Quantum key distribution (QKD) has been extensively studied for practical applications. Advantage distillation (AD) represents a key technique to extract highly correlated bit pairs from weakly correlated ones, thus improving QKD protocol performance, particularly in large-error scenarios. However, its practical implementation remains under-explored. In this study, the AD is integrated into the three-intensity decoy-state BB84 protocol and its performance is demonstrated on a high-speed phase-encoding platform. The experimental system employs an asymmetric Mach-Zehnder interferometer (AMZI) fabricated on a silicon dioxide optical waveguide chip for phase encoding, which is benefited from its low coupling loss and minimum waveguide transmission loss. Phase-randomized weak coherent pulses, generated by a distributed feedback laser at 625 MHz, are modulated into decoy states of varying intensities. The signals are encoded via an AMZI and attenuated to single-photon levels before transmission. At the receiver, another AMZI demodulates the signals detected by avalanche photodiodes in gated mode. Experiments conducted at 50 km and 105 km demonstrate secure key rates of 104 kbits/s and 59 bits/s, respectively. The results at shorter distances closely match theoretical predictions, while slight deviations at 105 km are attributed to signal attenuation and noise. Despite these challenges, the results obtained at 105 km highlight the effectiveness of AD in enhancing secure key rates in the large-error scenario. This study confirms the potential of AD in extending secure communication range of QKD. By leveraging the high integration and scalability of silicon dioxide photonic chips, the proposed system lays a foundation for large-scale QKD deployment, paving the way for developing advanced protocols and real-world quantum networks.
Quantum key distribution (QKD) has been extensively studied for practical applications. Advantage distillation (AD) represents a key technique to extract highly correlated bit pairs from weakly correlated ones, thus improving QKD protocol performance, particularly in large-error scenarios. However, its practical implementation remains under-explored. In this study, the AD is integrated into the three-intensity decoy-state BB84 protocol and its performance is demonstrated on a high-speed phase-encoding platform. The experimental system employs an asymmetric Mach-Zehnder interferometer (AMZI) fabricated on a silicon dioxide optical waveguide chip for phase encoding, which is benefited from its low coupling loss and minimum waveguide transmission loss. Phase-randomized weak coherent pulses, generated by a distributed feedback laser at 625 MHz, are modulated into decoy states of varying intensities. The signals are encoded via an AMZI and attenuated to single-photon levels before transmission. At the receiver, another AMZI demodulates the signals detected by avalanche photodiodes in gated mode. Experiments conducted at 50 km and 105 km demonstrate secure key rates of 104 kbits/s and 59 bits/s, respectively. The results at shorter distances closely match theoretical predictions, while slight deviations at 105 km are attributed to signal attenuation and noise. Despite these challenges, the results obtained at 105 km highlight the effectiveness of AD in enhancing secure key rates in the large-error scenario. This study confirms the potential of AD in extending secure communication range of QKD. By leveraging the high integration and scalability of silicon dioxide photonic chips, the proposed system lays a foundation for large-scale QKD deployment, paving the way for developing advanced protocols and real-world quantum networks.
Photonics integrated circuits provide a stable, compact and robust platform for the implementation of quantum key distribution (QKD), which can generate information-theoretic secure keys between distant parties. Here, we present a high-speed QKD tests with silica planar lightwave circuits based asymmetric Mach-Zehnder interferometer modules. To further enhance system performance and reduce system complexity, we employ the advantage distillation (AD) algorithm alongside the one-decoy method. The AD algorithm can effectively extract strongly correlated bit pairs from weakly correlated bit pairs, thereby significantly improving the key rate over long distances, where traditional post-processing methods fail to generate keys. With a clock rate of 625 MHz, our system achieves composable secret key rates of 3.32 Mbps at 2 dB loss and 1.85 kbps at 18 dB loss, respectively. These results represent the first experimental validation of AD algorithm, and pave the way for the development of QKD networks with photonic integration.
The advantage distillation (AD) method can significantly improve the bit error rate tolerance and transmission distance for different quantum key distribution (QKD) protocols. To enhance the transmission distance in a decoy-three-state QKD protocol, we analyze security using the AD method for the decoy-three-state QKD protocol with a weak-coherent source. The theoretical analysis results indicate that the AD method can significantly enhance the transmission distance of the decoy-three-state QKD protocol. Moreover, by applying the AD method, we experimentally realize the decoy-three-state QKD protocol with 130 km transmission distance. Our analysis results demonstrate that the AD method can significantly improve the performance of decoy-three-state QKD protocols, which can be applied in the quantum network in future research.
Quantum key distribution (QKD) is a promising method for sharing an information-theoretically secure secret key using the properties of quantum mechanics. Although QKD is the most practical field in quantum information science, its widespread adoption is constrained by high implementation costs. Despite the cost-effectiveness of propagating QKD with classical communication using wavelength division multiplexing (WDM), the noise generated by relatively strong classical signals degrades QKD performance. Even though several mitigation strategies exist, they often involve complexity or additional hardware. In this paper, we apply advantage distillation (AD) to enhance the performance of a practical decoy-state BB84 QKD system operating in a WDM environment. We perform finite-key analysis in both co-propagation and counter-propagation scenarios with three classical channels, and furthermore we examine the effects of varying the number of classical channels and the optical power per channel. A comparison of simulation results obtained with and without AD demonstrates that AD is robust to noise originating from classical channels. These results show that AD increases the secure key rate and transmission distance in the WDM-based QKD environment under both co-propagation and counter-propagation without requiring hardware changes. These findings suggest advantage distillation is a promising strategy for the widespread adoption of WDM-based QKD, including in challenging counter-propagation cases.
Abstract The advantage distillation (AD) technology has been proven to effectively improve the secret key rate and the communication distance of quantum key distribution (QKD). The mode-pairing quantum key distribution (MP-QKD) protocol can overcome a fundamental physical limit, known as the Pirandola–Laurenza–Ottaviani–Banchi bound, without requiring global phase-locking. In this work, we propose a method based on multi-step AD to further enhance the performance of MP-QKD. The simulation results show that, compared to one-step AD, multi-step AD achieves better performance in long-distance scenarios and can tolerate a higher quantum bit error rate. Specifically, when the difference between the communication distances from Alice and Bob to Charlie is 25 km, 50 km and 75 km, and the corresponding transmission distance exceeds 523 km, 512 km and 496 km, respectively, the secret key rate achieved by multi-step AD surpasses that of one-step AD. Our findings indicate that the proposed method can effectively promote the application of MP-QKD in scenarios with high loss and high error rate.
Quantum Key Distribution (QKD) is gaining significant interest due to its theoretical guarantee of unconditional security. Integrated optics offers distinct advantages compared to bulk optics, including high stability, flexibility, controllability, and robustness. We develop a planar lightwave circuit (PLC) silica asymmetric Mach-Zehnder interferometer (AMZI) module with temperature system at an accuracy of 0.1 ℃ including an AMZI chip with a 400ps delay and a single-chip microcomputer. The silica AMZI module is used to encode at Alice, and the same low loss AMZI module is used to decode at Bob at a clock repetition rate of 156 MHz. Two intensity states Z -basis (|0ñ, |1ñ) and two phase states X-basis (|+ñ, |-ñ) are prepared at Alice and detected at Bob successfully. The extinction ratio of |0ñ and |1ñ between first-slot and third-slot are about 17 dB. And the interference visibility of |+ñ, |-ñ between interference max and min of second-slot are about 88%. The estimated secret key rate and the quantum bit error rate (QBER) using a simulation model for a transmission distance of 20 km is 16.3 kbps and 0.0384, respectively.
Summary form only given. Quantum key distribution (QKD), a technique based on quantum physics, provides unconditional secure quantum keys to be shared between two or more clients (Alice and Bob) [1]. Most QKD systems are implemented in a point-to-point link using bulky and expensive devices. Consequently a large scale deployment of this technology has not been achieved. A solution may be integrated photonic circuits, which provide excellent performances (compact, good optical phase stability, new degrees of freedom), and are particularly suitable for the manipulation of quantum states in compact chips. Some recent experiments have already demonstrated conventional binary QKD systems, using polarization and phase reference degrees of freedom [2, 3]. In this paper, we show the first silicon chip-to-chip decoy-state BB84 protocol based on spatial degrees of freedom (the cores of a multi-core fiber-MCF-). By tuning cascaded Mach-Zehnder interferometers (MZIs), it is possible to prepare the quantum states in two mutually unbiased basis (MUBs) sets: basis X ϵ {|A〉, |B〉}, and basis Z {|A + B〉, |A - B〉}. |A〉 and |B〉 are the quantum states related to two individual cores of the MCF, while |A + B〉 and |A - B〉 represent the superposition of the quantum state between cores, combined with a positive/negative phase relation. A train of weak coherent pulses (5 kHz repetition and 10 ns wide) are injected into the transmitter chip (Alice), where multiple variable optical attenuators (VOAs) are used to decrease the number of photons per pulse (μμ). In Fig. 1(c) a stable bit error rate, well below the threshold limit for coherent attacks of 11%, is measured for more than 11 minutes.