Experimental transmission of quantum digital signatures over 90 km of installed optical fiber using a differential phase shift quantum key distribution system.

Quantum digital signatures (QDSs) apply quantum mechanics to the problem of guaranteeing message integrity and non-repudiation with information-theoretical security, which are complementary to the confidentiality realized by quantum key distribution (QKD). Previous experimental demonstrations have been limited to transmission distances of less than 5 km of optical fiber in a laboratory setting. Here we report, to the best of our knowledge, the first demonstration of QDSs over installed optical fiber, as well as the longest transmission link reported to date. This demonstration used a 90 km long differential phase shift QKD to achieve approximately one signed bit per second, an increase in the signature generation rate of several orders of magnitude over previous optical fiber demonstrations.

Experimental demonstration of quantum digital signatures over 43 dB channel loss using differential phase shift quantum key distribution.

Ensuring the integrity and transferability of digital messages is an important challenge in modern communications. Although purely mathematical approaches exist, they usually rely on the computational complexity of certain functions, in which case there is no guarantee of long-term security. Alternatively, quantum digital signatures offer security guaranteed by the physical laws of quantum mechanics. Prior experimental demonstrations of quantum digital signatures in optical fiber have typically been limited to operation over short distances and/or operated in a laboratory environment. Here we report the experimental transmission of quantum digital signatures over channel losses of up to 42.8 ± 1.2 dB in a link comprised of 90 km of installed fiber with additional optical attenuation introduced to simulate longer distances. The channel loss of 42.8 ± 1.2 dB corresponds to an equivalent distance of 134.2 ± 3.8 km and this represents the longest effective distance and highest channel loss that quantum digital signatures have been shown to operate over to date. Our theoretical model indicates that this represents close to the maximum possible channel attenuation for this quantum digital signature protocol, defined as the loss for which the signal rate is comparable to the dark count rate of the detectors.