26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Continuous variable quantum key distribution through a free space fading channel with minimal information leakage

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Quantum Science and Technology (QST)

Speaker

Josephine Dias (University of Queensland)

Description

Quantum key distribution (CVQKD) enables the distribution of provably secure keys for cryptography by exploiting fundamental principles of quantum mechanics. QKD protocols can be broadly classified as either discrete-variable QKD, encoding information in discrete quantum states, or continuous-variable (CV) QKD, which encodes information in the continuous amplitude and phase quadratures and uses homodyne or heterodyne detection. CV QKD offers several practical advantages because it employs standard telecommunication components, making it well suited for integration into existing optical fibre networks. A major challenge in implementing CVQKD is mitigating the effects of channel loss and noise, which limit both the secret key rate and the maximum achievable distance. Recent work has presented a heralded CVQKD protocol that can eliminate information leakage to an eavesdropper in a pure-loss channel of constant transmission. In this work, we investigate the performance of this protocol when the communication channel is instead a free-space channel of fluctuating transmission. In free-space links, fluctuations in transmissivity arise from atmospheric turbulence, introducing excess noise that can significantly degrade protocol performance. We analyse the security of the heralded protocol under these conditions and quantify the impact of this fading channel noise on the achievable secret key rate. Our analysis considers both individual and collective attacks. In individual attacks, the eavesdropper is restricted to performing independent measurements on each transmitted quantum state, whereas collective attacks allow the eavesdropper to store all transmitted states in a quantum memory and perform an optimal collective measurement later. Our findings show that the heralding protocol substantially suppresses the detrimental effects of free-space fading noise. We demonstrate that, under individual attacks, this heralded CVQKD protocol significantly outperforms conventional CVQKD protocols. These results highlight the potential of this heralding scheme as a practical approach for mitigating atmospheric fading and improving the performance of free-space CVQKD.