IIT-Gandhinagar scientists demo quantum link through 5.5 km of air

Indian researchers showcased a quantum-secure communications link spanning over five kilometers through open air, marking the first of its kind in India. The demonstration, conducted on September 27-28, connected the Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N) with IIT-Gandhinagar, using equipment provided by QNu Labs from Bengaluru.

Quantum-key distribution (QKD) is a technology aimed at enhancing communication security by generating a shared encryption key through the transmission of information encoded in photons. If an unauthorized party attempts to intercept these particles and measure their quantum states, errors will occur, detectable by the communicating parties.

This ensures secure key sharing using quantum physics. Previously, in 2025, IIT-Delhi and the Defence Research & Development Organisation had demonstrated a QKD link through a distance of slightly more than a kilometer, while ISRO had previously achieved a link over 300 meters. QKD is typically implemented on land using fiber-optic cables, requiring precise alignment and adjustments for atmospheric conditions.

In the IIT-Gandhinagar demo, scientists achieved a quantum bit error rate of less than 5%, indicating successful secure key generation at a rate of 230-260 bits per second. The system was able to encrypt and decrypt messages using a cryptographic platform at BISAG-N. Additionally, the researchers employed post-quantum cryptography (PQC) to provide an extra layer of security.

This open-air demonstration paves the way for deploying QKD links between satellites and ground stations, with China already launching the world's first QKD satellite, Micius, in 2016. India's National Quantum Mission aims to achieve satellite-based secure quantum communications between ground stations separated by up to 2,000 kilometers and a 2,000-kilometer inter-city QKD network using fiber-optic cables.