India has tested a quantum link that sends encryption keys through open air. Here is how the 5.56 km experiment works and why it matters.

The test ran between BISAG-N and IIT Gandhinagar. QNu Labs supplied the hardware. The government announced the result on October 3.

Quantum key distribution, or QKD, shares secret keys using quantum physics. The keys are carried by particles of light. Any snooping disturbs the particles and exposes the eavesdropper.

The Indian test hit an error rate under 5 percent. It produced keys at 230 to 260 bits per second. That is enough for test messages.

BISAG-N fed the keys into its Vedic Kavach platform. Messages were encrypted and decrypted with the quantum-made keys.

The key word is “free-space”. The link crossed open air, not fibre cable. That makes it useful where fibre cannot go.

Free-space QKD is a step toward satellite quantum links. China has led this field. India is now testing the same path.

The distance is modest. But the physics is proven. Bigger and longer links come next.