New Delhi: In a recent experimental breakthrough on secure quantum communication, researchers at IIT Delhi have achieved a trusted-node-free quantum key distribution (QKD) up to 380 km in standard telecom fiber with a very low quantum bit error rate (QBER).

This long secure length is the highest achieved so far, not only in India but first globally for the Differential Phase Shift (DPS) QKD protocol, keeping IIT Delhi at the forefront of research and development in quantum communication technologies. Such low QBER enables the DPS QKD scheme resistant to collective and individual attacks and implementable for various applications, such as securing financial transactions, medical records, and secret codes. It is also capable of securing network communication, such as the Internet of Things (IoT), and is ready to revolutionize the field of cyber security.

“This realization using state-of-the-art technology would not only help in reducing the need for trusted nodes for intercity or long-distance quantum key exchange, increasing the security of the cryptography scheme, but would also prove to be a crucial step towards the commercial production of long-distance secure practical QKD devices”, said Dr. Bhaskar Kanseri, lead researcher and Associate Professor at the Physics Department and Optics and Photonics Centre.

Prof. Kanseri added that in quantum communication, security is guaranteed by the laws of Quantum Physics and, in principle, it cannot be broken even using a quantum computer. This QKD demonstration shows methods to get rid of the intermediate trusted nodes, which are weak security loopholes and are vulnerable to several kinds of attacks. It paves the way for more secure long-distance communication useful for strategic areas such as defence and online banking, making digital transactions safer in the near future.

They conducted this study using the baseline error optimisation method at their Experimental Quantum Interferometry and Polarization (EQUIP) lab. According to Dr. Kanseri, the current DPS QKD demonstration for the first time optimizes most of the sources of errors, which are mainly due to the laser linewidth, modulation bandwidth, detector noise, and dispersion of fibers, resulting in the least QBER (less than 2.5%) achieved so far, which is an international record for such a large distance in fiber.

This study titled ‘Phase Encoded Quantum Key Distribution up to 380 km in Standard Telecom Grade Fiber Enabled By Baseline Error Optimization’ is recently published in the prestigious journal Nature Scientific Reports (https://doi.org/10.1038/s41598-023-42445-y). In this work, Prof. Bhaskar Kanseri was joined by research scholars Mr. Nishant Kumar Pathak, Mr. Sumit Chaudhary, and Ms. Sangeeta.

Photo: (In EQUIP lab) Sangeeta (left), Dr.  Bhaskar Kanseri (middle) and Nishant K. Pathak (right)

It is noteworthy that the team led by Dr. Kanseri, along with DRDO, has previously demonstrated the first Indian intercity quantum communication between Vindhyanchal and Prayagraj in 2022, which was using more than 100 km commercial-grade underground dark optical fiber.

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