New Delhi: A team of researchers at IIT Delhi have achieved a significant milestone in quantum communication by demonstrating the transmission of quantum-entangled photons alongside classical data over a 50-km optical fibre link.

Led by Prof. Bhaskar Kanseri, Physics Dept., IIT Delhi, the research addresses a major practical challenge in the development of future quantum communication networks: how to transmit fragile quantum signals through the same fibre-optic infrastructure that carries high-power conventional telecommunications signals.

Quantum entanglement is a fundamental phenomenon underpinning several emerging quantum technologies, including quantum key distribution (QKD), which offers new approaches to securing the exchange of sensitive information. However, integrating quantum signals with existing telecommunications infrastructure is technically challenging. Classical optical signals are typically much stronger than quantum signals and can generate noise that may disturb or obscure delicate quantum states.

The IIT Delhi demonstration shows that quantum and classical communications can coexist over the same optical-fibre infrastructure under carefully controlled conditions. This represents an important step towards the practical integration of quantum technologies with existing telecommunications networks in an optimal way.

The potential long-term applications of this achievement are significant. More mature quantum communication networks could contribute to enhanced security for sensitive communications involving financial institutions, government agencies, healthcare organisations and critical infrastructure. By making use of same fibre infrastructure for quantum and classical signal, such networks could also become more scalable and cost-effective to deploy.

For India, the achievement adds to the country's growing capabilities in quantum technologies and supports broader efforts to develop secure, next-generation communication systems. This is an internationally competitive demonstration, representing a significant Indian contribution and a large step towards developing practical quantum networks. (More details can be found here: https://doi.org/10.1016/j.optcom.2026.133728)  

Under the guidance of Prof. Kanseri, his PhD students Nishant Kumar Pathak and Abhay Singh Dulta also played a key role in this research work, which received funding through IIT Delhi's Institute of Eminence (IoE) grant and the National Quantum Mission (NQM) of the Department of Science and Technology (DST), Government of India.