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Physical Review A

One-decoy-state quantum key distribution with advantage distillation based on planar-lightwave-circuit-integration modules

Jiali Zhu, Xingyu Zhou, Hua-Jian Ding, Jingyang Liu, Chunhui Zhang, Jian Li, Junming An, Qin Wang

Published Jan 7, 2025• 5 citations
Publisher

Abstract

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.

DOI
10.1103/physreva.111.012608

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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.
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) 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.
Quantum key distribution (QKD) enables information-theoretically secure key establishment, yet its practical performance strongly depends on the behavior of singlephoton detectors. In high-speed systems, afterpulsing effect and dead time can distort detection statistics and cause substantial overestimation of the secure key rate if not properly modeled. To address this issue, we construct a625−MHz625-\text{MHz}625−MHzBB84-QKD system based on a silica planar-lightwave-circuit asymmetric MachZehnder interferometer chips, incorporate a dependency-modelbased description of detector afterpulse and dead time into the theoretical analysis. This model provides corrected estimations of gain and error rates that more accurately reflect the real detection process. Experimental results show that the system achieves secure key rate of 30.47 kbps at 18 dB channel loss. The strong agreement between the corrected model and measured data confirms that it effectively avoids key-rate overestimation and reliably predicts system performance under practical conditions. The demonstrated on-chip encoding-decoding architecture and refined detector modeling together highlight a promising route toward compact, stable, and high-speed QKD systems, offering valuable guidance for future metropolitan and large-scale quantum communication networks.
Photonic integrated circuits provide a compact and stable platform for quantum photonics. Here we demonstrate a silicon photonics quantum key distribution (QKD) encoder in the first high-speed polarization-based QKD field tests. The systems reach composable secret key rates of 1.039 Mbps in a local test (on a 103.6-m fiber with a total emulated loss of 9.2 dB) and 157 kbps in an intercity metropolitan test (on a 43-km fiber with 16.4 dB loss). Our results represent the highest secret key generation rate for polarization-based QKD experiments at a standard telecom wavelength and demonstrate photonic integrated circuits as a promising, scalable resource for future formation of metropolitan quantum-secure communications networks.
We developed a high-speed quantum key distribution (QKD) system integrated with a compact self-developed silica-based planar lightwave circuit chip and a micro-optics-based polarization module. Also, we demonstrated that our system can generate average secure keys at the rate of 701.22 kbps over a free-space link of 275 m in daylight by using effective noise filtering systems in the temporal, spectral, and spatial domains. Real-time beam tracking system was adopted to stabilize the fluctuation of the beam position.
Silica-based planar lightwave circuit (PLC) devices can offer great potential for quantum key distribution (QKD) with the benefits of low-loss, low-cost, large-scale integration, miniaturization, stability and mass production. A quantum decoding integrated chip for QKD based on silica PLC technology was demonstrated, which consists of a variable optical splitter (VOS), an asymmetric Mach–Zehnder interferometer (AMZI) with a thermo-optic phase modulator (TOPM) and a delay line (DL) whose delay time is 400ps, and a variable directional coupler (VDC). The balanced pulsepairs of double channels with measured delay times of 396ps and 398ps respectively were obtained in the conditions of both classical optics and single-photon transmissions. The chip has advantageous to achieve high interference visibilities of double channels simultaneously for BB84 phase and time-bin protocols.