Abstract
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.
Highlights
The widespread adoption of computers and the internet among global society, and the continuing increase in the number of digital payments, along with the widespread adoption of digital broadcasts, means that there are at least several exabytes of digital information transmitted each day[1, 2]
The optical systems required to implement quantum digital signature (QDS) are similar to those required for quantum key distribution (QKD), and it may be that both QDS and QKD schemes can operate in parallel along the same optical fibers using the same transmitting and receiving hardware
Additional optical attenuation has been combined with a fixed fiber length of 90 km to simulate extended transmission distances permitting operation to be demonstrated over a channel loss corresponding to 134 ± 3.8 km – the longest equivalent distance over which QDS has been shown to operate to date
Summary
The widespread adoption of computers and the internet among global society, and the continuing increase in the number of digital payments, along with the widespread adoption of digital broadcasts, means that there are at least several exabytes of digital information transmitted each day[1, 2]. To ensure non-repudiation and transferability, quantum digital signature (QDS) protocols distribute only partial information on the secret key, and does so in such a way that each recipient receives a different verification key. Unlike many other quantum communications protocols, here Bob and Charlie are the source of the photons and Alice is the receiver.
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