This research explores the fundamental principles of quantum computing and their application in enhancing communication security through Quantum Key Distribution (QKD) in free-space channels. Classical cryptographic methods face inherent limitations, particularly with the advent of quantum computational capabilities. Quantum mechanics, specifically the principles of superposition and entanglement, offers a robust framework for secure communication, ensuring that any attempt at eavesdropping inevitably perturbs the quantum state, thus revealing the intruder's presence. Through comprehensive simulations, this study analyzes the performance of QKD systems in free-space communication. Key parameters such as transmittance efficiency ( ), Quantum Bit Error Rate (QBER), and Secret Key Rate (SKR) are evaluated. Results indicate that transmittance efficiency in free space generally decreases with increasing zenith angle, with downlink scenarios (day and night) exhibiting higher efficiencies compared to uplink during the night. For all protocols, simulations demonstrate an increase in QBER and a corresponding decrease in SKR as the zenith angle increases, with downlink performance consistently surpassing uplink in terms of a higher SKR and a lower QBER
This research explores the fundamental principles of quantum computing and their application in enhancing communication security through Quantum Key Distribution (QKD) in free-space channels. Classical cryptographic methods face inherent limitations, particularly with the advent of quantum computational capabilities. Quantum mechanics, specifically the principles of superposition and entanglement, offers a robust framework for secure communication, ensuring that any attempt at eavesdropping inevitably perturbs the quantum state, thus revealing the intruder's presence. Through comprehensive simulations, this study analyzes the performance of QKD systems in free-space communication. Key parameters such as transmittance efficiency ( ), Quantum Bit Error Rate (QBER), and Secret Key Rate (SKR) are evaluated. Results indicate that transmittance efficiency in free space generally decreases with increasing zenith angle, with downlink scenarios (day and night) exhibiting higher efficiencies compared to uplink during the night. For all protocols, simulations demonstrate an increase in QBER and a corresponding decrease in SKR as the zenith angle increases, with downlink performance consistently surpassing uplink in terms of a higher SKR and a lower QBER
Quantum computing poses significant threats to conventional cryptographic techniques such as RSA and AES, motivating the need for quantum secure communication methods. Quantum Key Distribution (QKD) offers information theoretic security based on fundamental quantum principles. This paper presents a simulation-based analysis of well-known QKD protocols, namely BB84, B92, and E91, using the IBM Qiskit framework. Realistic quantum channel effects, including noise, decoherence, and eavesdropping, are modeled to evaluate protocol performance. Key metrics such as error rate, secret key generation, and security characteristics are analyzed and compared. The study highlights practical challenges in QKD implementation, including hardware limitations and channel losses, and discusses insights toward scalable and robust quantum communication systems. The results support the feasibility of QKD as a promising solution for secure communication in the quantum era.
There are substantial problems in sending quantum information safely over free-space channels because of air turbulence, diffraction, beam divergence, and noise. This study offers an extensive performance evaluation of quantum computing-based security methods utilised in free-space communication systems, specifically emphasising Quantum Secure Direct Communication (QSDC) and Quantum Key Distribution (QKD) protocols. The purpose of this work is to examine the attainable secret-key generation rates, assess the robustness of quantum security protocols in practical free-space environments, and contrast their effectiveness in preventing eavesdropping and signal degradation. This research employs quantum optics, turbulence theory, and quantum information theory to examine the performance constraints of continuous-variable (CV) coherent-state protocols amid fluctuating turbulence intensities. The suggested analytical approach simulates both fading and non-fading atmospheric channels to calculate essential rates and quantum bit error rates (QBER) for free-space quantum secure direct communication (QSDC) systems. Experimental findings and simulation outcomes indicate that free-space quantum channels can provide high-rate and long-distance secure communication when optimized using pilot-guided coherent-state protocols. The review shows how QSDC is better than regular QKD since it lets messages be sent directly without pre-shared keys. It also talks about how useful it may be for secure communication networks between satellites and between satellites and the earth. The paper closes by delineating the primary research deficiencies and suggesting avenues for improving protocol efficiency, error rectification, and turbulence mitigation in forthcoming global quantum communication systems.
Quantum communication leverages the principles of quantum mechanics, such as superposition and entanglement, for inherently secure data transmission that can detect any eavesdropping attempt. This research addresses the limitations of classical encryption by proposing a hybrid Quantum Key Distribution (QKD) protocol that integrates the Bennett & Brassard 1984 Protocol(BB84) and Scarani-Acín-Ribordy-Gisin 2004 Protocol(SARG04) protocols. The primary objective is to enhance resilience against advanced threats such as Photon Number Splitting (PNS) and collective attacks, which are significant vulnerabilities in standard QKD implementations. The quantum channel is modeled using Qiskit Aer's noise framework, incorporating fiber attenuation (0.1−0.25dB/km), depolarization (1−5%), and detector dark counts (0.01−0.03probability), varied across 10 rounds. A simulation spanning 10 rounds evaluated key metrics, including Quantum Bit Error Rate (QBER), photon loss, and final key entropy. The results demonstrate the protocol's robustness, achieving a 0 % QBER in 50 % of the trials, representing a significant improvement in secure key generation. The average QBER across all rounds was 12.5 %, which is well below the 11 % theoretical threshold for secure communication. The highest QBER recorded was5 0 %in Round 02, where high depolarization and an eavesdropping attempt were simulated. The work's findings indicate that the hybrid BB84-SARG04 protocol significantly enhances the security and reliability of quantum communication.
Satellite-based free-space quantum key distribution (QKD) provides a practical framework for achieving secure global communication beyond the limitations of optical fibers. In this work, the quantum bit error rate (QBER) and secure key rate of four representative protocols-BB84, B92, BBM92, and E91 are investigated over low earth orbit (LEO) links in both uplink and downlink configurations. The optical link is modeled using a Gaussian beam formalism, incorporating the effects of diffraction, pointing errors, atmospheric turbulence, and background noise contributions. The protocols are examined under day and night-time operating conditions, and their dependence on the zenith angle is analyzed. The findings show that downlink links generally exhibit lower QBER and higher secure key rates than uplinks, and among prepare-and-measure schemes, BB84 consistently outperforms B92, while in entanglement-based approaches, BBM92 achieves higher key rates than E91.
Quantum Key Distribution (QKD) has emerged as a fundamentally secure approach to communication in the era of quantum computing, offering protection against threats posed to classical cryptographic schemes such as RSA and Diffie-Hellman. This thesis presents a comprehensive performance analysis of satellite-based QKD protocols, focusing on both prepare-and-measure and entanglement-based schemes under realistic atmospheric and operational conditions. The study begins by introducing the theoretical foundations of quantum communication, including qubits, entanglement, and quantum entropy, and motivates the need for satellite-based QKD to overcome the distance limitations of fiber-based systems. Subsequently, the thesis evaluates four prominent QKD protocols-BB84, B92, BBM92, and E91-using a circular beam propagation model that incorporates atmospheric effects such as diffraction, turbulence, attenuation, and pointing errors, along with environmental noise contributions for uplink and downlink. Comparative numerical simulations reveal that protocol performance is strongly influenced by channel asymmetries, beam propagation characteristics, and noise, providing guidance on optimal protocol selection for low Earth orbit (LEO) satellite links. The research further investigates high-dimensional (HD) QKD protocols, specifically HD-BB84 and HD-Extended B92, using the elliptic-beam approximation to account for turbulence-induced distortions for both uplink and downlink. Simulations under vary ing system dimensions, weather conditions, and zenith angles demonstrate that HD-BB84 achieves higher key rates, superior noise tolerance, and more favorable probability distributions of the key rate compared to HD-Extended B92, highlighting the advantages of high-dimensional encoding for robust satellite-based QKD.
This thesis explores the critical advancements in quantum communication with a primary focus on the BB84 protocol, the foundation of Quantum Key Distribution (QKD). It delves into the theoretical principles, practical implementation using Qiskit, and performance evaluation through metrics like entropy, Quantum Bit Error Rate (QBER), and efficiency. Comparative analysis with alternative protocols, such as B92 and SARG04, highlights their advantages, limitations, and suitability for real-world applications. The work also addresses challenges like photon number splitting attacks and implementation imperfections, contributing to the development of robust quantum cryptographic systems. By bridging theory and practice, the thesis emphasizes the transformative potential of quantum cryptography in securing communication against both classical and quantum threats. This comprehensive study paves the way for advancements in secure, scalable quantum communication technologies.