India's Quantum Leap: First QKD Transmission Achieved Over Multi-Core Fibre

In a groundbreaking development for India’s secure communication future, the Centre for Development of Telematics (C-DOT), in collaboration with Sterlite Technologies Limited (STL), has successfully conducted the country’s first Quantum Key Distribution (QKD) transmission over a four-core Multi-Core Fibre (MCF). This marks a major step forward in creating a robust, quantum-secured digital infrastructure.

Quantum Key Distribution (QKD) is an advanced technology that allows for unbreakable encryption by using the principles of quantum physics. Traditionally, QKD requires a separate dedicated fibre—often called "dark fibre"—to carry delicate quantum signals, keeping them isolated from regular internet or telecom data. However, this can be costly and inefficient, especially at scale.

That’s where Multi-Core Fibre (MCF) comes in. MCF is a type of optical fibre that houses multiple data channels—or cores—within a single cable. This allows different signals to travel independently without interfering with each other. In this test, quantum signals were transmitted through one core, while high-speed user data traveled through the remaining three cores simultaneously. Remarkably, the QKD link remained stable over a distance of more than 100 km, even with heavy classical data traffic running alongside it. This proves that quantum communication can co-exist with traditional data transfer, all within the same fibre.

C-DOT, which operates under the Department of Telecommunications (DoT), has played a central role in building India’s quantum communication capabilities. The organisation has developed and deployed fully functional QKD systems, which have already received approval from the Telecommunication Engineering Centre (TEC). This gives India a solid foundation for building secure communication networks resistant to cyber threats.

Sterlite Technologies Limited (STL), known for its global leadership in optical networks and fibre manufacturing, has been instrumental in developing Multi-Core Fibre technology. STL’s MCF uses Space Division Multiplexing to significantly increase how much data a single fibre can carry. Their innovation supports the move toward future-ready, scalable fibre networks.

Dr. Rajkumar Upadhyay, CEO of C-DOT, highlighted that this collaboration marks a significant achievement for India’s telecom sector, making integrated quantum-classical communication a reality at a fraction of traditional costs. Rahul Puri, CEO of STL’s Optical Networking Business, echoed this sentiment, noting that this partnership reflects India's growing leadership in building advanced digital infrastructure through public-private cooperation.

This achievement is more than just a technical milestone—it lays the foundation for a cost-effective, secure, and resilient national quantum communication network. With continuous innovation and strategic partnerships, India is firmly positioning itself at the forefront of the global quantum revolution.