title: Experimental Satellite Quantum Communications.
abstract: Quantum communication (QC), namely, the faithful transmission of generic quantum states, is a key ingredient of quantum information science. Here we demonstrate QC with polarization encoding from space to ground by exploiting satellite corner cube retroreflectors as quantum transmitters in orbit and the Matera Laser Ranging Observatory of the Italian Space Agency in Matera, Italy, as a quantum receiver. The quantum bit error ratio (QBER) has been kept steadily low to a level suitable for several quantum information protocols, as the violation of Bell inequalities or quantum key distribution (QKD). Indeed, by taking data from different satellites, we demonstrate an average value of QBER=4.6% for a total link duration of 85 s. The mean photon number per pulse μ_{sat} leaving the satellites was estimated to be of the order of one. In addition, we propose a fully operational satellite QKD system by exploiting our communication scheme with orbiting retroreflectors equipped with a modulator, a very compact payload. Our scheme paves the way toward the implementation of a QC worldwide network leveraging existing receivers.
authors.affiliation: Dipartimento di Ingegneria dell'Informazione, Università degli Studi di Padova, Padova 35131, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Vallone
authors.affiliation: Dipartimento di Ingegneria dell'Informazione, Università degli Studi di Padova, Padova 35131, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Bacco
authors.affiliation: Dipartimento di Ingegneria dell'Informazione, Università degli Studi di Padova, Padova 35131, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Dequal
authors.affiliation: Dipartimento di Ingegneria dell'Informazione, Università degli Studi di Padova, Padova 35131, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Gaiarin
authors.affiliation: e-GEOS spa, Matera 75100, Italy.
authors.forename: Vincenza
authors.initials: V
authors.lastname: Luceri
authors.affiliation: Matera Laser Ranging Observatory, Agenzia Spaziale Italiana, Matera 75100, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Bianco
authors.affiliation: Dipartimento di Ingegneria dell'Informazione, Università degli Studi di Padova, Padova 35131, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Villoresi