Free-space quantum key distribution links in urban environment have demandingoperating needs, such as functioning in daylight and under atmosphericturbulence, which can dramatically impact their performance. Both effects areusually mitigated with a careful design of the field of view of the receiver.However, a trade-off is often required, since a narrow field of view improvesbackground noise rejection but it is linked to an increase inturbulence-related losses. In this paper, we present a high-speed automatictracking system to overcome these limitations. Both a reduction in thefield-of-view to decrease the background noise and the mitigation of the lossescaused by atmospheric turbulence are addressed. Two different designs arepresented and discussed, along with technical considerations for theexperimental implementation. Finally, preliminary experimental results of beamwander correction are used to estimate the potential improvement of both thequantum bit error rate and secret key rate of a free space quantum keydistribution system.
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