Quantum Key Distribution Research Articles

Designing optimal Quantum Key Distribution Networks based on Time-Division Multiplexing of QKD transceivers: qTDM-QKDN

Time-sharing of Quantum Key Distribution (QKD) transceivers with the help of optical switches and a central Software-Defined Networking (SDN) controller is a promising technique to better amortize the large investments required to build a Quantum Key Distribution Network (QKDN). In this work, we investigate the implications of introducing Time-Division Multiplexing (TDM) in trusted-relay QKDNs at the wide-area network scale in terms of performance and cost-saving. To this end, we developed both a Mixed Integer Linear Programming (qTDM-MILP) model and a Heuristic Algorithm (qTDM-HA) to solve the allocation of QKD transceivers and network resources for a novel switched QKDN operating scheme: qTDM-QKDN. Our heuristic method provides a close-to-optimal resource planning for the offline problem that computes the minimum number of QKD transceivers and optical switch ports at each node, as well as the number of quantum channels on each link required to satisfy a target set of end-to-end secret-keyrate demands. Moreover, both the model and the heuristic provide the time fractions that each QKD transceiver needs to peer with each neighbor QKD transceiver. We compared our proposed model and heuristic algorithm for cost minimization with non-time sharing QKD transceivers (nTDM) as baseline. The results show that qTDM can achieve substantial cost-savings in the range of 10%–40% compared to nTDM. Furthermore, this work sheds light on the selection of the value for the working cycle T and its influence on network performance.

Discrete modulation continuous variable quantum key distribution under fast fading channel

After decades of development, continuous variable quantum key distribution technology still cannot meet people’s needs for secure communication over long distances. Free-space quantum communication provides a new way for secure communication over long distances. However, because the communication connected in free space is inevitably affected by atmospheric turbulence, the transmission rate of the channel changes rapidly according to the probability distribution, making it difficult for the communication personnel to determine the transmission rate of the channel. At the same time, discrete modulated continuously variable quantum key Distribution protocol (DM-CVQKD) has certain advantages over Gauss modulated continuously variable quantum key Distribution protocol (GM-CVQKD) in the communication distance. Therefore, this paper analyzes the key rate of DM-CVQKD in this case (that is, in the fast attenuation channel), proves that it can resist the collective attack, and observes the relationship between the parameters and the key rate in the fast attenuation channel by numerical simulation and control variables. Finally, through the analysis of numerical simulation results, it is found that DM-CVQKD can still maintain a high key rate under certain conditions, which proves that long-distance free space quantum communication is feasible under certain conditions. At the same time, it was found that the performance of DM-CVQKD was affected by the extreme case where Eve completely controlled the instantaneous transmittance.

Assessing a binary quantum channel exploiting a silicon photomultiplier based hybrid receiver.

In quantum communication protocols, the use of photon-number-resolving detectors could open new perspectives by broadening the way to encode and decode information and merging the properties of discrete and continuous variables. In this work, we consider a quantum channel exploiting a silicon-photomultiplier-based receiver and evaluate its performance for quantum communication protocols under three possible configurations, defined by different post-processing of the detection outcomes. We investigate two scenarios: information transmission over the channel, quantified by the mutual information, and continuous-variable quantum key distribution, quantified by the key generation rate. The preliminary results encourage further use of this detection scheme in extended networks.

Measurement of dispersion properties in a short optical fiber for an efficient quantum frequency converter.

Optical fibers have played a pivotal role in the long-distance transportation of quantum states and quantum key distribution due to their low loss. They have garnered attention for photon-pair generation and quantum frequency conversion due to their engineered dispersion properties. Accurate measurement of dispersion properties is essential for these applications. In this study, we introduce a new method to measure the dispersion properties of short optical fibers using Bragg-scattering four-wave mixing (BS-FWM). We successfully measured properties, including zero group-velocity-dispersion wavelength, dispersion slope, and the nonlinear coefficient, for fiber lengths ranging from 9.7 m to 392.7 m. Furthermore, we achieved efficient quantum frequency conversion with an efficiency of 83.8±0.8% using parameters extracted from a 53.9-m-long optical fiber. Our research offers a valuable resource for improving the performance of fiber-based photon-pair sources and quantum frequency converters and has potential implications for advancing fiber-based quantum information processing.

Advancing quantum communication security: Metamaterial based quantum key distribution with enhanced protocols

AbstractQuantum 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.

Quantum private query protocol based on counterfactual quantum key distribution with noiseless attack

Quantum private query protocol based on counterfactual quantum key distribution with noiseless attack

Comparative Study of Fast Optimization Method for Four‐Intensity Measurement‐Device‐Independent Quantum Key Distribution Through Machine Learning

AbstractThe four‐intensity protocol for measurement‐device‐independent (MDI) quantum key distribution (QKD) is renowned for its excellent performance and extensive experimental implementation. To enhance this protocol, a machine learning‐driven rapid parameter optimization method is developed. This initial step involved a speed‐up technique that quickly pinpoints the worst‐case scenarios with minimal data points during the optimization phase. This is followed by a detailed scan in the key rate calculation phase, streamlining data collection to fit machine learning timelines effectively. Several machine learning models are assessed—Generalized Linear Models (GLM), k‐Nearest Neighbors (KNN), Decision Trees (DT), Random Forests (RF), XGBoost (XGB), and Multilayer Perceptron (MLP)—with a focus on predictive accuracy, efficiency, and robustness. RF and MLP were particularly noteworthy for their superior accuracy and robustness, respectively. This optimized approach significantly speeds up computation, enabling complex calculations to be performed in microseconds on standard personal computers, while still achieving high key rates with limited data. Such advancements are crucial for deploying QKD under dynamic conditions, such as in fluctuating fiber‐optic networks and satellite communications.

Continuous-variable quantum passive optical network

To establish a scalable and secure quantum network, a critical milestone is advancing from basic point-to-point quantum key distribution (QKD) systems to the development of inherently multi-user protocols designed to maximize network capacity. Here, we propose a quantum passive optical network (QPON) protocol based on continuous-variable (CV) systems, particularly the quadrature of the coherent state, which enables deterministic, simultaneous, and high-rate secret key generation among all network users. We implement two protocols with different trust levels assigned to the network users and experimentally demonstrate key generation in a quantum access network with 8 users, each with an 11 km span of access link. Depending on the trust assumptions about the users, we reach 1.5 and 2.1 Mbits/s of total network key generation (or 0.4 and 1.0 Mbits/s with finite-size channels estimation). Demonstrating the potential to expand the network’s capacity to accommodate tens of users at a high rate, our CV-QPON protocols open up new possibilities in establishing low-cost, high-rate, and scalable secure quantum access networks serving as a stepping stone towards a quantum internet.

Estimating the link budget of satellite-based Quantum Key Distribution (QKD) for uplink transmission through the atmosphere

Satellite-based quantum communications including quantum key distribution (QKD) represent one of the most promising approaches toward global-scale quantum communications. To determine the viability of transmitting quantum signals through the atmosphere, it is essential to conduct atmospheric simulations for both uplink and downlink quantum communications. In the case of the uplink scenario, the initial phase of the beam’s propagation involves interaction with the atmosphere, making simulation particularly critical. To analyze the atmosphere over the Indian subcontinent, we begin by validating our approach by utilizing atmospheric data obtained from the experiments carried out in the Canary Islands within the framework of Quantum Communication (QC). We also verify our simulation methodology by reproducing simulation outcomes from diverse Canadian locations, taking into account both uplink and downlink scenarios in Low Earth Orbit (LEO). In this manuscript, we explore the practicality of utilizing three different ground station locations in India for uplink-based QC, while also considering beacon signals for both uplink and downlink scenarios. The atmospheric conditions of various geographical regions in India are simulated, and a dedicated link budget analysis is performed for each location, specifically focusing on three renowned observatories: IAO Hanle, Aries Nainital, and Mount Abu. The analysis involves computing the overall losses of the signal and beacon beams. The findings indicate that the IAO Hanle site is a more suitable choice for uplink-based QC when compared to the other two sites.

Scenarios for Optical Encryption Using Quantum Keys

Optical communications providing huge capacity and low latency remain vulnerable to a range of attacks. In consequence, encryption at the optical layer is needed to ensure secure data transmission. In our previous work, we proposed LightPath SECurity (LPSec), a secure cryptographic solution for optical transmission that leverages stream ciphers and Diffie–Hellman (DH) key exchange for high-speed optical encryption. Still, LPSec faces limitations related to key generation and key distribution. To address these limitations, in this paper, we rely on Quantum Random Number Generators (QRNG) and Quantum Key Distribution (QKD) networks. Specifically, we focus on three meaningful scenarios: In Scenario A, the two optical transponders (Tp) involved in the optical transmission are within the security perimeter of the QKD network. In Scenario B, only one Tp is within the QKD network, so keys are retrieved from a QRNG and distributed using LPSec. Finally, Scenario C extends Scenario B by employing Post-Quantum Cryptography (PQC) by implementing a Key Encapsulation Mechanism (KEM) to secure key exchanges. The scenarios are analyzed based on their security, efficiency, and applicability, demonstrating the potential of quantum-enhanced LPSec to provide secure, low-latency encryption for current optical communications. The experimental assessment, conducted on the Madrid Quantum Infrastructure, validates the feasibility of the proposed solutions.

High-dimensional quantum key distribution using orbital angular momentum of single photons from a colloidal quantum dot at room temperature

High-dimensional quantum key distribution (HDQKD) is a promising avenue to address the inherent limitations of basic quantum key distribution (QKD) protocols. However, experimental realizations of HDQKD to date have relied on indeterministic photon sources that limit the achievable key rate. In this paper, we demonstrate a full emulation of a HDQKD system using a single colloidal giant quantum dot (gQD) as a deterministic, compact, and room-temperature single-photon source (SPS). We demonstrate a practical protocol by encoding information in a high-dimensional space (d = 3) of the orbital angular momentum of the photons. Our experimental configuration incorporates two spatial light modulators for encoding and decoding the spatial information carried by individual photons. Our experimental demonstration establishes the feasibility of utilizing high radiative quantum yield gQDs as practical SPSs for HDQKD. We also experimentally demonstrate surpassing the traditional d = 2 QKD capacity with comparable error rates, indicating a significant improvement in performance while maintaining reliability.

Mapping Guaranteed Positive Secret Key Rates for Continuous Variable Quantum Key Distribution.

The standard way to measure the performance of existing continuous variable quantum key distribution (CVQKD) protocols is by using the achievable secret key rate (SKR) with respect to one parameter while keeping all other parameters constant. However, this atomistic method requires many individual parameter analyses while overlooking the co-dependence of other parameters. In this work, a numerical tool is developed for comparing different CVQKD protocols while taking into account the simultaneous effects of multiple CVQKD parameters on the capability of protocols to produce positive SKRs. Using the transmittance, excess noise, and modulation amplitude parameter space, regions of positive SKR are identified to compare three discrete modulated (DM) CVQKD protocols. The results show that the M-QAM protocol outperforms the M-APSK and M-PSK protocols and that there is a non-linear increase in the capability to produce positive SKRs as the number of coherent states used for a protocol increases. The tool developed is beneficial for choosing the optimum protocol in unstable channels, such as free space, where the transmittance and excess noise fluctuate, providing a more holistic assessment of a protocol's capability to produce positive SKRs.

Security of partially corrupted quantum repeater networks

Abstract Quantum Key Distribution allows two parties to establish a secret key that is secure against computationally unbounded adversaries. To extend the distance between parties, quantum networks are vital. Typically, security in such scenarios assumes the absolute worst case: namely, an adversary has complete control over all repeaters and fiber links in a network and is able to replace them with perfect devices, thus allowing her to hide her attack within the expected natural noise. In a large-scale network, however, such a powerful attack may be infeasible. In this paper, we analyze the case where the adversary can only corrupt a subset of the repeater network connecting Alice and Bob, while some portion of the network near Alice and Bob may be considered safe from attack (though still noisy). We derive a rigorous finite key proof of security assuming this attack model, and show that improved performance and noise tolerances are possible. Our proof methods may be useful to other researchers investigating partially corrupted quantum networks, and our main result may be beneficial to future network operators.

Quantum key distribution with unbounded pulse correlations

Abstract Typical security proofs of quantum key distribution (QKD) require that the emitted signals are independent and identically distributed. In practice, however, this assumption is not met because intrinsic device flaws inevitably introduce correlations between the emitted signals. Although analyses addressing this issue have been recently proposed, they only consider a restrictive scenario in which the correlations have a finite and known maximum length that is much smaller than the total number of emitted signals. While it is expected that the magnitude of the correlations decreases as the pulse separation increases, the assumption that this magnitude is exactly zero after a certain point does not seem to have any physical justification. Concerningly, this means that the available analyses cannot guarantee the security of current QKD implementations. Here, we solve this pressing problem by developing a rigorous framework that, when combined with existing results, can guarantee security against pulse correlations of unbounded length. Our framework is rather general and could be applied to other situations for which the existing analyses consider a scenario that differs slightly from the actual one.

Issues of personal data protection when using cloud technologies

It is indicated that in today’s digital world, where the amount of stored and processed data is growing at a frantic pace, issues of personal data protection are becoming increasingly important. With the proliferation of cloud technologies that allow companies and individuals to store and process information on remote servers, a new spectrum of threats to data privacy and security is emerging. The article examines the issue of personal data protection when using cloud technologies, in particular, the need to integrate legal and technological aspects to ensure comprehensive protection. The impact of international regulatory acts, such as GDPR (General Data Protection Regulation) and CCPA (California Consumer Privacy Protection Act), on cloud data protection processes is analyzed. Particular attention is paid to problems arising from differences in the legal regimes of different countries, which complicate data management at the international level. The article examines in detail modern technical solutions, such as data encryption and multi­factor authentication, which are key elements in protecting confidential information. These technologies have been found to provide a high level of protection, but also have their vulnerabilities. Based on this, it is proposed to invest in the latest technologies, in particular quantum encryption and artificial intelligence, to improve the effectiveness of data protection. Practical cases of data leaks are separately considered, which emphasize the importance of proper configuration of security systems and regular monitoring. Analysis of the results of empirical research shows the need to adapt business processes to changes in the regulatory environment and introduce new technologies to reduce risks. Based on the received data, recommendations for organizations are formulated, which include reviewing data protection policies, investing in modern technologies and training employees. The conclusions of the article emphasize the need for a comprehensive approach to ensuring the protection of personal data in cloud environments. This involves taking into account both modern technologies and current legal requirements to ensure adequate data protection and minimize possible risks.

Modern quantum materials

Quantum phenomena, including entanglement, superposition, tunneling, and spin–orbit interactions, among others, are foundational to the development of recent innovations in quantum computing, teleportation, encryption, sensing, and new modalities of electronics, such as spintronics, spin-orbitronics, caloritronics, magnonics, twistronics, and valleytronics. These emerging technologies provide disruptive influences to global commercial markets. These remarkable advances in quantum technologies are nearly always enabled by the discovery of materials and their quantum behaviors. Such advances are governed by quantum principles that are strongly influenced by environmental, physical, topological, and morphological conditions such as very small length scales, short time durations, ultrahigh pressures, ultralow temperatures, etc., which lead to quantum behaviors that manifest as quantum tunneling, entanglement, superpositioning, superfluidity, low-dimensional, high-temperature and high-pressure superconductivity, quantum fluctuations, Bose–Einstein condensates, topological effects, and other phenomena that are not yet fully understood nor adequately explored. Here, we provide a review of quantum materials developed up to 2023. Remarkable advances in quantum materials occur daily, and therefore, by the time of publication, new and exciting breakthroughs will have occurred that are regrettably not covered herein.

Intensity correlations in measurement-device-independent quantum key distribution.

The intensity correlations due to imperfect modulation during the quantum-state preparation in a measurement-device-independent quantum key distribution (MDI QKD) system compromise its security performance. Therefore, it is crucial to assess the impact of intensity correlations on the practical security of MDI QKD systems. In this work, we propose a theoretical model that quantitatively analyzes the secure key rate of MDI QKD systems under intensity correlations. Furthermore, we apply the theoretical model to a practical MDI QKD system with measured intensity correlations, which shows that the system struggles to generate keys efficiently under this model. We also explore the boundary conditions of intensity correlations to generate secret keys. This study extends the security analysis of intensity correlations to MDI QKD protocols, providing a methodology to evaluate the practical security of MDI QKD systems.

Experimental demonstration of the time-dependent source side-channel and countermeasures in polarization-based BB84 QKD systems.

High-speed is one development tendency of the practical and commercial quantum key distribution (QKD) systems, and the gain-switched semiconductor laser (GSSL) and Sagnac interferometer have been popular components for high-speed commercial polarization-based BB84 QKD systems thanks to their stability, compactness and low cost. However, due to the finite extinction ratio (ER) of the GSSL, the time-dependent source side-channel, which is theoretically presented in [Phys. Rev. A106(6): 062618 (2022)10.1103/PhysRevA.106.062618], also exists in these QKD systems. In this article, we experimentally investigate this side-channel in the polarization-based BB84 QKD system. The results show an obvious correlation in the output polarization states between the weak leakage light and its adjacent pulses, which will cause information to leak. More importantly, we have proposed several countermeasures, retested the side channel, and developed a mathematical framework to quantitatively assess the impact of the time-dependent side channel and these countermeasures on the secure key rate. Finally, we offer a trade-off analysis that considers defense effectiveness, pulse impact, and cost for various countermeasures in QKD. This provides a practical recommendation for improving the security of QKD systems.

Quantum cryptography in the security of cognitive radio networks

Cognitive radio networks face challenges from malicious users who aim to disrupt decision-making during spectrum sensing and decrease spectrum efficiency. The proposed model seeks to distinguish between the presence and absence of primary user signals using energy detection and also it introduces a quantum-inspired outlier detection mechanism for cognitive radio networks to enhance security and reliability during spectrum sensing by ignoring the identified outliers. It employs BB84 quantum key distribution (QKD) protocol and one time pad for secure transmission of secondary user (SU) local decisions to the fusion center (FC), ensuring data integrity and confidentiality. These decisions are transmitted securely establishing a shared secret key between SU and FC and arrives at a global decision. To make the model more robust, we proposed another novel model with a modified BB84 protocol and compared the results of both the models, offering a robust solution for enhancing the reliability and performance of cognitive radio networks with proven results from simulation.

Quantum key distribution with a borosilicate-glass-matrix integrated photonic receiver

Quantum key distribution with a borosilicate-glass-matrix integrated photonic receiver