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

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.

Theoretical Investigation of a Spectrally Pure-State Generation from Isomorphs of KDP Crystal at Near-Infrared and Telecom Wavelengths

“…Figure 2(c, f) is useful for interference between the signal and idler photons from one SPDC source. The highly pure single photon sources at telecom wavelengths are very important for practical applications which require long-distance transmission in low-loss and low-cost optical fibers, for example, for quantum key distribution [60], quantum digital signature [61], quantum direct communication [62], quantum teleportation [63], quantum networks [64], etc.…”

Continuous-variable quantum digital signatures over insecure channels

“…After performing heterodyne measurement on mode C and receiving outcome c ∈ C, the state ρ j B|c (n) = c|Ψ Ψ|c can be used to calculate the Holevo information as before via Eqs. (12), (17). The states |Ψ B ′ 1 B2C and ρ j B|c (n) are derived in Appendix C. Finally, we note that Charlie's probability of measuring c ∈ C when Alice sends state |α k through the channel with transmission T and thermal noise input ρ th (n) is [25]…”

“…6, we can securely sign a 1 bit message with only L ∼ O 10 5 coherent states. Combined with fast sending rates typical to the CV platform, this opens up the possiblity of signing a message in times competitive with the O 10 −1 seconds found in DV schemes ( [17], and see Fig. 7 of [21]).…”

“…DV QDS relies on photon-number detection of either weak coherent pulses [13,14,[17][18][19] or single photons [16,20]. The relatively low dimensional Hilbert space required for these schemes allows for an advanced level of security analysis, and their high resilience to loss allows for long distances to be bridged securely, with O 10 −1 seconds required to sign a 1-bit message [17,21,22]. The first QDS scheme over insecure channels required a signature length of 7.7 × 10 5 to sign a 1 bit message, in a scheme similar to decoy-state QKD [13].…”

Quantum state correction using a measurement-based feedforward mechanism

“…This allows these conventional optical signals to be transmitted over intercontinental distances. The same deterministic amplification methods used in conventional optical communications cannot simply be applied usefully to low-photon-number quantum states, such as those transmitted in quantum key distribution (QKD) [1,2] or quantum digital signatures [3,4], due to the addition of amplifier noise which will render ineffective any measurement of the quantum properties of the state [5].…”