Compact implementation of high-dimensional mutually partially unbiased bases protocol

Transverse spatial mode of light is crucial in high-dimensional quantum key distribution (QKD). However, applications in realistic scenarios suffer from mode-dependent loss and the complexity of system, making it impractical to achieve higher-dimensional, longer-distance and low-cost communications. A mutually partially unbiased bases (MPUBs) protocol has been proposed to fundamentally eliminate the effects induced by mode-dependent loss for long propagation distances and limited sizes of apertures. Here, we demonstrate the first implementation of the MPUBs protocol in dimensions of d = 2, 4, 5 and 6. By performing a controlled unitary transformation, we can actively switch the measurement basis and enable a compact measurement system. In consequence, a higher encoding dimension is available under finite system resources, resulting in higher key rates and stronger noise resistance. Our work enhances the practicability of MPUBs protocol, and may promote the applications of high-dimensional QKD in quantum networks.

Automated summary

The transverse spatial mode of light plays a crucial role in high-dimensional quantum key distribution (QKD). However, practical applications face challenges such as mode-dependent loss and system complexity, which hinder achieving higher dimensions, longer distances, and lower costs in communications. To address these issues, a mutually partially unbiased bases (MPUBs) protocol has been proposed, which fundamentally eliminates the effects of mode-dependent loss for long propagation distances and limited aperture sizes. In this study, we successfully implemented the MPUBs protocol in dimensions of 2, 4, 5, and 6. By employing a controlled unitary transformation, we were able to actively switch the measurement basis and create a compact measurement system. As a result, we achieved higher encoding dimensions using finite system resources, leading to higher key rates and stronger noise resistance. Our work enhances the practicality of the MPUBs protocol and contributes to the advancement of high-dimensional QKD in quantum networks.