Proof-of-principle demonstration of free space semi-quantum key distribution based on the single-state protocol

Semi-quantum key distribution (SQKD) allows a quantum user and a classical user to share a string of secret keys, providing support for application scenarios that cannot withstand the high cost of quantum resources. In this paper, we propose what we believe to be the first proof-of-principle experimental demonstration of free space SQKD based on the single-state protocol, which is equipped with polarization encoding scheme employing the method of selective modulation. During the half-hour test time for each operation, the overall experiment obtained the original key rate of 107.2 kbps at the repetition frequency of 100 MHz, and the average bit error rate was determined to be 1.65