Finite key effects in satellite quantum key distribution

Abstract

Quantum key distribution (QKD) can provide secure means of communication that are robust to general quantum computing attacks. Satellite QKD (SatQKD) presents the means to overcome range limitations in fibre optic-based systems and achieve global coverage but raises a different set of challenges. For low-Earth orbit SatQKD, a major limitation is the restricted time window for quantum signal transmission and highly variable channel loss during a satellite overpass of an optical ground station. Here, we provide a systematic analysis of the finite block size effects on secret key length generation for low latency operation using BB84 weak coherent pulse decoy state protocols. In particular, we look at how the achievable single pass secret key length depends on various system parameters for different overpass geometries and calculate the total long-term-average key length. We find that optimisation of basis bias, pulse probabilities and intensities, and data selection, is crucial for extending the range of satellite trajectories and link efficiencies for which finite-block size keys can be extracted. The results also serve as a guide for system sizing of future SatQKD systems and the performance levels required for sources and detectors.

Medium-range terrestrial free-space QKD performance modelling and analysis

“…We characterize this by introducing the internal quantum bit error rate QBER I . 14,16 The final source of errors is due to after-pulsing. As we will be gating the detectors on and off, we should be able to keep this low.…”

“…For more details on the finite statistical estimation see. 14 6. Next error correction must be performed to obtain identical keys for Alice and Bob.…”

“…It is possible to improve upon these result by using a modified version of the Chernoff bound 19,20 that is outlined in detail in. 14 The security proof outlined in 16 uses the composable security framework, in which a protocol is said to be ε = s + c secure if it is c -correct and s -secret. 18 For all calculations presented we use c = 10 −15 and s = 10 −9 .…”

“…12,13 This protocol was chosen as it has low sifting losses and is more efficient in situations where we have a finite data set. 14 Furthermore, the use of decoy states avoids the need for a single photon source. It has also been shown to increase the range of the system.…”

Analysis of satellite-to-ground quantum key distribution with adaptive optics

“…In particular, considerable effort has been devoted to the estimation of the secret key rate achievable over a satellite link [11][12][13][14]. This is due to the fact that, unlike fiber connections, satellite links are subject to several specific effects, such as the impact of atmospheric turbulence on beam broadening and wandering [13,[15][16][17][18][19], the effect of divergence and pointing error [7,8], the wavelength shift due to Doppler effect and the finite duration of the key exchange, when the orbit considered is not geostationary [20].…”