Time-spectral control of accidental coincidences in daylight entanglement-based free-space QKD

Abstract:Daylight entanglement-based free-space quantum key distribution (QKD) is limited by accidental coincidences from receiver-admitted background light. We develop and experimentally validate a receiver-level framework anchored to measured singles rates and reference coincidence components, linking receiver bandwidth, accepted temporal width, and background-noise density to Bob singles, sifted-key rate, error rate, and quantum bit error rate (QBER) in telecom-wavelength BBM92 QKD. Indoor sweeps show that the sifted-key rate saturates near the source-matched bandwidth, whereas broader bandwidth or higher background mainly increases accidental contamination. Increasing the accepted temporal width leaves Bob singles nearly unchanged but directly raises QBER by enlarging the random-overlap probability. A two-dimensional design map calculated from the model shows that the temporal-window margin contracts rapidly with increasing background-to-signal ratio, while the bandwidth margin remains comparatively broad near source-matched filtering. A rooftop experiment demonstrates daylight operation over a 10 m free-space link, yielding a mean sifted-key rate of 2,811 cps and a mean QBER of 4.43%. This framework provides a quantitative basis for choosing receiver bandwidth and temporal acceptance to meet a target QBER under specified background conditions.

arXiv:2606.17365 [quant-ph]

(or arXiv:2606.17365v2 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2606.17365 Focus to learn more arXiv-issued DOI via DataCite

arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website.

Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them.

Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs.