Experimental Demonstration of Twin-Field Quantum Digital Signatures over 504 km

Abstract

Digital signatures are one of the security cornerstones of the current information age. Compared with classical digital signatures based on computational complexity, quantum digital signatures (QDS) theoretically guarantee data integrity, authenticity, and non-repudiation by quantum mechanics, showing great potential for development in cryptography and thus attracting widespread attention. However, the performance of existing QDS systems are still limited in rate and distance. Here we report the first experimental demonstration of twin-field QDS (TF-QDS) using a GHz system. We achieve a maximum transmission distance of 504 km fiber spools for both single-bit and multi-bit schemes, surpassing all existing state-of-the-art QDS experiments more than 200 km. Furthermore, by combining the one-time universal hash method, we achieve a maximum signature rate of 21.1 times per second for a 1 Mbit file over fiber distances up to 302 km. In this work, the signature rates of both single-bit scheme and multi-bit scheme are more than two orders of magnitude higher than that of previous works at similar distance. Our work provides a new record for long-distance and high-rate QDS, representing a significant step in the development of QDS.

Figures (4)

• Figure 1: Brief framework of TF-QDS. In distribution stage, Alice-Bob and Alice-Charlie independently perform TF-KGP with an optical switch (OS), where the weak coherent states (WCS) of Laser at each side are modulated by intensity modulators (IM) and phase modulators (PM), and then sent to an untrusted party David for measurement by a beam splitter (BS) and two detectors ($D_1$ and $D_2$). In messaging stage, Alice transmits the message and signature $(M,Sig_M)$ to Bob, and Bob then forwards them to Charlie. Finally, Bob and Charlie verify the signature. In the process of TF-QDS, there are a step of key exchange between Bob and Charlie.
• Figure 2: Experimental setup of TF-QDS. In the system, the light of Alice's master laser is split into two beams, in which one beam is for encoding, and the other is further split and respectively transmitted to Bob and Charlie. The light passes through the circulator (Cir) and injects the slave laser for seeding. By seed injection, Bob or Charlie separately locks the laser frequency with Alice's laser. Next, their light are filtered by a fiber Bragg grating (FBG), and then modulated by a encoder, which consists of polarization controller (PC), phase modulators (PMs), intensity modulators (IMs) and attenuator (ATT). The IMs are used to set the intensities of reference and signal pulses, and the PMs are used to encode the phase of pulses. The pulses are then attenuated by an ATT and sent out via fiber spools to David. At David’s measurement station, a multi-port optical switch (MOS) is used to choose which two parties' (Alice-Bob or Alice-Charlie) pulses for further measurement. Then the pulses pass through polarization compensation module, including a electronic polarization controller (EPC) and a polarization beam splitter (PBS). Finally, the pulses interfere at a beam splitter (BS) and are detected by superconducting nanowire single-photon detectors (SNSPDs).
• Figure 3: Signature rates (bps) of different works based on single-bit scheme. The solid curve and pentagram dots correspond to the simulation and experimental signature rates. Other works are An et al.AnXB, Richter et al.Richter, Collins et al.Collins2017, Roberts et al.Roberts, Yin17 et al.Yin2017, Zhang et al.Zhang, Ding et al.Ding.
• Figure 4: Signature rates (tps) of different works using multi-bit scheme. Here the rate is the times of signing $1$ Mbits message per second. The solid curve and pentagram dots correspond to the simulation and experimental signature rates in our experiment. Other works are Yin23 et al.Yin2023, Du et al.ChipQDS.