India has demonstrated its first free-space quantum key distribution link. The 5.56 km link ran between BISAG-N and IIT Gandhinagar, the government said on October 3.

The test used open air, not fibre. QNu Labs supplied the quantum hardware with its Armos system. The error rate stayed under 5 percent. Keys were produced at 230 to 260 bits per second.

BISAG-N fed the keys into its own Vedic Kavach post-quantum platform. Test messages were encrypted and decrypted with the quantum-generated keys.

Quantum key distribution uses physics to share encryption keys. Any attempt to intercept the keys disturbs the quantum states and reveals the eavesdropper.

Free-space links matter because they can connect places fibre cannot reach. They are also a step toward satellite-based quantum communication.

The distance is short by fibre standards. But the medium is the point. The keys crossed open air, proving the technique works outside the lab.

India joins a small group of countries testing quantum communication in the open. More trials are expected as the technology matures.