The Author is Former Director General of Information Systems and A Special Forces Veteran, Indian Army

Quantum communication is a field of applied quantum physics closely related to quantum information processing and quantum teleportation. Its most interesting application is protecting information channels against eavesdropping by means of quantum cryptography. Quantum computing uses qubits as basic resources, similar to how bits are used as basic resources in classical computing. Quantum key distribution (QKD) is a secure communication method which implements a cryptographic protocol involving components of quantum mechanics. It enables two parties to produce a shared random secret key known only to them, which can then be used to encrypt and decrypt messages. Quantum technology is evolving quickly and no doubt will have a significant impact not only on warfare but also in terms of national security.

Quantum key distribution (QKD) is a secure communication method which implements a cryptographic protocol involving components of quantum mechanics

In 2016, China launched the satellite 'Micius', which is solely dedicated to quantum information science. It has achieved several groundbreaking results that are bringing the once esoteric field of quantum cryptography into the mainstream. In 2017, a Chinese team, along with a group of researchers in Austria, used Micius to perform the world's first quantum-encrypted virtual teleconference between Beijing and Vienna. In June 2020, the Micius satellite successfully established an ultra-secure link between two ground stations separated by more than 1,000 km. China next planned launching and operating a quantum satellite in a higher orbit (10,000 km above Earth's surface). Micius orbits 500 km above earth but a satellite orbiting at 10,000 km above Earth would facilitate quantum communications between ground stations much farther apart from one another throughout the day.

It may be recalled that on December 9, 2020, the Defence Research and Development Organisation (DRDO) successfully demonstrated QKD-based communications between its two labs in Hyderabad to Defence Minister Rajnath Singh. In February 2022, scientists of the Ahmedabad-based Physical Research Laboratory (PRL) and Space Applications Centre (SAC) demonstrated hack-proof satellite-based communication. The technology, which uses the concept of "quantum entanglement" will make it impossible to hack any communication in future. The concept is at the core of futuristic quantum computing and also has applications in building unbreakable encryption technology and scientist's world over are working on it. The demonstration was conducted at SAC between two buildings 300 metres apart. During the demo, scientists indigenously created an atmospheric channel on the ground to share quantum-secure text, images and videos between the two points.

According to news reports of January 12, 2024, Russia and China successfully tested satellite-based quantum communication to communicate over a distance of about 4,000 km, according to the media reports of January 12, 2024. The test was enabled by China's 'Mozi' satellite. The test involved transmitting a message from a ground-receiving station in China linked to a Russian facility nearly 4,000 km away. The test was conducted in 2023, as described in a paper in mid-December by Alexey Fedorov, who is part of Russia's National University of Science and Technology, the Russian Quantum Centre (RQC).

Russia and China successfully tested satellite-based quantum communication to communicate over a distance of about 4,000 km

News reports of April 21, 2025 now confirm that India has achieved another breakthrough in quantum communications, in that, the Centre for Development of Telematics (C-DOT), jointly with Sterlite Technologies Limited (STL), has successfully tested India's first QKD transmission over a 4-core Multi-Core Fibre (MCF). This is a major milestone in the nation's journey towards quantum-secured communication networks. MCF enables data transmission across multiple cores within a single fibre, resulting in saving space and infrastructure costs. Moreover, QKD has the advantage of enabling physical separation of quantum and classical signals into distinct cores within single fibre; this allows simultaneous transmission of QKD and high-capacity data traffic on a single fibre without compromising quantum signal integrity thereby saving fibre cost.

C-DOT is India's premier telecom R&D centre under the Department of Telecommunications (DoT), Ministry of Communications. C-DOT has successfully developed and deployed industry-grade QKD systems. Sterlite Technologies Limited (STL) is a global provider of integrated digital networks, specialising in optical fibre manufacturing and network designs, with 10+ global manufacturing plants and a customer base spanning 100+ countries. STL has developed the MCF, achieving ultra-high transmission capacity per fibre within the same diameter. In this activity, the quantum signals of QKD were transmitted through one core, while simultaneously, the other three cores on the same fibre were used to carry high-speed user data. A stable QKD link was established over a distance exceeding 100 km, validating the robustness and stability of quantum communication even amidst high-capacity classical data traffic.

Centre for Development of Telematics (C-DOT), jointly with Sterlite Technologies Limited (STL), has successfully tested India's first QKD transmission over a 4-core Multi-Core Fibre (MCF)

Speaking at the occasion, Dr Rajkumar Upadhyay, CEO of C-DOT, stated, "This initiative is a key milestone for India's telecom ecosystem. This achievement clearly establishes the feasibility of integrated quantum-classical networks over next-generation optical fibres saving costs for QKD deployments drastically". Rahul Puri, CEO, Optical Networking Business, STL said, "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 MCF, we have demonstrated how cutting-edge optical innovations can revolutionise secure communication. We are committed to advancing India's quantum communication ambitions while driving global optical leadership. This milestone is a testament to the power of public-private partnerships in building a digitally sovereign and secure nation."

The successful testing of India's first QKD transmission over a MCF is a remarkable achievement, which will provide the foundation for a cost effective, secure and resilient quantum communication infrastructure for India.