Abstract
One of the challenges of implementing free-space quantum key distribution (QKD) systems working in daylight is to remove unwanted background noise photons from sunlight. Elaborate elimination of background photons in the spectral, temporal, and spatial domains is an indispensable requirement to decrease the quantum bit error rate (QBER), which guarantees the security of the systems. However, quantitative effects of different filtering techniques and performance optimization in terms of the secure key rate have not been investigated. In this study, we quantitatively analyze how the performance of the QBER and the key rates changes for different combinations of filtering techniques in a free-space BB84 QKD system in daylight. Moreover, we optimize the conditions of filtering techniques in order to obtain the maximum secure key rate.
Highlights
Free-space quantum key distribution (QKD) provides the availability of unconditionally secure communication for moving platforms and places without fiber-based infrastructure[1,2,3,4,5,6]
We investigate how background noise photons are reduced as the filtering techniques in the spectral, temporal, and spatial domains are installed with several different combinations in a polarization-based BB848 QKD system operating over a free-space distance of 275 m in daylight
Considering the fact that the spectral width of the laser sources is significantly narrower than 1 nm, noise photons can be even further diminished by using a narrower BPF, which will improve the performance of the QKD system[4,6,18]
Summary
Free-space quantum key distribution (QKD) provides the availability of unconditionally secure communication for moving platforms and places without fiber-based infrastructure[1,2,3,4,5,6]. There are several reports of successful demonstration of QKD systems under daylight conditions[3,4,5,6] They utilized multiple noise filtering techniques in the spectral, temporal, and spatial domains to effectively eliminate noise photons from sunlight. The detail system issues closely related to the filtering techniques, which are highly important for practical system implementation, have never been examined Issues, such as optimized temporal filtering window in terms of the secure key rate and fluctuations of the real-time key generation rate for different sizes of the spatial field of view (FOV), have never been quantitatively covered in the previous studies. We investigate how background noise photons are reduced as the filtering techniques in the spectral, temporal, and spatial domains are installed with several different combinations in a polarization-based BB848 QKD system operating over a free-space distance of 275 m in daylight. We further discuss some system issues related to filtering techniques for performance optimization of QKD systems in daylight
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