India Demonstrates First Free-Space Quantum Key Distribution Link

Context

QNu Labs, BISAG-N and IIT Gandhinagar demonstrated India’s first free-space Quantum Key Distribution (QKD) link, securely transmitting quantum keys over 5.56 km.

About Quantum Key Distribution (QKD)

• Nature: A quantum-secure communication technology that uses quantum mechanical principles to transmit encryption keys through open-air optical channels instead of fibre-optic cables.
• Aim: Develop tamper-resistant communication infrastructure capable of addressing future quantum-enabled decryption threats and support secure defence and satellite communications.

How Does QKD Work?

• Photon-Based Encoding: Encryption keys are encoded using individual photons.
• Free-Space Transmission: Pointing, Acquisition and Tracking (PAT) systems maintain alignment between transmitter and receiver across the open-air link.
• Eavesdropping Detection: Under the Heisenberg Uncertainty Principle and No-Cloning Theorem, interception or measurement of quantum states introduces detectable changes and errors.
• Key Generation: When the Quantum Bit Error Rate (QBER) remains within the acceptable limit, raw quantum bits are processed into shared symmetric encryption keys.

Key Features

• Range: Demonstrated secure transmission over 5.56 km without fibre infrastructure.
• Performance: Maintained QBER below 5% with key generation of about 230–260 bits per second.
• Dual-Layer Security: Combines quantum-based security hardware with post-quantum cryptography.
• Optical Alignment: Uses high-precision PAT systems to maintain laser alignment despite atmospheric turbulence and vibrations.
• Collaborative Model: Brings together private industry, government R&D and academic research.

Applications

• Space: Future satellite-to-ground and inter-satellite quantum communication.
• Defence: Secure communication for military, naval and mobile field operations.
• Critical Infrastructure: Protection of sensitive, nuclear, defence and space communications.
• Difficult Terrain: Secure links across rivers, valleys and disaster-affected areas where fibre deployment is difficult.

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