NEC Hybrid Quantum Key Distribution Extends Submarine Optical Communications Range
NEC Hybrid Quantum Key Distribution Extends Submarine Optical Communications Range
According to a report published by Quantum Zeitgeist, secure communication across long distances remains a challenge, especially for underwater systems such as submarines. Researchers at the Universidade de Santiago de Compostela, including Jesús Liñares, Xesús Prieto-Blanco, and Alexandre Vázquez-Martínez, together with Eduardo F. Mateo from NEC, developed a hybrid quantum cryptography method designed for these environments. Their research introduces a multichannel hybrid system that extends beyond the limits of current quantum key distribution (QKD) systems. By combining several optical channels with layered security, the team addresses vulnerabilities in submarine communication, building more resilient and secure underwater networks.
This approach positions each party at a coastline and leverages the difficulty of simultaneously accessing multiple submarine optical channels. The optical links stretching from the coastline to the continental platform operate using high-dimensional, autocompensating discrete-modulation continuous variable QKD (DM-CV-QKD). Several secret keys are created from these multiple channels and secured by passive or active protections across non-quantum optical links beyond the continental margin.
Auto-compensating DM-CV-QKD for Submarine Networks
The hybrid method strengthens submarine optical communication by combining quantum and classical cryptography with physical layer security. It employs auto-compensating DM-CV-QKD on continental platforms alongside classical cryptographic distribution for longer distances. This reduces system complexity and cost by minimizing the need for precise hardware adjustments, while addressing signal degradation. High-dimensional quantum states increase the rate of key generation and make eavesdropping more difficult. Network topologies distribute keys across multiple layers, while security mechanisms detect intrusion attempts on buried submarine cables. Techniques include Distributed Acoustic Sensing (DAS), monitoring of fiber disturbances, and both passive and active protections.
Passive security benefits come from buried cables, while active defenses detect and respond to tampering. Proposed methods include few-mode fibers to detect taps, multi-core fibers to complicate interception, DAS to sense vibrations from tapping, and monitoring fiber changes to detect intrusions. These combined methods create a practical system for long-distance submarine communication, overcoming QKD’s range limits and improving resilience against attacks.
Multi-Channel QKD for Long-Distance Security
The system employs multiple optical channels, making simultaneous interception more difficult. It is designed for coast-to-coast communication, compensating for signal degradation through high-dimensional DM-CV-QKD. By merging secret keys and adding layers of security, the network achieves higher resilience against attacks. Tests show that two-dimensional encoding performs better than two independent single channels, producing greater efficiency and higher key rates.
A central innovation is an autocompensating technique using a Half Wave Plate, which restores the polarization of quantum signals without requiring complex active systems. This simplifies deployment and ensures robust protection against disturbances in optical fiber transmission. The results show major improvements in secure communication, enabling long-distance and highly secure submarine links.
Hybrid QKD Enhances Submarine Communication
The hybrid system demonstrates that purely quantum solutions over long distances are impractical, and hybrid approaches offer a better balance. It uses coherent light product states through multiple or multi-core fibers to encode information securely. Although promising, further investigation is required to optimize physical layer protections for non-quantum channels and test resilience against advanced attacks.
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About Universidade de Santiago de Compostela
The Universidade de Santiago de Compostela (USC), located in Galicia, Spain, is one of the country’s oldest and most prestigious universities, with a history dating back to 1495. Renowned for its research excellence, USC has consistently contributed to advancements across multiple disciplines, including physics, engineering, computer science, and biomedical sciences. Its Faculty of Physics and related institutes have developed strong expertise in quantum optics, photonics, and cryptography, positioning the university as a leader in emerging quantum technologies.
USC has an international reputation for fostering innovation through collaboration with global research institutions, industry partners, and European Union research initiatives. In addition to its research focus, the university serves as a hub for higher education in Spain, offering programs across sciences, humanities, and technology. With a strong commitment to sustainability, social responsibility, and academic excellence, USC continues to drive forward-thinking projects that impact both academia and real-world applications.
About NEC
NEC Corporation, headquartered in Tokyo, Japan, is a global leader in information technology, networking, and communications. Founded in 1899, the company has a long history of pioneering technologies that shape modern digital infrastructure. NEC operates across sectors including telecommunications, smart cities, public safety, and enterprise IT solutions. A recognized innovator in quantum cryptography and secure communications, NEC has invested heavily in quantum technologies to strengthen next-generation cybersecurity and networking capabilities. The company has collaborated with universities and research institutions worldwide, developing advanced systems for quantum key distribution (QKD), photonics, and AI-driven network optimization.
NEC’s expertise extends into high-performance computing, biometric authentication, and cloud services, supporting governments and enterprises in building secure, efficient digital ecosystems. Guided by its vision of “Orchestrating a brighter world,” NEC integrates cutting-edge research with practical solutions, playing a vital role in global digital transformation and advancing secure communication technologies for critical infrastructure.
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