Indian scientists have demonstrated a quantum-secure communications link through open air across more than five times the distance covered in a similar test last year.
QNu Labs from Bengaluru supplied the equipment. QKD is a technology to make communications more secure. Two parties generate a shared encryption key by transmitting information encoded in particles in photons. In most instances where QKD is used on land, operators transmit the photons through fibre-optic cables. In open-air tests like the ones at IIT-Delhi and IIT-Gandhinagar, the particles travel through the atmosphere between two points with a direct line of sight. So the transmitter and the receiver need to be perfectly aligned, and scientists have to adjust the light signal passing between them for atmospheric turbulence and light pollution. When scientists fed this information into a cryptographic platform at BISAG-N, they were able to encrypt and decrypt messages. In the same demo, scientists also used post-quantum cryptography (PQC), a security paradigm in which information is safe from ‘hacking attempts’ made using both conventional and quantum computers. Combining QKD and PKC provides two layers of protection.
In the latest demo, on the night of September 27-28, scientists connected the Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N) and IIT-Gandhinagar. The feat has been described as India’s first free-space quantum-key distribution (QKD) link at a distance of 5.56 km. In 2025, scientists at IIT-Delhi and the Defence Research & Development Organisation had demonstrated a QKD link through just over a kilometre of free air. Four years prior, the Indian Space Research Organisation (ISRO) had demonstrated a QKD link over 300 m. The setup was able to generate the information required for secure keys at 230-260 bits per second.
