QNu Labs, an Indian deep-tech company, carried out the demonstration of India’s first free-space quantum key distribution (QKD) link in collaboration with Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N) at the Indian Institute of Technology, Gandhinagar. The field trial, spanning 5.6 kilometres was conducted on the night of September 27-28.
The Ministry of Electronics and Information Technology described the achievement as an important advance in the development of quantum-resilient communication systems. Unlike conventional quantum key distribution experiments that rely on fibre-optic cables, the new link transmitted quantum signals through the atmosphere, demonstrating secure key exchange across an open-air path.
The system used QNu Labs’ Armos hardware-based quantum key distribution platform and its Pointing, Acquisition and Tracking system. The latter is essential for maintaining alignment between transmitting and receiving terminals, particularly when optical signals must travel over several kilometres through the atmosphere.
During the trial, the link maintained a Quantum Bit Error Rate below 5 per cent and generated encryption keys at between 230 and 260 bits per second. The keys were subsequently integrated with BISAG-N’s Vedic Kavach platform, which combines post-quantum cryptography with quantum random-number generation.
Test messages were successfully encrypted and decrypted end to end. The architecture therefore combined two layers of protection: QKD at the hardware level and post-quantum cryptography at the software level. This arrangement is intended to preserve secure communications even if the quantum channel is temporarily disrupted.
QKD does not directly transmit ordinary messages. Instead, it creates and distributes encryption keys using quantum states of light. Because observing or measuring those states can disturb them, an interception attempt may introduce detectable errors. The communicating parties can then reject a compromised key and generate another one.
The technology is attracting attention as quantum computers threaten to weaken some widely used public-key systems, including those based on integer factorisation and elliptic-curve mathematics.
However, QKD is not a complete cybersecurity solution by itself. It requires specialised optical equipment, authenticated conventional communication channels and careful protection against implementation flaws. Post-quantum cryptography remains important because it can be deployed across existing digital networks.
Sunil Gupta, Co-founder and CEO, QNu Labs, said, “Quantum security will become meaningful at scale only when technologies can move beyond controlled laboratory environments and operate across real communication infrastructure. This field trial shows that QKD, supported by precise optical pointing and tracking, can be deployed over a multi-kilometre free-space link and integrated with a post-quantum security layer. The successful 5.56 km demonstration is an important step towards developing longer-distance quantum-secure networks and exploring architectures that can eventually support multiple nodes and satellite-based quantum communication.”
India’s latest demonstration extends an earlier free-space experiment by the Defence Research and Development Organisation and IIT Delhi. That 2025 trial covered more than one kilometre, recorded a secure key rate of approximately 240 bits per second and maintained a quantum bit error rate below 7 per cent.
Cmde Manish Tripathi (Retd.), In-charge, ISTF, IIT-G said, “The successful demonstration of a 5.56 km free-space QKD link provides a valuable field environment for advancing practical quantum communication technologies. The collaboration brings together academic research, indigenous technology and real-world experimentation, and demonstrates how these capabilities can be integrated to address the emerging requirements of secure communications.”
Dr Vinay Thakur, DG BISAG-N, said, “The integration of Vedic Kavach with QNu Labs’ QKD technology demonstrates the potential of combining post-quantum cryptography with quantum key distribution as complementary layers of security. The successful end-to-end application test is an important step towards developing practical quantum-resilient communication architectures that can evolve with emerging security requirements.”
The 5.56-kilometre result also aligns with the objectives of India’s National Quantum Mission, approved in 2023 with a budget of ₹6,003.65 crore. The programme seeks to build domestic capability in quantum computing, communication, sensing and materials, while supporting a future satellite-based secure communications network between ground stations separated by up to 2,000 kilometres.
The mission has already reported progress on longer fibre-based networks. A separate 2026 milestone involved a 1,000-kilometre quantum communication network using linked QKD segments. That achievement was reported as part of the government-backed effort to create a sovereign quantum-secure backbone for defence, finance and critical infrastructure.
Free-space systems could prove especially valuable where laying fibre is expensive or impractical, including mountainous regions, military theatres and links between ground stations and satellites. Atmospheric turbulence, weather, line-of-sight requirements and precise terminal alignment remain significant engineering challenges.
For India, the latest trial is therefore both a technical achievement and a field test of commercial readiness. Its success offers a platform for longer terrestrial links and future space demonstrations, while strengthening the country’s push to develop secure communications using domestically built technology.
