In a landmark step toward quantum-secure communication, C-DOT (Centre for Development of Telematics) and Sterlite Technologies Limited (STL) successfully conducted India’s first Quantum Key Distribution (QKD) over a 4-core Multi-Core Fibre (MCF). 

• The achievement marks a major technological leap, combining classical high-speed data and quantum channels in a single optical fiber, a milestone for India’s digital sovereignty and secure telecom infrastructure.

How Does QKD Work?

• Key Generation:
  • A sender (commonly referred to as Alice) sends photons encoded with a random key to the receiver (Bob) through an optical fibre.
  • Each photon is polarized (e.g., vertical, horizontal) representing binary data (0 or 1).
• Key Transmission:
  • Quantum properties ensure that observing the photon changes its state. Thus, any eavesdropping (by Eve) will disturb the transmission and alert the parties.
• Key Reconciliation and Privacy Amplification:
  • After the initial exchange, both parties compare a subset of bits over a public channel to detect eavesdropping.
  • If secure, they refine the key for encryption and communication.

Benefits of QKD-MCF

1. Enhanced Security: Virtually unbreakable encryption based on quantum laws.
2. Cost Efficiency: Eliminates the need for separate “dark fibres” for quantum channels.
3. High Data Capacity: Classical and quantum channels co-exist in one fibre.
4. Infrastructure Optimization: Saves physical space and installation costs.
5. Reduced Signal Interference: Dedicated cores ensure signal isolation.

Limitations of QKD Technology

1. Distance Constraints: Effective typically up to 100–200 km over fibre without repeaters.
2. High Implementation Cost: Requires specialized hardware and systems.
3. Speed and Efficiency: Slower than classical key exchange protocols.
4. Environmental Sensitivity: Photon states can be disrupted by noise and temperature changes.

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