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The integration of the continous-variable quantum key distribution(CVQKD) system is an important technical route with great potential value for constructing high-performance and low-cost CVQKD system. In all previous CVQKD studies, the quantum efficiency of the detector can be calibrated in advance and is considered to remain unchanged. But when the size of the system shrinks to the on-chip level, especially in the premise of non-uniform waveguide, heavy doping and other factors, effects such as free carrier absorption and scattering loss will become prominent, which will directly cause carriers undergo violent migration due to the tiny jitter of the local oscillator and further lead to dynamical variation of quantum efficiency of detection. In this paper, we propose a practical chip-based detector model, and numerous simulation results based on this model show that the practical system will face potential security threats due to the variable quantum efficiency. Moreover, two defense strategies are proposed to solve these practical security problems commonly exist in general chip-based CVQKD systems. This work breaks the inherent viewpoint that the quantum efficiency in the chip-based CVQKD system can still be calibrated in advance, and suggests a more rigorous consideration of practical security for development of chip-based CVQKD.

Continuous variable quantum key distribution (CV-QKD) can guarantee that two parties share secure keys even in the presence of an eavesdropper. However, the polarization direction of the coherent state transmitted in CV-QKD is susceptible to environmental disturbances during channel transmission, making it difficult to share keys consistently over long periods of time. Therefore, a CV-QKD system that can resist environmental disturbance is very urgent. In this paper, we propose a new optical architecture for CV-QKD based on the Faraday-Michelson interference (FMI) structure, and finally form an all-single-mode (SM) fiber-based stable CV-QKD system which employs transmitted local oscillator (TLO) scheme and discrete modulation coherent state (DMCS) protocol. Specifically, since the Faraday mirror rotates the polarization direction of light by 90 o , the birefringence effect of light can be effectively dealt with, thus ensuring the same polarization state of light before and after reflection. The final simulation results show that the theoretical secret key rate of this scheme can reach 139 kbps at 70 km, which can further improve the stability and robustness of CV-QKD in the real environment, and provide technical support for the next-generation high-stability QKD system.

The non-reciprocity of a Sagnac interferometer provides ultra-high sensitivity for parameter estimation and offers a wide range of applications, especially for optical fiber sensing. In this work, we study a new type of non-reciprocity existing in an optical fiber Sagnac interferometer where the polarization dependent loss is taken into consideration. In particular, this non-reciprocity is irrelevant to the physical effects that have been considered in previous studies, which originates from the geometric phases induced by a continuous-weak-measurement. Thus, it has a unique phenomenon of sudden phase transition, which may open a new way for the future design of high precision optical fiber sensors.

Continuous-variable quantum key distribution (CVQKD) with a real local oscillator (LO) has been extensively studied recently due to its security and simplicity. In this paper, we propose a novel implementation of a high-key-rate CVQKD with a real LO. Particularly, with the help of the simultaneously generated reference pulse, the phase drift of the signal is tracked in real time and then compensated. By utilizing the time and polarization multiplexing techniques to isolate the reference pulse and controlling the intensity of it, not only the contamination from it is suppressed, but also a high accuracy of the phase compensation can be guaranteed. Besides, we employ homodyne detection on the signal to ensure the high quantum efficiency and heterodyne detection on the reference pulse to acquire the complete phase information of it. In order to suppress the excess noise, a theoretical noise model for our scheme is established. According to this model, the impact of the modulation variance and the intensity of the reference pulse are both analysed theoretically and then optimized according to the experimental data. By measuring the excess noise in the 25km optical fiber transmission system, a 3.14Mbps key rate in the asymptotic regime proves to be achievable. This work verifies the feasibility of the high-key-rate CVQKD with a real LO within the metropolitan area.