Composable free-space continuous-variable quantum key distribution using discrete modulation

(2026)

Publication Type: Journal article

Publication year: 2026

Journal

Original Authors: Kevin Jaksch, Thomas Dirmeier, Yannick Weiser, Stefan Richter, Ömer Bayraktar, Bastian Hacker, Conrad Rößler, Imran Khan, Stefan Petscharning, Thomas Grafenauer, Michael Hentschel, Bernhard Ömer, Christoph Pacher, Florian Kanitschar, Twesh Upadhyaya, Jie Lin, Norbert Lütkenhaus, Gerd Leuchs, Christoph Marquardt

Book Volume: 12

Article Number: eadv1440

Issue: 24

Journal Issue: 24

DOI: 10.1126/sciadv.adv1440

Abstract

Continuous-variable (CV) quantum key distribution (QKD) allows for quantum secure communication with the benefit of being close to classical coherent communication. In recent years, CV QKD protocols using a discrete number of displaced coherent states have been studied intensively as the modulation can be directly implemented with real devices with finite resolution. Until now, experiments only calculated key rates in the asymptotic regime. Here, we present a CV QKD system using discrete modulation that is especially designed for atmospheric channels. We use polarization encoding to exploit the nonbirefringent nature of the turbulent atmosphere. This allows to expand CV QKD networks beyond the existing fiber backbone. In a laboratory demonstration with a static 3-decibel loss channel, we implemented a recently developed security proof allowing to calculate composable finite-size key rates against independently and identically distributed collective attacks. We applied the full QKD protocol including a quantum random number generator, error correction, and privacy amplification to extract secret keys.

Authors with CRIS profile

Involved external institutions

University of Waterloo (UW) Canada (CA) AIT Austrian Institute of Technology Austria (AT) Max-Planck-Institut für die Physik des Lichts (MPL) / Max Planck Institute for the Science of Light Germany (DE)