In a landmark milestone for India's digital and quantum future, the Centre for Development of Telematics (C-DOT), in collaboration with Sterlite Technologies Limited (STL), has achieved the nation’s first successful Quantum Key Distribution (QKD) transmission over a 4-core Multi-Core Fibre (MCF). This breakthrough underscores India's growing capabilities in the realm of quantum-secured communication networks. Multi-Core Fibre technology enables simultaneous transmission of data across multiple cores within a single fibre, significantly reducing physical space and infrastructure costs. Notably, QKD traditionally requires a dedicated dark fibre for quantum signal transmission. However, this achievement marks a paradigm shift, as MCF allows for the physical separation of quantum and classical signals within the same fibre — with one core carrying quantum signals and the remaining cores supporting high-speed user data. In this pioneering trial, quantum signals were transmitted through one core, while classical high-capacity data travelled through the other three cores, with a stable QKD link successfully maintained over a distance exceeding 100 km. This demonstrates the robustness and integrity of quantum communication even under concurrent classical data transmission, thereby enhancing the practicality and cost-efficiency of quantum-secured networks. C-DOT, India’s premier telecom R&D centre under the Department of Telecommunications (DoT), has developed and deployed industry-grade QKD systems that have received Technology Approval from the Telecommunication Engineering Centre (TEC). This latest accomplishment further strengthens its role in advancing the country’s quantum ecosystem. Sterlite Technologies Ltd. (STL), a global leader in optical networking solutions, has pioneered the development of Multi-Core Fibre leveraging Space Division Multiplexing to significantly increase transmission capacity. With a presence in over 100 countries and 10+ global manufacturing plants, STL remains at the forefront of building future-ready, scalable digital infrastructure. Commenting on the success, Dr Rajkumar Upadhyay, CEO, C-DOT, remarked, “This initiative marks a key milestone for India’s telecom ecosystem. It establishes the feasibility of integrated quantum-classical networks over next-gen optical fibres, drastically reducing QKD deployment costs.” Rahul Puri, CEO, Optical Networking Business, STL, added, “This breakthrough collaboration with C-DOT highlights India’s advancing capabilities in secure digital infrastructure. By integrating QKD with STL’s indigenous MCF technology, we are setting a new benchmark in secure communication and global optical leadership.” Both C-DOT and STL reaffirm their commitment to strengthening India’s position in the global quantum and optical networking landscape. This achievement lays a vital foundation for building a cost-effective, secure, and resilient national quantum communication infrastructure