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Limits and Security of Free-Space Quantum Communications

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Publication details

JournalPhysical Review Research
DateAccepted/In press - 5 Mar 2021
DatePublished (current) - 25 Mar 2021
Number of pages33
Original languageEnglish


The study of free-space quantum communications requires tools from quantum information theory, optics and turbulence theory. Here we combine these tools to bound the ultimate rates for key and entanglement distribution through a free-space link, where the propagation of quantum systems is generally affected by diffraction, atmospheric extinction, turbulence, pointing errors, and background noise. Besides establishing ultimate limits, we also show that the composable secret-key rate achievable by a suitable (pilot-guided and post-selected) coherent-state protocol is sufficiently close to these limits, therefore showing the suitability of free-space channels for high-rate quantum key distribution. Our work provides analytical tools for assessing the composable finite-size security of coherent-state protocols in general conditions, from the standard assumption of a stable communication channel (as typical in fiber-based connections) to the more challenging scenario of a fading channel (as typical in free-space links).

Bibliographical note

Results of the paper: (i) Ultimate limits/capacities of free-space quantum communications; (ii) General analytical toolbox for composable security analysis of CV-QKD protocols under general conditions (fiber and free-space). REVTeX 36 pages. 6 figures

    Research areas

  • quant-ph, cond-mat.other,,, physics.optics

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