Abstract
The future envisaged global-scale quantum-communication network will comprise various nodes interconnected via optical fibers or free-space channels, depending on the link distance. The free-space segment of such a network should guarantee certain key requirements, such as daytime operation and the compatibility with the complementary telecom-based fiber infrastructure. In addition, space-to-ground links will require the capability of designing light and compact quantum devices to be placed in orbit. For these reasons, investigating available solutions matching all the above requirements is still necessary. Here we present a full prototype for daylight quantum key distribution at 1550 nm exploiting an integrated silicon-photonics chip as state encoder. We tested our prototype in the urban area of Padua (Italy) over a 145 m-long free-space link, obtaining a quantum bit error rate around 0.5% and an averaged secret key rate of 30 kbps during a whole sunny day (from 11:00 to 20:00). The developed chip represents a cost-effective solution for portable free-space transmitters and a promising resource to design quantum optical payloads for future satellite missions.
Highlights
Quantum Key Distribution (QKD)[1,2,3,4] is the most advanced application of quantum information science, continuously improving in terms of new protocols[5,6] and experimental realizations[7,8,9,10].The potential of QKD is to allow secure communication between any two points on Earth
The QKD source and detection units, at Alice’s and Bob’s side respectively, are linked by a free-space channel established between the Department of Information Engineering (DEI) and the Luxor Laboratory (LUXOR) (Fig. 1a)
The feedback signal is provided by the centroid of an auxiliary beacon laser at 1064 nm acquired by a positionsensitive detector (PSD)
Summary
Quantum Key Distribution (QKD)[1,2,3,4] is the most advanced application of quantum information science, continuously improving in terms of new protocols[5,6] and experimental realizations[7,8,9,10].The potential of QKD is to allow secure communication between any two points on Earth. Regarding (i), the background noise due to sunlight poses a serious limitation on the achievable performance of day-time freespace QC, limiting most of the demonstrations obtained so far to night-time. For this reason, various studies have focused on the feasibility of daylight QKD24–29. To reduce the background noise due to the Sun and to maintain, at the same time, a good efficiency in the atmospheric transmission, the choice to use light signals in the telecom C-band (around 1550 nm) has only very recently started to be investigated[28,29]
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