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Chinese Physics Letters

Anti-Interference High-Speed Modulation Decoder for Quantum Key Distribution

Huaxing Xu, Shaohua Wang, Chang-Lei Wang, Ping Zhang

Published Dec 25, 2024• 2 citations
Publisher

Abstract

Abstract Quantum key distribution is increasingly transitioning toward network applications, necessitating advancements in system performance, including photonic integration for compact designs, enhanced stability against environmental disturbances, higher key rates, and improved efficiency. In this letter, we propose an orthogonal polarization exchange reflector Michelson interferometer model to address quantum channel disturbances caused by environmental factors. Based on this model, we designed a Sagnac reflector-Michelson interferometer decoder and verified its performance through an interference system. The interference fringe visibility exceeded 98% across all four coding phases at 625 MHz. These results indicate that the decoder effectively mitigates environmental interference while supporting high-speed modulation frequencies. In addition, the proposed anti-interference decoder, which does not rely on magneto-optical devices, is well-suited for photonic integration, aligning with the development trajectory for next-generation quantum communication devices.

DOI
10.1088/0256-307x/42/1/010303

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Abstract Quantum key distribution is increasingly transitioning toward network applications, necessitating advancements in system performance, including photonic integration for compact designs, enhanced stability against environmental disturbances, higher key rates, and improved efficiency. In this letter, we propose an orthogonal polarization exchange reflector Michelson interferometer model to address quantum channel disturbances caused by environmental factors. Based on this model, we designed a Sagnac reflector-Michelson interferometer decoder and verified its performance through an interference system. The interference fringe visibility exceeded 98% across all four coding phases at 625 MHz. These results indicate that the decoder effectively mitigates environmental interference while supporting high-speed modulation frequencies. In addition, the proposed anti-interference decoder, which does not rely on magneto-optical devices, is well-suited for photonic integration, aligning with the development trajectory for next-generation quantum communication devices.
Quantum key distribution (QKD) is gradually moving towards network applications. It is important to improve the performance of QKD systems such as photonic integration for compact systems, the stability resistant to environmental disturbances, high key rate, and high efficiency in QKD applications. In the letter, we propose a general quantum decoding model, namely orthogonal-polarizations-exchange reflector Michelson interferometer model, to solve quantum channel disturbance caused by environment. Based on the model, we give a quantum phase decoder scheme, i.e. a Sagnac configuration based orthogonal-polarizations-exchange reflector Michelson interferometer (SRMI). Besides the stability immune to quantum channel disturbance, the SRMI decoder can be fabricated with photonic integrated circuits, and suitable to gigahertz phase encoding QKD systems, and can increase the system efficiency because of the low insertion loss of the decoder.
Self-stabilization quantum key distribution (QKD) systems are often based on the Faraday magneto-optic effect such as “plug and play” QKD systems and Faraday–Michelson QKD systems. In this article, we propose a new anti-quantum-channel disturbance decoder for QKD without magneto-optic devices, which can be a benefit for the photonic integration and applications in magnetic environments. The decoder is based on a quarter-wave plate reflector–Michelson (Q–M) interferometer, with which the QKD system can be free of polarization disturbance caused by quantum channel and optical devices in the system. The theoretical analysis indicates that the Q–M interferometer is immune to polarization-induced signal fading, where the operator of the Q–M interferometer corresponding to Pauli Matrix σ2 makes it satisfy the anti-disturbance condition naturally. A Q–M interferometer based time-bin phase encoding QKD setup is demonstrated, and the experimental results show that the QKD setup works stably with a low quantum bit error rate about 1.3% for 10 h over 60.6 km standard telecommunication optical fiber.
In the letter, we propose an anti-quantum-channel disturbance decoder for quantum key distribution (QKD). The decoder is based on a quarter-wave plate reflector-Michelson (Q-M) interferometer, with which the QKD system can be free of polarization disturbance caused by quantum channel and optical devices in the system. The theoretical analysis indicates that the Q-M interferometer is immune to polarization-induced signal fading and its corresponding operator is Pauli Matrix σ2, which naturally satisfies the anti-disturbance condition. A Q-M interferometer based time-bin phase encoding QKD setup is demonstrated and the experimental results show that the QKD setup works stably with a low quantum bit error rate and an average safe key rate about 7.34 kbps over 50.4 km standard optical fiber for two hours in the lab.
Quantum key distribution (QKD) provides an attractive solution for secure communication. However, channel disturbance severely limits its application when a QKD system is transferred from the laboratory to the field. Here a high-speed Faraday-Sagnac-Michelson QKD system is proposed that can automatically compensate for the channel polarization disturbance, which largely avoids the intermittency limitations of environment mutation. Over a 50 km fiber channel with 30 Hz polarization scrambling, the practicality of this phase-coding QKD system was characterized with an interference fringe visibility of 99.35% over 24 h and a stable secure key rate of 306 k bits/s over seven days without active polarization alignment.
An intrinsically stable quantum key distribution system (QKD) with six polarization states encoded by phase modulation is introduced. The encoder and decoder are in the same structures that consist of two polarizing Sagnac interferometers connected in tandem. The six polarization states are determined and distinguished by different sets of phase shifts induced by two respective electrically-driven integrated phase modulators. A mean visibility of interference fringes is kept stable at 97.58% for an hour's performance. Theoretical and experimental analyses show that the proposed QKD system features intrinsically stability immune from environment fluctuation.
In polarization-encoding quantum key distribution (QKD) systems, achieving high-speed, robust, and low-error polarization modulation helps to increase the secure key rate (SKR). Moreover, the advanced QKD protocols place higher demands on the system’s photon preparation capability, which implies providing additional polarization states for practical implementation. Here, we redesign the Sagnac interferometer and utilize the non-reciprocity of the lithium niobate modulator to eliminate the reverse modulation that limits the modulation speed. The proposed scheme enables high-speed, robust, and low-error modulation with arbitrary polarization states. The average bit error rate (BER) for the 10 min measurement is 0.2332% with a system repetition frequency of 16.5 GHz.