Quantum Communication Networks Research Articles

Electro-optomechanical entanglement in two coupled optical cavities with an LC microwave circuit

We theoretically investigate entanglement in a hybrid quantum system comprising two optical cavities coupled to a shared microwave cavity via optomechanical interactions. Our results demonstrate that increasing the microwave input power and frequency in the allowed range enhances entanglement between the microwave–optical and optical–optical modes. We also show by change frequency of the one optical cavity in the communication domain that we still have entanglement. This ability to generate robust microwave–optical photon entanglement shows promise for various quantum technologies. Optical photons could enable secure quantum communication in optical fibers, while microwave photons allow transmission to satellites. Overall, this hybrid cavity optomechanical system offers prospects as an efficient source of entangled photon pairs, vital for implementing long-distance quantum communication networks.

Optimal quantum key distribution networks: capacitance versus security

The rate and security of quantum communications between users placed at arbitrary points of a quantum communication network depend on the structure of the network, on its extension and on the nature of the communication channels. In this work we propose a strategy for the optimization of trusted-relays based networks that intertwines classical network approaches and quantum information theory. Specifically, by suitably defining a quantum communication efficiency functional, we identify the optimal quantum communication connections through the network by balancing security and the quantum communication rate. The optimized network is then constructed as the network of the maximal quantum communication efficiency connections and its performance is evaluated by studying the scaling of average properties as functions of the number of nodes and of the network spatial extension.

High-visibility energy-time entanglement system enabled by a low-loss silicon-integrated platform.

Energy-time (E-T) entanglement is widely employed in long-distance quantum entanglement distribution due to its strong robustness against transmission fluctuations. In this Letter, we report what we believe to be the first silicon monolithically integrated E-T entanglement system, which integrates the photon sources, wavelength demultiplexers, and Franson interferometers on a single chip. Also, by utilizing low-loss multimode waveguides in Franson interferometers, we measured an on-chip quantum interference visibility of 99.66% (±0.47%), to our knowledge one of the highest values for integrated E-T entanglement systems reported to date. The quantum interference after 1- and 5-km fiber propagation shows visibilities of 96.72% (±0.78%) and 97.46% (±1.23%), respectively. These results demonstrate the potential of using silicon monolithic integration for advance E-T entanglement-based quantum communication networks.

Enhancing hierarchical remote preparation of an arbitrary n-qudit equatorial state by weak measurement and measurement reversal

Based on the demand for safer and more efficient quantum network communication, we propose two deterministic protocols to achieve the remote preparation of an arbitrary n-qudit equatorial states among multiple agents by selecting appropriate entanglement resources. The level of the agents varies depending on their authorities to restore the secret state. The superior agent requires the cooperation of the residual superior agents and any one of the subordinate agents, while the subordinate agent needs the help of all the other agents. To be emphasized, the recovery operations are deduced by general formulas that distinctly elucidate their relevance with the measurement outcomes. Additionally, we discuss the impact of amplitude damping noise and utilize weak measurement and measurement reversal to suppress noise.

Hierarchical remote preparation with multiple agents under the non-Markovian and Markovian noises

To meet the practical needs that the capabilities of agents in a quantum communication network are often different, we propose two deterministic schemes to achieve hierarchical remote preparation of an arbitrary single-qubit state by using cluster state as the entangled resource. One requires splitting the coefficients of the prepared state and the other does not due to the elaborately constructed measurement basis. The high-grade agent requires the help of all the other high-grade agents and any one of the low-grade agents to reconstruct the target state, while the low-grade agent needs the assistance of all the remaining agents. Comparing with the original scheme, ours are applicable to any number of agents and derive general expressions of recovery operators which clearly reveal the relationship with the measurement results. Moreover, the influences of diverse types of non-Markovian and Markovian noises are considered through calculating the fidelity of the output state.

Parameter optimization of SQCC-CVQKD based on genetic algorithm in the terahertz band

Recently, we proposed a continuous variable quantum key distribution (CVQKD) scheme based on simultaneous quantum and classical communication (SQCC) in the terahertz (THz) band. It performs classical modulation and quantum Gaussian modulation at the same coherent pulse at the sending end, and an amplifier is used to amplify and demultiplex the signal at the receiving end. However, the previous study set parameters based on prior knowledge which has significant limitations, and as the previous study showed, parameter selection is a crucial task that directly affects the performance of the system. In this paper, we use the genetic algorithm to optimize the parameter selection, and how the different conditions influence the optimal value of parameters is also analyzed. The simulation results show that the parameter optimized with the algorithm can make the scheme achieve a higher secret key rate which greatly improves the applicability of the SQCC scheme in the THz band. This work demonstrates the effectiveness of the scheme to construct wireless quantum communication networks.

Quantum Reversible Audio Steganalysis Using Quantum Schmidt Decomposition and Quantum Support Vector Machine

With the development of various methods of quantum steganography, the discovery of these secret communications has become a necessity. This paper presents the first quantum steganalysis approach that uses statistical features of the quantum frequency domain to detect the steganographic methods in quantum communication networks. In this method, by proposing different quantum circuits, statistical features such as quantum mean, quantum square mean root, quantum variance, and quantum standard deviation are extracted to increase the accuracy of distinguishing between stego and clean signals. In the proposed method, the Schmidt coefficient vector extracted from the Quantum Haar Wavelet Transform (QHWT) is used to calculate the statistical features of the audio signal so that the main and dominant coefficients below the frequency sub-bands of the audio signal can be identified and selected. The proposed method uses a Quantum Support Vector Machine (QSVM) to classify the extracted feature vectors. The higher accuracy of the proposed frequency-based steganalysis method indicates its higher efficiency in detecting stego and clean signals than the quantum steganalysis methods based on the time domain.

The construction of quantum network model based on formalized theory

With the rapid development of quantum communication, various types of quantum communication protocols emerge one after another, and their number has been very large. Usually a quantum communication protocol is expressed in long words. Formalized processing of quantum communication protocol can simplify its expression mode, which is conducive to fast reading and selection of required protocols according to actual application requirements. In this paper, quantum communication protocols that use entangled particles as quantum channels to transmit known or unknown quantum states are classified based on classification of set, and the classified protocols are described in formalized language. A new quantum communication network model is constructed by using the formalized quantum communication protocol.

Trust evaluation model immune to decoherent noise in quantum communication network

Trust evaluation model immune to decoherent noise in quantum communication network

Routing in quantum communication networks using reinforcement machine learning

This paper promotes reinforcement machine learning for route-finding tasks in quantum communication networks, where, due to the non-additivity of quantum errors, classical graph path or tree-finding algorithms cannot be used. We propose using a proximal policy optimization algorithm capable of finding routes in teleportation-based quantum networks. This algorithm is benchmarked against the Monte Carlo search. The topology of our network resembles the proposed 6 G topology and analyzed that quantum errors correspond to typical errors in realistic quantum channels.

Entanglement dynamics of photon pairs and quantum memories in the gravitational field of the earth

We investigate the effect of entanglement dynamics due to gravity – the basis of a mechanism of universal decoherence – for photonic states and quantum memories in Mach-Zehnder and Hong-Ou-Mandel interferometry setups in the gravitational field of the earth. We show that chances are good to witness the effect with near-future technology in Hong-Ou-Mandel interferometry. This would represent an experimental test of theoretical modeling combining a multi-particle effect predicted by the quantum theory of light and an effect predicted by general relativity. Our article represents the first analysis of relativistic gravitational effects on space-based quantum memories which are expected to be an important ingredient for global quantum communication networks.

Unveiling the electronic structure of GaSb/AlGaSb quantum dots emitting in the third telecom window

Epitaxially-grown semiconductor quantum dots (QDs) provide an attractive platform for the development of deterministic sources of high-quality quantum states of light. Such non-classical light sources are essential for quantum information processing and quantum communication. QDs emitting in the telecom wavelengths are especially important for ensuring compatibility with optical fiber systems required to implement quantum communication networks. To this end, GaSb QDs fabricated by filling local-droplet etched nanoholes are emerging as a viable approach, yet the electronic properties of such nanostructures have not been studied in detail. In this article, an insight into the electronic structure and carrier dynamics in GaSb/AlGaSb QDs is provided through a systematic experimental analysis of their temperature-dependent photoluminescence behavior. A steady-state rate equation model is used to reveal the relevant energy barriers for thermally activated carrier capture and escape processes. Furthermore, results of detailed theoretical simulations of quantum-confined energy states using the multi-band k·p model and the effective mass method are presented. The purpose of the simulations is to reveal the direct and indirect energy states, carrier wavefunctions, and allowed optical transitions for GaSb QDs with different physical dimensions.

Controlling the photon number coherence of solid-state quantum light sources for quantum cryptography

Quantum communication networks rely on quantum cryptographic protocols including quantum key distribution (QKD) based on single photons. A critical element regarding the security of QKD protocols is the photon number coherence (PNC), i.e., the phase relation between the vacuum and one-photon Fock state. To obtain single photons with the desired properties for QKD protocols, optimal excitation schemes for quantum emitters need to be selected. As emitters, we consider semiconductor quantum dots, that are known to generate on-demand single photons with high purity and indistinguishability. Exploiting two-photon excitation of a quantum dot combined with a stimulation pulse, we demonstrate the generation of high-quality single photons with a controllable degree of PNC. The main tuning knob is the pulse area giving full control from minimal to maximal PNC, while without the stimulating pulse the PNC is negligible in our setup for all pulse areas. Our approach provides a viable route toward secure communication in quantum networks.

Controlled Cyclic and Bidirectional Hybrid Quantum Communication of Arbitrary Two‐Qubit States

AbstractHybrid quantum communication with the combination of quantum teleportation and remote preparation is hopeful for promoting the development of quantum networks and enriching the diversity of quantum network communication. To improve the communication efficiency and enhance the scalability of the quantum networks, a meaningful protocol for controlled cyclic and bidirectional hybrid quantum communication of arbitrary two‐qubit states is proposed, which allows quantum information to be transmitted simultaneously in both directions among multiple participants. With the permission of one controller, each observer can simultaneously transmit arbitrary known two‐qubit states and unknown ones to their adjacent observers, by implementing remote preparation and quantum teleportation in the clockwise and counterclockwise directions. Furthermore, the participants just carry out some quantum measurements and recovery operations to achieve the communication target, and the desired states can be attained with a unit success probability, thus the protocol is deterministic. Finally, some comparisons are also made with other similar protocols, which shows that the protocol is better in qubit efficiency and communication capacity.

A dialogue protocol of quantum communication network based on cluster states

A dialogue protocol of quantum communication network based on cluster states

Artificial intelligence, anterior segment and refractive surgery: Which relationship and association?

Aims/Purpose: The goal of our work is to synthesize the different fields identified by AI in refractive surgery.Methods: Research in the literature of the different manifestations of artificial intelligence related to refractive surgery.Results: Several articles including reviews reported several studies done in this direction. Lops and al introduced the PRFI (Pentacam Random Forest Index) using data from 3 different countries. The PRFI has a sensitivity of 85.2% and specificity of 96.6%. Xie and Co developed PIRSS (Pentacam InceptionResNetV2 Screening) for refractive surgery with a little number of false positive in identifying normal cornea, suspected irregular and keratoconic cornea. AI has also been used in recommending the appropriate refractive surgery and nomograms used, Kamiya and al developed an ML‐based algorithm to predict the postoperative posterior chamber phakic intraocular lens (IOL) vault using preoperative AS‐OCT images of patients undergoing phakic IOL implantation to predict the achieved vault. These examples of studies and discoveries open new horizons in refractive surgery using AI.Conclusions: AI has been successfully used in the prediction of diagnosis of various corneal disorders, including IK, keratoconus, pterygium, endothelial diseases, and corneal graft‐related complications but also in refractive surgery; certainly it has limits but next to telemedicine, 5G/6G networks, Quantum Communication Networks and Internet of Medical Things, AI is likely to form part of the new health care revolution.

Quantum communication networks: Design, reliability, and security

Quantum communication networks: Design, reliability, and security

Numerical investigation of plasmon-enhanced emission from a nanofiber coupled single photon emitter

This study explores the enhancement of emission from a single photon emitter in a quantum communication network by coupling the source with an optical nanofiber and leveraging gold nanoparticles for Purcell enhancement. Large Purcell enhancements of more than 50 times were recently reported experimentally, but the understanding of important issues, including the maximum Purcell factor and limits to quantum efficiency due to ohmic losses, is still lacking. Our findings reveal that the reported experimental results are reasonable, and confirm that such composite devices provide a promising route for high-efficiency single photon sources coupled to an optical fiber-based quantum communication network.

Quantum graph theoretic encryption and dynamic key evolution in secure quantum communication networks

The dawn of the quantum era marks a pivotal moment in the evolution of digital communications, bringing forth both unparalleled potential and unprecedented challenges. This paper delves into the realm of Quantum Graph Theoretic Encryption and Dynamic Key Evolution, a frontier in the quest for impenetrable communication networks in the quantum computing age. Quantum computing, with its ability to perform complex calculations at speeds unattainable by traditional computers, offers a beacon of hope and a source of peril. The very principles that endow quantum computers with exceptional power also render traditional cryptographic methods vulnerable. This dichotomy underscores the urgency for innovative encryption techniques that can withstand the onslaught of quantum computational capabilities. When merged with the principles of quantum mechanics, graph theory opens a new dimension of cryptographic possibilities. However, the dynamic nature of digital communications necessitates more than just robust encryption; it requires agility. This is where the concept of Dynamic Key Evolution comes into play. This paper is structured to guide the reader through this novel integration of quantum mechanics, graph theory, and dynamic cryptography. We begin by laying a foundational understanding of quantum computing, followed by an exploration of graph theory in the context of encryption. We then introduce our proposed method of Quantum Graph Theoretic Encryption, highlighting its advantages and potential applications. Subsequently, we delve into the concept of Dynamic Key Evolution, illustrating its significance in maintaining the integrity of quantum encryption in a rapidly changing digital landscape.

Quadripartite entanglement from two-port resonator with second-order harmonic generation

Quantum entanglement is a crucial resource for performing quantum computing and constructing quantum communication networks. The preparation and manipulation of entangled light field are the basic elements of quantum communication. With the development of science and technology, multicolor multipartite entanglement is becoming a kind of special resource for quantum information, quantum networks, and quantum memory. In this paper, we propose a scheme of generating quadripartite entanglement among four output beams from a two-port frequency doubling resonator, in which a type-II phase matching nonlinear crystal is placed. We make two fundamental-frequency pump beams with the same frequency and vertical polarization pass through the nonlinear crystal to produce two frequency-doubling beams. There is a quadripartite entanglement between the frequency-doubling beams, which are output at two ports of the optical resonator, and the incident fundamental beams. Based on the transmission matrix from the coupled wave equation, the self-consistent equations of the intracavity modes and the corresponding noise properties of the output modes can be obtained. Then, the quadripartite entanglement produced from two second harmonic beams and two reflected fundamental-frequency pump beams, is verified by using the positive partial transposition criterion, in a wide range of pumping power and analysis frequency. The setup proposed in this work is compact and experimentally feasible. It is also convenient to separate the four entangled beams spatially, with different wavelengths and polarizations. When the beam wavelengths are matched with 1560 nm (low loss window of fiber) and 780 nm (atomic absorption line of Rb), this scheme can be more useful in both quantum communication and quantum memory.