Towards fully-fledged quantum and classical communication over deployed fiber with up-conversion module

TL;DR

This paper introduces an up-conversion assisted receiver for quantum key distribution over fiber, significantly improving noise tolerance and enabling co-propagation of quantum and classical signals at higher power levels.

Contribution

It presents a novel up-conversion based receiver that enhances co-propagation of quantum and classical signals in fiber networks, surpassing standard detectors in noise tolerance.

Findings

Achieves 4 dB higher classical power tolerance compared to standard receivers.

Demonstrates successful quantum key distribution over installed fiber links.

Shows improved performance in co-propagating quantum and classical signals.

Abstract

Quantum key distribution (QKD), the distribution of quantum secured keys useful for data encryption, is expected to have a crucial impact in the next decades. However, although the notable achievements accomplished in the last twenty years, many practical and serious challenges are limiting the full deployment of this novel quantum technology in the current telecommunication infrastructures. In particular, the co-propagation of quantum signals and high-speed data traffic within the same optical fiber, is not completely resolved, due to the intrinsic noise caused by the high intensity of the classical signals. As a consequence, current co-propagation schemes limit the amount of classical optical power in order to reduce the overall link noise. However, this ad-hoc solution restrains the overall range of possibilities for a large-scale QKD deployment. Here, we propose and demonstrate a new method, based on up-conversion assisted receiver, for co-propagating classical light and QKD signals. In addition, we compare the performances of this scheme with an off-the-shelf quantum receiver, equipped with a standard InGaAs detector, over different lengths of an installed fiber link. Our proposal exhibits higher tolerance for noise in comparison to the standard receiver, thus enabling the distribution of secret keys in the condition of 4 dB-higher classical power.