GHz-rate polarization-based QKD system for fiber and satellite applications

TL;DR

This paper presents a high-speed polarization-based QKD system operating at 1550 nm, achieving record secret key rates over fiber and free-space links, suitable for satellite and terrestrial quantum communication.

Contribution

The authors develop a 1.5 GHz repetition rate QKD system with a novel iPOGNAC scheme, demonstrating unprecedented secret key rates in field conditions for fiber and satellite applications.

Findings

Achieved a sustained secret key rate above 1 Mbps in daylight free-space experiments.

Demonstrated a secure key rate of about 10 Mbps at low losses.

Showed the system's capability for high-loss, low-block-length scenarios like satellite QKD.

Abstract

Quantum key distribution (QKD) leverages the principles of quantum mechanics to exchange a secret key between two parties. Despite its promising features, QKD also faces several practical challenges such as transmission loss, noise in quantum channels and finite key size effects. Addressing these issues is crucial for the large-scale deployment of QKD in fiber and satellite networks. In this paper, we present a 1550 nm QKD system realizing the efficient-BB84 protocol and based on the iPOGNAC scheme. The system achieved repetition rates up to 1.5~GHz and showed an intrinsic QBER of $\sim 0.4\%$. The system was first tested on a laboratory fiber link and then on an intermodal link in the field, consisting of both deployed fiber and a 620 m free-space channel. The experiment was performed in daylight conditions, exploiting the Qubit4Sync synchronization protocol. With this trial, we achieved a new benchmark for free-space BB84 QKD systems by generating a sustained secret key rate (SKR) above 1~Mb/s for 1 hour. Finally, exploiting a recently discovered finite-size bound, we achieved a secure key rate of about 10 Mb/s at low losses (5 dB), and around 6.5~kb/s in the high-loss (38.5 dB), low block length ($N=10^4$) regime. The latter results demonstrate the system's suitability for highly lossy and time-constrained scenarios such as QKD from low Earth orbit satellites.