India tests quantum-secure link across 5.56 kilometres of open air

Indian researchers have used a 5.56-kilometre open-air quantum link to help encrypt and decrypt test messages, covering more than five times the distance of a similar Indian trial in 2025.

The demonstration took place on the night of September 27–28 between IIT Gandhinagar and BISAG-N, a space-technology institute, using equipment supplied by Bengaluru-based QNu Labs.

The technology, called quantum key distribution, uses particles of light to establish shared encryption keys. Attempts to intercept and measure those particles introduce errors that the sender and receiver can detect. Unlike systems that send light through fibre-optic cables, this link transmitted it directly through the atmosphere.

That requires precise alignment between the transmitter and receiver, along with adjustments for atmospheric turbulence and light pollution. According to India’s Ministry of Electronics and Information Technology, the trial kept the proportion of incorrectly received quantum bits below 5%, a desirable level.

The team also combined the quantum link with software-based encryption designed to resist attacks from both conventional and quantum computers. Together, the systems successfully protected test messages from sender to receiver.

This was a ground-based demonstration, not a satellite connection. But testing reliable transmission through open air is an important step towards links between satellites and ground stations, a longer-term goal of India’s National Quantum Mission.