Software-defined polarization-diversity continuous-variable quantum key distribution heterodyne receiver

This paper presents a simple polarization-diversity heterodyne receiver for continuous-variable quantum key distribution (CV-QKD) using a symmetric 3 × 3 beam splitter and software-defined polarization demultiplexing. Unlike conventional architectures that duplicate the coherent detection front-end, the proposed design implements polarization diversity in the digital domain, significantly reducing optical hardware complexity. The proposed receiver architecture is validated through simulations and experiments. Results show that the receiver exhibits stable performance under arbitrary states of polarization, achieving a composable finite-size secret key rate (with 10 7 symbols) of 6.98 Mbps in back-to-back operation and 0.29 Mbps over 25 km of fiber, demonstrating robustness and suitability for metro-scale CV-QKD deployment.