Chinese researchers have achieved a major breakthrough in quantum secure direct communication (QSDC) by constructing a 300-kilometer fully connected network, according to a statement the research team sent to the Global Times on Monday.

The team from the Beijing Academy of Quantum Information Sciences (BAQIS) proposed a multipump expandable fully connected QSDC network in noisy environments, which is designed to reduce its complexity and increase the number of users while guaranteeing communication distance between users, according to the paper.

The quantum network represents a significant platform for the verification of the fundamental principles of quantum mechanics and the realization of quantum communication and computation.

The successful construction of this network paves the way for the practical application of quantum communication networks. This technology has the potential for adoption in sectors such as government communication and financial transactions, which demand extremely high levels of information security, said the BAQIS.

A major hurdle in QSDC development has been ensuring secure and reliable communication via quantum states, while the transmission distance and the number of users are two important factors that limit the realization of large-scale, scalable quantum communication networks, and existing quantum network construction techniques struggle to address these challenges simultaneously.

"In our recent research, we propose a long-distance large-scale and scalable fully connected QSDC network, which employs a double-pumped structure and the introduction of extra noise to successfully realize QSDC over 300 kilometers between four users in the network in pairs," the team said.

By using multipump technology, the team can exhibit reduced complexity. This advancement ensures that the fidelity of the entangled states shared among users post-communication remained above 85 percent, thereby robustly validating the scheme's effectiveness and reliability over extended distances, according to the paper.

The research findings include three key technical breakthroughs: overcoming traditional star-shaped network limitations to achieve scalable full connection, extending transmission distances to 300 kilometers through optimized entangled light source preparation, and establishing an error correction mechanism based on quantum state reconstruction to ensure stable multi-node communication, said the research team.

In February, Chinese research teams successfully achieved stable data transmission of 2.38 kilobits over a 104.8-kilometer standard fiber-optic network in a 168-hour experimental test. This represented a 4,760-fold improvement over the previous system, significantly advancing QSDC performance, the Xinhua News Agency reported.