Satellite-based links for quantum key distribution: beam effects and weather dependence

Abstract

The establishment of a world-wide quantum communication network relies on the synergistic integration of satellite-based links and fiber-based networks. The first are helpful for long-distance communication, as the photon losses introduced by the optical fibers are too detrimental for lengths greater than about 200 km. This work aims at giving, on the one hand, a comprehensive and fundamental model for the losses suffered by the quantum signals during the propagation along an atmospheric free-space link. On the other hand, a performance analysis of different quantum key distribution (QKD) implementations is performed, including finite-key effects, focusing on different interesting practical scenarios. The specific approach that we chose allows to precisely model the contribution due to different weather conditions, paving the way towards more accurate feasibility studies of satellite-based QKD missions. IntroductionQuantum key distribution (QKD) and quantum communication in general have the potential to revolutionise the way we communicate confidential information over the internet. The natural carriers for quantum information are photons, that are already widely used in classical networks of optical fibers to achieve high communication rates. Unfortunately, even though enormous improvements have been obtained in the last years [1, 2], scaling quantum communication protocols over long distances is very challenging, due to the losses experienced during the propagation inside the optical fibers. Several schemes for the realization of quantum repeaters have been proposed in recent years, that could allow to bridge long distances and naturally be implemented inside a quantum communication network [3][4][5][6][7]. Considering the important technological hurdles that quantum repeaters should overcome before becoming useful, satellite-based free-space links look like the most practical way to achieve long-distance QKD in the short term [8]. They can take advantage of the satellite technology and the optical communication methods developed in the last decades in the classical case. Various feasibility studies had addressed this topic in the last twenty years [8][9][10][11] and several experiments have definitely proved that the technology involved is ready for deployment [12][13][14][15][16].Optical satellite-based links have the important drawback of being strongly dependent on the weather conditions [17][18][19][20]. The presence of turbulent eddies and scattering particles like haze or fog generates random fluctuations of the relative permittivity of the air, on different length-and time-scales. This phenomenon affects the light propagation in a complicated way, inducing random deviations and deformations of any optical beam sent through the atmosphere. It results in reduced transmittance, because of geometrical losses due to the finite collection aperture, and random modifications of the phase front. A comprehensive model of these effects is then necessary, in order to precisely evaluate the performance of the link w...

Spooky action at a global distance: analysis of space-based entanglement distribution for the quantum internet

“…Including these extra elements would introduce extra attenuation factors (see, for e.g., section 2.1.1.4 of ref. 37 and refs 96,97 ), which would increase the overall satellite-to-ground transmission loss (see refs 78,98 for an analysis of satellite-to-ground quantum key distribution in a localized area that incorporates local weather conditions). We also point out that, especially in the daytime, background photons (e.g., from the sun) can reduce the fidelity of the distributed entangled pairs, because the receiver will collect those background photons in addition to the signal photons from the entanglement source.…”

“…The transmittance η sg generally depends on atmospheric conditions (such as turbulence and weather conditions) and on orbital parameters (such as altitude and zenith angle) 96,97,106 . In general, we can decompose η sg as η sg ¼ η fs η atm (8) where η fs is the free-space transmittance and η atm is the atmospheric transmittance.…”

Enhanced Uplink Quantum Communication With Satellites via Downlink Channels

“…To account for the extinction a transmissivity T ext = exp(−0.7 sec ζ) is adopted. For the loss due to the optical devices consider a transmissivity value T opt = 0.794 (1 dB) [42]. The total transmissivity of the channel is then simply,…”

“…Although originally proposed under the assumption of a horizontal channel, the elliptic-beam approximation was directly adopted in [55] to study the performance of CV-QKD in the downlink channel. In addition, the authors of [42] proposed a generalized channel modeling technique based on This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in a future issue of this journal, but has not been fully edited.…”

Quantum Technology: Advances and Trends

“…It has confirmed by simulations that quantum communication over a long distance could be realized not only employing medium-sized satellites (such as Micius of China), but also employing nano-satellites that permit to save costs of a global space-based quantum network substantially. A performance analysis of various QKD realizations was conducted, covering finite-key effects (with a focus on various interesting application scenarios) (Liorni et al, 2019).…”