Recently, a research collaboration team composed of experts from the Beijing Zhongke Guoguang Quantum Company, a quantum information enterprise in Beijing E-Town, together with those from the Aerospace Information Research Institute of the Chinese Academy of Sciences and Zhejiang University, has made significant progress in the practical application of continuous-variable quantum key distribution (CVQKD).

"The team has proposed a new CVQKD frame synchronization scheme based on quantum states and conducted performance analysis, providing new insights for further improving the practicality of quantum key distribution (QKD)," explained Zhao Yibo, chairman of Guoguang Quantum.

With the continuous development of quantum encryption technology, QKD systems have become increasingly important. 

In such systems, correct synchronization is the cornerstone for extracting secure keys. Synchronization algorithms typically include bit synchronization and frame synchronization, addressing such issues as the correct identification of sampling points in the signal and the correct identification of the starting bit of the data signal. 

However, due to the weak intensity of quantum signals and the low signal-to-noise ratio of the receiver, signal synchronization has become a challenge in key distribution systems.

To address this problem, researchers proposed a modulation-free CVQKD systems frame synchronization scheme. 

The sender publicly discloses a small number of quantum states, and the receiver utilizes the Gaussian distribution characteristics of quantum states to perform cross-correlation calculations between two sets of transmitted sequences and the disclosed quantum states, achieving frame synchronization. 

This synchronization scheme exhibits a high success rate under extremely low signal-to-noise ratios and any phase drift. 

It overcomes the drawbacks of traditional modulation schemes without increasing the complexity of the quantum key distribution system or reducing the duty cycle of the quantum signal.

It is reported that this scheme could provide a solution for the application of CVQKD systems, improve system reliability and security, and have important implications for promoting the practicality of QKD systems.