Advancing Secure Quantum Communication by Overcoming Challenges

Saumya Ranjan Behera1, Melvee George1, Urbasi Sinha1

1Light and Matter Physics Group, Raman Research Institute, Bangalore, 560080, India

Email: saumyarb@rri.res.in

In this talk, we’ll delve into recent advancements and challenges in the field of Quantum Key Distribution (QKD), focusing on our efforts to overcome key obstacles in both fibre and free-space communication channels. Firstly, we address the challenges posed by fibre birefringence and atmospheric effects on QKD. These phenomena introduce polarization scrambling, compromising the reliability of quantum communication. Based on our previous work, we present a passive polarization correction scheme, which mitigates these adverse effects without the need for resource-intensive active feedback mechanisms. Our approach, detailed in [1], demonstrates the feasibility of long distance QKD without active feedback, offering significant advantages in terms of scalability and efficiency.

In the current work, we extend this passive approach to long distance free-space QKD scenarios. Here, we encounter additional challenges, including varying lighting conditions, high background noise levels, and dynamic environmental changes. Having a 50-meter free- space optical link and the entanglement-based BBM92 QKD protocol, we showcase our experimental findings detailed in [2]. Our results highlight the successful implementation of QKD over the free-space optical link, under challenging real-world conditions.

By carefully managing our filtering techniques, we achieve an information-theoretic secure Quantum Bit Error Rate (QBER) of less than 11% on average, along with high key rates. Our experiments conducted over a 24-hour period yield results, proving the robustness and reliability of our approach in both daytime and nighttime conditions.

In addition, the talk will cover our ongoing research implementing and testing the same technique in a more complex experimental architecture involving a moving receiver, as well as our future plans.

References

[1] Chatterjee S, Goswami K, Chatterjee R, Sinha U. Polarization bases compensation towards advantages in satellite-based QKD without active feedback. Communications Physics. 2023 May 24;6(1):116.

[2] Behera SR, George M, Sinha U. Daytime and Night-time QKD over an atmospheric free space channel with passive polarisation bases compensation. arXiv preprint arXiv:2310.02115. 2023 Oct 3.