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.
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.
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.
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.
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.
Stability and robustness are important criteria to evaluate the performance of a quantum-key-distribution (QKD) system in real-life applications. However, the inherent birefringence effect of the fiber channel and disturbance caused by the variation of the deployment environment of the QKD system tremendously decrease its performance. To eliminate this adverse impact, we propose a polarization-insensitive phase-coding QKD system based on Sagnac--Mach-Zehnder interferometers. Verified by theoretical analysis and experimental tests, this QKD system is robust against channel polarization disturbance. The robustness and long-term stability of the QKD system is confirmed with a 10-day continuous operation over a 12.6-dB channel, which consists of a 50-km fiber spool and a polarization scrambler (2 rad/s). As a result, an average quantum bit error rate of 0.958 and a sustained secure key rate of 3.68 kbps are obtained. Moreover, the secure key rate of the QKD system for a typical channel loss of 10 dB reaches 6.89 kbps, and the achievable maximum transmission distance exceeds 125 km.
A free-space quantum key distribution (QKD) system based on mobile equipment can provide an effective method to construct a real-time full-coverage multi-node network. However, the existing free-space QKD systems based on mobile devices encounter the challenge regarding the lack of stability caused by equipment disturbance. The robustness of the QKD polarization encoder against mobile device disturbance will be significant. Owing to the inevitable disturbance in practical applications, even the polarization-maintaining fiber (PMF) cannot maintain its polarization-maintaining characteristics well, which in turn affects the stability of some systems based on PMF. Therefore, in order to ensure that stable coding can be achieved under disturbances, we propose a two-way differential modulation mode, in which stable coding can still be achieved even under disturbances. At the same time, in order to verify the actual anti-disturbance characteristics of the mode, the polarization-modulated unit (PMU) with a two-way differential modulation mode is used in this study to generate four long-term stable polarization states subjected to the disturbances with a frequency of 200 Hz. At the same time, the PMU has a higher insertion loss, which makes the influence of crosstalk on the system more obvious. We also discuss two ways i.e. the time domain and frequency domain, to reduce the crosstalk which is caused by the imperfection of the device. The experiment is performed at a repetition frequency of 250 MHz, and a commercial avalanche single-photon detector is used to detect the system’s quantum bit error rate (QBER). Under the condition of no disturbance, the average QBER is 0.39% in 2 h. Then a vibration of approximately 200 Hz is used to simulate the practical disturbances, the average QBER is 0.36% in 2 h, and the fluctuation range of the QBER is only within 0.2%. We propose the first feasible encoding scheme in disturbed environments to ensure the long-term stability of the encoded polarization states, which is expected to be used in the multi-node expansion of the quantum network.
Satellite-based quantum key distribution (QKD) holds the potential to establish global quantum communication networks. While satellite QKD has been demonstrated using polarization encoding, time-bin encoding offers distinct advantages, such as simplifying polarization-maintaining telescope designs and being insensitive to satellite-ground relative motion. In this work, we developed a 625-MHz QKD light source using a robust Sagnac-interferometer-based modulation scheme and subsequently demonstrated time-bin QKD over a 7 km urban terrestrial free-space channel. This experiment successfully operated over a channel traversing an equivalent atmospheric thickness and loss exceeding that of typical satellite-to-ground links, achieving a low quantum bit error rate of 0.87% and a secure key rate of 134 bps@51.4 dB. Furthermore, by using a half-wave plate to simulate the polarization-basis-rotation inherent in such links, we verified the robustness of time-bin encoding for satellite scenarios. The results validate time-bin encoding as a compelling alternative and lay the technical foundation for future satellite QKD applications.