India Pioneers Quantum Leap: C-DOT and STL Achieve First QKD Over Multi-Core Fibre

Quantum Key Distribution is a cutting-edge technology that allows two parties to share encryption keys with theoretically unbreakable security, safeguarded by the laws of quantum mechanics.

In a remarkable advancement in India’s technological journey, the Centre for Development of Telematics (C-DOT), in collaboration with Sterlite Technologies Limited (STL), has achieved a pioneering feat by successfully conducting India’s first Quantum Key Distribution (QKD) transmission over a 4-core Multi-Core Fibre (MCF). This milestone not only showcases India's growing strength in the quantum communication domain but also highlights the power of indigenous innovation and strategic partnerships between public research institutions and industry leaders.

A Paradigm Shift in Secure Communication

Quantum Key Distribution is a cutting-edge technology that allows two parties to share encryption keys with theoretically unbreakable security, safeguarded by the laws of quantum mechanics. Unlike traditional encryption techniques, which rely on complex mathematical algorithms, QKD ensures that any attempt to intercept the key is detectable, thereby making the communication inherently secure.

However, conventional QKD systems come with significant infrastructural challenges, often requiring a dedicated dark fibre solely for the quantum channel. This isolates the quantum signals from the noise generated by classical data traffic but increases deployment costs and logistical complexity.

The recent demonstration by C-DOT and STL offers an elegant and highly efficient solution to this limitation through the deployment of Multi-Core Fibre (MCF) technology.

How Multi-Core Fibre is Changing the Game

Multi-Core Fibre represents a revolutionary advancement in optical networking. Unlike standard single-core fibres, MCF contains multiple optical cores within a single cladding, allowing multiple streams of data to be transmitted independently over the same fibre strand. This technology enables both classical and quantum signals to coexist in the same physical cable, without interfering with one another.

In the groundbreaking trial conducted jointly by C-DOT and STL, quantum signals were transmitted through one dedicated core, while the remaining three cores carried high-speed classical data. The test was successfully conducted over a distance exceeding 100 kilometers — a key benchmark in proving the robustness, stability, and scalability of this integrated communication model.

Notably, the integrity of the quantum signal was preserved despite the proximity of high-capacity classical data traffic, validating the efficacy of MCF in facilitating secure quantum communication without the need for separate physical infrastructure. This translates into significant cost savings and reduced complexity in deploying quantum communication networks across existing and future fibre infrastructures.

The Power of Indigenous Innovation

The successful demonstration is also a testament to India’s growing expertise in quantum technology. C-DOT, India’s premier telecom R&D institution under the Department of Telecommunications (DoT), has been at the forefront of developing QKD systems aligned with international standards. These systems have not only been lab-tested but also received Technology Approval from the Telecommunication Engineering Centre (TEC), the nodal body responsible for technical standardization in Indian telecom networks.

Dr. Rajkumar Upadhyay, CEO of C-DOT, emphasized the strategic importance of the development: “This initiative is a key milestone for India’s telecom ecosystem. It demonstrates the technical feasibility of integrated quantum-classical networks using next-generation optical fibres, dramatically reducing the deployment costs for QKD. We are proud to lead the way in advancing India's secure communication capabilities."

STL’s Cutting-Edge Optical Innovation

Sterlite Technologies Limited (STL), a globally recognized leader in digital network infrastructure, played a crucial role in this innovation by developing and providing the Multi-Core Fibre used in the trial. With over 10 manufacturing facilities worldwide and a customer base spanning more than 100 countries, STL is known for driving advancements in optical networking, data centres, and enterprise connectivity.

STL’s MCF uses Space Division Multiplexing (SDM) in 4-core and 7-core fibre variants to drastically increase the transmission capacity per fibre without increasing the cable diameter. This innovation not only boosts scalability but also aligns with the growing demands for data-intensive applications, including quantum communications, AI, and IoT-based networks.

Rahul Puri, CEO of STL’s Optical Networking Business, expressed optimism about the broader implications of the achievement: “This breakthrough collaboration with C-DOT underscores India’s growing prowess in pioneering next-gen digital infrastructure. By successfully integrating QKD with our indigenously developed Multi-Core Fibre, we’ve demonstrated how advanced optical technologies can revolutionize secure communication. This is a proud moment for India’s innovation ecosystem and a step toward building a digitally sovereign nation.”

Toward a Quantum-Enabled Future

The successful demonstration of QKD over MCF is more than just a technological milestone — it is a foundational step toward realizing a secure, cost-effective, and scalable national quantum communication infrastructure. As countries around the world race to build quantum-secure networks to protect sensitive government, defense, and financial data, India’s proactive strides in this space signal a strong intent to lead in the quantum communication frontier.

Both C-DOT and STL have reaffirmed their commitment to advancing India's leadership in quantum-secured communications and next-generation optical networking. The collaboration serves as a prime example of how public-private partnerships can drive deep-tech innovation to meet national strategic objectives.

With this achievement, India moves one step closer to a future where ultra-secure, quantum-resilient communication becomes a mainstream reality — safeguarding the nation’s digital sovereignty in the evolving era of quantum computing.