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Conference on Lasers and Electro-Optics

Performance analysis of d-dimensional quantum cryptography with mode-dependent diffraction

Jiapeng Zhao, Mohammad Mirhosseini, Yiyu Zhou, Seyed Mohammad Hashemi Rafsanjani, Yongxiong Ren, Nicholas K. Steinhoff, G. A. Tyler, Alan Eli Willner, Robert W. Boyd

Published Jan 1, 2018• 0 citations
Publisher

Abstract

We analyze the degraded performance of QKD that results from mode-dependent diffraction in spatial-mode-encoded QKD systems. A pre-compensation method is proposed to solve this problem without sacrificing the security.
DOI
10.1364/cleo_at.2018.jth2a.19

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Standard protocols for quantum key distribution (QKD) require that the sender be able to transmit in two or more mutually unbiased bases. Here, we analyze the extent to which the performance of QKD is degraded by diffraction effects that become relevant for long propagation distances and limited sizes of apertures. In such a scenario, different states experience different amounts of diffraction, leading to state-dependent loss and phase acquisition, causing an increased error rate and security loophole at the receiver. To solve this problem, we propose a precompensation protocol based on preshaping the transverse structure of quantum states. We demonstrate, both theoretically and experimentally, that when performing QKD over a link with known, state-dependent loss and phase shift, the performance of QKD will be better if we intentionally increase the loss of certain states to make the loss and phase shift of all states equal. Our results show that the precompensated protocol can significantly reduce the error rate induced by state-dependent diffraction and thereby improve the secure key rate of QKD systems without sacrificing the security.
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