The demonstration generated secure-key data at 230–260 bits per second with a quantum bit error rate below 5%.
The September 27–28 test connected BISAG-N and IIT Gandhinagar using equipment from Bengaluru-based QNu Labs. It was described as India’s first free-space quantum key distribution (QKD) link over 5.56 km, more than five times the distance covered by IIT Delhi and DRDO in 2025.
QKD enables two parties to create a shared encryption key using photons. Attempts to intercept and measure their quantum states introduce errors the parties can detect. In open-air tests, transmitter and receiver must be precisely aligned, and researchers must account for atmospheric turbulence and light pollution.
India’s Ministry of Electronics and Information Technology said the quantum bit error rate was below 5%. Secure-key data was generated at 230–260 bits per second and used to encrypt and decrypt messages. Researchers also applied post-quantum cryptography as a second layer of protection.
The experiment is a step toward satellite-based QKD links. India’s National Quantum Mission aims for secure satellite communication between ground stations up to 2,000 km apart and a fibre-optic inter-city QKD network of similar length. ISRO previously demonstrated a 300-metre link.