Twin-field quantum key distribution without optical frequency dissemination

Abstract

Twin-field (TF) quantum key distribution (QKD) has rapidly risen as the most viable solution to long-distance secure fibre communication thanks to its fundamentally repeater-like rate-loss scaling. However, its implementation complexity, if not successfully addressed, could impede or even prevent its advance into real-world. To satisfy its requirement for twin-field coherence, all present setups adopted essentially a gigantic, resource-inefficient interferometer structure that lacks scalability that mature QKD systems provide with simplex quantum links. Here we introduce a technique that can stabilise an open channel without using a closed interferometer and has general applicability to phase-sensitive quantum communications. Using locally generated frequency combs to establish mutual coherence, we develop a simple and versatile TF-QKD setup that does not need service fibre and can operate over links of 100 km asymmetry. We confirm the setup’s repeater-like behaviour and obtain a finite-size rate of 0.32 bit/s at a distance of 615.6 km.

Advantages of Asynchronous Measurement-Device-Independent Quantum Key Distribution in Intercity Networks

“…The sending intensities and corresponding probabilities are selected by the users to obtain the optimal key rate for each link. Note that here we consider a 50% duty cycle for the TF-type protocols [57,67,70]. Asynchronous MDI-QKD here are listed in Table IV.…”

“…Table II shows simulated secret key rates for asynchronous MDI-QKD, sending-or-not-sending QKD (SNS-QKD) with actively odd-parity pairing (AOPP) [82], and phase-matching QKD (PM-QKD) [83] in the QKD intercity network. We assume that the quantum transmission duty ratio of the SNS-QKD and PM-QKD systems is 50% [57,67,70]. Note that duty cycle ratios are lower in many important TF-QKD experiments, for example, the duty ratio at 402 km is 22.4% in Ref.…”

“…Figure 4 presents the key rate per second versus fiber distance for asynchronous MDI-QKD, together with four-intensity time bin MDI-QKD [76], SNS-QKD (AOPP) [82], PM-QKD [83], four-phase TF-QKD [68], and four-intensity decoy-state QKD. For SNS-QKD (AOPP), PM-QKD, and four-phase TF-QKD, we set the duty cycle to 50%, Charlie's transmission loss at Alice's (Bob's) side to 2 dB, and the loss-independent misalignment error to 4.8% [70]. We assume an insert loss on Bob's side of 2 dB and a loss-independent misalignment error of e m = 0.02 for decoy-state QKD.…”

“…[56] applies entangled coherent state sources as untrusted relays to further increase the transmission distance of TF-QKD by reducing the signal-to-noise ratio at the measurement nodes. Several experimental achievements have shown the performance of twin-field QKD over large loss [57][58][59][60][61][62][63][64][65][66][67][68][69][70], and the maximum distance of TF-QKD has been experimentally increased to 830 kilometers [68]. The idea of single-photon interference has also been implemented in device independent QKD [71].…”

Experimental quantum secret sharing based on phase encoding of coherent states

“…We successfully generate secure key over various channel losses, up to 35 dB, under which a key rate of 85.3 bps can be obtained. Our protocol can be implemented by existing devices [60][61][62][63][64][65][66] while achieving security against coherent attacks, which provides a possible solution for the application of QSS. Furthermore, as dishonest participants are allowed in QSS schemes, our protocol can be directly used for efficient quantum digital signatures [24].…”