Secure Quantum Key Distribution Over VLC Networks for Next-Generation Smart Cities

Next-generation smart cities are increasingly reliant on high-speed, secure communication systems to support 6 G networks, IoT infrastructure, and autonomous systems. Classical cryptographic techniques are becoming vulnerable to quantum computing attacks, prompting the integration of quantum-secure communication mechanisms. In this context, Quantum Key Distribution (QKD) over Visible Light Communication (VLC) and Free Space Optical (FSO) networks offers a promising path toward ultra-secure, energy-efficient transmission. We propose an Entangled Photon Quantum Key Distribution (EP-QKD) framework that advances secure communication by integrating polarization-entangled photons, adaptive Quantum Bit Error Rate (QBER) optimization, and hybrid quantum-classical authentication anchored with blockchain. This advancement addresses critical limitations of traditional QKD systems—including high sensitivity to ambient interference, limited scalability, and high error rates—by employing entanglement-based noise resilience and real-time detection threshold control. Existing approaches to QoS and security—such as RSA-based encryption, BB84 and E91 protocols, and VLC-oriented modulation techniques—struggle with low secure key rates, high QBER under ambient light, and vulnerability to man-in-the-middle (MITM) attacks. EP-QKD overcomes these limitations by enhancing photon distribution fidelity, enabling decentralized authentication, and sustaining low error rates across dynamic urban optical environments. Experimental results demonstrate that EP-QKD achieves an average QBER of 1.2% and maintains QBER below 2.5% at 1000 lux, reducing errors by 40% over BB84 and 60% over E91. It attains secure key generation rates of over 1200 Mbps at 5 meters, outperforming BB84 and E91 by a significant margin. At 20 meters, EP-QKD maintains 300 Mbps, while BB84 drops to 40 Mbps. The MITM attack success rate is reduced to 0.01%, compared to 15% with BB84 + RSA. Additionally, EP-QKD achieves energy efficiency of 0.7 nJ/bit—nearly half of BB84’s requirement—making it suitable for energy-constrained IoT and mobile systems. Multi-user scalability testing confirms that EP-QKD can support up to 50 concurrent users with a key rate above 80 Mbps per user and QBER < 1.8%. A 3D analysis further shows that QBER remains below 5% even at 50 meters, demonstrating the framework’s robustness for long-distance secure optical communication. Overall, the proposed EP-QKD framework significantly enhances the performance, scalability, and resilience of quantum communication systems, making it a viable candidate for 6 G, IoT, and satellite-based secure infrastructure.