India achieves first free‑space quantum‑key link over 5.56 km

Indian scientists have set up the country’s first free‑space quantum‑key distribution link, sending encrypted photons across 5.56 km of open air.

Demonstration

The test was carried out on the night of 27‑28 September 2026 between the Bhaskaracharya National Institute for Space Applications and Geo‑informatics (BISAG‑N) and IIT‑Gandhinagar. QNu Labs of Bengaluru supplied the quantum hardware. The team achieved a quantum bit error rate below 5 percent and generated secure keys at 230‑260 bits per second, which were used to encrypt and decrypt messages at BISAG‑N.

Technical Details

In free‑space QKD the photons travel through the atmosphere, so the transmitter and receiver must stay precisely aligned despite turbulence and light pollution. QKD works by encoding the encryption key in individual photons; any attempt to measure them changes their state and creates errors that reveal interception. The experiment also ran post‑quantum cryptography (PQC) alongside QKD, giving a double layer of protection; PQC uses mathematical algorithms that remain hard to break even for future quantum computers. Earlier Indian trials reached only about one kilometre (IIT‑Delhi and DRDO, 2025) and 300 m (ISRO, 2022). China’s Micius satellite, launched in 2016, and Jinan‑1 in 2022, already demonstrate satellite‑to‑ground QKD.

Context

These open‑air trials are steps toward the National Quantum Mission’s goal of satellite‑based secure links over 2 000 km and an inter‑city fibre network of the same length.