However, the limitation of resources often leads to the quantum channels constructed by distributed entangled pairs being incompatible with the transmitted states. In order to overcome this problem, a novel Joint Remote State Preparation protocol was proposed for transmitting general multi‐qudit states over quantum networks, providing a promising pathway to utilise the available Einstein‐Podolsky‐Rosen (EPR) channels with different levels. Several scenarios under noisy environments were discussed and some properties of the fidelity when transmitting the multi‐qudit state were demonstrated. It was demonstrated that both the prepared state and the kind of the noises could restrict the number of the participant nodes. Our scheme leverages the existing quantum resources, which addresses the issue of insufficient entanglement resources. This approach is easily adaptable to other quantum network structures, offering a potential solution for constructing a universal quantum network.

Abstract The medical information system is rich in datasets, but no intelligent systems can easily analyse the disease. Recently, ML (Machine Learning)‐based algorithms have acted as a handy diagnostic tool to identify whether a person is affected by thyroid or not. However, they produced classification with low accuracy and led to misclassification. Hence, the proposed system combines quantum computing with ML techniques to enhance computational power and precision. The system employs modified QPSO (Quantum Particle Swarm Optimisation) for feature selection since its searching performance is better than that of conventional PSO for selecting the optimum global position of the particle, thus selecting the relevant feature. Whereas, the QSVM (Quantum Support Vector Machine) is implemented for more accurate classification than classical SVM, as it tends to capture complex patterns in data produced due to high dimensional feature space applied by quantum kernel functions. This combination of modified QPSO and QSVM tends to increase the performance accuracy significantly. The efficiency of the proposed model is measured based on derivative parameters, such as F‐1‐score, recall, precision and accuracy, with corresponding confusion matrix and ROC. Further, the classification is compared with other traditional approaches to predict the accuracy of the proposed model with traditional methods.

Abstract The quantum communication channel is considered to be eavesdropped when the signal Quantum Bit Error Rate (QBER) exceeds a defined theoretical limit and is thus considered a figure of merit parameter for assessing the security of a quantum channel. This work presents a general mathematical model considering device imperfections and various sources of errors for estimating signal QBER in polarisation encoded satellite‐based QKD systems. QBER performance for satellite‐to‐ground downlink scenarios has been investigated for multiple sky brightness conditions (day time and night time operations), two operating wavebands: 800 and 1550 nm as well as for different quantum transmitter and quantum receiver architectures. Further, a novel QBER estimation analysis for inter‐satellite QKD links has also been presented. The estimation results obtained from the developed model have been validated against and found in good agreement with the measured results of the only reported satellite‐to‐ground QKD experiments till date. The presented QBER modelling and analysis will aid in system engineering and efficient design of future satellite‐based QKD systems.

Abstract In QKD‐enabled optical networks (QKD‐enabled ONs), fragmentation is one of the serious issues which can be mitigated through appropriate management of network resources. Thus, efficient allocation of network resources during routing and resource assignment is important to minimise the impact of time slot fragmentation in the quantum signal channel (QSCh) of QKD‐enabled ONs. The authors address the fragmentation problem in the QSCh and propose a new fragmentation‐suppressed routing and resource assignment (FS‐RRA) approach. To evaluate the performance and to analyse the effect of time slot fragmentation in QSCh of QKD‐enabled ONs, the proposed FS‐RRA approach is compared with two existing resource assignment approaches, namely, the first‐fit (FF) and random‐fit (RF) for two different networks. Simulation results show that the proposed approach reduces fragmentation by 2.97% and 6.69% for NSFNET and 1.77% and 5.91% for UBN24 in terms of external fragmentation compared to FF and RF, respectively. Furthermore, the proposed approach reduces blocking by 4.03% and 14.28% for NSFNET and 2.61% and 13.44% for UBN24 and improves resource utilisation up to 3.44% and 5.96% for NSFNET and 3.08% and 7.64% for UBN24 compared to FF and RF, respectively.

In the era of the Fourth Industrial Revolution, quantum technology is entering the scene with the promise of radically changing the technological paradigm. Quantum computing, simulation, quantum communications and the combination of this technology with artificial intelligence are opening up new horizons of innovation that could revolutionize various industries. Along with its enormous potential, this technology brings legal, ethical and social challenges that require detailed analysis and an interdisciplinary approach. The industrial deployment of quantum technology entails dilemmas regarding human rights, cyber security and national security, as well as the risk of exacerbating inequality, technological exclusion and algorithmic discrimination. With regard to artificial intelligence enhanced by quantum computing technology, we can speak of a completely new facet of the problem of the opacity of algorithms, which is determined not only by the cognitive limitations of the human mind, but stems from the indefinability of the world described by the laws of quantum mechanics. In light of the above, the thesis can be advanced that the classical approach to the principle of transparency and the postulates of creating algorithms that will clearly present the path to the final result, which are part of the broad current of creating ethical and explainable artificial intelligence, may prove difficult to realize in relation to Quantum AI. In the era of the Fourth Industrial Revolution, we are therefore faced with the challenge of implementing new instruments for testing, certifying and inspecting algorithms, such as tools for analyzing and visualizing the results of quantum algorithms, which will be suited to the specifics of Quantum AI and ensure the ethical correctness of the systems. This article will identify selected areas of application of quantum technology, and thus the potential benefits and risks of quantum technology, and also analyze the need to develop ethical and legal standards that allow for the sustainable and socially responsible development of these disruptive technologies.

Photochromic materials are of great interest because they enable the fabrication of photo-activated switches. In this study, an experiment is proposed in which two chromene-based photochromic layers were inserted into the arms of a Mach–Zehnder interferometer. The chromene was studied from the perspective of optical absorption to determine the wavelength-dependent complex refractive index. Impinging ultraviolet light on one of the chromene layers induces a transition from the closed to the open form of the chromene, resulting in different phase shifts in the two arms of the interferometer. This results in a change in the probability of detecting a photon by the two detectors after the second mirror of the Mach–Zehnder interferometer. The experiment may be of interest to researchers working in the fields of quantum information and quantum communications.

Significant progress has been achieved in leveraging atomic systems for the effective operation of quantum networks, which are essential for secure and long-distance quantum communication protocols. The key elements of such networks are quantum nodes that can store or generate both single and entangled photon pairs. The primary mechanisms leading to the production of single and entangled photon pairs revolve around established techniques such as parametric down-conversion, four-wave mixing, and stimulated Raman scattering. In contrast to solid-state platforms, atomic platforms offer a more controlled approach to the generation of single and entangled photon pairs, owing to the progress made in atom manipulation techniques such as trapping, cooling, and precise excitation schemes facilitated by the use of lasers. This review article delves into the techniques implemented for generating single and entangled photon pairs in atomic platforms, starting with a detailed discussion of the fundamental concepts associated with single and entangled photons and their characterization techniques. The aim is to evaluate the strengths and limitations of these methodologies and offer insights into potential applications. Additionally, the article will review the extent to which these atomic-based systems have been integrated into operational quantum communication networks.

Abstract Wireless quantum optical communications over multipath channels with uncorrelated scattering still seem to be an open issue, although classical optical transmission was already considered, however, neglecting Bose–Einstein distributed thermal noise photons, leading to results that cannot be applied here. A viable way forward is proposed.

Abstract Long‐distance free space quantum key distribution based on CubeSats can be used to establish global quantum secure communication networks, with potential commercial applications benefitting from the low cost of its design and launch. Detecting single‐photon level optical pulses sent from space requires highly accurate and robust timing systems to pick out signals from the noise. For such high‐loss applications, we envisage a low‐repetition (sub‐MHz) beacon laser emitting short (ns) high‐peak‐power pulses from which interpolated quantum signal arrival windows can be derived. We firstly study theoretically the effects of jitter on the efficiency of gating quantum signals including all important jitter sources, and then experimentally investigated it by changing the clock jitter, and the result shows that the greater jitter will reduce the gating rate of the signal. The experimental interpolation error is tested against loss under laboratory conditions giving results close to our model. We also found that the jitter introduced by the Doppler effect can be ignored with a repetition rate larger than 1 kHz. This model can be directly used for the performance analysis and optimisation of all quantum and non‐quantum systems using similar synchronisation schemes over terrestrial free space or fibre.

Abstract The emergence of quantum technologies has led to groundbreaking advancements in computing, sensing, secure communications, and simulation of advanced materials with practical applications in every industry sector. The rapid advancement of the quantum technologies ecosystem has made it imperative to assess the maturity of these technologies and their imminent acceleration towards commercial viability. The current status of quantum technologies is presented and the need for a quantum‐ready ecosystem is emphasised. Standard Quantum Technology Readiness Levels (QTRLs) are formulated and innovative models and tools are defined to evaluate the readiness of specific quantum technology. In addition to QTRLs, Quantum Commercial Readiness Levels (QCRLs) is introduced to provide a robust framework for evaluating the commercial viability and market readiness of quantum technologies. Furthermore, relevant indicators concerning key stakeholders, including government, industry, and academia are discussed and ethics and protocols implications are described, to deepen the understanding of the readiness for quantum technology and to support the development of a robust and effective quantum ecosystem.

Abstract The evolution of quantum computers is considered a serious threat to public‐key cryptosystems (e.g. RSA, ECDSA, ECDH, etc.). This is indeed a big concern for security of the Internet and other data communication and storage systems. The reason is that public‐key schemes are the basis in the generation of shared symmetric keys that are used to perform data encryption/decryption in communication and data transfer protocols. One possible approach to address this issue is to use Quantum Key Distribution (QKD) (instead of public‐key schemes) for the ultra‐secure generation of symmetric keys. QKD is a physical layer technology that allows two parties (equipped with optical communication interfaces) to generate secure random keys over a quantum channel that is immune to eavesdropping threats. The keys are then used by symmetric encryption schemes (e.g. AES) to encrypt data over classical channels. This allows us to have data encryption/decryption without needing a public‐key scheme. However, due to its inherent characteristics, the implementation of QKD has mostly been considered in particular contexts only (e.g. backhaul networks, point‐to‐point connections, optical networks, etc.). This indeed limits the utility of QKD technology to only some particular applications while it has the potential to be used in a wide range of used cases. Motivated by this (increasing the usability of QKD technology), in this study, the authors propose a model that enables SDN‐based networks to utilise QKD technology and provide QKD security service (i.e., random key generation service) to network applications and security protocols in a practical and efficient way. In the proposed approach, secret keys are generated based on the distribution of quantum entanglement between QKD nodes deployed in the network. The significant characteristic of our proposed model is that it does not rely on quantum repeaters to operate. This also improves the efficiency of the employed QKD mechanisms in terms of the key generation rate.

Abstract The security of data communications is one of the crucial challenges that our society is facing today. Quantum Key Distribution (QKD) is one of the most prominent methods for guaranteeing ultimate security based on the laws of quantum physics. In this work, the results obtained during the Italian Industry 4.0 Quantum Testbed (II4QuTe) project are reported where the authors realised a QKD testbed securely connecting the Competence Industry Manufacturing 4.0 (CIM4.0) located in Torino and a TIM edge node located 10 km away from the testbed. The edge node accommodates the server providing computation capabilities for managing the real‐time data generated by the machines within the CIM4.0 digital factory pilot line, thus gracefully integrating QKD with the MEC (Multi‐access Edge Computing) paradigm. The experiment was conducted for more than 69 h, establishing an average key generation rate of 5.125 keys/s (AES‐256 keys) and demonstrating the stability of the entire end‐to‐end encryption system.

Abstract In recent times, secure quantum communication in layered networks has emerged as an important area of study. The authors harness the potential offered by multidimensional states in secure quantum communication with only one quantum participant and all the other classical participants. Three protocols are proposed for—(i) entanglement‐based layered semi‐quantum key distribution, (ii) layered semi‐quantum secret sharing, and (iii) integrated layered semi‐quantum key distribution and secret sharing to share secret information in arbitrarily layered networks. These protocols integrate the features of semi‐quantum communication in layered networks. All three protocols allow for simultaneous distribution of secure information in all the layers of a network, thanks to the employment of multidimensional states. These protocols are presented for a small network of at most five participants and three layers and show the robustness of the same against various eavesdropping strategies. Finally, a detailed procedure is provided for generalisations of the proposed protocols to distribute keys/secrets in any arbitrarily structured quantum network.

In a variant of communication tasks, players cooperate in choosing their local strategies to compute a given task later, working separately. Utilizing quantum bits for communication and sharing entanglement between parties is a recognized method to enhance performance in these situations. In this work, we introduce the game for which three parties, Alice, Bob and Charlie, would like to discover the hidden order in which they make the moves. We show the advantage of quantum strategies that use shared entanglement and local operations over classical setups for discriminating operations’ composition order. The role of quantum resources improving the probability of successful discrimination is also investigated. Our research provides a basis for examining computational model featuring a specific gate set while examining the diverse operations achievable through permutations of its elements.

Bit-transmission can be enhanced by the use of quantum detection techniques, realizing a joint-detection receiver (JDR) that is able to decode transmitted signals via a collective operation and achieve the Holevo channel capacity. Explicit JDR designs proposed so far employ the Hadamard or Fourier transform to perform a phase-to-intensity translation of the information encoding, effectively falling in the class of on-off-keying (OOK) modulation techniques; they improve over classical decoders but fall short of the Holevo capacity, particularly at large signal mean photon number $n\gtrsim1$ . Here we introduce new families of decoders based on multi-pulse and multi-level codes. We compute the rate of these codes exactly, and provide a comprehensive study of their performance. We show that multi-pulse codes can approach the rate of OOK closely, providing a simplified design for quantum-enhanced communication in the photon-starved regime; furthermore, multi-level codes can approach generalized-OOK strategies with multiple pulse types, thus they can be employed in the larger photon-number regime.

We develop a novel key routing algorithm for quantum key distribution (QKD) networks that utilizes a distribution of keys between remote nodes, i.e., not directly connected by a QKD link, through multiple non-overlapping paths. This approach focuses on the security of a QKD network by minimizing potential vulnerabilities associated with individual trusted nodes. The algorithm ensures a balanced allocation of the workload across the QKD network links, while aiming for the target key generation rate between directly connected and remote nodes. We present the results of testing the algorithm on two QKD network models consisting of 6 and 10 nodes. The testing demonstrates the ability of the algorithm to distribute secure keys among the nodes of the network in an all-to-all manner, ensuring that the information-theoretic security of the keys between remote nodes is maintained even when one of the trusted nodes is compromised. These results highlight the potential of the algorithm to improve the performance of QKD networks.

Quantum computing provides a revolution in computational competences, leveraging the principles of quantum mechanics to process data in fundamentally novel ways. This paper explores the profound implications of quantum computing on cryptography, focusing on the vulnerabilities it introduces to classical encryption methods such as RSA and ECC, and the emergence of quantum-resistant algorithms. We review the core principles of quantum mechanics, including superposition and entanglement, which underpin quantum computing and cryptography. Additionally, we examine quantum encryption algorithms, particularly Quantum Key Distribution (QKD) protocols and post-quantum cryptographic methods, highlighting their potential to secure communications in the quantum era. This analysis emphasizes the urgent need for developing robust quantum-resistant cryptographic solutions to safeguard sensitive information against the imminent threats posed by advancing quantum technologies.

Abstract The introduction of quantum communications, enabled by advancements in quantum computing, is expected to play a significant role in the field of communications. Inherent properties of quantum objects, such as superposition and entanglement, have the potential to provide novel solutions to overcome the challenges encountered by classical communication systems in bandwidth‐intensive applications such as media transmission. This research explores the performance of a quantum communication system in image transmission using quantum superposition and investigates its performance using a simple quantum channel model. With an increase in channel noise, there are significant gains in the rate distortion performance of images transmitted over the quantum channel compared to an ideal classical channel. This novel attempt at constructing a quantum communication‐based image transmission system indicates the potential of the approach to be applied to satisfy the ever‐increasing demands of high‐quality media transmission applications.

In the aftermath of unparalleled disruptive technologies, the quantum realm has become a fundamental field of research due to unrivaled computational power and super-secure communication. In addition to conventional networks, a new word in the quantum domain is quantum network. The quantum network uses quantum communication (QC) to send quantum information bits known as qubits, to predetermined destination nodes. It governs the new quantum mechanics notions like superposition, quantum entanglement, the no-cloning theorem, and quantum teleportation. Quantum communication, like classical communication, is prone to noise, which is known as quantum decoherence. Quantum decoherence is a significant barrier to the implementation of a global quantum network. It deteriorates the quantum information, causing it to lie in an undetermined state. Environmental factors that cause quantum entanglement loss are the key factors that cause qubits to lose their states. To mitigate the impact of quantum decoherence, quantum error correction codes (QECC) and entanglement distillation have proved their potential. They add extra qubits or maintain entanglements among quantum networks. This survey presents quantum mechanics principles, quantum decoherence, and techniques to mitigate the effect of quantum decoherence. At the end, we highlighted some challenges in the realization of the quantum network, along with some projected applications.

Quantum internetworking is a recent field that promises numerous interesting applications, many of which require the distribution of entanglement between arbitrary pairs of users. This article deals with the problem of scheduling in an arbitrary entanglement swapping quantum network—often called first-generation quantum network—in its general topology, multicommodity, loss-aware formulation. We introduce a linear algebraic framework that exploits quantum memory through the creation of intermediate entangled links. The framework is then employed to apply Lyapunov drift minimization (a standard technique in classical network science) to mathematically derive a natural class of scheduling policies for quantum networks minimizing the square norm of the user demand backlog. Moreover, an additional class of Max-Weight-inspired policies is proposed and benchmarked, reducing significantly the computation cost at the price of a slight performance degradation. The policies are compared in terms of information availability, localization, and overall network performance through an ad hoc simulator that admits user-provided network topologies and scheduling policies in order to showcase the potential application of the provided tools to quantum network design.

Quantum information processing leverages the principles of quantum mechanics, utilizing qubits, to improve computational and communicative tasks. In this realm, the quantum channel’s capacity is pivotal in determining the efficiency and accuracy of quantum information handling, with its performance being significantly influenced by channel noise. Our study aims to establish a holistic hybrid quantum noise model to determine the quantum channel capacity. In this paper, we formulated a mathematical expression for this capacity and conducted simulations for both Gaussian and non-Gaussian inputs. A hybrid noise model is constructed by convolution of Poisson-distributed quantum noise with classical additive white Gaussian noise. We characterized the quantum-classical noise and the received signal using Gaussian Mixture Models. The maximum amount of quantum information that can be reliably transmitted over a quantum channel (per use of the channel) is determined by its capacity, and entropy and related quantities like mutual information play a role in calculating this capacity. Our formulation of quantum channel capacity is derived from the mutual information shared between the transmitter and receiver, encompassing the entropies of the signals. The quantum channel presents a higher capacity-to-signal-to-noise ratio for Gaussian inputs than non-Gaussian ones.

Quantum technologies are increasingly recognized as groundbreaking advancements set to redefine the landscape of computing, communications, and sensing by leveraging quantum phenomena, like entanglement and teleportation. Quantum technologies offer an interesting set of advantages such as unconditional security, large communications capacity, unparalleled computational speed, and ultra-precise sensing capabilities. However, their global deployment faces challenges related to communication ranges and geographical boundaries. Non-terrestrial networks (NTNs) have emerged as a potential remedy for these challenges through providing free-space quantum links to circumvent the exponential losses inherent in fiber optics. Through the utilization of free-space optical (FSO) and Li-Fi links, NTNs provide an effective method for transmitting quantum states over extensive distances. This paper delves into the dynamic interplay between quantum technologies and NTNs to unveil their synergistic potential. We also investigate their integration challenges and the potential solutions to foster a symbiotic convergence of quantum and NTN functionalities while identifying avenues for enhanced interoperability. Specifically, quantum communication over NTNs imposes challenges in communication channel reliability, network flexibility, and scalability. To enhance channel reliability, multicarrier transmission techniques and spatial diversity strategies, including quantum MIMO (q-MIMO) transmission schemes, can be employed. Introducing the software defined networking (SDN) model facilitates flexible network configurations. In NTN-based quantum infrastructure, technologies like trusted relays, measurement device independent (MDI), and quantum repeaters can address scalability concerns efficiently. This paper not only offers useful insights into the mutual advantages but also presents future research directions, aiming to inspire additional studies and advance this interdisciplinary collaboration.

The reliable provision of entangled qubits is an essential precondition in a variety of schemes for distributed quantum computing. This is challenged by multiple nuisances, such as errors during the transmission over quantum links, but also due to degradation of the entanglement over time due to decoherence. The latter can be seen as a constraint on the latency of the quantum protocol, which brings the problem of quantum protocol design into the context of latency–reliability constraints. We address the problem through hybrid schemes that combine: indirect transmission based on teleportation and distillation, and direct transmission, based on quantum error correction (QEC). The intuition is that, at present, the quantum hardware offers low fidelity, which demands distillation; on the other hand, low latency can be obtained by QEC techniques. It is shown that, in the proposed framework, the distillation protocol gives rise to asymmetries that can be exploited by asymmetric quantum error correcting code, which sets the basis for unique hybrid distillation and coding design. Our results show that ad hoc asymmetric codes give, compared with conventional QEC, a performance boost and codeword size reduction both in a single-link and in a quantum network scenario.

Vehicular quantum communication terminals (VQCTs) are crucial for establishing global-scale quantum networks. High-precision line-of-sight (LOS) pointing is essential for fast and reliable acquisition in satellite-based quantum key distribution (QKD). The pointing accuracy of VQCTs is affected by attitude measurement errors, mechanical structure errors, and structural instability errors resulting from platform movement. By mounting attitude sensors on the LOS of VQCTs, we directly measure the LOS attitude. This completely eliminates the impact of mechanical structure errors and structural instability errors on pointing accuracy. Furthermore, we propose a line-of-pointing calibration method and a pointing model for VQCTs based on LOS attitude measurement. The pointing accuracy of this model is primarily reliant on the accuracy of attitude sensors. Two experiments were conducted to validate the effectiveness of our model. One is the star pointing experiment, comparing with the existing pointing model for VQCTs, our model significantly reduces the pointing errors by 93%, from 1296″ to 87.8″. This substantiates that our model eliminates mechanical structure errors and structural instability errors. Another is the successful acquisition of a quantum communication satellite, which demonstrates the feasibility of the proposed model for implementing the satellite-to-motion platform QKD and global-scale quantum networks.

Abstract The quantum internet is a cutting‐edge paradigm that uses the unique characteristics of quantum technology to radically alter communication networks. This new network type is expected to collaborate with 6G networks, creating a synergy that will fundamentally alter how we communicate, engage, and trade information. The improved security, increased speed, and increased network capacity of the quantum internet will lead to the emergence of a broad variety of new applications and services. The current state of quantum technology and its integration with 6G networks are summarised in this study, with an emphasis on the key challenges and untapped possibilities. The main goal is to get knowledge about how the quantum internet might impact communication in the future and alter several economic and societal sectors.

Abstract In this article, a protocol for information lossless teleportation using W states is proposed. Firstly, the information lossless teleportation of an unknown state with a maximally entangled W‐state channel, which protects the original unknown state information even in case of teleportation failure is investigated. Next, we generalise our scheme to non‐maximally entangled W‐state channels. Finally, the principle of the proposed scheme is validated by performing experiments on the quantum circuit simulator Quirk. Our study shows that W states can be used to teleport any quantum state without information loss through single‐qubit measurements and local unitary operations.

Abstract The authors devised a protocol that allows two parties, who may malfunction or intentionally convey incorrect information in communication through a quantum channel, to verify each other's measurements and agree on each other's results. This has particular relevance in a modified version of the quantum coin flipping game. The key innovation of the authors’ work includes the new design of a quantum coin that excludes any advantage of cheating, by which the long‐standing problem of the fair design of the game is, affirmatively, solved. Furthermore, the analysis is extended to N‐parties communicating with each other, where multiple solutions for the verification of each player's measurement is proposed. The results in the N‐party scenario could have particular relevance for the implementation of future quantum networks, where verification of quantum information is a necessity.