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Gandhinagar
India has successfully demonstrated its first free-space Quantum Key Distribution (QKD) link over 5.56 km, marking a significant step towards building secure communication networks that could eventually connect satellites and ground stations. The field trial was conducted by deep-tech startup QNu Labs in collaboration with the Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N) and IIT Gandhinagar.
The trial, conducted on the night of September 27-28, established a secure quantum communication channel between BISAG-N and IIT Gandhinagar. The system maintained a quantum bit error rate below 5 per cent and generated secure keys at 230-260 bits per second. These keys were integrated with BISAG-N’s post-quantum cryptography-enabled Vedic Kavach platform, allowing test messages to be encrypted and decrypted successfully.
Unlike conventional fibre-based QKD, the free-space system transmits quantum signals through open air using optical technology. This makes it particularly relevant for locations where laying fibre is difficult, while also providing a potential technological pathway towards satellite-based quantum communication.
A key component of the demonstration was QNu Labs’ Pointing, Acquisition and Tracking (PAT) system, which maintained the optical link across the 5.56-km distance. The trial combined hardware-based QKD with a second layer of post-quantum cryptography, offering greater resilience if the physical quantum channel is temporarily disrupted.
The achievement comes as India advances its quantum technology capabilities under the National Quantum Mission. Future applications could include secure government, defence and critical-infrastructure communications, as well as satellite-to-ground and satellite-to-satellite links.
The 5.56-km test remains a ground-based demonstration rather than a satellite communication system. However, officials and researchers say it provides an important foundation for extending quantum-secure links over longer distances and eventually developing space-based quantum communication networks.