Quantum Communication Channel Research Articles

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.

Information and mathematical model of quantum communication channel state control processes

The most protected and stable communication systems today are quantum channels of information transmission and processing. Thanks to the unique properties of photons as information elements, it becomes possible to monitor and analyze the state of information flows in communication or information transmission channels. Physical attributes such as spin, polarization, radiation frequency, phase synchronization, and the quantum entanglement effect can be tracked and interpreted online to improve the quality and reliability of information in computer systems. In order to effectively use information in support or decision support systems, it is necessary to carefully formalize the processes and indicators of quantum systems for the creation of information processing and transmission, for which information and mathematical models should be created that describe the state of the quantum communication channel (QCC).The information model should allow the convolution of the information space. The mathematical model must prove the processes of tracking the states of quantum information and provide a description of the phase state of indicators of the quantum environment. A lock in a closed space with established cause-and-effect relationships is equal to a system of clear logic.The authors summarize the experience of developing and implementing the method of simulated dynamic modeling of events in an abstract communication channel, which allows formalizing and classifying cause-and-effect relationships of quantum carriers in the analyzed channels. It is proposed to use a unified neural network for the organization of SPPR in quantum-mechanical information transmission systems. Such a network could provide an automatic intelligent system state analysis mode. Such an analysis makes it possible to classify the aggregates of current system parameters to the level of diagnostics of the state of information flows and conclusions based on such diagnostics with the support of decision-making about the quality and reliability of the transmitted information. Such a system, working in OLAP (Online analytical processing) mode, could automatically manage the process of generation and transmission of information, reacting without human intervention to emerging critical errors or attempts at unauthorized system hacking. The observer effect leads to the fact that an attempt to measure the state of a photon inevitably causes an almost instantaneous change in this state. Attempting to parallelize a photon has the same consequences. This cannot be unnoticeable during further authorized acceptance of information. The analyzed quantum communication channel (QCM) consists of a set of technological elements distributed in space. The channel works in its own time, which is formed by clock pulses and creates a flow of information.

On the possibility of implementing a quantum entanglement distribution in a biosystem: Microtubules

The paper considers the possibility of implementing a quantum entanglement distribution in the cell microtubule. It has been shown that a quantum entanglement distribution proposed in the paper determines the process of quantum state teleportation through microtubule tryptophan chain. The work shows that the system of tryptophans in a microtubule essentially is a quantum network that consists of: spatially spaced nodes — tryptophans, quantum communication channels connecting tryptophans and qubits transmitted through these communication channels. The connection between the process of quantum teleportation in living nature and its classical analogue is discussed. The quantum protocol established in the work determines the possible principle of quantum information transmission in biosystems and also in the similar nanostructures.

Cryptographic algorithm for multi-path distribution of entangled states of orbital angular momentum based on Fibonacci values

Drawing inspiration from the Fibonacci sequence and its complementary Lucas sequence, this paper introduces an innovative encryption and decryption algorithm tailored for multi-path quantum key distribution. The algorithm capitalizes on the high-quality orbital angular momentum entangled states, harnessing the mathematical elegance of Fibonacci numbers to construct block diagonal matrices. These matrices serve as the foundation for the simultaneous execution of key distribution across multiple communication paths in a structured block distribution format. The encryption process is facilitated through a combination of linear mappings, employing specific transition matrices to manage the cryptographic flow. The security underpinning of this method is firmly rooted in the Heisenberg Uncertainty Principle, a fundamental tenet of quantum mechanics, which ensures the confidentiality and integrity of the quantum communication channel. This approach paves the way for a novel encryption paradigm, fortifying the security framework of quantum communication networks.

Approaches to Developing Key Distribution Protocols Based on Quantum Key Distribution

Quantum protocols for generating shared secret keys represent an effective method of ensuring secure information transmission using quantum communication channels. However, they are limited in scalability due to the physical constraints of quantum channels, which necessitates the use of classical communication channels for exchanging information between participants. This leads to the necessity of developing security threat models and network protection, especially in the case of hybrid networks, where quantum channels are used alongside classical ones. The peculiarity of constructing quantum key distribution protocols is associated with the costliness of implementation and implies the inevitable use of classical communication channels for key distribution. This paper addresses the task of ensuring the security of communication between subscribers not directly connected by quantum channels, through intermediary nodes, and analyzes threats from internal and external adversaries. Special attention is paid to situations where both types of adversaries have information about the processes and protocols in the network. The paper examines widely used key distribution protocols employed in practice. It describes the main security requirements applied to key distribution protocols, and presents the results of an analysis of the compliance of the discussed protocols with these requirements

Design constraints for Unruh-DeWitt quantum computers

The Unruh-DeWitt particle detector model has found success in demonstrating quantum information channels with non-zero channel capacity between qubits and quantum fields. These detector models provide the necessary framework for experimentally realizable Unruh-DeWitt quantum computers with near-perfect channel capacity. We propose spin-qubits with gate-controlled coupling to Luttinger liquids as a laboratory setting for Unruh-DeWitt detectors and explore general design constraints that underpin their feasibility in this and other settings. We present several experimental scenarios including graphene ribbons, edges states in the quantum spin Hall phase of HgTe quantum wells, and the recently discovered quantum anomalous Hall phase in transition metal dichalcogenides. Theoretically, through bosonization, we show that Unruh-DeWitt detectors can carry out quantum computations and identify when they can make perfect quantum communication channels between qubits via the Luttinger liquid. Our results point the way toward an all-to-all connected solid state quantum computer and the experimental study of quantum information in quantum fields via condensed matter physics.

Coherent equalization of linear quantum systems

This paper introduces a H∞-like methodology of coherent filtering for equalization of passive linear quantum systems to help mitigate degrading effects of quantum communication channels. For such systems, which include a wide range of linear quantum optical devices and signals, we seek to find a near optimal equalizing filter which is itself a passive quantum system. The problem amounts to solving an optimization problem subject to constraints dictated by the requirement for the equalizer to be physically realizable. By formulating these constraints in the frequency domain, we show that the problem admits a convex H∞-like formulation. This allows us to derive a set of suboptimal coherent equalizers using J-spectral factorization. An additional semidefinite relaxation combined with the Nevanlinna–Pick interpolation is shown to lead to a tractable algorithm for the design of a near optimal coherent equalizer.

Design of coherent passive quantum equalizers using robust control theory

The paper develops a methodology for the design of coherent equalizing filters for quantum communication channels. Given a linear quantum system model of a quantum communication channel, the aim is to obtain another quantum system which, when coupled with the original system, mitigates degrading effects of the environment. The main result of the paper is a systematic equalizer synthesis algorithm which relies on methods of state–space robust control design via semidefinite programming.

Quantum BER estimation modelling and analysis for satellite‐based quantum key distribution scenarios

AbstractThe 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.

Transmission of light–matter entanglement over a metropolitan network

We report on the transmission of telecom photons entangled with a multimode solid-state quantum memory over a deployed optical fiber in a metropolitan area. Photon pairs were generated through spontaneous parametric downconversion, with one photon stored in a rare-earth-based quantum memory, and the other, at telecommunication wavelengths, traveling through increasing distances of optical fiber, first in the laboratory and then outside in a deployed fiber loop. We measured highly non-classical correlations between the stored and the telecom photons for storage times up to 25 µs and for a fiber separation up to 50 km. We also report light–matter entanglement with a two-qubit fidelity up to 88%, which remains constant within error bars for all fiber lengths, showing that the telecom qubit does not suffer decoherence during the transmission. Finally, we moved the detection stage of the telecom photons to a different location placed 16 km away, and confirmed the non-classical correlations between the two photons. Our system was adapted to provide the transmission of precise detection times and synchronization signals over long quantum communication channels, providing the first steps for a future quantum network involving quantum memories and non-classical states.

Quantum walks-based simple authenticated quantum cryptography protocols for secure wireless sensor networks

Wireless sensor networks (WSNs) play a crucial role in various applications, ranging from environmental monitoring to industrial automation that require high levels of security. With the development of quantum technologies, many security mechanisms may be hacked due to the promising capabilities of quantum computation. To address this challenge, quantum protocols have emerged as a promising solution for enhancing the security of wireless sensor communications. One of the common types of quantum protocols is quantum key distribution (QKD) protocols, which are investigated to allow two participants with fully quantum capabilities to share a random secret key, while semi-quantum key distribution (SQKD) protocols are designed to perform the same task using fewer quantum resources to make quantum communications more realizable and practical. Quantum walk (QW) plays an essential role in quantum computing, which is a universal quantum computational paradigm. In this work, we utilize the advantages of QW to design three authenticated quantum cryptographic protocols to establish secure channels for data transmission between sensor nodes: the first one is authenticated quantum key distribution (AQKD), the second one is authenticated semi-quantum key distribution (ASQKD) with one of the two participants having limited quantum capabilities, and the last one is ASQKD but both legitimate users possess limited quantum resources. The advantages of the proposed protocols are that the partners can exchange several different keys with the same exchanged qubits, and the presented protocols depend on a one-way quantum communication channel. In contrast, all previously designed SQKD protocols rely on two-way quantum communication. Security analyses prove that the presented protocols are secure against various well-known attacks and highly efficient. The utilization of the presented protocols in wireless sensor communications opens up new avenues for secure and trustworthy data transmission, enabling the deployment of resilient WSNs in critical applications. This work also paves the way for future exploration of quantum-based security protocols and their integration into WSNs for enhanced data protection.

Quantum walk-based protocol for secure communication between any two directly connected nodes on a network

The utilization of quantum entanglement as a cryptographic resource has superseded conventional approaches to secure communication. Security and fidelity of intranetwork communication between quantum devices is the backbone of a quantum network. This work presents an protocol that generates entanglement between any two directly connected nodes of a quantum network to be used as a resource to enable quantum communication across that pair in the network. The protocol is based on a directed discrete-time quantum walk and paves the way for private inter-node quantum communication channels in the network. We also present the simulation results of this protocol on random networks generated from various models. We show that after implementation, the probability of the walker being at all nodes other than the source and target is negligible and this holds independent of the random graph generation model. This constitutes a viable method for the practical realisation of secure communication over any random network topology.

Integral formula for quantum relative entropy implies data processing inequality

Integral representations of quantum relative entropy, and of the directional second and higher order derivatives of von Neumann entropy, are established, and used to give simple proofs of fundamental, known data processing inequalities: the Holevo bound on the quantity of information transmitted by a quantum communication channel, and, much more generally, the monotonicity of quantum relative entropy under trace-preserving positive linear maps – complete positivity of the map need not be assumed. The latter result was first proved by Müller-Hermes and Reeb, based on work of Beigi. For a simple application of such monotonicities, we consider any `divergence' that is non-increasing under quantum measurements, such as the concavity of von Neumann entropy, or various known quantum divergences. An elegant argument due to Hiai, Ohya, and Tsukada is used to show that the infimum of such a `divergence' on pairs of quantum states with prescribed trace distance is the same as the corresponding infimum on pairs of binary classical states. Applications of the new integral formulae to the general probabilistic model of information theory, and a related integral formula for the classical Rényi divergence, are also discussed.

The SWITCH test for discriminating quantum evolutions

We study different quantum circuits that can discriminate between two arbitrary quantum evolution operators. These circuits can be used to check whether two quantum operators are equal or not and to estimate a fidelity measure telling how close the operators are. This operator comparison is related to the SWAP test for discriminating two quantum states. In terms of their practical realization, we comment possible laboratory implementations with light along the same lines of recent experimental realizations of quantum superpositions of causal orders exploiting the different degrees of freedom of photons. We also discuss hardware efficient realizations for noisy intermediate scale quantum computers. Finally, we comment potential applications to the discrimination of quantum communication channels and to the search for simpler quantum circuits in quantum compilers.

Effect of Marine Bubbles on the Performance of Underwater Quantum Communication Channel

Effect of Marine Bubbles on the Performance of Underwater Quantum Communication Channel

Near-Infrared Optical Transmitting Module for Service Channel of Atmospheric Quantum Communication Line

This work presents an optical transmitting module operating in the near-infrared wavelength range for the organization of a wireless service channel in an atmospheric optical quantum communication channel. The main characteristics were measured to demonstrate the functionality of the module and to assess the quality of the transmitted signal, such as the values of the error vector magnitude and the eye diagram opening level. It was determined that the transmitting module can operate at symbol rates up to 5 GBaud. In addition, the optimal signal modulation parameters were found and the possible bit rate of data transmission in the atmospheric optical communication channel was estimated: a QPSK-modulated signal with a carrier frequency of 80 MHz and a symbol rate of 50 MBaud allowed to get a bit rate of 100 Mbit/s with an EVM value of 14%.

Effect of Sea Ice on Performance of Underwater Quantum Communication Channels

Effect of Sea Ice on Performance of Underwater Quantum Communication Channels

Security of Bennett–Brassard 1984 Quantum-Key Distribution under a Collective-Rotation Noise Channel

The security analysis of the Ekert 1991 (E91), Bennett 1992 (B92), six-state protocol, Scarani–Acín–Ribordy–Gisin 2004 (SARG04) quantum key distribution (QKD) protocols, and their variants have been studied in the presence of collective-rotation noise channels. However, besides the Bennett–Brassard 1984 (BB84) being the first proposed, extensively studied, and essential protocol, its security proof under collective-rotation noise is still missing. Thus, we aim to close this gap in the literature. Consequently, we investigate how collective-rotation noise channels affect the security of the BB84 protocol. Mainly, we study scenarios where the eavesdropper, Eve, conducts an intercept-resend attack on the transmitted photons sent via a quantum communication channel shared by Alice and Bob. Notably, we distinguish the impact of collective-rotation noise and that of the eavesdropper. To achieve this, we provide rigorous, yet straightforward numerical calculations. First, we derive a model for the collective-rotation noise for the BB84 protocol and parametrize the mutual information shared between Alice and Eve. This is followed by deriving the quantum bit error rate (QBER) for two intercept-resend attack scenarios. In particular, we demonstrate that, for small rotation angles, one can extract a secure secret key under a collective-rotation noise channel when there is no eavesdropping. We observe that noise induced by rotation of 0.35 radians of the prepared quantum state results in a QBER of 11%, which corresponds to the lower bound on the tolerable error rate for the BB84 QKD protocol against general attacks. Moreover, a rotational angle of 0.53 radians yields a 25% QBER, which corresponds to the error rate bound due to the intercept-resend attack. Finally, we conclude that the BB84 protocol is robust against intercept-resend attacks on collective-rotation noise channels when the rotation angle is varied arbitrarily within particular bounds.

Detecting quantum capacities of continuous-variable quantum channels

Quantum communication channels and quantum memories are the fundamental building blocks of large-scale quantum communication networks. Estimating their capacity to transmit and store quantum information is crucial in order to assess the performance of quantum communication systems and to detect useful communication paths among the nodes of future quantum networks. However, the estimation of quantum capacities is a challenging task for continuous-variable systems, such as the radiation field, for which a complete characterization via quantum tomography is practically unfeasible. Here we introduce a method for detecting the quantum capacity of continuous-variable communication channels and memories without performing a full process tomography. Our method works in the general scenario where the devices are used a finite number of times, can exhibit correlations across multiple uses, and can change dynamically under the control of a malicious adversary. The method is experimentally friendly and can be implemented using only finitely squeezed states and homodyne measurements.

A Secured Half-Duplex Bidirectional Quantum Key Distribution Protocol against Collective Attacks

Quantum Key Distribution is a secure method that implements cryptographic protocols. The applications of quantum key distribution technology have an important role: to enhance the security in communication systems. It is originally inspired by the physical concepts associated with quantum mechanics. It aims to enable a secure exchange of cryptographic keys between two parties through an unsecured quantum communication channel. This work proposes a secure half-duplex bidirectional quantum key distribution protocol. The security of the proposed protocol is proved against collective attacks by estimating the interception of any eavesdropper with high probability in both directions under the control of the two parties. A two-qubit state encodes two pieces of information; the first qubit represents the transmitted bit and the second qubit represents the basis used for measurement. The partial diffusion operator is used to encrypt the transmitted qubit state as an extra layer of security. The predefined symmetry transformations induced by unitary in conjunction with the asymmetrical two-qubit teleportation scheme retain the protocol’s secrecy. Compared to the previous protocols, the proposed protocol has better performance on qubit efficiency.