Realization of High-Reliable Coherent-State Quantum Secure Communication

Continuous-variable quantum secure communication encoded by Gaussian mapping offers high-capacity and high transmission rates. For the theoretically secure encryption scheme of a 1-time pad, a highly reliable coherent-state quantum secure communication system has been established, and its security has been quantitatively evaluated using Wyner's wiretap channel theory. We also propose an information reconstruction scheme based on multidimensional rotation to extract secret messages at low-to-medium signal-to-noise ratios. Meanwhile, to address the unbalanced optical path, we design a self-balanced homodyne detector based on a programmable gain amplifier, achieving an electronic noise variance of $1.624\times {10}^{-7}$ $V^2$ and a bandwidth of 715 MHz. In 10-km optical fiber transmission, the system successfully achieved secure transmission of the dichroic image, processed 1,536 information blocks, each containing $2^{10}$ continuous variables, with a block error rate of approximately $8.78\times {10}^{-5}$ , and ultimately achieved the secrecy capacity of $2.44\times {10}^5$ bits per second.