Applicability of Squeezed- and Coherent-State Continuous-Variable Quantum Key Distribution over Satellite Links.

Ivan Derkach,Vladyslav C Usenko

doi:10.3390/e23010055

Abstract

We address the applicability of quantum key distribution with continuous-variable coherent and squeezed states over long-distance satellite-based links, considering low Earth orbits and taking into account strong varying channel attenuation, atmospheric turbulence and finite data ensemble size effects. We obtain tight security bounds on the untrusted excess noise on the channel output, which suggest that substantial efforts aimed at setup stabilization and reduction of noise and loss are required, or the protocols can be realistically implemented over satellite links once either individual or passive collective attacks are assumed. Furthermore, splitting the satellite pass into discrete segments and extracting the key from each rather than from the overall single pass allows one to effectively improve robustness against the untrusted channel noise and establish a secure key under active collective attacks. We show that feasible amounts of optimized signal squeezing can substantially improve the applicability of the protocols allowing for lower system clock rates and aperture sizes and resulting in higher robustness against channel attenuation and noise compared to the coherent-state protocol.

Highlights

Quantum key distribution (QKD) [1,2,3] is well known to have its goal in developing methods for sharing a secret key between legitimate users, who can lately use the key for the confidential information transfers
We show that in this regime the protocols appear to be extremely sensitive to strong channel attenuation and large amounts of data are required for successful realization of continuous variables (CV) QKD over satellites, which contradicts relatively short passage times
We studied applicability of CV QKD over satellite links considering coherent and squeezed-state protocols, taking into account realistic satellite passage, atmospheric effects, finite data ensemble size, system clock rate and data processing efficiency

Summary

Introduction

Quantum key distribution (QKD) [1,2,3] is well known to have its goal in developing methods (protocols) for sharing a secret key between legitimate users, who can lately use the key for the confidential information transfers. While discrete-variable protocols were recently successfully tested over the satellite links [6,7,8,9], the applicability of satellite-based CV QKD remains less studied It was considered in the asymptotic regime of the infinitely many quantum states [10,11], which is never the case in practice. Possible solutions to circumvent the problem can be (i) use of squeezed states, that reduce requirements on the data ensemble size and can tolerate stronger attenuation and channel noise; (ii) relaxation of security assumptions considering individual attacks or passive eavesdropping, introducing no excess noise; (iii) increase of the link transmittance using larger telescopes in the downlink regime; (iv) increase of the repetition rate of the system in order to accumulate larger statistics. Already under the strict assumption of collective eavesdropping attacks and untrusted channel noise, CV QKD protocols using feasible squeezing should be applicable with low-orbit satellites, while in the assumption of passive eavesdropping squeezed-state CV QKD can tolerate up to 43 dB of channel attenuation, which paves the way towards realization over geostationary satellites

Security of CV QKD

CV QKD over Satellite Channels

Quantum Channel and Protocol Parameters

Satellite-to-Ground Channel Model

Security Evaluation

Conclusions and Discussion