The linear constraint of secret key rate capacity is overcome by the twin-field quantum key distribution (QKD). However, the complex phase-locking and phase-tracking technique requirements throttle the real-life applications of the twin-field protocol. The asynchronous measurement-device-independent (AMDI) QKD, also called the mode-pairing QKD, protocol can relax the technical requirements and keep the similar performance of the twin-field protocol. Here, we propose an AMDI-QKD protocol with a nonclassical light source by changing the phase-randomized weak coherent state to a phase-randomized coherent-state superposition in the signal state time window. Simulation results show that our proposed hybrid source protocol significantly enhances the key rate of the AMDI-QKD protocol, while exhibiting robustness to imperfect modulation of nonclassical light sources.
The linear constraint of secret key rate capacity is overcome by the twin-field quantum key distribution (QKD). However, the complex phase-locking and phase-tracking technique requirements throttle the real-life applications of the twin-field protocol. The asynchronous measurement-device-independent (AMDI) QKD, also called the mode-pairing QKD, protocol can relax the technical requirements and keep the similar performance of the twin-field protocol. Here, we propose an AMDI-QKD protocol with a nonclassical light source by changing the phase-randomized weak coherent state to a phase-randomized coherent-state superposition in the signal state time window. Simulation results show that our proposed hybrid source protocol significantly enhances the key rate of the AMDI-QKD protocol, while exhibiting robustness to imperfect modulation of nonclassical light sources.
Abstract In principle, the asynchronous measurement-device-independent quantum key distribution (AMDI-QKD) can surpass the key rate capacity without phase tracking and phase locking. However, practical imperfections in sources or detections would dramatically depress its performance. Here, we present an improved model on AMDI-QKD to reduce the influence of these imperfections, including intensity fluctuation, the afterpulse effect, and the dead time of detectors. Furthermore, we carry out corresponding numerical simulations. Simulation results show that, by implementing our present work, it can have more than 100 km longer secure transmission distance and one order of magnitude enhancement in the key generation rate after 320 km compared with the standard method. Moreover, our model can still break the Pirandola–Laurenza–Ottaviani–Banchi (PLOB) bound even under realistic experimental conditions.
Twin-field quantum key distribution can overcome the secret key capacity of repeaterless quantum key distribution via single-photon interference.However, to compensate for the channel fluctuations and lock the laser fluctuations, the techniques of phase tracking and phase locking are indispensable in experiment, which drastically increase experimental complexity and hinder free-space realization.We herein present an asynchronous measurement-device-independent quantum key distribution protocol that can surpass the secret key capacity even without phase tracking and phase locking.Leveraging the concept of time multiplexing, asynchronous two-photon Bell-state measurement is realized by postmatching two interference detection events.For a 1 GHz system, the new protocol reaches a transmission distance of 450 km without phase tracking.After further removing phase locking, our protocol is still capable of breaking the capacity at 270 km.Intriguingly, when using the same experimental techniques, our protocol has a higher key rate than the phase-matching-type twin-field protocol.In the presence of imperfect intensity modulation, it also has a significant advantage in terms of the transmission distance over the sending-or-not-sendingtype twin-field protocol.With high key rates and accessible technology, our work provides a promising candidate for practical scalable quantum communication networks.
Abstract Asynchronous quantum key distribution protocol (AMDI‐QKD) is a high performance quantum key distribution protocol while it can outperform the Pirandola–Laurenza–Ottaviani–Banchi (PLOB) bound without the need of phase‐locking and phase‐tracking techniques. However, the protocol applies the relative phase information of the communicating parties for encoding, and the drift of the reference frame inevitably affects the performance of the QKD system, whereas reference frame independent quantum key distribution (RFI‐QKD) has the advantage of tolerating the slow change of the reference frame. In this study, a reference frame‐independent asynchronous quantum key distribution (RFI‐AMDI‐QKD) scheme is proposed, which does not require phase alignment between the interferometers of both parties, and it is shown that the protocol can transmit over long distances and is robust to the drift of the reference frame.
Abstract Quantum key distribution (QKD) is a theoretically unconditionally secure key distribution method based on quantum mechanical principles. Currently, most QKD protocols encode information in the phase domain, making the phase error rate a crucial physical parameter for evaluating protocol performance. In phase-post-selected QKD protocols, the phase error rate depends on interference measurements within non-zero phase intervals, which introduce inherent errors unrelated to eavesdropping and consequently leads to overestimation of the phase error rate. Precise analysis of phase errors can effectively reduce the protocol’s phase error rate, thereby enhancing its performance. In previous work, phase error analysis methods were primarily applied to QKD protocols under asymptotic conditions. In this study, we extend this precise phase error analysis approach to the finite-key regime of asynchronous measurement-device-independent QKD (AMDI-QKD). The performance of the original and enhanced AMDI-QKD protocols was compared under different pulse intensities through numerical simulation, and the results indicate that, compared to the original AMDI-QKD, the enhanced AMDI-QKD protocol combined with precise error analysis can extend the transmission distance by nearly 20 km and effectively reduce the phase error rate.
Variations of phase-matching measurement-device-independent quantum key distribution (PM-MDI QKD) protocols have been investigated before, but it was recently discovered that this type of protocol (under the name of twin-field QKD) can beat the linear scaling of the repeaterless bound on secret key capacity. We propose a variation of PM-MDI QKD protocol, which reduces the sifting cost and uses non-phase-randomized coherent states as test states. We provide a security proof in the infinite key limit. Our proof is conceptually simple and gives tight key rates. We obtain an analytical key rate formula for the loss-only scenario, confirming the square root scaling and also showing the loss limit. We simulate the key rate for realistic imperfections and show that PM-MDI QKD can overcome the repeaterless bound with currently available technology.
The transmission loss of photons during quantum key distribution (QKD) process leads to the linear key rate bound for practical QKD systems without quantum repeaters. Phase matching quantum key distribution (PM-QKD) protocol, an novel QKD protocol, can overcome the constraint with a measurement-device-independent structure, while it still requires the light source to be ideal. This assumption is not guaranteed in practice, leading to practical secure issues. In this paper, we propose a modified PM-QKD protocol with a light source monitoring, named PM-QKD-LSM protocol, which can guarantee the security of the system under the non-ideal source condition. The results show that our proposed protocol performs almost the same as the ideal PM-QKD protocol even considering the imperfect factors in practical systems. PM-QKD-LSM protocol has a better performance with source fluctuation, and it is robust in symmetric or asymmetric cases.