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Modern Physics Letters B

Twin-field quantum key distribution over free-space optical channels in the presence of atmospheric turbulence

Yuqing Huang, Zhongqi Sun, Tianqi Dou, Jipeng Wang, Zhenhua Li, Fen Zhou, Yanxin Han, Haiqiang Ma

Published Jan 6, 2022• 1 citation
Publisher

Abstract

Future quantum communication networks envisaged on a global scale will include various networks interlinked via optical fiber and free space channels. In recent years, quantum key distribution (QKD) protocol based on optical fiber has been extensively studied. Twin-field QKD (TF-QKD) may enable 550 km QKD using standard optical fiber without quantum repeaters. However, the performance of TF-QKD in free-space channel is still unclear. In this paper, a free-space channel model is proposed with specific turbulence characterization discussed. Here, the key rate of TF-QKD under multiple scenarios considering the variation of turbulence and different link configuration is investigated. Simulation results demonstrate that the performance of free-space TF-QKD is related to link configuration and turbulence motion which is determined by surface feature, time and height. Furthermore, TF-QKD protocol is a potential scheme for the free-space quantum communication.

DOI
10.1142/s0217984921505928

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Future quantum communication networks envisaged on a global scale will include various networks interlinked via optical fiber and free space channels. In recent years, quantum key distribution (QKD) protocol based on optical fiber has been extensively studied. Twin-field QKD (TF-QKD) may enable 550 km QKD using standard optical fiber without quantum repeaters. However, the performance of TF-QKD in free-space channel is still unclear. In this paper, a free-space channel model is proposed with specific turbulence characterization discussed. Here, the key rate of TF-QKD under multiple scenarios considering the variation of turbulence and different link configuration is investigated. Simulation results demonstrate that the performance of free-space TF-QKD is related to link configuration and turbulence motion which is determined by surface feature, time and height. Furthermore, TF-QKD protocol is a potential scheme for the free-space quantum communication.
As a practical version of twin-field quantum key distribution (TF-QKD), phase-matching quantum key distribution (PM-QKD) is able to surpass the linear bound without quantum repeaters. Implementing PM-QKD through free space can guarantee two parties to share unconditionally secure keys between ground stations and mobile platforms. However, atmospheric turbulence decreases the free-space secure key rate as the result of fluctuations of transmittances caused by it. This paper includes two works we do. First, for generality, we derive the secure key rate formula of 4-intensity PM-QKD based on asymmetric channel transmittances. Second, we numerically simulate the performance of PM-QKD in free space and ideal circumstance to study the effect of the atmospheric turbulence.
Free-space quantum key distribution (QKD) allows two distant parties to share secret keys with information-theoretic security, which can pave the way for satellite-ground quantum communication to set up a global network for sharing secret message. However, free-space channels in the presence of atmospheric turbulence are affected by losses and fluctuating transmissivity which further affect the quantum bit error rate and the secure key rate. To implement free-space QKD, it is indispensable to study the effect of atmospheric turbulence. Different models have been used to describe the probability distribution for channel transmission coefficient under atmospheric turbulence, including the log-normal distribution and K distribution. In this paper, we focus on free space measurement-device-independent quantum key distribution (MDI-QKD) under K-distributed strong atmospheric turbulence. The MDI-QKD can close all loopholes on detection and achieve a similar performance to QKD, relying on time-reversed version of entanglement-based QKD protocol. Threshold post-selection method is adopted to restrain detrimental effects of the atmospheric turbulence, which is based on the selection of the intervals with higher channel transmissivity. By combining the general MDI-QKD system model with this method, we present a framework for the optimal choice of threshold. Our simulation result shows that the optimal threshold is dependent on the turbulence intensity and expected channel loss. Furthermore, compared with the original MDI-QKD protocols, the proposed protocol with threshold post-selection method can acquire a considerable better performance in key rate, especially in regions of high turbulence and high loss. What is more, this is instructive to the building of a practical free-space MDI-QKD system with better performance.
Quantum Key Distribution (QKD) offers information-theoretic security, making it a cornerstone of future cryptographic infrastructures in the era of quantum computing. However, long-distance deployment of conventional QKD protocols is limited by channel losses, detector noise, and the fundamental repeaterless Pirandola-Laurenza-Ottaviani-Banchi (PLOB) bound. To address these challenges, this paper investigates the Twin-Field QKD (TF-QKD) protocol, which enables secure key exchange over long-haul optical fibers by exploiting single-photon interference at an untrusted intermediate node. An elaborate system model is provided with optical channel impairments, imperfections of detector and phase stabilization conditions. Finite-key analysis, error correction as well as privacy amplification are placed and made together in order to increase robustness of protocol against practical attacks. The simulation data show that TFQKD can reach secure key rates of over 500 km and is out of reach of decoy-state QKD but nearly close to fundamental limits. These results demonstrate that TF-QKD has the potential to practicalize quantumsecure communication at large scale and in a costeffective way, which can constitute a sub-unit of the future quantum internet.
Future quantum networks will be composed of both terrestrial links for metropolitan and continent-scale connections and space-based links for global coverage and infrastructure resilience. However, the propagation of quantum signals through the atmosphere is severely impacted by the effects of turbulence. This is even more the case for entanglement-based quantum communication protocols requiring two free-space channels to be considered simultaneously. In this work, we assess the advantage of turbulence mitigation by adaptive optics, in particular during daytime link operation, so as to increase the coupling of the received signal into an optical fiber. We show in particular that this improves the performance of entanglement-based quantum key distribution by up to a few hundred bits per second when compared with the uncorrected scenario
Abstract Quantum Key Distribution (QKD) has been widely applied due to its theoretical one-time pad encryption. Typically employing laser beam as carrier, quantum states are transmitted through optical fibers or free-space channels, with the latter being more commonly adopted. However, compared to optical fibers, free-space links are more susceptible to external environmental factors, particularly atmospheric conditions. Beam propagation through the atmosphere experiences diffraction, refraction, and intensity attenuation, which can degrade key distribution efficiency and even prevent key generation at the receiver. The atmospheric turbulence poses the most significant challenge in all influencing factors, especially for the commonly encountered moderate-to-strong turbulence regimes. Therefore, in this work, we develop a phase screen model and turbulence-dominated transmittance model to comprehensively investigate the impact of various key parameters on optical beam propagation through turbulent atmospheres. Furthermore, we derive the key rate for the CV-QKD protocol using a TMSV (two-mode squeezed vacuum) state and perform numerical simulations.
Quantum key distribution (QKD) generates information-theoretical secret keys between two parties based on the physical laws of quantum mechanics. Following the advancement in quantum communication networks, it becomes feasible and economical to combine QKD with classical optical communication through the same fiber using dense wavelength division multiplexing (DWDM) technology. This study proposes a detailed scheme of TF-QKD protocol with DWDM technology and analyzes its performance, considering the influence of quantum channel number and adjacent quantum crosstalk on the secret key rates. The simulation results show that the scheme further increases the secret key rate of TF-QKD and its variants. Therefore, this scheme provides a method for improving the secret key rate for practical quantum networks.