Hybrid Photon based Free-space Quantum Key Distribution Testbed (Left Image)

The DRDO Industry Academia–Centre of Excellence (DIA-CoE), IIT-Delhi demonstrated quantum communications technologies in New Delhi. It has been developed by their collaborative initiative of the entanglement based quantum key distribution approaches for robust and secure communication, demonstrating entanglement distribution and quantum key distribution (QKD) over a 50 km fibre link in laboratory. A separate field test has demonstrated entanglement distribution and QKD over 8 km of optical fibre in IIT-Delhi campus.

In another initiative of quantum research, Free-space Entanglement distribution was demonstrated using the BBM-92 protocol, a key QKD method, between two tables separated by 20 meters in the lab and 80m in the open space. This experiment demonstrated short-range quantum communication in a free-space setup.

In an innovative experiment, Hybrid entanglement has been demonstrated in a free-space environment, achieving a Quantum Bit Error Rate (QBER) of around 6% in the laboratory over a distance of 10m in the lab. In addition, QKD systems supporting multiple independent channels driven by a single source are also being explored with promising results. These open the door for more flexible, multi-protocol quantum communication systems.

In achieving the above breakthrough, an all-fibre heralded photon source with second-order correlation function (g² ~ 0.01) at rates reaching hundreds of kHz is developed. This innovation is vital for single-photon generation, a critical requirement for secure quantum communication. An all-fibre entangled photon source has also been developed with high visibility. The Bell test parameter for this source is more than 2.6, exhibiting strong quantum entanglement, which is essential for protocols like BBM-92.

For free space quantum communication experiments, Free-space heralded single photon source has been demonstrated with a heralding rate of over 4 million counts/sec. This development enables robust free-space quantum communication.

Following India's First Quantum Key Distribution (QKD) demonstration between the cities of Prayagraj and Vindhyachal, separated by 100 km, by DRDO labs and IIT-(D) in February 2022, many new initiatives have been taken by DRDO and IIT-(D).

In addition, indigenisation of various components like quantum sources and detectors are initiated. These include single photon sources on LNOI, SNSPD and periodically poled non-linear crystals. These projects are launched at IIT-Delhi in collaboration with DRDO labs like DYSL-QT and SSPL and are funded by Directorate of Futuristic Technology Management under its deep tech initiatives aimed at fostering cutting-edge innovations in defence technology.

Through its projects at the DIA-CoE, IIT-D, DRDO have created a strong national foot-print in QKD with breakthroughs in fibre and free space areas. Quantum communication holds significant potential for enhancing security in strategic sectors, such as defence and finance, by providing robust and tamper-evident communication channels.

The DRDO Industry Academia–Centre of Excellence (DIA-CoE) is a collaborative initiative between DRDO and IIT-Delhi, established at IIT-Delhi. The CoE is developing various quantum communication technologies like development of fibre and free-space (polarization/hybrid photon) based Quantum Key Distributions Technologies, Quantum Sources, Quantum Detectors and Non-linear Crystals.