Free-space quantum signatures using heterodyne detection

TL;DR

This paper demonstrates a practical quantum signature scheme using heterodyne detection in free-space channels, improving signature rate and efficiency over previous unambiguous measurement methods.

Contribution

It introduces the use of heterodyne detection for quantum signatures, enhancing efficiency and practicality in real-world free-space communication environments.

Findings

Heterodyne detection always provides a measurement result, increasing protocol efficiency.

Experimental demonstration over 1.6 km noisy free-space channel shows feasibility.

Heterodyne detection improves signature rate compared to unambiguous 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. 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 1.6km 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.