Explained: India's 1-km quantum leap that makes eavesdropping impossible

Remember Salman Khan in the movie Judwaa —double trouble, one reflex? The actor plays twin brothers mysteriously synced-up: punch one, the other flinches. That David Dhawan comedy, believe it or not, offers a fun primer on something that even baffled Einstein—quantum entanglement.
Fast forward to today, the same concept is driving cutting-edge communication systems. Scientists from the Defence Research and Development Organisation (DRDO) and IIT Delhi have achieved a significant milestone: demonstrating quantum entanglement-based secure communication over one kilometre in open air. This isn't lab science—it's the start of building unhackable communication systems for military, financial, and governance sectors.
Why is quantum-secure communication necessary?
As data breaches grow more complex, traditional encryption struggles to keep up. Secure communication is no longer optional—it's critical. Quantum technologies offer a way to make eavesdropping nearly impossible by alerting both sender and receiver the moment someone tries to intercept the message.
What is quantum entanglement and why is it game-changing?
Quantum entanglement means two particles are mysteriously linked—change one, and the other responds instantly, even from far away. It defies conventional physics.
Think of entangled particles as magical dice: roll one in Delhi, and the matching die in Chennai shows the same number instantly. Or imagine whispering a secret across a stadium knowing no one else—not even with microphones or tech—can hear it. That's what India just pulled off using quantum entanglement.
How does quantum communication work?
Conventional internet communication sends binary data—0s and 1s—over cables or satellites. Quantum communication uses particles like photons that exist in fragile 'quantum states' (qubits).
The breakthrough lies in Quantum Key Distribution (QKD), which securely transmits encryption keys. If someone tries to tap in, the act of observing alters the quantum state—alerting users to a breach immediately.
DRDO and IIT Delhi demonstrated QKD across open air with:
A secure key rate of 240 bits per second (bps)
An error rate below 7 per cent
One kilometre of secure free-space communication
What did India achieve and who benefits?
India entered the quantum communication era by showing that it's possible to build hack-proof links using light particles in open air. The DRDO-IIT Delhi achievement includes:
One kilometre of secure communication without wires
A quantum key transmission rate of 240 bps
Low error margin of under 7 per cent
This lays the foundation for encrypted communication across banks, the armed forces, government systems, and telecom networks. The demonstration supports India's National Quantum Mission and advances domestic capabilities in photonics and long-distance quantum networking.
How does this compare to global quantum efforts?
Globally, most QKD systems function over short distances (20–50 km) using fibre optics. India's one-km free-space demonstration puts it in league with nations like China and the US, which are racing to build satellite-based quantum networks.
While China conducted a 1,200 km quantum satellite link via Micius, India's leap lies in achieving secure entanglement communication in open air — a milestone for building urban and battlefield quantum networks.

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