title: Free-Space Quantum Signatures Using Heterodyne Measurements.
abstract: Digital signatures guarantee the authorship of electronic communications. Currently used "classical" signature schemes rely on unproven computational assumptions for security, while quantum signatures rely only on the laws of quantum mechanics to sign a classical message. Previous quantum signature schemes have used unambiguous quantum measurements. Such measurements, however, sometimes give no result, reducing the efficiency of the protocol. Here, we instead use heterodyne detection, which always gives a result, although there is always some uncertainty. We experimentally demonstrate feasibility in a real environment by distributing signature states through a noisy 1.6 km free-space channel. Our results show that continuous-variable heterodyne detection improves the signature rate for this type of scheme and therefore represents an interesting direction in the search for practical quantum signature schemes. For transmission values ranging from 100% to 10%, but otherwise assuming an ideal implementation with no other imperfections, the signature length is shorter by a factor of 2 to 10. As compared with previous relevant experimental realizations, the signature length in this implementation is several orders of magnitude shorter.
authors.affiliation: School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland.
authors.forename: Callum
authors.initials: C
authors.lastname: Croal
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1/Building 24, 91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, 91058 Erlangen, Germany.|Department of Physics, University of Otago, 730 Cumberland Street, Dunedin 9016, New Zealand.
authors.forename: Christian
authors.initials: C
authors.lastname: Peuntinger
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1/Building 24, 91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, 91058 Erlangen, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Heim
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1/Building 24, 91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, 91058 Erlangen, Germany.
authors.forename: Imran
authors.initials: I
authors.lastname: Khan
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1/Building 24, 91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, 91058 Erlangen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Marquardt
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1/Building 24, 91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, 91058 Erlangen, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Leuchs
authors.affiliation: School of Informatics, University of Edinburgh, 10 Crichton Street, Edinburgh EH8 9AB, United Kingdom.
authors.forename: Petros
authors.initials: P
authors.lastname: Wallden
authors.affiliation: SUPA, Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt Universiity, David Brewster Building, Edinburgh EH14 4AS, United Kingdom.
authors.forename: Erika
authors.initials: E
authors.lastname: Andersson
authors.affiliation: School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland.
authors.forename: Natalia
authors.initials: N
authors.lastname: Korolkova