DRDO and IIT Delhi Demonstrate Free-Space Entanglement QKD Over a Kilometre

DRDO and IIT Delhi have demonstrated India's first entanglement-based free-space quantum secure communication, sending a quantum-encrypted key more than one kilometre across the IIT Delhi campus on 16 June 2025. The work, led by Prof. Bhaskar Kanseri's group, achieved a secure key rate of roughly 240 bits per second at a quantum bit error rate (QBER) below 7 percent. Those figures are modest but significant in what they prove: a working entanglement-based link through open air.

Why entanglement, and why free-space

Most fielded quantum key distribution sends single photons down optical fibre. This demonstration instead uses entangled photon pairs sent through free space. Quantum mechanics guarantees that any attempt to intercept the photons disturbs their correlations and exposes the eavesdropper. Doing this over an open-air optical path is the harder engineering problem, because the beam must survive atmospheric turbulence, scattering and pointing errors.

The reason to solve it is the destination: satellite QKD. Fibre cannot carry quantum signals across oceans or continents without trusted relay nodes, but a free-space link can be pointed at the sky. A ground-based free-space channel is the stepping stone to ground-to-satellite secure links, where a satellite distributes entangled photons to widely separated ground stations. The dual-use defence value is why DRDO is the partner: assured, eavesdropping-evident communications for the armed forces are a strategic capability.

The strategic backdrop

The motivation is competitive as much as scientific. China leads the field through its Micius satellite, which demonstrated intercontinental entanglement-based QKD years ago, and that lead is what India is working to close. The IIT Delhi result feeds a broader national effort: the RRI-ISRO satellite-QKD programme, SAQTI, funded at over ₹15 crore, is advancing toward a dedicated QKD microsatellite.

For an investor, the read is that India's quantum-communications stack is maturing from fibre-based metro QKD toward the free-space and satellite layer that confers strategic reach. The bits-per-second numbers will matter commercially only once the link goes to orbit, but proving entanglement-based free-space communication on the ground is the necessary first milestone, and India has now cleared it.