Title:	Polarization bases compensation towards advantages in satellite-based QKD without active feedback
Authors:	Chatterjee, Sourav Goswami, Kaumudibikash Chatterjee, Rishab Sinha, Urbasi
Issue Date:	24-May-2023
Publisher:	Nature Publishing Group
Citation:	Communications Physics, 2023, Vol. 6, Article No.166
Abstract:	Long-distance photonic implementations of quantum key distribution protocols have gained increased interest due to the promise of information-theoretic security against unauthorized eavesdropping. However, a significant challenge in this endeavor is photon-polarization getting affected due to the birefringence of fibers in fiber-based implementations, or variation of reference frames due to satellite movement in long-haul demonstrations. Conventionally, active feedback-based mechanisms are employed for real-time polarization tracking. Here, we propose and demonstrate an alternative approach via a proof-of-principle experiment over an in-lab entanglement-based (BBM92) protocol. In this approach, we perform a quantum state tomography to arrive at optimal measurement bases for any one party resulting in maximal (anti-)correlation in measurement outcomes of both parties. Our polarization-entangled bi-photons have 94% fidelity with a singlet state and a Concurrence of 0.92. By considering a representative 1 ns coincidence window span, we achieve a quantum-bit-error-rate (QBER) of ≈5%, and a key rate of ≈35 Kbps. The performance of our implementation is independent of any local polarization rotation. Finally, using optimization methods we achieve the best trade-off between the key rate, QBER, and balanced key symmetry. Our approach obviates the need for active polarization tracking. It is also applicable to such demonstrations with non-maximally entangled states and prepare-and-measure-based protocols with partially polarized single-photon sources.
Description:	Open Access
URI:	http://hdl.handle.net/2289/8104
ISSN:	2399-3650 (Online)
Alternative Location:	https://doi.org/10.1038/s42005-023-01235-8
Copyright:	2023 The Author(s)
Appears in Collections:	Research Papers (LAMP)

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