Polarization-multiplexed co-transmission of continuous-variable QKD and quantum noise stream cipher

Quantum noise stream cipher (QNSC) is an encryption technique that leverages redundant information obscured by quantum noise to achieve an exponential increase in attack complexity, while continuous-variable quantum key distribution (CV-QKD) can provide such redundant information by generating secret keys. Notably, the optical architectures employed in these two schemes exhibit significant similarities. In this work, we employ polarization division multiplexing (PDM) to enhance channel capacity, enabling simultaneous transmission of signals under two different protocols over a single channel. To mitigate dynamic polarization state variations induced during signal propagation, we implement a polarization-interleaved subcarrier modulation (PISCM) scheme. We demonstrate that at a transmission distance of 20 km, the QKD secure key rate can be maintained at 4.93 Mbps, while the QNSC transmission rate reaches 100 Mbps. The expansion of the key rate from 4 Mbps to 400 Mbps using a linear feedback shift register (LFSR) enables synchronization with the 100 Mbps QNSC signal, realizing a promising pathway toward an integrated communication and encryption system.