Free-space quantum signatures using heterodyne measurements

Callum Croal, Christian Peuntinger, Bettina Heim, Imran Khan, Christoph Marquardt, Gerd Leuchs, Petros Wallden, Erika Andersson, Natalia Korolkova

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)


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.

Original languageEnglish
Article number100503
Number of pages5
JournalPhysical Review Letters
Issue number10
Publication statusPublished - 2 Sept 2016


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